Lithium ion battery positive electrode sheet, preparation method thereof and lithium ion battery

Abstract

The present invention provides a lithium-ion battery positive electrode sheet, a preparation method thereof, and a lithium-ion battery. The preparation method comprises: mixing a positive electrode conductive agent with a solid electrolyte and then stirring at high speed to obtain a mixed conductive agent; mixing a positive electrode active material with the solid electrolyte and stirring at low speed for a period of time, then mixing with the mixed conductive agent and stirring at low speed for a second period of time to obtain an intermediate mixture; mixing the intermediate mixture with a binder and a solvent to obtain a positive electrode slurry, and then coating, baking, and cold pressing in sequence to obtain a lithium-ion battery positive electrode sheet. The method of the present invention improves the conductivity of the positive electrode material by adding a solid electrolyte to the positive electrode active material and the positive electrode conductive agent, suppresses the increase in the internal impedance of the battery cell during discharge, thereby suppressing excessive temperature rise, ensuring sufficient release of battery capacity, and extending the service life of the lithium-ion battery; the method is simple to operate, has low raw material and process costs, and has a wide range of applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a lithium ion battery positive electrode sheet, a preparation method thereof and a lithium ion battery. Background Art

[0002] In recent years, with the continuous development of lithium-ion battery technology, it has been widely used in various fields such as digital, electronic information, transportation, and energy storage. Traditional lithium-ion batteries are mainly composed of components such as battery housing, positive electrode sheet, negative electrode sheet, separator, and electrolyte. Among them, the positive and negative electrode sheets are important factors affecting the performance of lithium-ion batteries. The electrode sheets are usually formed by evenly coating the positive and negative electrode slurries on the corresponding current collectors. Therefore, the composition of the positive and negative electrode slurries and the quality of the coating process will directly affect the overall performance of the lithium-ion battery.

[0003] Based on the structure and composition characteristics of lithium-ion batteries, the positive electrode material is an extremely important factor affecting battery performance. The positive electrode material is not stable during the charge and discharge process, and is often accompanied by side reactions between the material surface and the electrolyte, degradation of the material's crystal structure, fragmentation of the electrode structure, or shedding of the active coating. Therefore, the positive electrode material needs to be improved. Currently, common improvement measures include doping and surface coating. Solid-state electrolytes, as important modified materials for lithium-ion batteries, have good application prospects in the current preparation of all-solid-state lithium-ion batteries due to their high ionic conductivity.

[0004] CN 109273760A discloses a lithium-ion battery electrode sheet with a solid electrolyte layer and a coating method. The coating method comprises: sequentially coating and drying a lithium-ion battery active material slurry to obtain a base lithium-ion battery electrode sheet, and then performing a secondary coating and drying of the solid electrolyte slurry, that is, coating the solid electrolyte slurry on the base lithium-ion battery electrode sheet to obtain a lithium-ion battery electrode sheet with a solid electrolyte layer. In this method, the solid electrolyte layer is formed separately to hinder the growth of the SEI film and lithium dendrites, and does not improve the active material itself. Different improvement methods will bring different effects.

[0005] CN 111900394A discloses a coating structure for a lithium-ion battery positive electrode material, its preparation method, and its use. The preparation method comprises: coating the surface of the positive electrode material with an electronically conductive particle layer by mechanical fusion; then coating the surface of the electronically conductive particle layer with a solid electrolyte layer by a liquid phase method to obtain the coating structure for the lithium-ion battery positive electrode material. This method uses coating to modify the positive electrode material, similarly forming a solid electrolyte layer, rather than using the solid electrolyte as a component of the electrode slurry, representing a different improvement direction.

[0006] In summary, for the preparation of lithium-ion battery positive electrode sheets, it is necessary to select appropriate improvement methods based on the composition of the positive electrode slurry and the characteristics of the solid electrolyte, to improve the conductivity of the positive electrode material, suppress the temperature rise during lithium-ion battery discharge, and ensure that the battery capacity is fully released. Summary of the Invention

[0007] In response to the problems existing in the prior art, the purpose of the present invention is to provide a lithium-ion battery positive electrode sheet, a preparation method thereof, and a lithium-ion battery. The method improves the conductivity of the positive electrode material by adding solid electrolytes to the positive electrode active material and the positive electrode conductive agent respectively, suppresses the increase in the internal impedance of the battery cell during discharge, thereby suppressing excessive temperature increase, ensuring the full release of the battery capacity, and improving the battery life.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In one aspect, the present invention provides a method for preparing a positive electrode sheet for a lithium-ion battery, the method comprising the following steps:

[0010] (1) mixing a positive electrode conductive agent and a solid electrolyte and stirring them at high speed to obtain a mixed conductive agent;

[0011] (2) mixing the positive electrode active material with the solid electrolyte and stirring at a low speed for a first stage, then mixing with the mixed conductive agent obtained in step (1) and stirring at a low speed for a second stage to obtain an intermediate mixture;

[0012] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent to obtain a positive electrode slurry, and then the positive electrode slurry is coated, baked and cold pressed in sequence to obtain a lithium-ion battery positive electrode sheet.

[0013] In the present invention, the preparation of the positive electrode sheet of a lithium-ion battery is improved by adding a solid electrolyte. The present invention is to stir and mix the solid electrolyte with the positive electrode active material and the positive electrode conductive agent respectively, and then prepare the positive electrode slurry. The addition of the solid electrolyte can effectively improve the conductivity of the positive electrode material, thereby reducing the internal impedance of the battery cell, so that the internal temperature of the battery will not rise too much during the discharge process, thereby ensuring the discharge capacity and service life of the battery, and extending the service life of the lithium-ion battery. The method is simple to operate, has low raw material and process costs, and has a wide range of applications.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the positive electrode conductive agent in step (1) includes any one of conductive carbon black, carbon nanotubes or conductive graphite, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of conductive carbon black and carbon nanotubes, a combination of carbon nanotubes and conductive graphite, a combination of conductive carbon black, carbon nanotubes and conductive graphite, etc.

[0016] Preferably, the solid electrolyte in step (1) comprises any one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum titanium phosphate or lithium aluminum germanium phosphate, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of lithium lanthanum zirconium oxide and lithium lanthanum titanium oxide, a combination of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide, a combination of lithium lanthanum titanium oxide and lithium aluminum titanium phosphate, a combination of lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide and lithium aluminum germanium phosphate, a combination of lanthanum zirconium oxide, lithium lanthanum titanium oxide and lithium lanthanum zirconium tantalum oxide, and the like.

[0017] Preferably, the particle size of the solid electrolyte in step (1) is 100 to 3000 nm, for example, 100 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm or 3000 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0018] Preferably, the amount of the positive electrode conductive agent added in step (1) accounts for 0.5 to 1.5 wt% of the positive electrode active material in step (2), for example, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt% or 1.5 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0019] Preferably, the amount of the solid electrolyte added in step (1) accounts for 0.05 to 0.3 wt% of the positive electrode active material in step (2), for example, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0020] As a preferred technical solution of the present invention, the rotation speed of the high-speed stirring in step (1) is 2000-4000 r / min, for example, 2000 r / min, 2500 r / min, 3000 r / min, 3500 r / min or 4000 r / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the high-speed stirring time in step (1) is 60 to 90 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the mixed conductive agent obtained after the high-speed stirring in step (1) is vacuumed and set aside.

[0023] In the present invention, the positive electrode conductive agent and the solid electrolyte need to be stored in a vacuum after mixing because if the positive electrode material absorbs water during the preparation process, the slurry will easily become jelly-like, affecting the processing performance and battery performance. Therefore, vacuum storage is required during the step-by-step operation.

[0024] As a preferred technical solution of the present invention, the positive electrode active material in step (2) includes any one of nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP) or lithium manganese oxide (LMO), or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, a combination of lithium nickel cobalt aluminum oxide and lithium iron phosphate, a combination of lithium iron phosphate and lithium manganese oxide, a combination of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium iron phosphate, etc.

[0025] Preferably, the solid electrolyte in step (2) comprises any one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum titanium phosphate or lithium aluminum germanium phosphate, or a combination of at least two thereof. Typical but non-limiting examples of the combination include: a combination of lithium lanthanum zirconium oxide and lithium lanthanum titanium oxide, a combination of lithium lanthanum zirconium oxide and lithium lanthanum zirconium tantalum oxide, a combination of lithium lanthanum titanium oxide and lithium aluminum titanium phosphate, a combination of lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide and lithium aluminum germanium phosphate, a combination of lanthanum zirconium oxide, lithium lanthanum titanium oxide and lithium lanthanum zirconium tantalum oxide, and the like.

[0026] Preferably, the particle size of the solid electrolyte in step (2) is 100 to 3000 nm, for example, 100 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm or 3000 nm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0027] Preferably, the amount of the solid electrolyte added in step (2) accounts for 0.1 to 0.3 wt% of the positive electrode active material in step (2), for example, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0028] In the present invention, the amount of solid electrolyte added is an important factor affecting the performance of the electrode sheet. If the amount of solid electrolyte added is too little, the conductivity cannot be fully improved, thereby failing to suppress excessive temperature increase. If the amount of solid electrolyte added is too much, the adhesion during coating will be too low, which may easily cause problems such as bulging and foil breakage.

[0029] As a preferred technical solution of the present invention, the rotation speed of the low-speed stirring in step (2) is 100 to 500 r / min, for example, 100 r / min, 200 r / min, 300 r / min, 400 r / min or 500 r / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the time for the low-speed stirring in step (2) is 30 to 60 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the rotation speed of the second stage low-speed stirring in step (2) is 500-1500 r / min, for example, 500 r / min, 800 r / min, 1000 r / min, 1200 r / min, 1350 r / min or 1500 r / min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0032] Preferably, the time for the second stage low-speed stirring in step (2) is 60 to 90 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0033] In the present invention, different stirring rates are used when the positive electrode conductive agent and the positive electrode active material are mixed with the solid electrolyte respectively. The former adopts high-speed stirring, which is mainly due to the characteristics of the positive electrode conductive agent itself. For example, carbon nanotubes need to be stirred at high speed into filaments to exert their effect. The latter adopts low-speed stirring because the powdered raw materials need to be stirred at low speed to avoid dust splashing. The stirring rate can be increased during the overall mixing because the powdered particles are no longer easily splashed after the solvent is added.

[0034] As a preferred technical solution of the present invention, the binder in step (3) includes polyvinylidene fluoride (PVDF).

[0035] Preferably, the solvent in step (3) comprises N-methylpyrrolidone.

[0036] Preferably, the amount of the binder added in step (3) accounts for 0.5 to 1.5 wt% of the positive electrode active material in step (2), for example, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt% or 1.5 wt%, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0037] Preferably, the amount of the solvent added in step (3) accounts for 10 to 15 wt% of the positive electrode active material in step (2), for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] Preferably, the viscosity of the positive electrode slurry in step (3) is 4000-7000 mPa·s, for example, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s, 6000 mPa·s, 6500 mPa·s or 7000 mPa·s, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0039] As a preferred technical solution of the present invention, the positive electrode slurry in step (3) is coated on the current collector.

[0040] Preferably, the current collector comprises aluminum foil.

[0041] Preferably, the baking temperature in step (3) is 100-120°C, for example, 100°C, 105°C, 110°C, 115°C or 120°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the cold pressing pressure in step (3) is 25 to 45T, such as 25T, 30T, 35T, 40T or 45T, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] On the other hand, the present invention provides a lithium ion battery positive electrode obtained by the above preparation method.

[0044] In addition, the present invention also provides a lithium-ion battery, which includes the above-mentioned lithium-ion battery positive electrode sheet.

[0045] Preferably, the lithium-ion battery is assembled from a positive electrode sheet, a negative electrode sheet, a separator and a casing, and then sealed after adding an electrolyte.

[0046] As a preferred technical solution of the present invention, the negative electrode sheet is obtained by coating, baking and cold pressing the negative electrode slurry in sequence.

[0047] Preferably, the negative electrode slurry comprises a negative electrode active material, a negative electrode conductor and a binder.

[0048] Preferably, the negative electrode active material includes silicon carbon and / or graphite.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The method of the present invention improves the conductivity of the positive electrode material by adding solid electrolytes to the positive electrode active material and the positive electrode conductive agent, thereby suppressing the increase in the internal impedance of the battery cell during discharge, thereby suppressing excessive temperature increase. After discharge, the battery temperature does not exceed 80°C, ensuring the full release of the battery capacity and extending the service life of the lithium-ion battery;

[0051] (2) The method of the present invention is simple to operate, has low raw material and process costs, and has a wide range of applications. DETAILED DESCRIPTION

[0052] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0053] The specific embodiment of the present invention provides a lithium ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0054] (1) mixing a positive electrode conductive agent and a solid electrolyte and stirring them at high speed to obtain a mixed conductive agent;

[0055] (2) mixing the positive electrode active material with the solid electrolyte and stirring at a low speed for a first stage, then mixing with the mixed conductive agent obtained in step (1) and stirring at a low speed for a second stage to obtain an intermediate mixture;

[0056] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent to obtain a positive electrode slurry, and then the positive electrode slurry is coated, baked and cold pressed in sequence to obtain a lithium-ion battery positive electrode sheet.

[0057] The following are typical but non-limiting examples of the present invention:

[0058] Example 1:

[0059] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0060] (1) mixing a positive electrode conductive agent and a solid electrolyte and then stirring them at high speed, wherein the positive electrode conductive agent is conductive carbon black, the solid electrolyte is lithium lanthanum zirconium oxide, the average particle size of the solid electrolyte is 500 nm, the amount of the positive electrode conductive agent added accounts for 1.0 wt % of the positive electrode active material, and the amount of the solid electrolyte added accounts for 0.15 wt % of the positive electrode active material, the speed of the high-speed stirring is 3000 r / min, and the time is 75 min to obtain a mixed conductive agent, which is then vacuumed and set aside;

[0061] (2) mixing the positive electrode active material with the solid electrolyte and then performing a low-speed stirring for a period of time, wherein the positive electrode active material is lithium nickel cobalt manganese oxide, the solid electrolyte is lithium lanthanum zirconium oxide, and the average particle size thereof is 500 nm, and the amount of the solid electrolyte added accounts for 0.15 wt % of the positive electrode active material, and the rotation speed of the low-speed stirring for a period of time of 500 r / min and 45 min, and then mixing with the mixed conductive agent obtained in step (1) and performing a low-speed stirring for a period of time of 2nd period of time, wherein the rotation speed of the low-speed stirring for a period of time of 1000 r / min and 75 min, to obtain an intermediate mixture;

[0062] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent, wherein the binder is polyvinylidene fluoride, and the amount thereof added is 1.0 wt % of the positive electrode active material; and the solvent is N-methylpyrrolidone, and the amount thereof added is 12 wt % of the positive electrode active material, to obtain a positive electrode slurry, wherein the viscosity of the positive electrode slurry is 5000 mPa·s. The positive electrode slurry is then coated on an aluminum foil, and then baked and cold pressed, wherein the baking temperature is 110° C. and the cold pressing pressure is 30T, to obtain a lithium ion battery positive electrode sheet.

[0063] Example 2:

[0064] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0065] (1) mixing a positive electrode conductive agent and a solid electrolyte and then stirring them at high speed, wherein the positive electrode conductive agent is carbon nanotubes, the solid electrolyte is lithium lanthanum titanium oxide, the average particle size of the solid electrolyte is 1000 nm, the amount of the positive electrode conductive agent added accounts for 0.5 wt % of the positive electrode active material, and the amount of the solid electrolyte added accounts for 0.1 wt % of the positive electrode active material, the speed of the high-speed stirring is 2000 r / min, and the time is 90 min to obtain a mixed conductive agent, which is then vacuumed and set aside;

[0066] (2) mixing the positive electrode active material with the solid electrolyte and performing a first stage of low-speed stirring, wherein the positive electrode active material is lithium nickel cobalt aluminum oxide, the solid electrolyte is lithium lanthanum titanium oxide, and the average particle size thereof is 1000 nm, and the amount of the solid electrolyte added accounts for 0.1 wt % of the positive electrode active material, and the rotation speed of the first stage of low-speed stirring is 200 r / min and the time is 60 min. Then, mixing with the mixed conductive agent obtained in step (1), performing a second stage of low-speed stirring, and the rotation speed of the second stage of low-speed stirring is 600 r / min and the time is 90 min to obtain an intermediate mixture;

[0067] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent, wherein the binder is polyvinylidene fluoride, and the amount thereof added is 0.5wt% of the positive electrode active material; the solvent is N-methylpyrrolidone, and the amount thereof added is 15wt% of the positive electrode active material, to obtain a positive electrode slurry, wherein the viscosity of the positive electrode slurry is 6000mPa·s; the positive electrode slurry is then coated on an aluminum foil, and then baked and cold pressed, wherein the baking temperature is 100°C and the cold pressing pressure is 45T, to obtain a lithium ion battery positive electrode sheet.

[0068] Example 3:

[0069] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0070] (1) mixing a positive electrode conductive agent and a solid electrolyte and stirring them at high speed, wherein the positive electrode conductive agent is conductive graphite, the solid electrolyte is lithium titanium aluminum phosphate, the average particle size of the solid electrolyte is 2000 nm, the amount of the positive electrode conductive agent added accounts for 1.5 wt % of the positive electrode active material, and the amount of the solid electrolyte added accounts for 0.3 wt % of the positive electrode active material, the speed of the high-speed stirring is 4000 r / min, the time is 60 min, and a mixed conductive agent is obtained, which is then vacuumed and set aside;

[0071] (2) mixing the positive electrode active material and the solid electrolyte and performing a first stage of low-speed stirring, wherein the positive electrode active material is lithium iron phosphate, the solid electrolyte is lithium titanium aluminum phosphate, and the average particle size thereof is 2000 nm, and the amount of the solid electrolyte added accounts for 0.3 wt % of the positive electrode active material, and the rotation speed of the first stage of low-speed stirring is 400 r / min and the time is 30 min, and then mixing with the mixed conductive agent obtained in step (1) and performing a second stage of low-speed stirring, the rotation speed of the second stage of low-speed stirring is 1500 r / min and the time is 60 min, to obtain an intermediate mixture;

[0072] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent, wherein the binder is polyvinylidene fluoride, and the amount thereof added is 1.5wt% of the positive electrode active material; the solvent is N-methylpyrrolidone, and the amount thereof added is 10wt% of the positive electrode active material, to obtain a positive electrode slurry, wherein the viscosity of the positive electrode slurry is 4000mPa·s; the positive electrode slurry is then coated on an aluminum foil, and then baked and cold pressed, wherein the baking temperature is 120°C and the cold pressing pressure is 25T, to obtain a lithium ion battery positive electrode sheet.

[0073] Example 4:

[0074] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0075] (1) mixing a positive electrode conductive agent and a solid electrolyte and then stirring them at a high speed, wherein the positive electrode conductive agent is conductive carbon black and carbon nanotubes in a mass ratio of 1:1, the solid electrolyte is lithium lanthanum zirconium tantalum oxide, the average particle size of the solid electrolyte is 100 nm, the amount of the positive electrode conductive agent added accounts for 0.8 wt % of the positive electrode active material, and the amount of the solid electrolyte added accounts for 0.2 wt % of the positive electrode active material, the speed of the high-speed stirring is 2500 r / min, and the time is 70 min to obtain a mixed conductive agent, which is then vacuumed and set aside;

[0076] (2) mixing the positive electrode active material with the solid electrolyte and then performing a low-speed stirring for a period of time, wherein the positive electrode active material is lithium manganate, the solid electrolyte is lithium lanthanum zirconium tantalum oxide, and the average particle size thereof is 200 nm, and the amount of the solid electrolyte added accounts for 0.25 wt % of the positive electrode active material, and the rotation speed of the low-speed stirring for a period of time is 200 r / min and 50 min, and then mixing with the mixed conductive agent obtained in step (1) and performing a low-speed stirring for a period of time of a second period of time, wherein the rotation speed of the low-speed stirring for a period of time is 1200 r / min and 80 min, to obtain an intermediate mixture;

[0077] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent, wherein the binder is polyvinylidene fluoride, and the amount thereof added accounts for 1.2 wt % of the positive electrode active material; the solvent is N-methylpyrrolidone, and the amount thereof added accounts for 11 wt % of the positive electrode active material, to obtain a positive electrode slurry, wherein the viscosity of the positive electrode slurry is 7000 mPa·s; the positive electrode slurry is then coated on an aluminum foil, and then baked and cold pressed, wherein the baking temperature is 105° C. and the cold pressing pressure is 35T, to obtain a lithium ion battery positive electrode sheet.

[0078] Example 5:

[0079] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof, the preparation method comprising the following steps:

[0080] (1) mixing a positive electrode conductive agent and a solid electrolyte and stirring them at high speed, wherein the positive electrode conductive agent is conductive graphite, the solid electrolyte is lithium aluminum germanium phosphate, the average particle size of the solid electrolyte is 1500 nm, the amount of the positive electrode conductive agent added accounts for 1.2 wt % of the positive electrode active material, and the amount of the solid electrolyte added accounts for 0.05 wt % of the positive electrode active material, the speed of the high-speed stirring is 3500 r / min, the time is 80 min, to obtain a mixed conductive agent, and evacuating the mixture for standby use;

[0081] (2) mixing the positive electrode active material and the solid electrolyte and performing a first stage of low-speed stirring, wherein the positive electrode active material is lithium nickel cobalt manganese oxide, the solid electrolyte is lithium lanthanum zirconium oxide, and the average particle size thereof is 2500 nm, and the amount of the solid electrolyte added accounts for 0.15 wt % of the positive electrode active material, and the rotation speed of the first stage of low-speed stirring is 250 r / min and the time is 40 min. Then, mixing with the mixed conductive agent obtained in step (1), performing a second stage of low-speed stirring, and the rotation speed of the second stage of low-speed stirring is 800 r / min and the time is 70 min to obtain an intermediate mixture;

[0082] (3) The intermediate mixture obtained in step (2) is mixed with a binder and a solvent, wherein the binder is polyvinylidene fluoride, and its addition amount accounts for 0.8wt% of the positive electrode active material; the solvent is N-methylpyrrolidone, and its addition amount accounts for 14wt% of the positive electrode active material to obtain a positive electrode slurry, and the viscosity of the positive electrode slurry is 5500mPa·s. The positive electrode slurry is then coated on an aluminum foil, and then baked and cold pressed. The baking temperature is 115°C, and the cold pressing pressure is 40T to obtain a lithium ion battery positive electrode sheet.

[0083] Example 6:

[0084] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof. The preparation method refers to the method in Example 1, with the only difference being that the amount of solid electrolyte added in step (2) accounts for 0.5 wt % of the positive electrode active material.

[0085] Example 7:

[0086] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof. The preparation method refers to the method in Example 2, with the only difference being that the stirring speed in step (1) is 1000 r / min.

[0087] Example 8:

[0088] This embodiment provides a lithium-ion battery positive electrode sheet and a preparation method thereof. The preparation method refers to the method in Example 1, with the only difference being that the rotation speed of the low-speed stirring in step (2) is 1000 r / min.

[0089] Comparative Example 1:

[0090] This comparative example provides a lithium-ion battery positive electrode sheet and a preparation method thereof. The preparation method refers to the method in Example 1, with the only difference being that no solid electrolyte is added in steps (1) and (2), but the positive electrode active material and the positive electrode conductive agent are directly stirred at a low speed.

[0091] The lithium ion battery positive electrode sheets prepared in Examples 1-8 and Comparative Example 1 were used to assemble lithium ion batteries. The other structural components used were the same. After the lithium ion batteries were fully charged, discharge performance tests were performed. Under two test conditions of discharge current of 20 A and 30 A, the discharge capacity and the final temperature after discharge were tested. The results are shown in Table 1.

[0092] Table 1 Discharge performance test results of Examples 1-8 and Comparative Example 1

[0093]

[0094]

[0095] As can be seen from Table 1, when the positive electrode sheets prepared by the methods of Examples 1-5 are used to assemble lithium-ion batteries, the lithium-ion batteries have high discharge capacity and good cycle performance, and can suppress excessive temperature rise and extend service life; in Example 6, the amount of solid electrolyte added is relatively high. Although it can also play a role in suppressing temperature rise, it will cause the electrode sheet to be too hard, the adhesion force becomes smaller, and it is easy to fall off during the charge and discharge process, affecting the cycle performance; in Example 7, due to the low stirring rate when the positive electrode conductive agent and the solid electrolyte are mixed, the carbon nanotubes cannot be effectively dispersed into filaments and embedded in the positive electrode material, affecting the conductivity and discharge performance of the battery; in Example 8, due to the high stirring rate when the positive electrode active material and the solid electrolyte are mixed, the powdered particles are easily sputtered, resulting in stratification of light and heavy particles, thereby affecting the dispersion effect of the solid electrolyte, affecting the improvement of the conductivity of the battery, and weakening the effect of suppressing temperature rise;

[0096] In Comparative Example 1, since no solid electrolyte is added, the conductivity of the positive electrode material is weak, the internal impedance of the battery cell is large, and the battery temperature is high after discharge, which seriously affects the discharge capacity and service life.

[0097] From the above embodiments and comparative examples, it can be seen that the method of the present invention improves the conductivity of the positive electrode material by adding solid electrolytes to the positive electrode active material and the positive electrode conductive agent respectively, thereby suppressing the increase in the internal impedance of the battery cell during discharge, thereby suppressing excessive temperature increase. The battery temperature does not exceed 80°C after discharge, ensuring the full release of the battery capacity and extending the service life of the lithium-ion battery. The method is simple to operate, has low raw material and process costs, and has a wide range of applications.

[0098] While the present invention uses the above-described embodiments to illustrate the detailed methods of the present invention, the present invention is not limited to the above-described detailed methods, nor does it necessarily rely on the above-described detailed methods for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the methods of the present invention, additions of auxiliary steps, and selections of specific methods are all within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a positive electrode sheet for a lithium ion battery, characterized in that: The preparation method comprises the following steps: (1) mixing a positive electrode conductive agent and a solid electrolyte and then stirring them at a high speed, wherein the positive electrode conductive agent is carbon nanotubes, and the rotation speed of the high-speed stirring is 2000-4000 r / min to obtain a mixed conductive agent; (2) mixing the positive electrode active material with the solid electrolyte and stirring them at a low speed for a period of time, wherein the rotation speed of the first period of low speed stirring is 100-500 r / min, and then mixing them with the mixed conductive agent obtained in step (1) and stirring them at a low speed for a period of time, wherein the rotation speed of the second period of low speed stirring is 500-800 r / min, to obtain an intermediate mixture; (3) mixing the intermediate mixture obtained in step (2) with a binder and a solvent to obtain a positive electrode slurry, and then coating, baking and cold pressing the positive electrode slurry in sequence to obtain a lithium-ion battery positive electrode sheet; The amount of the solid electrolyte added in step (1) accounts for 0.05-0.2 wt % of the positive electrode active material in step (2); the amount of the positive electrode conductive agent added in step (1) accounts for 0.5-1.5 wt % of the positive electrode active material in step (2); the particle size of the solid electrolyte in step (1) is 100-3000 nm; The amount of the solid electrolyte added in step (2) accounts for 0.1-0.3 wt % of the positive electrode active material in step (2); the particle size of the solid electrolyte in step (2) is 100-3000 nm; The solid electrolyte in step (1) comprises any one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum titanium phosphate or lithium aluminum germanium phosphate, or a combination of at least two thereof; The high-speed stirring time in step (1) is 60 to 90 minutes; The positive electrode active material in step (2) includes any one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate or lithium manganese oxide, or a combination of at least two thereof; The solid electrolyte in step (2) comprises any one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum titanium phosphate or lithium aluminum germanium phosphate, or a combination of at least two thereof; The time of the low-speed stirring in step (2) is 30 to 60 minutes; The time of the second stage low-speed stirring in step (2) is 60 to 90 minutes.

2. The preparation method according to claim 1, characterized in that The mixed conductive agent obtained after the high-speed stirring in step (1) is vacuumed and set aside.

3. The preparation method according to claim 1, characterized in that The binder in step (3) includes polyvinylidene fluoride.

4. The preparation method according to claim 1, characterized in that The solvent in step (3) includes N-methylpyrrolidone.

5. The preparation method according to claim 1, characterized in that The amount of the binder added in step (3) accounts for 0.5-1.5 wt % of the positive electrode active material in step (2).

6. The preparation method according to claim 1, characterized in that The amount of the solvent added in step (3) accounts for 10-15 wt % of the positive electrode active material in step (2).

7. The preparation method according to claim 1, characterized in that The viscosity of the positive electrode slurry in step (3) is 4000~7000mPa·s.

8. The preparation method according to claim 1, characterized in that In step (3), the positive electrode slurry is coated on the current collector.

9. The preparation method according to claim 8, characterized in that The current collector includes aluminum foil.

10. The preparation method according to claim 1, characterized in that The baking temperature in step (3) is 100-120°C.

11. The preparation method according to claim 1, characterized in that The cold pressing pressure in step (3) is 25~45T.

12. A lithium ion battery positive electrode obtained according to the preparation method according to any one of claims 1 to 11.

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-ion battery positive electrode sheet according to claim 12.

14. The lithium-ion battery according to claim 13, wherein: The lithium-ion battery is assembled from a positive electrode sheet, a negative electrode sheet, a separator and a shell, and then sealed after adding electrolyte.

15. The lithium-ion battery according to claim 14, characterized in that The negative electrode sheet is obtained by coating, baking and cold pressing the negative electrode slurry in sequence.

16. The lithium-ion battery according to claim 15, characterized in that The negative electrode slurry comprises a negative electrode active material, a negative electrode conductor and a binder.

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