阅读说明：本技术 一种极片和锂离子电池 (Pole piece and lithium ion battery ) 是由 张国军 梁世硕 刘永飞 张博 于 2021-03-18 设计创作，主要内容包括：本发明提供一种极片和锂离子电池。本发明第一方面提供了一种极片,所述极片包括集流体、功能层和安全涂层,所述集流体的表面涂覆有功能层,所述功能层远离集流体的表面涂覆有安全涂层；所述安全涂层包括气凝胶粉体、聚合物微球粉体和粘结剂。本申请提供的安全涂层,具有轻质、高孔隙率和高耐热等特性,在保证锂离子电池安全性的基础上,可提高锂离子电池的能量密度和电化学性能。(The invention provides a pole piece and a lithium ion battery. The invention provides a pole piece, which comprises a current collector, a functional layer and a safety coating, wherein the functional layer is coated on the surface of the current collector, and the safety coating is coated on the surface of the functional layer away from the current collector; the safety coating comprises aerogel powder, polymer microsphere powder and a binder. The safety coating has the characteristics of light weight, high porosity, high heat resistance and the like, and can improve the energy density and the electrochemical performance of the lithium ion battery on the basis of ensuring the safety of the lithium ion battery.)

1. A pole piece is characterized by comprising a current collector, a functional layer and a safety coating, wherein the surface of the current collector is coated with the functional layer, and the surface of the functional layer, far away from the current collector, is coated with the safety coating;

the safety coating comprises aerogel powder, polymer microsphere powder and a binder.

2. The pole piece of claim 1, wherein the aerogel powder is SiO₂Aerogel powder, TiO₂Aerogel powder, Al₂O₃One or more of aerogel powders.

3. The pole piece of claim 1 or 2, wherein the polymer microsphere powder is one or more of polyacrylonitrile, polystyrene, polyvinyl alcohol, polyvinyl chloride, polyamide, polyimide, polyethylene, polypropylene, acrylate-vinyl acetate copolymer, propylene-ethylene copolymer, styrene-divinylbenzene copolymer, ethylene-vinyl acetate copolymer, polypropylene/rubber copolymer and polyethylene/rubber copolymer.

4. The pole piece of any one of claims 1 to 3, wherein the aerogel powder has a pore size of 2 to 60nm and a density of 0.2 to 0.5mg/cm³。

5. The pole piece of any one of claims 1 to 3, wherein the melting point of the polymer microsphere powder is 80 to 160 ℃ and the particle size is 0.01 to 10 μm.

6. The pole piece of any one of claims 1 to 5, wherein the mass ratio of the aerogel powder, the polymer microsphere powder and the binder is (20-60): (10-50): (0.5-20).

7. The pole piece of claim 1, wherein the safety coating has a thickness of 2-12 μm.

8. The pole piece of claim 1, wherein the functional layer comprises an active layer.

9. The pole piece of claim 1, wherein the functional layer comprises, in order in a direction away from the current collector, an electrically conductive layer and an active layer.

10. A lithium ion battery, characterized in that the lithium ion battery comprises the pole piece of any one of claims 1 to 9.

Technical Field

The invention relates to a pole piece and a lithium ion battery, and relates to the technical field of lithium ion batteries.

Background

In recent years, with the demand for energy density of lithium ion batteries is higher and higher, the problem of safety performance of the lithium ion batteries is more and more prominent, and when the lithium ion batteries are abused under extrusion, needling, overcharge and the like, short circuit is easy to occur inside the lithium ion batteries, so that a large amount of heat is accumulated, thermal runaway is easy to occur, and further the problems of fire, explosion and the like are caused.

The contact internal resistance can be increased and the risk of thermal runaway can be reduced by arranging the safety coating on the surface of the pole piece, but the energy density of the lithium ion battery is reduced and the electrochemical performance of the lithium ion battery is poor due to the common safety coating such as a ceramic layer. Therefore, how to provide a pole piece is concerned more and more with improving the energy density and the electrochemical performance of the lithium ion battery on the basis of ensuring the safety of the lithium ion battery.

Disclosure of Invention

The invention provides a pole piece which is used for improving the energy density and the electrochemical performance of a lithium ion battery on the basis of ensuring the safety of the lithium ion battery.

The invention also provides a lithium ion battery comprising the pole piece, and the lithium ion battery has better safety, energy density and electrochemical performance.

The invention provides a pole piece, which comprises a current collector, a functional layer and a safety coating, wherein the functional layer is coated on the surface of the current collector, and the safety coating is coated on the surface of the functional layer away from the current collector;

the safety coating comprises aerogel powder, polymer microsphere powder and a binder.

The invention provides a pole piece, which comprises a current collector, a functional layer and a safety coating, wherein the functional layer mainly comprises materials required by the pole piece to play corresponding functions, for example, the functional layer is an active layer and comprises active substances, the functional layer is coated on the surface of the current collector, and the safety coating is coated on the surface of the functional layer far away from the current collector. In order to avoid the loss of the energy density and the electrochemical performance of the lithium ion battery as much as possible and improve the energy density and the electrochemical performance of the lithium ion battery on the basis of ensuring the safety of the lithium ion battery, the safety coating provided by the invention comprises aerogel powder, polymer microsphere powder and a binder, wherein the aerogel powder refers to aerogel particles with a nano-pore structure, and the aerogel particles are used as an insulating material, so that the reaction speed of a pole piece during thermal runaway or short circuit can be effectively reduced, the reaction activity of the pole piece is reduced, and the safety of the lithium ion battery is further ensured; the nano-scale pore structure in the aerogel powder is beneficial to increasing the contact area between the electrode and the electrolyte, improving the absorption efficiency of the electrolyte and improving the conduction efficiency of lithium ions, thereby improving the electrochemical properties of the lithium ion battery such as multiplying power, circulation and the like; in addition, the aerogel powder also has the characteristics of low density, good heat resistance and the like, and is beneficial to improving the energy density and the heat resistance of the lithium ion battery; the polymer microsphere powder is spherical polymer particles with the particle size of more than a few microns and less than hundreds of microns, has a low melting point, can be fused into an insulating film without pores or with few pores from spherical particles under the condition of overheating, plays a certain role in thermal shutdown, and can further improve the safety of the lithium ion battery; the adhesive is used as one of important components in the lithium ion battery pole piece, and is used for the adhesive action between aerogel powder and polymer microsphere powder and between the safety coating and the pole piece. In the actual application process, the materials can be mixed to prepare the safety coating slurry, and the safety coating slurry is coated on the surface of the functional layer to obtain the safety coating, so that the pole piece can be obtained. The pole piece that this application provided, it includes safe coating to this safe coating has characteristics such as light, high porosity and high heat-resisting, on the basis of guaranteeing lithium ion battery security, can improve lithium ion battery's energy density and electrochemical performance.

In one embodiment, the functional layer comprises an active layer, that is, the pole piece comprises a current collector, an active layer and a safety coating, and the active layer and the safety coating are sequentially coated on the surface of the current collector in a stacking manner.

Fig. 1 is a schematic structural diagram of a pole piece according to an embodiment of the present invention, and as shown in fig. 1, the pole piece includes a current collector 101, an active layer 102, and a safety coating 103, where the active layer 102 is coated on an upper surface of the current collector 101, and the safety coating 104 is coated on an upper surface of the active layer 102 away from the current collector 101.

In another embodiment, in order to further reduce the internal resistance of the lithium ion battery and improve the electrochemical performance of the lithium ion battery, the functional layer may further include a conductive layer, that is, the pole piece includes a current collector, a conductive layer, an active layer, and a safety coating, and the conductive layer, the active layer, and the safety coating are sequentially coated on the surface of the current collector in a stacked manner.

Fig. 2 is a schematic structural diagram of a pole piece according to another embodiment of the present invention, and as shown in fig. 2, the pole piece includes a current collector 101, a conductive layer 104, an active layer 102, and a safety coating 103, where the conductive layer 104 is coated on an upper surface of the current collector 101, the active layer 103 is coated on an upper surface of the conductive layer 104 away from the current collector 101, and the safety coating 103 is coated on an upper surface of the active layer 102 away from the conductive layer 104.

The current collector, the conducting layer and the active layer in the pole piece can be arranged according to the conventional technical means in the field, and the safety coating is mainly described in detail as follows:

in combination with the use characteristics of the lithium ion battery, the materials used for the safety coating provided by the application are specifically as follows: the aerogel powder is SiO₂Aerogel powder, TiO₂Aerogel powder, Al₂O₃One or more of aerogel powder;

the polymer microsphere powder is one or more of polyacrylonitrile, polystyrene, polyvinyl alcohol, polyvinyl chloride, polyamide, polyimide, polyethylene, polypropylene, acrylate-vinyl acetate copolymer, propylene-ethylene copolymer, styrene-divinylbenzene copolymer, ethylene-vinyl acetate copolymer, polypropylene/rubber copolymer and polyethylene/rubber copolymer;

the binder is one or more of carboxymethyl cellulose, acrylate, styrene butadiene rubber, sodium polyacrylate, polyurethane, polyethyleneimine and polyvinylidene fluoride.

In order to further improve the electrochemical performance and energy density of the lithium ion battery, the pore diameter and density of the aerogel powder should be within a certain range, specifically, the pore diameter of the aerogel powder is 2-60 nm; the density of the aerogel powder is 0.2-0.5mg/cm³。

Because the polymer can be fused into an insulating film without pores or with few pores from spherical particles under the condition of overheating, the melting point of the polymer microsphere powder is 80-160 ℃ in combination with the temperature range of the lithium ion battery when thermal runaway occurs.

Considering the film forming characteristic of the polymer microsphere after melting, the particle size of the polymer microsphere powder is not too large, otherwise, the pores of the safety coating are too large, the polymer microsphere powder is not easy to form a film after melting, and the electrochemical performance of the lithium ion battery is affected due to the too small particle size of the polymer microsphere powder, so that the particle size of the polymer microsphere powder is 0.01-10 mu m, and when the particle size of the polymer microsphere powder is too large, the polymer microsphere powder in the corresponding particle size range can be prepared by air flow crushing and the like.

Based on the difference of the characteristics of the aerogel powder and the polymer microsphere powder, when the mass ratio of the aerogel powder to the polymer microsphere powder is different, the comprehensive performance of the lithium ion battery comprising the safety coating is different, and in order to take the safety, the energy density and the electrochemical performance of the lithium ion battery into consideration, the mass ratio of the aerogel powder to the polymer microsphere powder to the binder is (20-60): (10-50): (0.5-20).

When at least two materials are included in the aerogel powder, or the polymer microsphere powder, or the binder, the total mass of the two materials should be maintained within the above mass range.

In order to further increase the energy density of the lithium ion battery, the thickness of the safety coating is not too thick, and in particular, the thickness of the safety coating is 2 to 12 μm.

The pole piece provided by the invention can be a positive pole piece or a negative pole piece, and a person skilled in the art can set the pole piece according to actual production needs, for example, when the pole piece is the positive pole piece, the pole piece comprises a positive pole current collector, a conductive layer, a positive pole active layer and a safety coating, wherein the positive pole current collector is an aluminum foil, the conductive layer comprises a conductive agent and a binder, the positive pole active layer comprises a positive pole active substance, a conductive agent and a binder, and the mass ratio of the positive pole active substance to the conductive agent to the binder is (90-97): (0.1-5): (0.5-5), the positive active material is one or more of NCM811, NCA and NCM622, and the thickness of the positive active layer is 10-150 μm. When the pole piece is a negative pole piece, the pole piece comprises a negative pole current collector, a conductive layer, a negative pole active layer and a safety coating, wherein the negative pole current collector is a copper foil, the conductive layer is the same as the positive pole piece, and the negative pole active layer comprises a negative pole active substance, a conductive agent and a binder.

In the preparation process of the pole piece, the required materials can be mixed according to a certain mass ratio to prepare slurry, and the slurry is sequentially coated on the functional surface of the current collector, for example, when the pole piece is a positive pole piece, a conductive agent and a binder are dissolved in a solvent according to a certain mass ratio and are uniformly mixed to prepare conductive layer slurry, and the conductive layer slurry is uniformly coated on the surface of the positive pole current collector to obtain a conductive layer; dissolving a positive active substance, a conductive agent and a binder in a solvent NMP according to a certain mass ratio to prepare active layer slurry, and uniformly coating the active layer slurry on the surface of the conductive layer far away from a current collector to obtain a positive active layer; and finally, uniformly mixing aerogel powder, polymer microsphere powder and a binder to prepare safe coating slurry, and uniformly coating the safe coating slurry on the surface of the active layer far away from the conductive layer to obtain a safe coating, thereby obtaining the positive plate.

In the preparation process of the safety coating, the used solvent can be NMP, and the mass ratio of the aerogel powder, the polymer microsphere powder, the binder and the solvent is (20-60): (10-50): (0.5-20): (5-80).

In conclusion, the pole piece provided by the application comprises the safety coating, and the safety coating has the characteristics of light weight, high porosity, high heat resistance and the like, so that the energy density and the electrochemical performance of the lithium ion battery can be improved on the basis of ensuring the safety of the lithium ion battery.

The invention provides a lithium ion battery in a second aspect, wherein the lithium ion battery comprises any one of the pole pieces.

The lithium ion battery provided by the invention can be prepared by combining the conventional technical means in the field on the basis of the pole piece by a person skilled in the art. The lithium ion battery provided by the invention has better safety, energy density and electrochemical performance.

The implementation of the invention has at least the following advantages:

1. the pole piece that this application provided, it includes safe coating to this safe coating has characteristics such as light, high porosity and high heat-resisting, on the basis of guaranteeing lithium ion battery security, can improve lithium ion battery's energy density and electrochemical performance.

2. The lithium ion battery provided by the application has better safety, energy density and electrochemical performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic diagram of a pole piece structure according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a pole piece structure according to another embodiment of the present invention.

Description of reference numerals:

101-a current collector;

102-an active layer;

103-a security coating;

104-conductive layer.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Aerogel powder, polymer microsphere powder, and binder used in the examples below are all commercially available.

Example 1

The pole piece that this embodiment provided is the positive plate, has the structure shown in fig. 2, including anodal mass flow body, conducting layer, anodal active layer and safety coating, wherein:

the positive current collector is aluminum foil, and the thickness of the positive current collector is 12 mu m;

the conductive layer comprises 4 parts by mass of conductive agent Super P and 2.5 parts by mass of binder styrene butadiene rubber, the thickness is 0.9 mu m, and the surface density is 1.3g/m²；

The active layer includes 97 parts by mass of a positive electrode active material lithium nickel cobalt manganese oxide (NCM811), 1.1 parts by mass of a positive electrode conductive agent Super P, and 1.9 parts by mass of PVDF (5130), and has a thickness of 90 μm;

the safety coating layer comprises 55 parts by mass of SiO₂Aerogel powder, 45 parts by mass of polystyrene microsphere powder and 5 parts by mass of binder PVDF, wherein the thickness is 2 microns;

wherein, SiO₂The aerogel powder has a pore diameter of 2nm and a density of 0.2mg/cm³；

The melting point of the polystyrene microsphere powder is 120 ℃, and the D50 is 0.8 mu m.

The preparation method of the pole piece provided by the embodiment comprises the following steps:

1. adding 4 parts by mass of conductive agent Super P and 2.5 parts by mass of binder styrene butadiene rubber into deionized water, uniformly mixing, and performing ball milling reinforcement dispersion by adopting a high-speed ball mill, wherein the particle size of ball milling beads is 0.3mm, the rotating speed of the ball mill is 1500rpm, and the time is 2 hours, so as to obtain conductive layer slurry;

uniformly coating the conductive layer slurry on two surfaces of a 12-micron aluminum foil in a micro-gravure coating mode, and drying at 50 ℃ to obtain a conductive layer;

2. adding 97 parts by mass of a positive electrode active material lithium nickel cobalt manganese oxide (NCM811), 1.1 parts by mass of conductive agent conductive carbon black (Super P) and 1.9 parts by mass of binder PVDF (5130) into NMP, and uniformly stirring under the action of a vacuum stirrer to obtain positive electrode active layer slurry;

uniformly coating the positive electrode slurry on the surface of the conductive layer far away from the aluminum foil, drying at 105 ℃ for 5h, and transferring to a 120 ℃ oven for drying for 1h to obtain an active layer with a positive electrode;

3. 55 parts by mass of SiO₂Adding NMP into aerogel powder, 45 parts by mass of polystyrene microsphere powder and 5 parts by mass of binder PVDF, and uniformly stirring under the action of a vacuum stirrer to obtain safe coating slurry with the solid content of 30%;

and uniformly coating the safe coating slurry on the surface of the active layer far away from the conductive layer, drying at 80 ℃ for 2h, and transferring to a 65 ℃ oven for vacuum drying for 1h to obtain the positive plate.

Example 2

The pole piece that this embodiment provided is the positive plate, has the structure shown in fig. 2, including anodal mass flow body, conducting layer, anodal active layer and safety coating, wherein:

the positive current collector is aluminum foil, and the thickness of the positive current collector is 12 mu m;

the conductive layer comprises 3.5 parts by mass of conductive agent Super P and 0.8 part by mass of binder carboxymethylcellulose sodium, and has a thickness of 1 μm and an areal density of 1.2g/m²；

The active layer includes 97 parts by mass of a positive electrode active material lithium nickel cobalt manganese oxide (NCM811), 1.1 parts by mass of a positive electrode conductive agent Super P, and 1.9 parts by mass of PVDF (5130), and has a thickness of 90 μm;

the security coating comprises 30 parts by mass of SiO₂Aerogel powder and 10 parts by mass of TiO₂Aerogel powder, 50 parts by mass of EVA (ethylene-vinyl acetate copolymer) microsphere powder and 5 parts by mass of binder PVDF, wherein the thickness is 12 mu m;

wherein, SiO₂The aerogel powder has a pore diameter of 5nm and a density of 0.4mg/cm³；

TiO₂The aerogel powder has a pore diameter of 8nm and a density of 0.5mg/cm³；

The melting point of the EVA (ethylene-vinyl acetate copolymer) microsphere powder is 105 ℃, and the D50 is 1.2 mu m.

Example 3

The electrode sheet and the manufacturing method thereof provided in this example can be referred to example 1, except that the safety coating layer includes 55 parts by mass of TiO₂Aerogel powder, 45 parts by mass of styrene-divinylbenzene copolymer microsphere powder and 5 parts by mass of adhesivePVDF as the agent;

wherein, TiO₂The aerogel powder has an aperture of 35nm and a density of 0.35mg/cm³；

The melting point of the styrene-divinylbenzene copolymer microsphere powder is 125 ℃, and the D50 is 0.9 mu m.

Example 4

The electrode sheet and the manufacturing method thereof provided in this example can refer to example 2, except that the safety coating layer includes 25 parts by mass of TiO₂Aerogel powder, 25 parts by mass of Al₂O₃Aerogel powder, 45 parts by mass of propylene-ethylene copolymer microsphere powder and 5 parts by mass of binder PVDF;

wherein, TiO₂The aerogel powder has a pore diameter of 60nm and a density of 0.3mg/cm³；

Al₂O₃The aerogel powder has a pore diameter of 55nm and a density of 0.35mg/cm³；

The melting point of the propylene-ethylene copolymer microsphere powder is 120 ℃, and the D50 is 1.3 mu m.

Comparative example 1

The electrode sheet and the preparation method thereof provided by the present comparative example can be referred to example 1, except that the safety coating layer includes 95 parts by mass of boehmite powder and 5 parts by mass of binder PVDF.

Comparative example 2

The electrode plate and the preparation method thereof provided by the comparative example can refer to example 2, and the difference is that the safety coating comprises 95 parts by mass of lithium lanthanum zirconium tantalum oxygen powder and 5 parts by mass of binder PVDF.

Preparing a laminated cell by matching the positive plate provided in the examples 1 to 4 and the comparative examples 1 to 2 with the negative plate and the diaphragm, and further packaging, injecting and forming to obtain the lithium ion battery:

the preparation method of the negative plate comprises the following steps: adding 95 parts by mass of graphite powder, 1 part by mass of conductive agent carbon black SP, 1.5 parts by mass of CMC and 2.5 parts by mass of SBR into deionized water, and uniformly stirring under the action of a vacuum stirrer to prepare cathode active layer slurry;

uniformly coating the slurry of the negative active layer on the surface of a copper foil with the thickness of 6 microns, drying at 85 ℃ for 6 hours, and transferring to a 90 ℃ oven for drying for 2 hours to obtain a negative plate;

the membrane is a commercial membrane.

The lithium ion batteries prepared according to the examples 1 to 4 and the comparative examples 1 to 2 were further tested for energy density, safety and discharge DCR, and the specific test results are shown in table 1:

the energy density testing method comprises the following steps: charging the lithium ion battery at 0.33C and discharging at 0.33C, and testing to obtain the discharge energy of the lithium ion battery; further testing to obtain the weight of the lithium ion battery; and calculating the energy density of the lithium ion battery according to the energy density which is the discharge energy/weight.

The safety tests include an overcharge test, a puncture test and a 150 ℃ hot box test, wherein:

the needling test method comprises the following steps: by usingThe high temperature resistant steel needle (the conical angle of the needle tip is 45 degrees to 60 degrees, the surface of the needle is smooth and clean and has no rust, oxide layer and oil stain), the needle penetrates through the high temperature resistant steel needle at the speed of (25 +/-5) mm/s from the direction vertical to the polar plate of the storage battery, the penetrating position is preferably close to the geometric center of the punctured surface, and the steel needle stays in the storage battery.

150 ℃ hot box test method: the test object was placed in a temperature box and heated under the following conditions: the temperature box is increased from the test environment temperature to 150 +/-2 ℃ at the speed of 5 ℃/min, and the heating is stopped after the temperature is maintained for 30 min.

The overcharge test method comprises the following steps: after the current is charged to 1.5 times or 150% SOC of the charging termination voltage in a constant current manner, the charging is stopped.

The discharge DCR test method comprises the following steps:

1. RT, discharging at a constant current of 1C to a termination voltage, stopping discharging, and standing for 1 h;

2. RT, changing from constant current charging at 1C to termination voltage to constant voltage charging, stopping charging until charging current is reduced to 0.05C, and standing for 1 h;

3. RT, discharging at a constant current of 1C until the end voltage, stopping discharging, wherein the discharge capacity is C0, and standing for 1 h;

4. RT, changing from constant current charging at 1C to termination voltage to constant voltage charging, stopping charging until charging current is reduced to 0.05C, and standing for 1 h;

5. and RT, discharging to 50% SOC at a constant current of 1C, standing for 1h, and testing DCR.

Table 1 results of performance tests of lithium ion batteries provided in examples 1 to 4 and comparative examples 1 to 2

As shown in table 1, compared with comparative examples 1-2, the lithium ion battery provided by the present application can effectively pass overcharge and needling tests, and the heat resistance of the lithium ion battery provided by the present application is significantly improved; meanwhile, the energy density of the lithium ion battery is improved, the discharge DCR is reduced, and the lithium ion battery has better energy density and electrochemical performance compared with comparative examples 1-2. As can be seen from the data provided in examples 1 to 4, when the safety coating includes different aerogel powders and polymer microsphere powders, the performance of the lithium ion battery is different, and specifically, a suitable material and a mass ratio of each material can be selected according to the actual production situation.

In conclusion, the pole piece provided by the application comprises the safety coating, and the safety coating has the characteristics of light weight, high porosity, high heat resistance and the like, so that the energy density and the electrochemical performance of the lithium ion battery can be improved on the basis of ensuring the safety of the lithium ion battery.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.