CN116417611B

CN116417611B - Lithium-ion battery positive electrode additive, positive electrode plate and lithium-ion battery

Info

Publication number: CN116417611B
Application number: CN202111680874.2A
Authority: CN
Inventors: 李娜; 焦晓朋; 扶梅; 谭义江
Original assignee: BYD Co Ltd; Shenzhen BYD Auto R&D Co Ltd
Current assignee: BYD Co Ltd; Shenzhen BYD Auto R&D Co Ltd
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2025-01-14
Anticipated expiration: 2041-12-30
Also published as: CN116417611A

Abstract

The invention provides a positive electrode additive of a lithium ion battery, which is Li _xA_yC₂O₄, wherein A is at least one selected from K ⁺ and Na ⁺. The invention also provides a lithium ion battery positive electrode plate containing the lithium ion battery positive electrode additive and a lithium ion battery containing the positive electrode plate. Due to the introduction of doping atom A in the Li _xA_yC₂O₄ structure, li is easier to be separated out in the charging process, and the Li has a low lithium removal potential. The material is used as a positive electrode additive, can realize decomposition and lithium removal under a lower voltage condition, and avoids irreversible structural change of a positive electrode active substance under a continuous high charging voltage condition, thereby improving the stability and the cycle performance of the battery.

Description

Positive electrode additive of lithium ion battery, positive electrode plate and lithium ion battery

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a lithium ion battery positive electrode additive material, a positive electrode plate and a lithium ion battery.

Background

When the lithium ion battery is charged and discharged for the first time, the solid-liquid interface of the electrode and the electrolyte reacts to form a passivation film, namely an SEI film, on the surface of the electrode material. The formation of the SEI film consumes part of lithium ions, increases the irreversible capacity of the lithium ion battery for the first time, and reduces the charge and discharge efficiency. Therefore, lithium needs to be added to the electrode material to offset lithium ion consumption caused in the SEI film formation process, and the capacity and energy density of the battery are improved.

In literature "Sophie Solchenbach et al.Lithium Oxalate as Capacity and Cycle-Life Enhancer in LNMO/Graphite and LNMO/SiG Full Cells.Journal of The Electrochemical Society,165(3)：A512-A524", li ₂C₂O₄ material is reported to decompose and delithiate at around 4.7V. Li ⁺ generated during decomposition of Li ₂C₂O₄ can migrate to the negative electrode, supplement active lithium consumed by formation of a negative electrode SEI film, and the Li ₂C₂O₄ material can be used as a lithium supplementing material. However, the report shows that Li ₂C₂O₄ has a potential of decomposing and extracting lithium ions (delithiation potential) as high as 4.7V, and is only suitable for high-voltage lithium ion battery systems, such as LiNi _0.5Mn_1.5O₂ (working voltage 4.7-4.8V), and for most positive electrode materials, the delithiation potential value is far higher than the charge cut-off voltage, especially for ternary materials, the higher the charge voltage, the larger the irreversible change of the structure occurs, and the structural stability and the cycle performance are seriously affected. The delithiation potential of Li ₂C₂O₄ limits its application as a lithium-supplementing material.

Disclosure of Invention

The invention aims to provide a lithium ion battery positive electrode additive with a lower decomposition lithium removal potential, a positive electrode plate containing the additive material and a lithium ion battery.

The first aspect of the present invention provides a positive electrode additive for a lithium ion battery, wherein the positive electrode additive for a lithium ion battery is Li _xA_yC₂O₄, a is at least one selected from K ⁺ and Na ⁺, x+y=2, and 1< x <2.

In the additive material Li _xA_yC₂O₄, the cation Li ⁺ is +1, the valence state of the doped cation A is +1 as same as that of Li ⁺, the difference is that the ionic radius is that the radius of A ⁺(Na⁺ is 97pm, the radius of K ⁺ is 133 pm) and is larger than that of Li ⁺(Li⁺, the radius of the doped ion A ⁺ has an influence mechanism on Li _xA_yC₂O₄ delithiation potential, namely, the doped ion A ⁺ replaces part of Li in Li ₂C₂O₄, lattice distortion is caused by large-radius A ⁺ ions, the lattice layer spacing is enlarged, the distance between Li ⁺ and anions in the same molecule is enlarged, the acting force between the Li ⁺ and the anions is weakened, therefore, li ⁺ in Li _xA_yC₂O₄ is easier to decompose and release active lithium in the charging process, and Li _xA_yC₂O₄ has a low decomposition delithiation potential.

The lithium ion battery positive electrode additive can decompose and remove active lithium under lower voltage (namely has lower lithium removal potential), the lithium removal potential is reduced to below 4.6V, the active lithium removed by the additive is used for supplementing the consumption of negative electrode SEI film to lithium, and the low lithium removal potential avoids irreversible damage of various material structures in the battery under high voltage, so that the capacity, stability and other electrochemical performances of the battery are improved. The delithiation potential refers to the potential at which the positive electrode additive of the lithium ion battery is decomposed and Li ⁺ is extracted to release active lithium.

In some embodiments of the present invention, the value of x is 1.5.ltoreq.x <2, and preferably 1.9.ltoreq.x <2.

In some embodiments of the present invention, the lithium removal potential of the Li _xA_yC₂O₄ is not higher than 4.6V, and preferably, the lithium removal potential of the Li _xA_yC₂O₄ is 4.1V to 4.6V.

In some embodiments of the present invention, the Li _xA_yC₂O₄ has an average particle diameter of 50nm to 10. Mu.m, preferably 100nm to 1. Mu.m.

The second aspect of the invention provides a positive electrode plate of a lithium ion battery, which comprises a positive electrode active material and the positive electrode additive of the lithium ion battery provided by the first aspect of the invention.

In some embodiments of the invention, the positive electrode sheet of the lithium ion battery comprises a positive electrode current collector and a positive electrode material layer arranged on the positive electrode current collector, wherein the positive electrode material layer meets the following condition (1) or (2):

(1) The positive electrode material layer comprises a lithium ion battery positive electrode additive and a positive electrode active material which are mixed together;

(2) The positive electrode material layer includes a positive electrode active material layer and a positive electrode additive material layer disposed on the positive electrode active material layer, the positive electrode active material layer including a positive electrode active material, and the positive electrode additive material layer including a positive electrode additive of a lithium ion battery.

Specifically, the "positive electrode material layer", "positive electrode active material layer" and "positive electrode additive material layer" may further include materials required for forming a pole piece, such as a conductive agent and a binder, which may be selected from conductive agents and binders commonly used in the art, in addition to the above-mentioned positive electrode additive and/or positive electrode active material of a lithium ion battery, and will not be described herein.

The positive electrode active material is at least one selected from LiFePO ₄、LiMn₂O₄ and nickel-cobalt-manganese ternary materials (NCM), and in the positive electrode plate of the lithium ion battery, the ratio r of the mass of the positive electrode additive of the lithium ion battery to the mass of the positive electrode active material meets 0<r and is less than or equal to 0.15.

The third aspect of the invention provides a lithium ion battery, which comprises the positive plate of the lithium ion battery provided by the second aspect of the invention.

The technical scheme of the invention has the following beneficial effects:

(1) The lithium ion battery anode additive provided by the invention is decomposed to generate active lithium and gas, so that lithium supplementation is realized. Charging the battery in a proper charge-discharge interval can decompose the positive electrode additive material Li _xA_yC₂O₄, and the decomposition products are active lithium Li ⁺ and gas carbon dioxide CO ₂.Li⁺ for supplementing active lithium consumed by SEI, so that the battery capacity is improved.

(2) The lithium ion battery anode additive provided by the invention has low lithium removal potential and high lithium removal specific capacity. Due to the introduction of doping atoms A in the Li _xA_yC₂O₄ structure, the lattice distortion layer spacing of A with a large ion radius is increased, so that acting force between Li and anions is weakened, li is easier to be separated out in the charging process, and the Li has a low lithium removal potential. The material is used as a positive electrode additive, and can realize decomposition and lithium removal under the condition of lower voltage. The additive is suitable for anode material systems such as LiFePO ₄、LiMn₂O₄, NCM and the like, realizes decomposition at low voltage of 4.1-4.6V, completes lithium supplementation of the anode, and avoids irreversible structural change of anode active substances under the condition of continuous high charging voltage, thereby improving the stability and the cycle performance of the battery.

Additional features and advantages of the present invention will be set forth in the detailed description which follows.

Drawings

Fig. 1 is a charge-discharge curve of battery samples S3, S4, S5, and DS 1at a charge-discharge magnification of 0.1C;

fig. 2 is a charge-discharge curve of battery samples S4 and S6 at a charge-discharge magnification of 0.1C.

Detailed Description

The first aspect of the invention provides a positive electrode additive of a lithium ion battery, wherein the positive electrode additive of the lithium ion battery is Li _xA_yC₂O₄, A is at least one of K ⁺ and Na ⁺, x+y=2, and 1< x <2.

In the lithium ion battery positive electrode additive Li _xA_yC₂O₄, the A ions are K ⁺、Na⁺ or the combination of K ⁺ and Na ⁺, the radius 97pm of Na ⁺, the radius 133pm of K ⁺ and the radius 68pm of Li ⁺. Different doping of A ions has different degrees of influence on the lattice interlayer spacing, and the larger the radius of the A ions is, the larger the lattice interlayer spacing of Li _xA_yC₂O₄ is, the weaker the adsorption effect between Li ⁺ and anions is, and the lower the delithiation potential is. The ion A and Li are +1 valence, the larger the radius of the ion A, the larger the interlayer spacing of the Li _xA_yC₂O₄ lattice, and the weaker the acting force between Li and O in the same lattice.

In the Li _xA_yC₂O₄ material, the charge neutrality principle, that is, x+y=2, needs to be satisfied between the ratio y of a and the ratio x of Li.

In the Li _xA_yC₂O₄ material, the A ion has the function of weakening the acting force between the Li ion and the anion in the same crystal lattice, reducing the delithiation potential of the material and not participating in providing active lithium ions to the anode. When the Li ion duty ratio x is small, namely the doped A duty ratio y is high, the delithiation potential of the Li _xA_yC₂O₄ material is reduced, which means that when Li _xA_yC₂O₄ is taken as a positive electrode additive, active lithium can be decomposed and released under lower voltage, and the charge cut-off voltage of a conventional battery can be better compatible, but the content of available active lithium of Li _xA_yC₂O₄ can be reduced, the lithium supplementing specific capacity is low, so that the Li duty ratio x is not too low, the A is taken as the doped ion of the additive material Li _xA_yC₂O₄, and the A duty ratio is not too high. When x=2, the Li _xA_yC₂O₄ material does not contain A, at the moment, the Li ratio is high, the theoretical mass specific capacity is 526mAh/g, but no influence of the positive ion A on the lattice interlayer spacing is caused, the delithiation potential of the material is high, and the compatibility with the charge cut-off voltage of a conventional battery is poor, so that the Li ratio x is not excessively high. Considering the two aspects of lithium removal potential and lithium supplementing capacity of the additive material comprehensively, wherein x is 1< x <2. In this range, the effect of the large ion radius a on the lattice spacing of Li _xA_yC₂O₄ is enough to ensure the preferential extraction of Li, so that the decomposition potential of the additive material Li _xA_yC₂O₄ is not higher than 4.6V, the positive electrode active material, the electrolyte and other battery components are not affected, meanwhile, the higher lithium supplementing specific capacity of the Li _xA_yC₂O₄ material is ensured, more active lithium can be provided to compensate the active lithium consumed by the negative electrode SEI, and the lithium supplementing effect of the additive material as a positive electrode additive is not affected. Preferably, 1.5.ltoreq.x <2, and more preferably, 1.9.ltoreq.x <2.

The Li _xA_yC₂O₄ has a delithiation potential of not higher than 4.6V, and preferably the Li _xA_yC₂O₄ has a delithiation potential of 4.1V to 4.6V. The lithium removal potential can ensure that Li _xA_yC₂O₄ has higher lithium supplementing specific capacity, provides more active lithium to compensate the active lithium consumed by the negative electrode SEI, and can not influence positive electrode active substances, electrolyte and other battery components.

Li _xA_yC₂O₄ is used as an additive material capable of providing active lithium ions, and besides the large radius of the A ions of the Li _xA_yC₂O₄ causes the interlayer spacing of a crystal lattice to be large, the acting force between anions and Li is weakened so as to facilitate Li _xA_yC₂O₄ delithiation, and good conductivity is required to be ensured in the charging process. Since the additive material Li _xA_yC₂O₄ itself is poor in conductivity, it is required to make a more sufficient contact with the conductive agent to improve its conductive properties. When the particle size of Li _xA_yC₂O₄ is too large, the proportion of Li _xA_yC₂O₄ in contact with the conductive agent accounting for the total amount of Li _xA_yC₂O₄ is low, so that the decomposition speed is slow, the delithiation potential is possibly increased, the decomposition of Li _xA_yC₂O₄ is incomplete when the electrode is polarized to the cut-off voltage, active lithium in Li _xA_yC₂O₄ cannot be completely released to exert the maximum lithium supplementing effect, when the particle size of Li _xA_yC₂O₄ is small, the Li _xA_yC₂O₄ is fully contacted with the conductive agent, the decomposition of Li _xA_yC₂O₄ is facilitated, but the process difficulty of processing Li _xA_yC₂O₄ with smaller particle size is high, secondary agglomeration of Li _xA_yC₂O₄ with smaller particle size is easy to occur, and the stability in air is poor, so that water absorption is easy. therefore, the particle size of Li _xA_yC₂O₄ is preferably 50nm to 10 μm, more preferably 100nm to 1 μm, by combining the decomposition and lithium supplementing properties and physical and chemical properties of the additive Li _xA_yC₂O₄ material.

The second aspect of the invention provides a positive electrode plate of a lithium ion battery, which comprises the positive electrode additive of the lithium ion battery provided by the first aspect of the invention.

In the invention, the positive electrode plate of the lithium ion battery comprises a positive electrode current collector and a positive electrode material layer arranged on the positive electrode current collector, wherein Li _xA_yC₂O₄ is taken as an additive material, and the mode of introducing the additive material into the positive electrode material layer comprises, but is not limited to, a direct mixing method, a coating method and the like. The method comprises the steps of directly mixing Li _xA_yC₂O₄ with positive electrode active materials, a conductive agent, a binder and the like, carrying out slurry pulling coating to obtain a positive electrode material layer containing positive electrode additive materials Li _xA_yC₂O₄, wherein the positive electrode material layer contains a lithium ion battery positive electrode additive, a positive electrode active material, a conductive agent and a binder which are mixed together, and carrying out coating method, namely mixing Li _xA_yC₂O₄ with the conductive agent and the binder, carrying out slurry pulling coating on the positive electrode active material layer containing the positive electrode active materials, the conductive agent and the binder to obtain a multi-layer positive electrode material layer containing the positive electrode additive materials, wherein the positive electrode material layer contains the positive electrode active materials and the positive electrode additive materials arranged on the positive electrode active material layer, and the positive electrode additive materials layer contains a lithium ion battery positive electrode additive, a conductive agent and a binder.

When Li _xA_yC₂O₄ is used as a positive electrode additive material to realize lithium supplementation of a negative electrode, the doping amount of A cations in Li _xA_yC₂O₄ and the doping amount of Li _xA_yC₂O₄ can be set by comprehensively considering the lithium removal potential and the lithium removal specific capacity according to the highest charge cut-off voltage bearable by a battery system, and the maximum lithium supplementation capacity can be obtained on the premise of not influencing the battery system. For example, the positive electrode sheet of the lithium ion battery includes a positive electrode active material, the types of which include, but are not limited to, liFePO ₄、LiMn₂O₄ and NCM ternary materials, and the positive electrode active material may be selected from at least one of LiFePO ₄、LiMn₂O₄ and nickel cobalt manganese ternary materials. Specifically, the corresponding chemical formula of the NCM ternary material is LiNi _aCo_bMn_1-a-bO₂, wherein 0< a <1,0< b <1.

The irreversible capacity loss in the reference battery system accounts for 0-20%, and the delithiated capacity contributed by the positive electrode additive should be approximately equal to the loss value in order to compensate for the partially lost capacity. The lithium removal specific capacity of the positive electrode additive and the specific capacity of the positive electrode active material are comprehensively considered, and the ratio r of the mass of the positive electrode additive to the mass of the positive electrode active material in the positive electrode plate of the lithium ion battery can be 0<r-0.15.

Among them, the binder and the conductive agent are the conventional choices in the field of batteries. For example, the binder may be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin (e.g., polyethylene, polypropylene, polystyrene), sodium carboxymethyl cellulose (CMC), sodium alginate, etc., but is not limited thereto. The conductive agent may employ at least one of carbon black (e.g., acetylene black, ketjen black), carbon Nanotubes (CNT), graphene, carbon fiber, graphite, etc., but is not limited thereto. In addition, the positive electrode current collector may include, but is not limited to, a metal film, a foam metal mesh, etc., and may specifically be an aluminum foil, a carbon-coated aluminum foil, etc.

In a third aspect, the present invention provides a lithium ion battery, including the positive electrode sheet of the lithium ion battery provided in the second aspect of the present invention.

In addition to the positive electrode plate of the lithium ion battery provided by the second aspect of the invention, the lithium ion battery disclosed by the invention can further comprise a negative electrode plate, a diaphragm and electrolyte.

In the application, the negative electrode plate is a conventional choice in the field of batteries. The diaphragm is used for separating the positive pole piece from the negative pole piece to keep the insulativity between the positive pole piece and the negative pole piece, the diaphragm, the positive pole piece and the negative pole piece together form a battery cell of the battery, the battery cell is accommodated in a battery shell, and the battery shell can be an aluminum plastic film. The separator may be a polymer separator, a non-woven fabric or other common separator for batteries, including but not limited to a single-layer PP (polypropylene) film, a single-layer PE (polyethylene) film, a double-layer PP/PE, a double-layer PP/PP, a triple-layer PP/PE/PP or other separator. Electrolyte is injected into the battery shell, the electrolyte is a medium for transmitting lithium ions between the positive pole piece and the negative pole piece, and the specific composition of the electrolyte is a conventional choice in the battery field, so that the electrolyte is not limited.

The preparation method of the lithium ion battery comprises the steps of sequentially laminating a positive electrode plate, a diaphragm and a negative electrode plate to form a battery core, accommodating the battery core in a battery shell, injecting electrolyte, and sealing the battery shell to obtain the lithium ion battery.

The invention is described in further detail below by way of examples and with reference to the accompanying drawings.

Example 1

Li _1.05K_0.95C₂O₄ with the average grain diameter of 300nm is used as a positive electrode material, acetylene black is used as a conductive agent, polyvinylidene fluoride (PVDF) is used as a binder, N-methylpyrrolidone (NMP) is used as a dispersing agent, the materials are uniformly mixed according to the mass ratio of positive electrode to acetylene black to PVDF to NMP=85:10:5:50, aluminum foil is used as a current collector for coating, and then the materials are placed in a 120 ℃ oven for vacuum drying for 24 hours, and then the positive electrode plate is manufactured after tabletting and cutting. The method comprises the steps of taking a metal lithium sheet as a negative electrode, taking a cellgard 2400 polypropylene porous membrane as a diaphragm, taking a mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) of 1mol/L LiPF ₆ (EC and DMC volume ratio is=1:1) as an electrolyte, and completing the assembly of a test battery in a glove box filled with argon gas to obtain a battery sample S1.

Example 2

The battery sample S2 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.5K_0.5C₂O₄ having an average particle diameter of 300 nm.

Example 3

The battery sample S3 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.9K_0.1C₂O₄ having an average particle diameter of 300 nm.

Example 4

A battery sample S4 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.94K_0.06C₂O₄ having an average particle diameter of 300 nm.

Example 5

A battery sample S5 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.98K_0.02C₂O₄ having an average particle diameter of 300 nm.

Example 6

A battery sample S6 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.94Na_0.06C₂O₄ having an average particle diameter of 300 nm.

Example 7

The battery sample S7 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.94K_0.03Na_0.03C₂O₄ having an average particle diameter of 300 nm.

Example 8

The battery sample S8 was produced by the method of reference example 1, except that the positive electrode material used was Li _1.94K_0.06C₂O₄ having an average particle diameter of 1. Mu.m.

Example 9

The positive electrode sheet was produced by the method of reference example 1, except that the positive electrode materials used were LiFePO ₄ and Li _1.0sK_0.95C₂O₄ (300 nm) in a mass ratio of 90:10. Graphite is used as a cathode material, styrene-butadiene rubber (SBR) is used as a binder, sodium carboxymethylcellulose (CMC) is used as a thickener, water (H ₂ O) is used as a dispersing agent, the graphite, the SBR, the CMC and the H ₂ O=100:3:2:50 are uniformly mixed according to the mass ratio, then the mixture is coated on a copper foil, and then the copper foil is placed in a 90 ℃ oven for drying for 24 hours, and then the copper foil is pressed into tablets, and the negative plate is manufactured after cutting. The assembly of the test cell was completed in a glove box filled with argon, with the porous membrane of celgard2400 polypropylene as a separator, and a mixed solution of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 of 1mol/L LiPF ₆ as an electrolyte, to obtain a cell sample S9.

Example 10

The battery sample S10 was produced by the method of reference example 9, except that the positive electrode materials used were LiFePO ₄ and Li _1.5K_0.5C₂O₄ in a mass ratio of 90:10.

Example 11

The battery sample S11 was produced by the method of reference example 9, except that the positive electrode materials used were LiFePO ₄ and Li _1.94K_0.06C₂O₄ in a mass ratio of 90:10.

Example 12

The battery sample S10 was produced by the method of reference example 9, except that the positive electrode materials used were LiFePO ₄ and Li _1.94K_0.03Na_0.03C₂O₄ in a mass ratio of 90:10.

Example 13

(1) LiFePO ₄ is taken as an anode active material, acetylene black is taken as a conductive agent, polyvinylidene fluoride (PVDF) is taken as a binder, N-methylpyrrolidone (NMP) is taken as a dispersing agent, the anode active material, the acetylene black, the PVDF, the NMP=85:10:5:50 are uniformly mixed according to the mass ratio, aluminum foil is taken as an anode current collector for coating, and then the anode current collector is placed in a 120 ℃ oven for vacuum drying for 24 hours, so that an anode active material layer is obtained.

(2) Uniformly mixing acetylene black and PVDF and NMP=85:10:5:50 according to the mass ratio of Li _1.94K_0.06C₂O₄ (average particle size is 300 m) to obtain mixed slurry, coating the mixed slurry on the positive electrode active material layer prepared in the step (1), then placing the positive electrode active material layer in a 120 ℃ oven for vacuum drying for 24 hours, and tabletting and cutting the positive electrode active material layer to obtain the composite positive electrode sheet. In the positive electrode plate, the mass ratio of LiFePO ₄ to Li _1.94K_0.06C₂O₄ is 90:10.

(3) Graphite is used as a cathode material, styrene-butadiene rubber (SBR) is used as a binder, sodium carboxymethylcellulose (CMC) is used as a thickener, water (H ₂ O) is used as a dispersing agent, the graphite, the SBR, the CMC and the H ₂ O=100:3:2:50 are uniformly mixed according to the mass ratio, then the mixture is coated on a copper foil, and then the copper foil is placed in a 90 ℃ oven for drying for 24 hours, and then the cathode pole piece is manufactured after tabletting and cutting. And (3) taking the composite positive electrode plate prepared in the step (2) as a positive electrode plate, taking a cellgard 2400 polypropylene porous membrane as a diaphragm, taking a mixed solution (volume ratio of 1mo1/LLiPF ₆) of Ethylene Carbonate (EC) and dimethyl carbonate (DMC) as an electrolyte, and completing the assembly of a test battery in a glove box filled with argon to obtain a battery sample S13.

Comparative example 1

The battery sample DS1 was produced by the method of reference example 1, except that the positive electrode material used was Li ₂C₂O₄.

Comparative example 2

The battery sample DS2 was produced by the method of reference example 9, except that the positive electrode material used was LiFePO ₄.

Quantitative elemental analysis

According to EPA6010D-2018D inductively coupled plasma atomic emission spectrometry, quantitative analysis of Li element by adopting an ICP-OES-inductively coupled plasma emission spectrometer, and quantitative analysis of A element by adopting an AAS-atomic absorption spectrophotometer according to GB/T9723-2007 chemical reagent and general rules of flame atomic absorption spectrometry. In the results of the quantitative elemental analysis test in table 1,

Li _xA_yC₂O₄:

Li mass percent = Li total mass/(li+a) total mass;

mass percent a = a total mass/(li+a) total mass;

the transformation calculation can then yield x and y, respectively.

Table 1 shows the elemental quantitative analysis of 8 different Li _xA_yC₂O₄ in examples 1-8. And according to the mass ratio of the Li and the A element, calculating the corresponding molar ratio, namely correspondingly calculating the x and y values in the Li _xA_yC₂O₄.

TABLE 1

Li _xA_yC₂O₄ material decomposition Performance test

Specific capacity for first delithiation (mAh/g) =capacity for first delithiation/mass of active substance

Theoretical first lithium removal specific capacity (mAh/g) =theoretical Li total removal capacity/mass of active substance

Wherein, the first lithium removal specific capacity measured by S1-S8 reflects the lithium removal specific capacity of the Li _xA_yC₂O₄ material. The method for testing the first lithium removal specific capacity comprises the steps of charging a battery sample to a cut-off voltage of 4.6V or 4.8V at a charging current density of 0.1C in a constant current charging mode in a blue battery test cabinet, and stopping operation to obtain the first lithium removal specific capacity.

The calculation method of the theoretical Li total extraction capacity (corresponding to the theoretical first lithium removal specific capacity) is as follows:

(1) 1mol of Li _xA_yC₂O₄ material can be delithiated xmol;

(2) The charged quantity ＝x mol*6.02*10²³mol^-1*1.602*10^-19C＝x mol*6.02*10²³mol^-1*1.602*10^-19A·S＝xmol*6.02*10²³mol^-1*1.602*10^-19*(1000/3600)mAh, of x mol of Li is used for obtaining the electric quantity with the unit of mAh;

(3) Dividing the electric quantity calculated in the step (2) by the mass of Li _xA_yC₂O₄ in g to obtain the theoretical first lithium removal specific capacity, wherein the unit of the theoretical first lithium removal specific capacity is mAh/g.

The testing method of the primary charging voltage platform comprises the steps of charging a battery sample to a cut-off voltage of 4.6V or 4.8V at a charging current density of 0.1C in a constant current charging mode in a blue battery testing cabinet to stop operation, and obtaining a charging voltage-specific capacity curve (primary charging and discharging curve), wherein the platform of the charging voltage-specific capacity curve corresponds to the primary charging voltage platform of the battery.

Examples 1-8 all use the Li _xA_yC₂O₄ material as the battery positive electrode body, and the purpose is to more intuitively and simply test the Li _xA_yC₂O₄ material lithium removal potential (corresponding to the first charging voltage plateau measured by the battery sample of examples 1-8) and the lithium removal specific capacity (corresponding to the first lithium removal specific capacity measured by the battery sample of examples 1-8), and verify the Li _xA_yC₂O₄ as the battery positive electrode additive in the next part of lithium supplementing performance test.

In examples 1-8, the positive host material of the battery was Li _xA_yC₂O₄, and during the first charge, li _xA_yC₂O₄ began to split off lithium at a certain voltage plateau to release active lithium. The Li _xA_yC₂O₄ decomposition performance includes two aspects, namely the first lithium removal specific capacity and the second lithium removal potential. The first delithiation specific capacities of the battery samples S1-S8 of examples 1-8 reacted with the active lithium capacities of Li _xA_yC₂O₄ that released lithium, the delithiation potentials corresponding to the potentials required for Li _xA_yC₂O₄ to decompose and release active lithium, and the ease of Li _xA_yC₂O₄ to decompose and delithiate, were reacted by the first charge voltage plateau of the battery samples S1-S8 in examples 1-8. When the lithium removal potential is reached, li _xA_yC₂O₄ decomposes and releases lithium ions, and the lower the lithium removal potential and the higher the lithium removal specific capacity, the better the lithium supplementing performance when Li _xA_yC₂O₄ is used as a positive electrode additive.

(1) Comparison of Li _xA_yC₂O₄ decomposition Properties with K ⁺ cation, different Li ratios

Fig. 1 is a charge-discharge curve of battery samples S3, S4, S5, and DS1 at a charge-discharge magnification of 0.1C. The results of the tests of the first lithium removal specific capacity and the first charge voltage plateau of examples 1 to 5 and comparative example DS1 are shown in Table 2. The theoretical primary lithium removal specific capacity is found to be higher along with the increase of the Li ratio, which is because the partially substituted K does not participate in decomposition removal and does not contribute capacity, the theoretical primary lithium removal specific capacity is compared with the actual primary lithium removal specific capacity, S1, S2, S3, S4 and S5 are completely removed under 4.6V, the theoretical amount of active lithium is released, the DS1 is free of A cation doped Li ₂C₂O₄, the actual primary lithium removal specific capacity only occupies 64.6% of the theoretical value under the cut-off voltage of 4.8V, li is not completely removed, the primary charging voltage platform, namely the Li removal platform potential (lithium removal potential), the higher the Li ratio is, the less doped A cations are, the lithium removal potential is higher, DS1-4.7V > S5-4.55V > S4-4.51V > S3-4.47V > S2-4.23V > S1-4.11V. Therefore, the Li _xA_yC₂O₄ material portion Li is substituted with K and its delithiation potential decreases.

TABLE 2

The test results of fig. 1 and table 2 show that the dilithiation potential of the DS1 sample is 4.7V, the DS1 sample is not decomposed when the charge cutoff potential is set at 4.6V, the first dilithiation specific capacity is about zero, and the S1, S2, S3, S4 and S5 samples have higher first dilithiation specific capacities than the DS1 sample in the battery system with the cutoff potential of 4.6V, which means that Li _xA_yC₂O₄ of the present invention can provide more active lithium to the negative electrode than Li ₂C₂O₄. Meanwhile, the S1, S2, S3, S4 and S5 samples have lower primary charging voltage platforms compared with DS1, which indicates that when Li _xA_yC₂O₄ is used as a positive electrode additive material, lithium can be decomposed and removed to release active lithium under the condition of lower voltage, the influence of high charging voltage on the structure of the positive electrode active material can be avoided, and the stability and the cycle performance of the battery are improved.

When Li _xA_yC₂O₄ is used as a positive electrode additive material to realize lithium supplementation of a negative electrode, the lithium removal potential and the lithium removal specific capacity of Li _xA_yC₂O₄ can be comprehensively considered according to the highest charge cut-off voltage bearable by a battery system, and the maximum lithium supplementation capacity can be obtained on the premise of not influencing the battery system.

(2) Comparison of Li _xA_yC₂O₄ Material decomposition Properties with Li occupancy, different K ⁺ and Na ⁺

Fig. 2 is a charge-discharge curve of battery samples S4 and S6 at a charge-discharge magnification of 0.1C, and test results of the first delithiation specific capacity and the first charge voltage plateau are shown in table 3. It can be found that the theoretical first lithium removal specific capacity has small difference under the condition that the Li ratio is consistent and the relative atomic mass of only a small amount of doped A ions K and Na is different, and basically consistent, the theoretical first lithium removal specific capacity is compared with the actual first lithium removal specific capacity, S4 and S6 are completely removed under 4.6V to release the theoretical amount of active lithium, the first charging voltage platform is the lithium removal potential, the difference of the lithium removal potential is shown to be mainly related to the ion radius of doped cations, the ion radius is respectively S4-K ⁺-133pm＞S6-Na⁺ -97pm, the larger the ion radius causes lattice distortion, the larger the layer spacing is, the weaker the acting force between Li and anions is correspondingly caused, the lithium removal is easy to be carried out in the charging process, and the lower the lithium removal potential (the first charging voltage platform) is. Therefore, the Li _xA_yC₂O₄ material has a reduced lithium removal potential by replacing part of Li with A, and the practically available active lithium capacity is improved.

In Table 3, the Li _xA_yC₂O₄ material co-doped with K ⁺ and Na ⁺ is completely delithiated at 4.6V to release the theoretical amount of active lithium, and the first charge voltage plateau, namely the delithiated potential, shows S7-4.52V, which is intermediate between S4 and S6, and the performance is also related to the ionic radius. Therefore, the co-doping of K+ and Na ⁺ can also reduce the lithium removal potential of the Li _xA_yC₂O₄ material, and the practically available active lithium capacity is improved.

TABLE 3 Table 3

(3) Comparison of Li _1.94K_0.06C₂O₄ Material decomposition Properties of different particle sizes

The decomposition performance (first lithium removal specific capacity and first charging voltage platform) of the Li _1.94K_0.06C₂O₄ materials with different particle sizes is shown in table 4, the theoretical and actual first lithium removal specific capacities are compared, S4 and S8 are completely removed under 4.6V to release the theoretical amount of active lithium, and the first charging voltage platform is compared to remove lithium potential, so that S7-4.57V > S4-4.51V is shown, and the difference of the lithium removal potential is mainly related to the particle size of the Li _1.94K_0.06C₂O₄ material. S4 is a particle with an average particle diameter of 300nm, S8 is a large particle with an average particle diameter of 1 μm, and the smaller the particle diameter is, the better the electric contact with a conductive agent, an electrolyte and the like, the smaller the battery polarization is, the lower the corresponding delithiation potential is, and the larger the particle diameter is, the larger the battery polarization is, resulting in higher delithiation potential.

TABLE 4 Table 4

3. Lithium supplementing performance test of Li _xA_yC₂O₄ material

Examples 9-13 were lithium iron phosphate battery systems incorporating Li _xA_yC₂O₄ material as the positive electrode additive material, and the positive electrode materials described in S9-S12 and DS2 were identical in mass, and the total mass of LiFePO ₄ and Li _1.94K_0.06C₂O₄ in S13 was identical to the mass of the positive electrode materials described in S9-S12. The lithium supplementing effect of the Li _xA_yC₂O₄ material is verified, the decomposed and separated active lithium can be used for compensating the active lithium consumed by the negative electrode SEI, and the battery capacity is improved.

The charge and discharge regimes of batteries S9-13 and DS2 were 4.6V for the charge cut-off voltage and 2.00V for the discharge cut-off voltage. The first charge and discharge capacities of batteries S9-13 and DS2 are listed in Table 5, and the results show that the positive active material LiFePO ₄ of the DS2 battery has a first charge exertion capacity of 1082.1mAh, the generation of negative SEI consumes about 12% of active lithium, so that only 952.2mAh can be embedded in the first discharge, and the positive electrode of S9-13 introduces additive Li _xA_yC₂O₄ to decompose in the charging process to provide active lithium, the discharge capacity of the battery is basically the same as the charge capacity of DS2, which indicates that the active lithium provided by decomposition in the charging process of Li _xA_yC₂O₄ can meet SEI film consumption, sufficient active lithium is supplemented, and sufficient active lithium can be enabled to be discharged and embedded in LiFePO ₄. The Li _xA_yC₂O₄ material can supplement active lithium consumed by the negative electrode SEI film, so that the capacity of the battery is remarkably improved.

TABLE 5

Battery numbering	First charge capacity mAh	First discharge capacity mAh
			S9	1194.3	1069.1
S10	1239.9	1069.6
			S11	1290.3	1075.3
S12	1309.2	1073.7
			S13	1291.7	1077.1
DS2	1082.1	952.2

Claims

1. The positive electrode additive of the lithium ion battery is characterized in that the positive electrode additive of the lithium ion battery is Li _xA_yC₂O₄, A is at least one of K+ and Na+, x+y=2, and 1< x <2;

The average particle size of Li _xA_yC₂O₄ is 50 nm-10 μm.

2. The positive electrode additive for lithium ion batteries according to claim 1, wherein in said Li _xA_yC₂O₄, 1.5.ltoreq.x <2.

3. The positive electrode additive for lithium ion batteries according to claim 1, wherein in said Li _xA_yC₂O₄, 1.9.ltoreq.x <2.

4. The positive electrode additive for a lithium ion battery according to claim 1, wherein the delithiation potential of Li _xA_yC₂O₄ is not higher than 4.6V.

5. The positive electrode additive for lithium ion batteries according to claim 1, wherein the Li _xA_yC₂O₄ has a delithiation potential of 4.1v to 4.6v.

6. The positive electrode additive for lithium ion batteries according to claim 1, wherein the average particle diameter of Li _xA_yC₂O₄ is 100nm to 1 μm.

7. A positive electrode plate of a lithium ion battery is characterized in that the positive electrode plate of the lithium ion battery comprises the components of claim 1-1

6, The positive electrode additive of the lithium ion battery.

8. The positive electrode tab for a lithium ion battery according to claim 7, wherein the positive electrode tab for a lithium ion battery comprises a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector, the positive electrode material layer satisfying the following condition (1) or (2):

(1) The positive electrode material layer comprises the positive electrode additive and a positive electrode active material of the lithium ion battery;

(2) The positive electrode material layer comprises a positive electrode active material layer and a positive electrode additive material layer arranged on the positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode active material, and the positive electrode additive material layer comprises the positive electrode additive of the lithium ion battery.

9. The positive electrode plate of the lithium ion battery according to claim 7 or 8, wherein the positive electrode plate of the lithium ion battery comprises a positive electrode active material, the positive electrode active material is selected from at least one of LiFePO ₄、LiMn₂O₄ and nickel-cobalt-manganese ternary materials, and the ratio r of the mass of the positive electrode additive of the lithium ion battery to the mass of the positive electrode active material in the positive electrode plate of the lithium ion battery is 0<r or less than 0.15.

10. A lithium ion battery, characterized in that the lithium ion battery comprises the positive electrode sheet of the lithium ion battery according to any one of claims 7 to 9.