CN111384371A - Compression-resistant positive active material and electrochemical energy storage device - Google Patents

Abstract

The invention relates to the technical field of batteries, in particular to a pressure-resistant positive electrode active material and an electrochemical energy storage device. The positive electrode active material includes secondary particles composed of primary particles, the number σ of the primary particles per unit spherical area in the SEM image of the secondary particles is 5/μm ² to 30/μm ² , and the secondary particles are The single particle compressive strength of the secondary particles is 60 MPa to 300 MPa, and the molecular formula of the positive electrode active material is Li _x Ni _y Co _z M _k Me _p O _r A _m , 0.95≤x≤1.05, 0≤y≤1, 0≤ z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2, M is selected from Mn and/or Al, Me is selected from Zr, Zn, A combination of one or more of Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, A is selected from a combination of one or more of N, F, S, Cl . The positive electrode active material of the present invention has a compact particle structure and high single particle compressive strength, and the lithium ion battery using the positive electrode active material of the present invention has good cycle performance, low volume expansion rate and good power. academic performance.

Description

A pressure-resistant positive electrode active material and electrochemical energy storage device

technical field

The invention relates to the technical field of batteries, in particular to a pressure-resistant positive electrode active material and an electrochemical energy storage device.

Background technique

With the continuous escalation of energy crisis and environmental problems, the development of new green energy has become imminent. Lithium-ion batteries have the advantages of high specific energy, wide application temperature range, low self-discharge rate, long cycle life, good safety performance, and no pollution, and have been used in various fields. Lithium-ion batteries have been gradually tried all over the world as the energy system of automobiles to replace traditional diesel locomotives. However, currently commonly used lithium iron phosphate (LiFePO ₄ ), low nickel ternary (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), etc., cannot fully meet the requirements of power batteries for lithium ions due to the limitations of the properties of the materials themselves. Demand for energy density of battery cathode active materials. Increasing the nickel content of the high-nickel ternary cathode material can improve the energy density of the battery. Therefore, the high-nickel ternary cathode material is one of the main research objects of power batteries at present. However, with the increase of nickel content, the direct side reaction between the positive electrode active material and the electrolyte also intensifies, and the cycle performance deteriorates significantly, which is one of the bottlenecks in the current mass production and commercialization.

At present, at the material level, the main means to solve the cycle performance are mainly element content optimization, increase doping and coating modification technology. These three methods can improve the cycle performance to a certain extent, but there is still a gap with the market demand. Due to the high nickel content and strong surface activity of polycrystalline high-nickel ternary materials, it is easy to have side reactions with the electrolyte, resulting in a significant deterioration of the cell cycle performance, which is one of the main difficulties in current market applications. Through the research, it is found that the ternary cathode material will have the phenomenon of particle cracking during the cycle process, and the cell failure analysis shows that the particle cracking is the main reason for the deterioration of the cell cycle performance. Therefore, how to improve the particle breakage in the cycle process is particularly important for the improvement of cycle performance.

SUMMARY OF THE INVENTION

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a positive electrode active material with a compact structure and good compressive performance and an electrochemical energy storage device using the positive electrode active material. Cathode active materials with better ionic performance can improve the cycle life of the battery, control the volume expansion rate during the cycle, and improve the kinetic performance of the battery.

In order to achieve the above purpose and other related purposes, one aspect of the present invention provides a positive electrode active material, the positive electrode active material includes secondary particles composed of primary particles, and the number σ of the primary particles per unit area in the SEM spectrum of the secondary particles is It is 5 pieces/μm ² to 30 pieces/μm ² , the single particle compressive strength of the positive active material is 60 MPa to 300 MPa, and the molecular formula of the positive active material is Li _x Ni _y Co _z M _k Me _p O _r A _m , 0.95≤ x≤1.05, 0≤y≤1, 0≤z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2, M is selected from Mn And/or Al, Me is selected from the combination of one or more in Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, A is selected from N, F, A combination of one or more of S and Cl.

Another aspect of the present invention provides a positive electrode material, comprising the positive electrode active material of the present invention, wherein the surface of the positive electrode active material is provided with an outer cladding layer, the outer cladding layer includes a cladding element, and the outer cladding layer has a cladding layer. The cladding element is selected from one or a combination of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P.

Another aspect of the present invention provides a method for measuring the number of primary particles per unit spherical surface area of secondary particles in the positive electrode active material or the positive electrode material of the present invention, comprising the following steps:

(1) Select a positive electrode active material sample with a particle size of the average particle size D _v of the secondary particles of 50±20%, carry out SEM inspection on the sample, and obtain an SEM spectrum at a multiple of 10K;

(2) According to the SEM spectrum obtained in step (1), the number σ of primary particles per unit spherical surface area in the positive electrode active material is calculated by the following formula:

σ=(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

in,

x1 represents the number of primary particles on the lateral direction of the lower edge of the image in the SEM image of the secondary particle at a multiple of 10K;

x2 represents the number of primary particles in the lateral direction of the upper edge of the image in the SEM image of the secondary particle at a multiple of 10K;

y1 represents the number of primary particles in the longitudinal direction of the left edge of the picture in the SEM image of the secondary particle with a multiple of 10K;

y2 represents the number of primary particles in the longitudinal direction of the right edge of the picture in the SEM image of the secondary particle with a multiple of 10K;

A represents the actual measurement length in the lateral direction of the SEM image of the secondary particle with a multiple of 10K, in mm;

B represents the actual measured longitudinal length of the SEM image of the secondary particle with a multiple of 10K, in mm;

C represents the actual measured length when the scale is 1 μm in the SEM image of the secondary particle with a multiple of 10K, and the unit is mm/μm;

When calculating the number of primary particles in the SEM image of the 10K multiple of the secondary particles, as long as a part of the primary particle appears, it is regarded as one primary particle.

Another aspect of the present invention provides an electrochemical energy storage device comprising the positive electrode active material or positive electrode material of the present invention.

Compared with the prior art, the beneficial effects of the present invention are:

The positive electrode active material of the present invention includes secondary particles composed of primary particles. The secondary particles have a compact structure, high compressive strength and moderate ion transmission distance, which can effectively improve the problem of particle cracking in the cycle process, and avoid the problem of particle cracking during the cycle. The problem of gas generation caused by crushing is eliminated, and the ion conduction performance is excellent, so the lithium ion battery using the positive electrode active material of the present invention has good cycle performance, low volume expansion rate and good dynamic performance.

Description of drawings

Figure 1 is a graph showing the compressive strength of particles in Example 4 of the present invention.

Figure 2 is a graph showing the compressive strength of particles of Comparative Example 3 of the present invention.

Figure 3 is a diagram of the compressive strength testing device of the present invention.

FIG. 4 is a SEM image of the particles of Example 1 of the present invention at 10K times.

Detailed ways

The positive electrode active material, the positive electrode material, and the electrochemical energy storage device using the positive electrode active material or the positive electrode material according to the present invention are described in detail below.

A first aspect of the present invention provides a positive electrode active material, the positive electrode active material includes secondary particles composed of primary particles, and the number σ of primary particles per unit spherical surface area in the SEM image of the secondary particles is 5 /μm ² to 30 pieces/μm ² , the single particle compressive strength of the secondary particles is 60 MPa to 300 MPa, and the molecular formula of the positive electrode active material is Li _x Ni _y Co _z M _k Me _p O _r A _m , 0.95 ≤x≤1.05, 0≤y≤1, 0≤z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2, M is selected from Mn and/or Al, Me is selected from the combination of one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, A is selected from N, F A combination of one or more of , S, and Cl. The positive active material of lithium metal transition oxide is secondary particles composed of primary particles. Compared with single crystal particles, the polarization of secondary particles is smaller, which can effectively reduce the internal resistance of lithium-ion batteries; however, due to the internal resistance of secondary particles There is a certain gap between the primary particles, and different synthesis processes lead to obvious differences in the binding force between the primary particles. By controlling the number of primary particles per unit spherical surface area on the surface of the secondary particles, the tightness of the surface structure of the secondary particles can be improved. solidity. The positive electrode active material in the present invention has high surface structure compactness, excellent single particle compressive strength, and moderate ion transmission distance, which can improve the particle cracking problem in the cycle process, and at the same time ensure good ion-conducting performance of the positive electrode active material. It is ensured that the lithium ion battery using the positive electrode active material of the present invention has good cycle performance, low volume expansion rate and good dynamic performance.

In the positive electrode active material provided by the present invention, the positive electrode active material is a lithium transition metal oxide. Due to the segregation of a certain element content during the preparation process, the lithium element in the molecular formula of the positive electrode active material may be to a certain extent. In the presence of lithium-poor or lithium-rich conditions, when the relative content of lithium is in the range of 0.95≤x≤1.05, it has little effect on the capacity of the positive electrode active material. Optionally, the relative content of lithium is 0.95≤x≤ 1. 1≤x≤1.05.

In the positive electrode active material provided by the present invention, preferably, the positive electrode active material is a ternary lithium transition metal oxide containing Ni, Co, and at least one element of Mn or Al at the same time, and the molecular formula of the positive electrode active material is Medium: 0<y<1, 0<z<1, 0<k<1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2.

As a further preferred embodiment of the present invention, the positive electrode active material is a high-nickel positive electrode active material, and in the molecular formula of the positive electrode active material, 0.50<y≤0.95, 0.05≤z≤0.2, 0.05≤k≤0.4, 0≤ p≤0.05. Specifically, the positive active material may be LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Co _0.25 Mn _0.25 O ₂ , LiNi _0.55 Co _0.15 Mn _0.3 O _2. LiNi _0.55 Co _0.1 Mn _0.35 O ₂ , LiNi _0.55 Co _0.05 Mn _0.4 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.85 Co 0.8 _0.05 Mn _0.1 O ₂ , LiNi _0.88 Co _0.05 Mn _0.07 O ₂ , LiNi _0.9 Co _0.05 Mn _0.05 O ₂ , LiNi _0.72 Co _0.18 Al _0.1 O ₂ , LiNi _0.81 Co _0.045 Mn _0.045 Al _0.1 O ₂ . The active material after partial substitution and modification of Me and/or A pair, wherein Me is selected from one of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb or a combination of more than one, A is selected from a combination of one or more of N, F, S, and Cl.

More preferably, in the molecular formula of the positive electrode active material, 0.70≤y≤0.95, 0≤z≤0.2, 0≤k≤0.2, 0≤p≤0.05.

In the present invention, the positive electrode active material with higher nickel content is selected. Since the higher the relative content of Ni element, the higher the theoretical gram capacity of the material, the volume energy density of the battery can be effectively improved, but the high nickel positive electrode active material The amount of residual lithium on the surface is higher, and the particles are more likely to be broken. By controlling the surface compactness of the secondary particle and the compressive strength of the single particle of the high-nickel cathode active material, the gas production problem of the high-capacity battery during the cycle can be effectively solved. , improve the energy density and service life of the battery.

In the positive electrode active material provided by the present invention, the single particle compressive strength of the secondary particles refers to "the particle size fluctuates by 10% up and down the average particle size D _v 50, and a single secondary particle is regarded as a single particle, Under the action of external force, the minimum pressure when crushing". In the present invention, the single particle compressive strength of the secondary particles is selected from 60MPa～300MPa, 60MPa～80MPa, 80MPa～100MPa, 100MPa～120MPa, 120MPa～150MPa, 150MPa～180MPa, 180MPa～200MPa, 200MPa～220Mpa, 220MPa～240Mpa, 240MPa～260MPa, 260MPa～280MPa, 280MPa～300MPa.

In the positive electrode active material provided by the present invention, the powder compaction density of the positive electrode active material is not less than 3.3 g/cm ³ . The positive electrode active material of the present invention has good compression resistance and high powder compaction density. Therefore, in the process of making the pole piece, it can withstand a large pressure without breaking, which is beneficial to improve the compaction density of the positive pole piece. , improve the volume energy density of the battery.

In the positive electrode active material provided by the present invention, the D _v 10 of the secondary particles is 2 μm to 8 μm, the D _v 50 is 5 μm to 18 μm, and the D _v 90 is 10 μm to 30 μm. Optionally, D _v 10 is 2μm～3μm, 3μm～4μm, 4μm～5μm, 5μm～6μm, 6μm～7μm, 7μm～8μm, D _v 50 is 5μm～18μm, 5μm～8μm, 8μm～10μm, 10μm～ 12μm, 12μm～15μm, 15μm～18μm, D _v 90 is 10μm～30μm, 10μm～15μm, 15μm～20μm, 20μm～25μm, 25μm～30μm.

In the positive electrode active material provided by the present invention, the secondary particles are obtained by stacking the primary particles in the extending direction of the primary particles, the primary particles are rod-shaped, cone-shaped, or needle-shaped, and the primary particles are extended and stacked along the radial direction thereof. Secondary particles are formed. The length of the primary particles is 100 nm to 1000 nm, and the cross-sectional width is 50 nm to 400 nm. Optionally, the length of the primary particle is 100nm～1000nm, 100nm～200nm, 200nm～300nm, 300nm～400nm, 400nm～500nm, 500nm～600nm, 600nm～700nm, 700nm～800nm, 800nm～900nm, 900nm～1000nm; The cross-sectional widths are 50 nm to 400 nm, 50 nm to 100 nm, 100 nm to 150 nm, 150 nm to 200 nm, 200 nm to 300 nm, 300 nm to 350 nm, and 350 nm to 400 nm.

As a preferred embodiment of the present invention, the ratio of the length of the primary particles to the width of the radial section is 2-20, 2-5, 5-8, 8-10, 10-12, 12-15, 15-18 , 18 to 20.

In the positive electrode active material provided by the present invention, the BET of the secondary particles is 0.3m ² /g～0.8m ² /g, 0.3m ² /g～0.4m ² /g, 0.4m ² /g～0.5m ² /g, 0.5m ² /g to 0.6m ² /g, 0.6m ^{2 /g to 0.7m 2 /g, 0.7m 2 /g to 0.8m 2 / g .}

In the positive electrode active material provided in the present invention, when the volume particle diameter of the secondary particles is distributed within the above range, it can ensure that the specific surface area of the positive electrode active material is low and the ion transport distance is moderate. When the particle size of the secondary particles is within the above range, further controlling the length, width and ratio of the length to the radial section width of the primary particles within the above range can ensure that the surface and internal structure of the formed secondary particles have higher Density, the transport distance of lithium ions between primary particles is moderate, and it is also beneficial to improve the mechanical strength of secondary particles.

In the positive electrode active material provided by the present invention, in the secondary particles, at least part of the surfaces of the primary particles that are not at the outermost position are provided with an inner coating layer, the inner coating layer includes a coating element, and the inner coating layer includes a coating element. The cladding elements of the cladding layer are selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P in one or more combinations. The cladding elements of the inner cladding layer are not reflected in the molecular formula Li _x Ni _y Co _{z M k} Me _p O _r Am of the positive electrode active material, and generally the clad elements of the inner clad layer do not enter the crystal lattice.

As a preferred embodiment of the present invention, the cladding elements of the inner cladding layer are at least two or more selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P. In the present invention, the inner coating layer on the surface of the primary particle contains oxides formed by at least two or more of the above-mentioned elements, which can improve the adhesion stability of the inner coating layer on the surface of the primary particle, so that the inner coating layer has both Certain ionic conductivity and electronic conductivity can reduce the influence of the inner coating layer on the polarization of the positive electrode active material, thereby effectively avoiding the direct contact between the positive electrode active material and the electrolyte, reducing side reactions with the electrolyte, and avoiding the cycle process. A large amount of gas in the medium, while ensuring low impedance, excellent cycle and rate performance of the battery.

The second aspect of the present invention provides a positive electrode material, including the positive electrode active material of the first aspect of the present invention, wherein the surface of the positive electrode active material is provided with an outer coating layer, and the coating element of the outer coating layer is selected from Al, Ba, Zn , a combination of one or more of Ti, Co, W, Y, Si, Sn, B, P.

As a preferred mode of the present invention, while the outer coating layer is provided on the surface of the positive electrode material, the inner coating layer is provided on the surface of at least part of the primary particles in the non-outermost position of the secondary particles. Further preferably, the coating material of the outer coating layer and the inner coating layer is the same.

As a preferred embodiment of the present invention, the cladding elements of the outer cladding layer are at least two or more selected from Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P. In the present invention, the outer cladding layer on the surface of the positive electrode active material contains oxides formed by at least two or more of the above-mentioned elements, which can improve the adhesion stability of the outer cladding layer on the surface of the positive electrode active material, and make the outer cladding layer more stable. It has both ionic conductivity and electronic conductivity to reduce the influence of the outer coating on the polarization of the positive electrode active material, thereby effectively avoiding the direct contact between the positive electrode active material and the electrolyte, reducing side reactions with the electrolyte, and avoiding A large amount of gas is generated during the cycle, while ensuring low impedance and excellent cycle and rate performance of the battery.

In the cathode material provided by the present invention, the outer cladding layer is a continuous and/or discontinuous layered cladding layer; preferably, the outer cladding layer is a continuous first cladding layer and a non-continuous cladding layer. In the composite form of the continuous second coating layer, it is more preferable that the substance forming the discontinuous coating layer is different from the substance of the continuous coating layer. Wherein, the elements forming the discontinuous cladding layer are selected from one or more combinations of Al, Ba, Zn, Ti, and Co, and the elements forming the continuous cladding layer are selected from W, Y, Si, B, A combination of one or more of P and Sn.

In the positive electrode material provided by the present invention, the discontinuous layered coating layer can be a discrete island-shaped outer coating layer, and the discontinuous coating layer can act like a "nano-nail" on the surface of the positive electrode active material In this way, it can not only be firmly combined with the positive electrode active material, effectively reduce the probability of the positive electrode active material particles breaking during the cycle, and the discontinuous layered coating can also enhance the positive electrode active material. The bonding force between them increases the overall mechanical strength of the positive active material (especially in the form of secondary particles formed by agglomeration of primary particles) and is not easily broken. At the same time, a continuous coating layer is formed on the surface of the positive electrode active material, which can effectively reduce the surface roughness of the positive electrode material, reduce the specific surface area of the positive electrode material, and then reduce the effective contact area between the surface of the positive electrode material and the electrolyte, and reduce the surface of the positive electrode material. The side reaction of the electrolyte avoids the side reaction between the surface of the positive electrode material and the electrolyte to generate a large amount of gas.

A third aspect of the present invention provides a method for measuring the number of primary particles per unit spherical surface area of secondary particles in the positive electrode active material of the first aspect of the present invention or the positive electrode material of the second aspect, comprising the following steps:

(1) Select a positive electrode active material sample with a particle size of the average particle size D _v of the secondary particles of 50±20%, carry out SEM inspection on the sample, and obtain an SEM spectrum at a multiple of 10K;

(2) According to the SEM pattern obtained in step (1), calculate the number σ (pieces/μm ² ) of primary particles per unit area in the positive electrode active material by the following formula:

σ=(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

in,

x1 represents the number of primary particles on the lateral direction of the lower edge of the image in the SEM image of the secondary particle at a multiple of 10K;

x2 represents the number of primary particles in the lateral direction of the upper edge of the image in the SEM image of the secondary particle at a multiple of 10K;

y1 represents the number of primary particles in the longitudinal direction of the left edge of the picture in the SEM image of the secondary particle with a multiple of 10K;

y2 represents the number of primary particles in the longitudinal direction of the right edge of the picture in the SEM image of the secondary particle with a multiple of 10K;

A represents the actual measurement length in the lateral direction of the SEM image of the secondary particle with a multiple of 10K, in mm;

B represents the actual measured longitudinal length of the SEM image of the secondary particle with a multiple of 10K, in mm;

C represents the actual measured length when the scale is 1 μm in the SEM image of the secondary particle with a multiple of 10K, and the unit is mm/μm;

When calculating the number of primary particles in the SEM image of the 10K multiple of the secondary particles, as long as a part of the primary particle appears, it is regarded as one primary particle.

In the present invention, the number σ of the primary particles per unit spherical surface area can be intuitively characterized by the above method, which truly reflects the size and distribution of the primary particles on the surface of the secondary particles. Particle size, the method of calculating the number of primary particles in the SEM image of the secondary particles at 10K times is an effective way to objectively characterize the compactness of the spherical structure of the secondary particles composed of the primary particles.

The fourth aspect of the present invention provides a method for preparing the positive electrode active material of the first aspect of the present invention, and the method for the positive electrode active material should be known to those skilled in the art, for example, it may include: those skilled in the art may According to the elemental composition of the positive electrode active material, select the appropriate raw material and ratio of the positive electrode active material. For example, the raw materials of the positive electrode active material may include ternary material precursors of nickel, cobalt, manganese and/or aluminum, lithium source, Me source, A source, etc., and the ratio between the raw materials is usually referred to the ratio of each element in the positive electrode active material. Proportion to match. More specifically, the ternary material precursor may include but not limited to Ni _1/3 Co _1/3 Mn _1/3 (OH) ₂ , Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ , Ni _0.5 Co _0.25 Mn _0.25 (OH) ₂ , Ni _0.55 Co _0.15 Mn _0.3 (OH) ₂ , Ni _0.55 Co _0.1 Mn _0.35 (OH) ₂ , Ni _0.55 Co _0.05 Mn _0.4 (OH) ₂ , Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ , Ni _0.75 Co _0.1 Mn _0.15 (OH) ₂ , Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ , Ni _0.88 Co _0.05 Mn _0.07 (OH) ₂ , 0.9Ni _0.8 Co _0.2 (OH) ₂ ·0.1Al(OH) ₃ , 0.9Ni _0.9 Co _0.05 Mn _0.05 (OH) ₂ ·0.1Al(OH) ₃ , the lithium source can be a lithium-containing compound, and the lithium-containing compound can be including but not limited to LiOH·H ₂ O, LiOH, Li A combination of one or more of ₂ CO ₃ , Li ₂ O, etc., the Me source can generally be a compound containing Me element, and the compound containing Me element can be a compound containing Zr, Zn, Cu, Cr, Mg , one or more of oxides, nitrates and carbonates of at least one element in Fe, V, Ti, Sr, Sb, Y, W, Nb, and the A source can be a compound containing A element , the A element-containing compound may be a combination including but not limited to one or more of LiF, NaCl, Na ₂ S, Li ₃ N, and the like. For another example, the sintering conditions may be 800° C. and oxygen concentration ≥ 20%.

The preparation method of the positive electrode active material may further comprise that an inner coating layer is provided on the surface of the primary particle at least part of the non-outermost position in the secondary particle, and the method of forming the inner coating layer on the surface of the primary particle is suitable for It should be known to those skilled in the art that, for example, it may include: sintering the primary particles in the presence of a compound containing a coating element to form an inner coating layer on the surface of the primary particles. For another example, when the inner layer coating material and the outer layer coating material are the same, the inner layer coating process and the outer layer coating process can be combined into a one-step process, and the coating material can pass through the surface of the secondary particle and the pores inside, The outer surfaces of the secondary particles and at least part of the inner primary particles are simultaneously coated. Those skilled in the art can select appropriate types, proportions and sintering conditions of compounds containing coating elements according to parameters such as the composition of the inner coating layer, the powder compressive strength of the positive electrode active material, and the resistivity of the resistivity powder. For example, the compound containing the coating element may be oxide, nitrate, phosphoric acid containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P Salts, carbonates, etc., for example, the used amount of the compound containing the coating element may be 0.01%-0.5%, and the sintering condition may be high-temperature sintering at 200°C to 700°C.

A fifth aspect of the present invention provides a method for preparing the positive electrode material of the second aspect of the present invention, comprising: forming an outer cladding layer on the surface of the positive electrode active material of the first aspect of the present invention.

The method of forming the outer coating layer on the surface of the positive electrode active material should be known to those skilled in the art, for example, it may include: sintering the positive electrode active material in the presence of a compound containing a coating element, so as to form a coating on the positive electrode active material. An outer coating is formed on the surface of the active material. Those skilled in the art can select appropriate types, proportions and sintering conditions of compounds containing coating elements according to parameters such as the composition of the outer coating layer, the powder compressive strength of the positive active material, and the resistivity of the resistivity powder. For example, the compound containing the coating element may be oxide, nitrate, phosphoric acid containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P Salts, carbonates, etc., for example, the used amount of the compound containing the coating element may be 0.01%-0.5%, and the sintering condition may be high-temperature sintering at 200°C to 700°C.

A sixth aspect of the present invention provides an electrochemical energy storage device comprising the positive electrode active material of the first aspect of the present invention or the positive electrode material of the second aspect of the present invention.

In the electrochemical energy storage device according to the sixth aspect of the present invention, it should be noted that the electrochemical energy storage device may be a supercapacitor, a lithium ion battery, a lithium metal battery or a sodium ion battery. In the embodiments of the present invention, only an embodiment in which the electrochemical energy storage device is a lithium ion battery is shown, but the present invention is not limited thereto.

In a lithium ion battery, it includes a positive pole piece, a negative pole piece, a separator spaced between the positive pole piece and the negative pole piece, and an electrolyte, wherein the positive pole piece includes the positive active material of the first aspect of the present invention or the positive electrode material of the second aspect of the present invention. The method for preparing the lithium ion battery should be known to those skilled in the art, for example, the positive electrode, separator and negative electrode can each be a layer body, so that they can be cut into the target size and then sequentially. Stacked, it can also be rolled to target dimensions for use in forming cells, and can be further combined with electrolytes to form lithium-ion batteries.

In a lithium ion battery, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer on the positive electrode current collector, the positive electrode material layer comprising the positive electrode active material of the first aspect of the present invention or the positive electrode active material of the second aspect of the present invention Positive electrode material, binder, conductive agent. Those skilled in the art can choose a suitable method to prepare the positive electrode sheet. For example, it may include the following steps: after mixing the positive electrode active material or the positive electrode material, the binder and the conductive agent to form a slurry, then coating the positive electrode current collector . The binder usually includes a fluoropolyolefin-based binder, and water is usually a good solvent relative to the fluoropolyolefin-based binder, that is, the fluoropolyolefin-based binder is usually It has good solubility in water, for example, the fluorine-containing polyolefin-based binder may include but not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymer, etc. or their modifications (for example, carboxylic acid, Modified acrylic acid, acrylonitrile, etc.) derivatives, etc. The conductive agent can be various conductive agents suitable for lithium ion (secondary) batteries in the art, for example, can be including but not limited to acetylene black, conductive carbon black, carbon fiber (VGCF), carbon nanotube (CNT), A combination of one or more of Ketjen Black and the like. The positive electrode current collector can usually be a layered body, and the positive electrode current collector is usually a structure or part that can collect current. , the positive electrode current collector may include but not limited to metal foil, etc., more specifically may include but not limited to copper foil, aluminum foil, etc.

In a lithium ion battery, the negative electrode sheet usually includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector, and the negative electrode active material layer usually includes a negative electrode active material. The negative electrode active material can be a variety of materials in the art that are suitable for the negative electrode active material of lithium-ion batteries, for example, can be including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microspheres, silicon-based materials A combination of one or more of , tin-based materials, lithium titanate, or other metals that can form alloys with lithium, and the like. Wherein, the graphite can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be selected from elemental silicon, silicon-oxygen compounds, silicon-carbon composites, and silicon alloys A combination of one or more of tin-based materials; the tin-based material can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be any material suitable for use as a negative electrode current collector for lithium ion batteries in the art. For example, the negative electrode current collector can include but not limited to Metal foil, etc., more specifically may include but not limited to copper foil and the like.

In a lithium ion battery, the separator can be any material suitable for lithium ion battery separators in the art, for example, it can be polyethylene, polypropylene, polyvinylidene fluoride, aramid, polypara A combination of one or more of ethylene phthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers, among others.

In a lithium-ion battery, the electrolyte may be any electrolyte suitable for lithium-ion batteries in the art. For example, the electrolyte usually includes an electrolyte and a solvent, and the electrolyte may generally include a lithium salt, etc. More specifically , the lithium salt may be an inorganic lithium salt and/or an organic lithium salt, etc., specifically including but not limited to, the lithium salt may be selected from LiPF ₆ , LiBF ₄ , LiN(SO ₂ F) ₂ (abbreviated as LiFSI ), LiN(CF ₃ SO ₂ ) ₂ (abbreviated as LiTFSI), LiClO ₄ , LiAsF ₆ , LiB(C ₂ O ₄ ) ₂ (abbreviated as LiBOB), LiBF ₂ C ₂ O ₄ (abbreviated as LiDFOB) one or more combinations. For another example, the concentration of the electrolyte may be between 0.8 mol/L and 1.5 mol/L. The solvent can be a variety of solvents suitable for the electrolyte of lithium ion batteries in the art, and the solvent of the electrolyte is usually a non-aqueous solvent, preferably an organic solvent, specifically including but not limited to ethylene carbonate, carbonic acid, etc. A combination of one or more of propylene ester, butylene carbonate, pentenyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, etc. or their halogenated derivatives.

The beneficial effects of the present invention are further described below in conjunction with the embodiments.

In order to make the invention purpose, technical solution and beneficial technical effect of the present invention clearer, the present invention is further described in detail below with reference to the embodiments. However, it should be understood that the embodiments of the present invention are only for explaining the present invention, not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. The specific experimental conditions or operating conditions are not specified in the examples, and are made according to conventional conditions, or according to the conditions recommended by the material supplier.

Furthermore, it should be understood that the mention of one or more method steps in the present invention does not exclude that other method steps may also be present before and after said combined step or that other method steps may be inserted between these expressly mentioned steps, unless otherwise There are descriptions; it should also be understood that the combined connection relationship between one or more devices/devices mentioned in the present invention does not exclude that there may be other devices/devices before and after the combined device/device or explicitly mentioned in these Other devices/devices can be inserted between the two devices/devices unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the arrangement order of each method step or limiting the scope of the present invention. In the case where the technical content is not substantially changed, it should also be regarded as the scope in which the present invention can be implemented.

In the following examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

1. Preparation of batteries

Example 1

1. Preparation of cathode materials

1) Nickel sulfate, manganese sulfate, and cobalt sulfate are configured into a solution with a concentration of 1 mol/L in a molar ratio of 8:1:1, and a hydroxide co-precipitation technology is used to prepare a nickel-cobalt-manganese ternary material precursor Ni _0.8 Co. _0.1 Mn _0.1 (OH) ₂ . In the process of preparing the precursor, the initial pH value during co-precipitation was controlled to be 9.5, the ammonia concentration was 0.4M, and the post-reaction aging time was 5h.

2) The above-mentioned nickel-cobalt-manganese ternary material precursor Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and Li-containing compound LiOH·H ₂ O are placed in a mixing device in a molar ratio of 1:1.05 for mixing, and then placed in a mixing device. Sinter at 800°C in an atmosphere furnace, and after cooling, mechanical grinding is used to form the positive electrode active material matrix; the above-mentioned positive electrode active material matrix and additive Al ₂ O ₃ are placed in a mixing equipment in a mass ratio of 100:0.3 for mixing, and then placed Sintering was carried out at 450° C. in an atmosphere furnace to form a positive electrode material coated with Al ₂ O ₃ .

2. Preparation of positive electrode pieces

Step 1: Mix the prepared positive electrode material, binder polyvinylidene fluoride, and conductive agent acetylene black according to a mass ratio of 98:1:1, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer Obtain the positive electrode slurry; uniformly coat the positive electrode slurry on the aluminum foil with a thickness of 12 μm;

Step 2: drying the coated pole piece in an oven at 100℃～130℃;

Step 3: After cold pressing and slitting, a positive pole piece is obtained.

3. Preparation of negative pole piece

Mix the negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black according to the mass ratio of 97:1:1:1, add deionized water, and under the action of a vacuum mixer The negative electrode slurry was obtained; the negative electrode slurry was uniformly coated on the copper foil with a thickness of 8 μm; the copper foil was dried at room temperature and then transferred to a 120°C oven to dry for 1 hour, and then the negative electrode pole piece was obtained by cold pressing and slitting.

4. Electrolyte preparation

The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:20:60, in an argon atmosphere glove box with a water content of <10ppm , the fully dried lithium salt with a concentration of 1 mol/L is dissolved in an organic solvent, and mixed uniformly to obtain an electrolyte solution.

5. Preparation of isolation film

Choose 12μm thick polypropylene separator.

6. Preparation of battery

Stack the positive pole piece, the separator film and the negative pole piece in order, so that the separator is placed between the positive and negative pole pieces to play the role of isolation. Then, after baking at 80°C to remove water, the corresponding non-aqueous electrolyte is injected, sealed, and the finished battery is obtained after standing, hot and cold pressing, formation, fixture, and volume separation.

Example 2

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the pH value of the precursor preparation process is adjusted to 10.5, the ammonia concentration is 0.3M, and the aging time after the reaction is 3h.

Example 3

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the pH value of the precursor preparation process during co-precipitation is adjusted to 11, the ammonia concentration is 0.2M, and the aging time after the reaction is 5h.

Example 4

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: in the process of preparing the precursor, the pH value during co-precipitation is adjusted to 10, the ammonia concentration is 0.4M, and the aging time after the reaction is 2h.

Example 5

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the pH value of the precursor is adjusted to 11.5 during co-precipitation, the ammonia concentration is 0.3M, and the aging time after the reaction is 2h.

Example 6

Basically the same as Example 1, the difference lies in the preparation method of the cathode material: in the process of preparing the precursor, the pH value during co-precipitation is adjusted to 9.8, the ammonia concentration is 0.3M, and the aging time after the reaction is 4h.

Example 7

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the relative content of Ni, Co, and Mn elements in the precursor is 0.75:0.1:0.15, and the pH value during the co-precipitation is adjusted during the preparation of the precursor. 10.2. The ammonia concentration is 0.5M and the aging time after the reaction is 6h.

Example 8

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the relative content of Ni, Co, and Mn elements in the precursor is 0.6:0.2:0.2, and the pH value during co-precipitation is adjusted during the preparation of the precursor. 11.5, the ammonia concentration is 0.6M, and the aging time after the reaction is 3h.

Example 9

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the relative content of Ni, Co, and Mn elements in the precursor is 0.55:0.15:0.3, and the pH value of the co-precipitation is adjusted during the preparation of the precursor. 11.2. The ammonia concentration is 0.3M, and the aging time after the reaction is 2h.

Example 10

Basically the same as Example 1, the difference lies in the preparation method of the positive electrode material: the relative content of Ni, Co, and Mn elements in the precursor is 0.33:0.33:0.33, and the pH value during the co-precipitation is adjusted during the preparation of the precursor. 10.9, the ammonia concentration is 0.4M and the aging time after the reaction is 3h.

Comparative Example 1

The preparation method of Comparative Example 1 refers to the preparation method of Example 1 as described above, and the difference lies in the preparation method of the positive electrode material: the pH value during the co-precipitation is adjusted to 11, the ammonia concentration is 0.5M during the preparation of the precursor, and the reaction The subsequent aging time was 6h.

Comparative Example 2

The preparation method of Comparative Example 2 refers to the preparation method of Example 1 as described above, and the difference lies in the preparation method of the positive electrode material: the pH value during the co-precipitation is adjusted to 12, the ammonia concentration is 0.6 M during the preparation of the precursor, and the reaction The subsequent aging time was 7h.

Comparative Example 3

The preparation method of Comparative Example 3 refers to the preparation method of Example 1 as described above, and the difference lies in the preparation method of the positive electrode material: the pH value during the preparation of the precursor is adjusted to be 10.5 during co-precipitation, the ammonia concentration is 0.1 M, and the reaction The subsequent aging time was 6h.

2. Performance test

The positive electrode materials prepared in Examples 1-10 and Comparative Examples 1-3 were taken, and the single particle compressive strength, number σ of primary particles, compaction density and BET in the unit sphere area of the secondary particles were tested. The test results are shown in Table 2.

1. Test method for compressive strength

(1) Place the sample on the stage;

(2) Move the indenter down to the sample at a speed of 0.1 μm/min until it can contact the sample;

(3) Record the pressure and displacement of the indenter at the moment of contact;

(4) Continue to squeeze the particles downward at a constant speed until the particles are broken;

2. BET test method

The BET test was carried out by the national standard method, the GB/T 19587-2004 test method for the determination of the specific surface area of solid substances by gas adsorption BET method.

3. Test method of compaction density

The compaction density test was carried out using the GB/T 24533-2009 test method for lithium-ion battery graphite negative electrode materials on the national standard, and the test pressure was 5 tons.

4. Determination of the number of particles at a time

For testing the number of primary particles per unit area in the secondary particles, and the SEM image of the 10K multiple of the sample prepared in Example 1 is shown in Figure 4, the primary particles of the product are calculated as follows.

Calculate the number of primary particles in a unit area of 1μm×1μm according to the formula σ=(x1+x2)/2*(y1+y2)/2/(A/C*B/C). The calculation results are shown in Table 1 middle.

σ ₁ =(32+32)/2*(22+23)/2/(112/10*75/10)=8.5 pieces/μm ² .

The calculation methods of other embodiments and comparative examples are the same, and the calculation results are shown in Table 2.

Table 1 Number of primary particles per unit spherical surface area of Example 1

5. Battery cycle performance test method

Under the constant temperature environment of 45°C, at 2.8V ~ 4.2V, charge to 4.2V according to 1C, then charge to 4.2V at constant voltage at 4.2V, let stand for 5min, and then discharge to 2.8V according to 1C, the capacity Denoted as Dn (n=0, 1, 2...), repeat the previous process until the capacity decays to 80% of the initial capacity, and record the number of cycles of the lithium-ion battery. Table 3 shows the results of Examples 1 to 10 and Comparative Examples 1 to 3.

6. Test method for high temperature gas production of batteries

After the battery was fully charged to 4.2V at 1C, it was left for 30 days in a 70°C incubator. The initial volume of the battery and the volume after standing for 30 days were measured by the drainage method to obtain the volume expansion rate of the battery.

Volume expansion rate (%) of the battery=(volume after standing for 30 days/initial volume-1)×100%.

The test results are shown in Table 3.

7. 1/3C capacity test method

The lithium-ion battery was left for 2 hours at a constant temperature of 25°C, then charged at 1/3C to 4.2V at 2.8V to 4.2V, and then charged at a constant voltage at 4.2V until the current ≤ 0.05mA, and left for 5 minutes. , and then discharge to 2.8V according to 1C, record the capacity of the lithium ion battery; divide the test value of the capacity by the mass of the positive electrode material in the lithium ion battery, which is the 1/3C capacity of the positive electrode material. The test results are shown in Table 3.

Table 2 Examples 1-10 and Comparative Examples 1-3 Positive electrode active material powder characterization

Table 3 Battery electrochemical performance test results of Examples 1-10 and Comparative Examples 1-3

It can be found from Table 2 and Table 3 that the relative contents of Ni, Co and Mn elements in the positive electrode materials of Examples 1 to 6 and Comparative Examples 1 to 3 are the same. The number of primary particles and the compressive strength of a single particle are within a specific range. Therefore, in Examples 1 to 6, the particle microstructure of the positive electrode material is relatively compact, the mechanical strength of the powder material is higher, and the capacity is better. Fracture is unlikely to occur during tablet preparation or cycling. The cycle performance of the lithium ion batteries prepared from the positive electrode materials in Examples 1 to 6 is significantly higher than that of Comparative Examples 1 to 3, and the volume expansion rate during the cycle is significantly reduced. Among them, the number of primary particles in the unit sphere area of the positive electrode material in Comparative Example 1 is moderate, and the compressive strength of a single particle is low, indicating that the bonding force between primary particles in the secondary particles is weak, so the prepared positive electrode plate It is difficult to improve the compaction of the anode material; at the same time, the secondary particles are prone to rupture during the cold pressing of the pole piece and the cycle process, resulting in a large number of fresh surfaces in the positive electrode material being in direct contact with the electrolyte, resulting in serious gas production and poor cycle performance. In Comparative Example 2, the number of primary particles in the unit sphere area of a single particle of the positive electrode material is low, and the compressive strength of a single particle is too high, indicating that the size of the primary particles inside the secondary particles is too large and adjacent to each other. The pores between the primary particles are less, resulting in higher polarization of the positive electrode material and lower ion transport rate, so the internal resistance of the battery is higher, and the cycle performance of the battery is deteriorated. In Comparative Example 3, the number of primary particles per unit sphere area of the positive electrode material is too high, and the compressive strength of a single particle is moderate, indicating that the primary particle size of the secondary particles of the positive electrode material is low and the BET is high, so the formation of The gas production of the lithium-ion battery is still large and the cycle performance is poor.

In Examples 7 to 10, the relative contents of Ni, Co, and Mn elements in the lithium transition metal oxide in the positive electrode material were different, and the number of primary particles in the unit sphere area of the positive electrode material and the compressive strength of a single particle were In a specific range, with the decrease of Ni content, the discharge capacity of Li-ion battery is slightly reduced, but the cycle performance and gas generation problems are obviously optimized.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form or substance. It should be pointed out that for those skilled in the art, without departing from the method of the present invention, the Several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. All those skilled in the art, without departing from the spirit and scope of the present invention, can utilize the above-disclosed technical content to make some changes, modifications and equivalent changes of evolution, all belong to the present invention. Equivalent embodiments; at the same time, any modification, modification and evolution of any equivalent changes made to the above embodiments according to the essential technology of the present invention still fall within the scope of the technical solutions of the present invention.

Claims (11)

1. A positive electrode active material comprising secondary particles composed of primary particles, the number σ of the primary particles in a unit spherical surface area in an SEM spectrum of the secondary particles being 5 pieces/μm²About 30 pieces/. mu.m²The single-particle compressive strength of the secondary particles is 60MPa to 300MPa,

the molecular formula of the positive active material is Li_xNi_yCo_zM_kMe_pO_rA_mX is more than or equal to 0.95 and less than or equal to 1.05, Y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, r is more than or equal to 2, M is more than or equal to 0 and less than or equal to 2, M + r is less than or equal to 2, M is selected from Mn and/or Al, Me is selected from one or more combinations of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and A is selected from one or more combinations of N, F, S, Cl.

2. The positive electrode active material according to claim 1, wherein in the formula of the positive electrode active material, y is 0.70. ltoreq. y.ltoreq.0.95, z is 0. ltoreq. z.ltoreq.0.2, k is 0. ltoreq. k.ltoreq.0.2, and p is 0. ltoreq. p.ltoreq.0.05.

3. The positive electrode active material according to claim 1, wherein the powder compacted density of the positive electrode active material is not less than 3.3g/cm³。

4. The positive electrode active material according to claim 1, wherein D of the secondary particles_v10 is 2 to 8 μm, D_v50 is 5 to 18 μm, D_v90 is 10 to 30 μm.

5. The positive electrode active material according to claim 4, wherein the secondary particles are primary particles stacked in an extending direction of the primary particles, the primary particles have a rod shape, a cone shape, or a needle shape, the primary particles have a length of 100nm to 1000nm, the primary particles have a radial cross-sectional width of 50nm to 400nm, and preferably, a ratio of the length of the primary particles to the radial cross-sectional width is 2 to 10.

6. The positive electrode active material according to claim 1, wherein the secondary particles have a BET of 0.3m²/g～0.8m²/g。

7. The positive electrode active material according to claim 1, wherein at least a part of the primary particle surfaces at non-outermost positions in the secondary particles are provided with an inner coating layer comprising a coating element selected from one or more combinations of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P.

8. A positive electrode material, comprising the positive electrode active material as claimed in any one of claims 1 to 7, wherein an outer cladding layer is arranged on the surface of the positive electrode active material, the outer cladding layer comprises a cladding element, and the cladding element of the outer cladding layer is selected from one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B and P.

9. The positive electrode material according to claim 8, wherein the outer clad layer is a continuous and/or discontinuous clad layer; preferably, the outer cladding layer is a composite form of a continuous first cladding layer and a non-continuous second cladding layer; more preferably, the substance of the discontinuous coating layer is different from the substance of the continuous coating layer.

10. A method for determining the number of primary particles per unit sphere surface area of the secondary particles in the positive electrode active material according to any one of claims 1 to 7 or the positive electrode material according to any one of claims 8 to 9, comprising the steps of:

(1) selecting the average particle diameter D of the secondary particles_vPerforming SEM detection on 50 +/-20% of positive active material samples to obtain SEM spectra under 10K times;

(2) calculating the number σ of primary particles in the surface area of a unit sphere in the positive electrode active material according to the SEM spectrum obtained in the step (1) by the following formula:

σ＝(x1+x2)/2*(y1+y2)/2/(A/C*B/C)

wherein,

x1 represents the number of primary particles in the transverse direction of the lower edge of the picture in an SEM picture of the secondary particles by a factor of 10K;

x2 represents the number of primary particles in the lateral direction of the upper edge of the picture in the SEM image of the secondary particles by a factor of 10K;

y1 represents the number of primary particles in the longitudinal direction at the left edge of the picture in an SEM picture of 10K times the number of secondary particles;

y2 represents the number of primary particles in the longitudinal direction at the right edge of the picture in an SEM picture of a multiple of 10K of the secondary particles;

a represents the actual measured length in mm in the transverse direction of the SEM image of the secondary particle by a factor of 10K;

b represents the actual measured length in mm of the longitudinal direction of the SEM image of the secondary particle by a factor of 10K;

c represents the corresponding actual measured length in mm/μm at a scale of 1 μm in an SEM image of the secondary particles at a magnification of 10K;

when the number of primary particles in the SEM image of the secondary particles by a factor of 10K is calculated, one primary particle is calculated as long as a part of the primary particles appears.

11. An electrochemical energy storage device comprising the positive electrode active material according to any one of claims 1 to 7 or the positive electrode material according to any one of claims 8 to 9.

Images