CN106159269A - A kind of preparation method of high-voltage lithium ion batteries cathode pole piece - Google Patents

Abstract

The invention discloses a preparation method of a negative electrode sheet of a high-voltage lithium-ion battery, which is to add an organic acid ester to the negative electrode slurry of a traditional lithium-ion battery to artificially form an initial SEI film on the surface of the negative electrode. When the battery is activated When directly participating in the reaction of forming the SEI film, modifying the interface structure of the electrolyte and the negative electrode material, reforming the components of the SEI film to improve the stability of the SEI film and the transport of lithium ions, to prevent the electrolyte from forming on the surface of the negative electrode under high voltage. Side reactions such as continuous decomposition occur. The negative electrode sheet of the battery can be well applied to high-voltage lithium-ion batteries, improve the cycle performance of the full battery under high voltage, solve the problem of lack of compatible graphite negative electrode materials for new high-voltage positive electrode materials, and more importantly, break through high-voltage lithium-ion batteries. The bottleneck of high energy density lithium-ion batteries under voltage is difficult to industrialize and develop, making it a reality to increase the energy density of current lithium-ion batteries from the perspective of increasing voltage.

Description

A kind of preparation method of high-voltage lithium-ion battery negative pole piece

technical field

The invention relates to a lithium-ion battery, in particular to a method for preparing a negative pole piece of a high-voltage lithium-ion battery.

Background technique

Since Sony manufactured the first generation of commercial lithium-ion batteries in 1990, it has occupied a large share in the existing market, and its development momentum has grown rapidly, especially in recent years due to people's excessive use of non-renewable energy sources such as oil and coal. Exploitation and utilization have accelerated the depletion of fossil resources and brought severe global environmental problems. People have to vigorously develop renewable energy like electric energy. Among them, how to effectively store and rationally use electric energy is the most researched. Compared with traditional secondary batteries (lead-acid, nickel-cadmium, nickel-metal hydride batteries, etc.), lithium-ion batteries have higher energy density and operating voltage, low pollution and longer service life, and have occupied more and more The market is high-efficiency energy storage components and electric energy release systems. However, compared with modern development and industry needs, such as artificial intelligence, portable electronic devices such as mobile phones, cameras, notebooks, and mobile phones, their low energy density greatly hinders their development space and application range, especially the development of electric vehicles. Li-ion batteries with high energy density are more urgently needed. The energy density of lithium ions is determined by the working voltage and the capacity of the material, and increasing its working voltage is a simple and feasible way to increase the energy density of batteries. For example, the charging cut-off voltage of the existing commercial LiCoO ₂ is 4.2V, and the corresponding specific capacity is 140 mAh g ^-1 . A specific capacity of about 190 mAh g ^-1 can be obtained when the charge cut-off voltage is increased to 4.5 V, which significantly improves its energy density. However, the corresponding side reactions of the battery under high voltage are intensified, and the electrolyte solution is decomposed. It is difficult for the full battery under high voltage to be a practical commodity and serve the society. Similarly, the spinel-structured high-voltage cathode material represented by LiNi _0.5 Mn _1.5 O ₄ (LNMO) has a 4.7V (Vs Li ⁺ /Li) high-voltage charge-discharge platform with a specific capacity of 146.7 mAh g ^-1 . The energy density can reach or even exceed 220wh/kg, while the energy density of a single battery at this stage is only 110~150wh·kg ^-1 , and the preparation cost of LNMO cathode material is low and the method is simple, it has excellent high-current charge and discharge performance and high safety, etc. advantage. Unfortunately, based on the existing technology, the electrochemical performance of LNMO/graphite full battery has not yet reached the level of practical application. In particular, the specific capacity of the full battery decreases significantly with the cycle, which greatly restricts its high voltage and high performance. Energy Density Li-ion Battery Development. In addition, there are many kinds of high-voltage cathode materials, such as phosphate-based LiCoPO ₄ , LiMnPO ₄ , etc., which also have the same problem. Therefore, the key to realizing a commercial lithium-ion battery system with high energy density at high voltage lies in the development and The matching negative electrode material and electrolyte.

In order to improve the electrochemical performance of lithium-ion full batteries under high voltage, it is also an important way to explore high-voltage electrolyte additives and optimize the electrolyte formula, but the additives themselves will also affect the resistance and capacity of the battery. The starting point of the present invention is to explore from the aspect of the negative electrode, and proposes to start directly from the solid electrolyte membrane (SEI) with the most violent battery reaction, and try to modify and modify the SEI membrane under high voltage conditions; The resource is abundant, the preparation is simple and the cost is cheap, and now in the actual commercial application of lithium-ion batteries, graphitic carbon materials still occupy the dominant position of the negative electrode materials of lithium-ion batteries. Therefore, the negative electrode material for the high-voltage lithium battery of the present invention is also carried out on the graphite material, has direct commercial value, and can be directly put into production.

Contents of the invention

In order to solve the problems of poor cycle performance and serious capacity fading of current high-voltage lithium-ion full batteries, the present invention provides a method for preparing negative pole pieces of high-voltage lithium-ion batteries, which improves the performance of high-voltage lithium-ion full batteries from the aspect of negative electrodes of lithium-ion batteries. Cycle performance, so as to realize its commercial value.

The technical scheme that realizes the object of the present invention is:

A method for preparing a high-voltage lithium-ion battery negative pole piece, comprising the following steps:

(1) First dissolve a certain amount of binder in deionized water to make a uniform water-based viscous slurry mother liquor;

(2) Then add the conductive agent and the negative electrode material into the slurry mother liquor, and after being uniformly dispersed, add the organic acid ester for mixing and beating to make the negative electrode slurry;

(3) Put the negative electrode slurry prepared in step (2) in a vacuum state of -0.08MPa ~ -0.1MPa, keep the vacuum for 0.5h~20h, and control the vacuum temperature at 20~50°C to ensure that the organic acid grease is dispersed to the negative electrode material surface;

(4) Sieve the slurry in step (3) to obtain a fineness of 15 ~ 45um, and coat it on the negative electrode conductive copper foil by roller coating or spraying, and obtain the negative electrode with the initial SEI film structure on the surface after drying sheet, assembled with the positive electrode sheet to form a battery system, and finally use a constant current of 0.02C~0.5C for chemical formation to obtain a stable SEI film;

The batching of described negative pole is made by negative pole material, conductive agent, binding agent and organic acid ester, and its ratio is respectively:

Anode material 75~90%

Binder 1~5%

Conductive agent 2~5%

Organic acid ester 1~20%

After the batching is completed, it is dissolved in deionized water to obtain negative electrode slurry. The solid content of the slurry is 25-55%, and the viscosity is 1000-5000mPa.s.

In the above preparation method, the beating temperature in step (2) is 20-50° C., and the humidity is 5-20%.

In step (4), the coating speed of the roller coating method is 3-10m/min, and the baking temperature is 70-110°C; the coating speed of the spray coating method is 5-13m/min, and the oven temperature is 70-110°C; The thickness of the prepared negative electrode sheet is 0.02-0.2mm.

The negative electrode material is at least one of natural graphite, artificial graphite, composite graphite, soft carbon, and hard carbon.

The conductive agent is at least one of conductive graphite (including SP, KS-6, carbon nanotubes); carbon fiber (CF).

The binder is at least one of water-based hydroxymethylcellulose (CMC), styrene-butadiene rubber (SBR), and binder LA133.

The organic acid ester is at least one of organic titanate, organic silicate, and organic phosphate

The high-voltage lithium-ion battery negative electrode sheet prepared by the method of the present invention can be matched with the following high-voltage positive electrode materials to prepare commercial full batteries: LiMn ₂ O ₄ with spinel structure, LiNi _0.5 Mn _1.5 O ₄ , Li _z Ni _x Mn _1-x O ₂ ; Li _z Co _1-(x+y) Ni _x Mn _y O ₂ (where x, y, x+y<1, z≥1); olivine structure LiMPO ₄ or Li ₂ MPO ₄ F (M=Co, Mn, Ni); LiNiVO ₄ , LiMeSO ₄ F (Me=Co, Ni, Cu), high-voltage layered LiCoO ₂ (charge cut-off voltage ≥ 4.3V).

The method of the present invention is to modify the surface of the negative electrode with an organic acid ester, and the organic acid ester participates in the formation of the SEI film during the charge and discharge process, modifies the interface structure between the electrolyte and the negative electrode material, and reforms the components of the SEI film to improve its SEI. Membrane stability and lithium ion transport can prevent side reactions such as continuous decomposition of the electrolyte on the surface of the negative electrode under high voltage.

The negative pole piece of the present invention is mainly used as a lithium-ion battery with a working voltage higher than 4.3V, and the voltage of a traditional lithium-ion battery is generally below 4.0V (LiCoO ₂ /carbon material, LiFePO ₄ /carbon material, LiMn ₂ O ₄ / Carbon materials, etc.), for example, the negative pole piece prepared by Chinese patent CN201210221178 is also used in low-voltage lithium batteries, and the oxidation decomposition of organic electrolyte is limited under this voltage. From the perspective of energy density, increasing the voltage of lithium batteries will inevitably lead to an increase in energy density. The higher the voltage, the higher the energy density. However, when the voltage is higher than 4.3V, the electrolyte will decompose rapidly, and the decomposition products will adhere to the surface of the negative electrode to form The thicker SEI film hinders the transmission channel of lithium ions, which leads to the reduction of cycle life and rapid decline of capacity of lithium ion batteries. When the charging voltage reaches 4.8V, the battery basically has no cycle capacity.

Compared with the present technology, the preparation method of the negative pole piece of the high-voltage lithium-ion battery of the present invention:

(1) The present invention is developed on the basis of traditional negative electrode materials for lithium-ion batteries. It is used as negative electrode materials for high-voltage lithium-ion batteries. The preparation method is simple and feasible, and the cost is low and easy to implement. Industrial production.

(2) The battery negative pole piece prepared by the present invention can be well applied to high-voltage lithium-ion batteries, such as the existing LiNi _0.5 Mn _1.5 O ₄ , high-voltage LiCoO ₂ , Li ₃ V ₂ (PO ₄ ) ₃ , LiCoPO ₄ , Li ₂ CoPO ₄ F, Li ₂ FeSiO ₄ , Li ₂ FePO ₄ F and other new high-voltage cathode materials can improve the cycle performance of full batteries under high voltage and solve the lack of compatibility of new high-voltage cathode materials. The issue of graphite anode materials, more importantly, is to break through the bottleneck of high-energy-density lithium-ion batteries under high voltage, which is difficult to industrialize and develop, making it a reality to increase the energy density of current lithium-ion batteries from the perspective of increasing voltage.

(3) The preparation method of the present invention is compared with the negative electrode sheet prepared by adding inorganic additives (Li ₂ CO ₃ ), and the negative electrode sheet prepared by the present invention can be better applied to the battery system under high voltage. Compared with the reaction at low voltage, its high voltage poses a more severe challenge to the anode material of lithium-ion batteries, not only to ensure excellent electrochemical performance such as first-time efficiency and large specific capacity, but also to ensure its electrolytic performance at high voltage. The heterogeneous catalytic effect of liquid is the lowest. Compared with inorganic negative electrode additives, organic acid esters can better participate in the formation of SEI film in situ during charge and discharge, and solidify and modify the structure of SEI film to prevent further decomposition of electrolyte.

Description of drawings

Fig. 1 is the comparison curve of the first charge and discharge of the full battery assembled by the battery negative pole pieces prepared in Comparative Examples 1, 2 and Examples 1, 2, 3 of the present invention and matched with 4.7V high-voltage positive LNMO;

Figure 2 is a comparison curve of the cycle performance of the full battery assembled in Comparative Examples 1, 2 and Examples 1, 2, and 3 of the present invention.

Fig. 3 is the discharge curve diagram of different cycle times of the full battery assembled by the battery negative electrode sheet matched with the 4.7V high-voltage positive electrode LNMO prepared by Comparative Example 1 and Examples 1, 2, and 3 of the present invention, respectively 1st, 5th, and 10th. , 20, 50 discharge curves.

detailed description

The content of the present invention will be described in further detail below in conjunction with specific embodiments and drawings, but the present invention is not limited to the following embodiments.

Comparative example 1

The conventional negative pole sheet prepared by common graphite material comprises the following steps:

(1) Dissolve 3% CMC in deionized water to make viscous slurry mother liquor;

(2) After the slurry mother liquor is fully mixed, add 2% conductive agent and mix to prepare conductive slurry;

(3) After uniform dispersion, add 90% natural graphite material, control the beating temperature to 25°C, and the humidity to 10%;

(4) After the materials are mixed evenly, adjust the viscosity of the slurry to 4000mPa.s and the solid content to 48%;

(5) Put the slurry in a vacuum state of -0.08MPa, keep the vacuum state for 5 hours, and the vacuum temperature is 25°C;

(6) After sieving the prepared slurry to a fineness of 30um, it is coated on the negative electrode conductive copper foil or copper grid by roller coating, the coating speed is 5m/min, and the oven baking temperature is distributed in steps Among them, the highest temperature is 95°C, and the lowest temperature on both sides is 85°C. After drying, the thickness of the negative electrode is 0.168mm, and the surface density of one side of the negative electrode is 104g/m ² .

Comparative example 2

Adopt conventional negative electrode additive Li ₂ CO ₃ Lithium-ion battery graphite negative pole sheet prepared, comprises the following steps:

Steps (1)-(2) are the same as Comparative Example 1, step (3) after adding natural graphite, add an aqueous solution with a content of 1wt% inorganic Li ₂ CO ₃ as a negative electrode additive; adjust the viscosity of the slurry to 4000mPa.s, solid The content is 48%; as in Comparative Example 1, the vacuum operation is continued, sieved and coated, and dried to obtain a negative electrode sheet containing inorganic Li ₂ CO ₃ additives. The thickness and density of the negative electrode sheet are the same as in Comparative Example 1.

As one of the main components of the SEI film, inorganic Li ₂ CO ₃ can effectively reduce the decomposition degree of the electrolyte in the formation of the SEI film, improve the first-time efficiency of the lithium-ion battery during the battery formation process, and improve the cycle life of the battery. It plays an important role, and it is also commonly used as a common additive in negative electrode slurry ingredients in battery systems.

Example 1

Adopting the method of the present invention to prepare the negative pole piece of high-voltage lithium-ion battery comprises the following steps:

Steps (1)-(2) are the same as Comparative Example 1, step (3) adds organic titanate with a mass fraction of 10% after adding natural graphite; adjust the viscosity of the slurry to 4000mPa.s, and the solid content is 48%; Proportion 1 continued vacuum operation, sieving and coating, and after drying, a negative electrode sheet with an initial state organic titanate SEI film structure on the surface was obtained. The thickness and single-side surface density of the negative electrode sheet were the same as those of Comparative Example 1. After the battery is formed, organic titanate participates in and modifies the SEI film to stabilize the SEI film and make it more resistant to high voltage conditions.

Example 2

Adopting the preparation method of the present invention to prepare the negative pole piece of high-voltage lithium-ion battery comprises the following steps:

Steps (1)-(2) are the same as Comparative Example 1, step (3) adds organic titanate with a mass fraction of 15% after adding natural graphite; adjust the slurry viscosity to 4000mPa.s, and the solid content is 48%; Proportion 1 continues vacuum operation, sieving and coating, and after drying, a negative electrode sheet with an initial SEI film structure on the surface is obtained.

Example 3

Adopting the preparation method of the present invention to prepare the negative pole piece of high-voltage lithium-ion battery comprises the following steps:

Steps (1)-(2) are the same as Comparative Example 1, and step (3) adds organic phosphate with a mass fraction of 10% after adding natural graphite; adjust the viscosity of the slurry to 4000mPa.s, and the solid content is 48%; as in the comparative example 1 Continue vacuum operation, sieving and coating, and after drying, a negative electrode sheet with an initial SEI film structure on the surface is obtained.

The performance test parameters of the full battery composed of the lithium-ion battery negative pole piece prepared in the above examples and comparative examples and the high-voltage positive electrode material LNMO are shown in Table 1.

The test data in this table is based on the LAND electrochemical test system, and its test conditions: the full battery cycle performance test voltage range is 3.4~4.8V, the first charge and discharge cycle is performed twice at 0.5C, and then 60 cycles with 1C constant current charge and discharge (where 1C=146.7mAh/g).

Table 1

As can be seen from the data in Table 1, the initial efficiency of the high-voltage full battery assembled by the conventional graphite negative pole piece is generally lower than that of the full battery assembled by the high-voltage negative pole piece prepared by the present invention, which means that ordinary graphite is used as the battery negative pole surface to form The SEI film is unstable and cannot effectively prevent the decomposition of the electrolyte, and its side reactions are much higher than that of the negative electrode sheet prepared by the present invention. Similarly, the capacity retention data of the full battery after 60 cycles has also confirmed that the negative electrode sheet prepared by the present invention has excellent performance under high voltage conditions, and the capacity decay trend is slow as the cycle progresses, which improves the actual performance of high-voltage lithium-ion batteries. service life. In addition, the 2nd and 60th cycle discharge average voltages of the full battery assembled by the conventional graphite negative pole piece are significantly lower than the full battery prepared in Examples 1, 2, and 3 of the present invention, indicating that the conventional graphite negative pole piece is more advanced than the present invention. The internal polarization of the full battery composed of negative pole pieces is serious, and many side reactions occur.

Referring to Figure 1, the comparison curves of the first charge and discharge of the full battery assembled by the battery negative pole pieces prepared in Comparative Examples 1, 2 and Examples 1, 2, and 3 of the present invention matched with 4.7V high-voltage positive LNMO can be seen from the figure: The first discharge platform of the LNMO full battery assembled with the negative pole piece prepared by ordinary graphite in Examples 1, 2, and 3 of the present invention is maintained at about 4.6V and the platform is relatively flat. The discharge platform of the ordinary graphite comparative example is not obvious, inclined and the discharge voltage The platform is significantly lower than 4.6V. Combined with the first charging platform, it can be judged according to the potential difference between the charging and discharging platforms, the potential difference of Comparative Example 1 is much greater than that of Examples 1, 2, and 3 of the present invention, indicating that the negative pole piece obtained by ordinary graphite is used as a high voltage In the battery, the battery is severely polarized and has many side reactions. In addition, the side reaction is most obvious in the process of forming the SEI film for the first time. The degree of the side reaction directly affects the first efficiency of the battery. A high first efficiency means that the side reaction is small; a low first efficiency means that the side reaction is severe. According to the first charge and discharge data and Table 1, it can be clearly seen that the first efficiency of the full battery assembled into the negative pole piece prepared by ordinary graphite is only 59.82%, which is obviously lower than the negative pole piece prepared by the present invention, indicating that the present invention obtains The negative pole piece can reduce the occurrence of side reactions under high voltage. It is worth mentioning that the negative electrode sheet obtained by traditionally doping Li ₂ CO ₃ also has a higher initial efficiency, which shows that the addition of Li ₂ CO ₃ also inhibits the decomposition of the electrolyte when the SEI film is formed for the first time.

Referring to Fig. 2, the cycle performance comparison curves of the full battery assembled by the negative pole piece of the battery prepared in Comparative Examples 1, 2 and Examples 1, 2, and 3 of the present invention matched with 4.7V high-voltage positive electrode LNMO can be seen from the figure: The negative electrode sheet made of graphite is used in a high-voltage LNMO full battery. As the cycle progresses, the capacity decays seriously. After the 50th cycle, the capacity is only 83.10% of the initial capacity; The capacity has basically no decay, and the capacity after the 50th cycle is 97.51% of the initial capacity, reflecting a stable cycle life under high voltage. In addition, Comparative Example 2 is a negative electrode sheet obtained by traditionally doping Li ₂ CO ₃ . According to the cycle curve of the full battery, it can be seen that although the battery has a high specific capacity within the initial 10 cycles, the specific capacity decreases with time after 10 cycles. The capacity decays rapidly as the cycle progresses, indicating that the negative electrode sheet prepared by traditionally adding Li ₂ CO ₃ is not suitable for high-voltage lithium-ion batteries.

Referring to Fig. 3, the discharge curves of the first, 5th, 10th, 20th and 50th discharge curves of the full battery assembled by the negative pole piece of the battery prepared in Comparative Example 1 and Examples 1, 2, and 3 of the present invention matched with the 4.7V high-voltage positive electrode LNMO , it can be clearly seen from the figure that the state of the voltage platform and the degree of capacity attenuation under different times can be seen by referring to Figure 3. Compared with Comparative Example 1, the consistency of the full battery discharge platform of Embodiments 1, 2, and 3 of the present invention remains good. , and the consistency of the capacity is also very good, indicating that the negative pole piece prepared by the method of the present invention can be completely applied to the lithium-ion battery system of the high-voltage system and has excellent performance.

Claims (8)

1. the preparation method of a high-voltage lithium ion batteries cathode pole piece, it is characterised in that comprise the following steps:

(1) first a certain amount of binding agent is dissolved in deionized water, makes uniform tackiness slurry mother solution；

(2) then conductive agent and negative material are added in slurry mother solution, after dispersed, add organic acid esters mixing and beat Slurry, makes cathode size；

(3) cathode size that step (2) prepares is placed in vacuum state-0.08MPa ~-0.1MPa, keeps vacuum time 0.5h ~ 20h, true temp controls at 20 ~ 50 DEG C, it is ensured that acylate is distributed to negative material surface；

(4) step (3) slurry is sieved that to obtain fineness be 15 ~ 45um, use roller coat or spraying method to be coated in negative pole and lead On electrolytic copper paper tinsel, i.e. obtain surface after drying and there is the cathode pole piece of initial state SEI membrane structure, be assembled into cell body with anode pole piece System, finally uses constant current 0.02C ~ 0.5C to carry out chemical conversion and obtains stable SEI film；

The dispensing of described negative pole is made up of negative material, conductive agent, binding agent and organic acid esters, and its ratio is respectively:

Negative material 75 ~ 90%

Binding agent 1 ~ 5%

Conductive agent 2 ~ 5%

Organic acid esters 1 ~ 20%

Dispensing is dissolved in deionized water after completing and obtains cathode size, and slurry solid content is 25 ~ 55%, and viscosity is 1000 ~ 5000 mPa.s。

The preparation method of high-voltage lithium ion batteries cathode pole piece the most according to claim 1, it is characterised in that: step (2) described making beating temperature is 20 ~ 50 DEG C, and humidity is 5 ~ 20%.

The preparation method of high-voltage lithium ion batteries cathode pole piece the most according to claim 1, it is characterised in that: step (4) coating speed of described roll coating model is 3 ~ 10m/min, and baking temperature is 70 ~ 110 DEG C；The coating speed of spraying method is 5 ~ 13m/min, oven temperature is 70 ~ 110 DEG C；The thickness preparing cathode pole piece is 0.02 ~ 0.2mm.

The preparation method of high-voltage lithium ion batteries cathode pole piece the most according to claim 1, it is characterised in that: described negative Pole material is at least one in native graphite, Delanium, composite graphite, soft carbon, hard carbon.

The preparation method of high-voltage lithium ion batteries cathode pole piece the most according to claim 1, it is characterised in that lead described in: Electricity agent is that electrically conductive graphite includes SP, KS-6 and CNT；At least one in carbon fiber (VGCF).

The preparation method of high-voltage lithium ion batteries cathode pole piece the most according to claim 1, it is characterised in that: described viscous Knot agent is at least one in aqueous hydroxymethyl cellulose (CMC), butadiene-styrene rubber (SBR), binding agent LA133.

7. according to the preparation method of the high-voltage lithium ion batteries cathode pole piece described in claim 1, it is characterised in that: described Organic acid esters is at least one in organic titanate, organosilicon acid esters, organophosphorus ester.

8. answering of the high-voltage lithium ion batteries cathode pole piece prepared according to the preparation method described in any one of claim 1-7 With, it is characterised in that: this high-voltage lithium ion batteries cathode pole piece can match system with the positive electrode of following high voltage type The standby full battery of business, the LiMn of spinel structure₂O₄, LiNi_0.5Mn_1.5O₄, Li_zNi_xMn_1-xO₂；Li_zCo_1-(x+y)Ni_xMn_yO₂(its In, x, y, x+y ＜ 1, z >=1)；Olivine structural LiMPO₄Or Li₂MPO₄F (M=Co, Mn, Ni)；LiNiVO₄, LiMeSO₄F (Me=Co, Ni, Cu), high voltage stratiform LiCoO2(charge cutoff voltage >=4.3V).