CN115732633A - A kind of high energy density lithium-ion battery silicon-based negative plate and preparation method thereof - Google Patents

Abstract

The invention discloses a high-energy-density lithium ion battery silicon-based negative plate, which comprises a current collector, an inner coating coated on the surface of the current collector, a middle coating coated on the surface of the inner coating and an outer coating coated on the surface of the middle coating; the inner coating and the middle coating both comprise silicon oxide and single-particle graphite, and the mass ratio of the silicon oxide to the single-particle graphite in the inner coating is 15-30:70-85, wherein the mass ratio of the silicon oxide to the single-particle graphite in the middle coating is 88-95:5-12, and the outer coating is a single-particle graphite layer. The silicon-based negative plate prepared by the invention has high silicon material content, the weight of the negative plate is greatly reduced, the expansion of the negative plate is effectively slowed down, the prepared lithium ion battery has good energy density and electrical property, and the expansion rate of the silicon-based negative plate before and after circulation and the expansion rate of the lithium ion battery are obviously lower than that of the conventional negative plate with a single-layer structure and a double-layer structure.

Description

A kind of high energy density lithium-ion battery silicon-based negative plate and preparation method thereof

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode sheet of a high energy density lithium ion battery and a preparation method thereof.

Background technique

At present, graphite-based negative electrode materials are still the mainstream negative electrode materials used in lithium-ion batteries. Its theoretical gram capacity of 372mAh/g severely limits its ability to increase the energy density of lithium-ion batteries. At present, relatively good artificial graphite, its actual The gram capacity is only 340-355mAh/g, and the development potential has reached the bottleneck, and it has been unable to meet the needs of lithium-ion batteries for small volume and high energy density.

Among many negative electrode materials, silicon-based negative electrodes have extremely high lithium storage capacity (pure silicon theoretically 4200mAh/g) and abundant resources, and the gram capacity of silicon oxide can also reach a high capacity of 1400-1500mAh/g. Graphite is the most competitive material for the anode of next-generation lithium-ion batteries. However, the high expansion and contraction coefficient of the silicon-based negative electrode makes it pulverized continuously during the lithium-deintercalation cycle, which destroys the overall structure of the silicon-based negative electrode material, continuously consumes active lithium, and rapidly decays in cycle performance, which limits its large-scale application. In addition, due to the expansion/contraction of the silicon-based material, the contact surface between the coated area and the current collector is easily separated during the cycle, which increases the contact gap between the material area and the current collector, causing the material area to gradually lose electrical contact. , the internal resistance of the battery is greatly increased, and the cycle decay of the battery is accelerated, so this poses a huge challenge to the cycle stability of the electrode structure.

Therefore, the traditional single-layer pole piece structure design can no longer meet the demand. In this regard, a large number of researchers have done a lot of work on the pole piece structure design of the silicon-based negative electrode, which mainly includes multi-layer structure design to reduce the expansion of the silicon-based negative electrode. , patent CN 112968148 A reports a lithium ion battery negative electrode sheet and a lithium ion battery, the lithium ion battery negative electrode sheet includes a first negative electrode active material layer and a second negative electrode active material layer, the first layer is carbon material, the second The layer is made of silicon material, and the DC resistance of the lithium ion battery constructed by the first negative electrode active material layer is smaller than that of the lithium ion battery constructed by the second negative electrode active material layer. Such a structural design can improve the performance of the silicon-based material, However, the bottom layer uses almost pure carbon negative electrode, which is limited to increase the energy density, and cannot solve the problem of the expansion of the upper layer of silicon, and needs to use laser drilling, which is difficult to operate and difficult to realize industrialization; patent CN 114678490 A reports a Lithium-ion battery negative electrode sheet, including a two-layer structure, the bottom graphite buffer layer and the upper layer silicon carbon layer, to obtain a lithium-ion battery negative electrode sheet with excellent first-time efficiency and coating adhesion, but the problem of the expansion of silicon materials in the electrode structure has not yet been solved. has been solved.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high-energy-density lithium-ion battery silicon-based negative electrode sheet and its preparation method. The silicon-based negative electrode sheet has a high content of silicon material, which greatly reduces the weight of the negative electrode sheet and effectively slows down the negative electrode. The expansion of the sheet makes the prepared lithium-ion battery take into account good energy density and electrical properties. The expansion rate of the silicon-based negative electrode sheet before and after cycling and the expansion rate of the lithium-ion battery are significantly lower than those of the conventional single-layer and double-layer structure. .

Technical scheme of the present invention is:

A silicon-based negative electrode sheet for a high energy density lithium-ion battery, comprising a current collector, an inner coating coated on the surface of the current collector, a middle coating coated on the inner coating surface, and an outer coating coated on the middle coating surface Coating; both the inner coating and the middle coating include silicon oxide and single particle graphite, the mass ratio of silicon oxide and single particle graphite in the inner coating is 15-30:70-85, and the middle coating contains silicon oxide The mass ratio of silicon and single particle graphite is 88-95:5-12, and the outer coating is a single particle graphite layer.

The particle size D50 of the single particle graphite is 5-7 μm; both sides of the current collector are coated with an internal coating, and the surface of each layer of internal coating is coated with a middle coating, and each layer of the middle coating The surface of the layer is coated with an outer coating; the total density of both sides of the inner coating is 25-35g/m ² , and the total density of both sides of the middle coating is 65-75g/m ² , the total surface density of both sides of the outer coating is 15-23g/m ² .

The inner coating also includes an inner layer conductive agent and an inner layer binder. In the inner layer, silicon oxide and single particle graphite are used as the main material of the inner layer, the main material of the inner layer, the inner layer conductive agent and the inner layer main material. The mass ratio of the inner layer binder is 89-94:1-5:3-6. The inner layer conductive agent includes a liquid inner layer conductive agent and a powder inner layer conductive agent. The liquid inner layer conductive agent is composed of a single One or more of walled carbon nanotubes, multi-walled carbon nanotubes and composite conductive agents are mixed and dispersed in water. The inner conductive agent of the powder is superconducting carbon black, nano-carbon fiber conductive agent and multi-layer graphene powder One or more of them are mixed, the inner layer binder includes polyacrylic binder and styrene-butadiene rubber binder, and the mass ratio of polyacrylic binder and styrene-butadiene rubber binder is 6 -10:1, the slurry for internal coating has a solid content of 30-35% and a viscosity of 2500-4000mpas.

The middle layer coating also includes a middle layer conductive agent and a middle layer binder. In the middle layer coating, silicon oxide and single particle graphite are used as the middle layer main material, and the middle layer main material, the middle layer conductive agent and the middle layer binder The mass ratio is 84-89:2-4:6-10, and the middle layer conductive agent is a liquid middle layer conductive agent, and the liquid middle layer conductive agent is composed of single-walled carbon nanotubes, multi-walled carbon nanotubes and composite conductive agents. One or more kinds are mixed and dispersed in water, the middle layer binder includes polyacrylic acid binder and carboxymethyl cellulose sodium binder, polyacrylic acid binder and carboxymethyl cellulose sodium binder The mass ratio of the agent is 7-10:1, the solid content of the slurry for coating the middle layer coating is 18-23%, and the viscosity is 1500-3000mpas.

The outer coating also includes an outer conductive agent and an outer binder, and the mass ratio of the single particle graphite, the outer conductive agent and the outer binder in the outer coating is 93-96:1-3 : 1-4, the outer conductive agent includes a liquid outer layer conductive agent and a powder outer layer conductive agent, and the liquid outer layer conductive agent is composed of a single-walled carbon nanotube, a multi-walled carbon nanotube and a composite conductive agent or multiple mixed and dispersed in water, the powder outer conductive agent is one or more of superconducting carbon black, nano-carbon fiber conductive agent and multi-layer graphene powder, the outer binder includes poly Acrylic binder and styrene-butadiene rubber binder, the mass ratio of polyacrylic binder and styrene-butadiene rubber binder is 2-4:1, and the slurry solid content of coating outer layer coating is 36-44%, the viscosity is 1000-2500mpas.

The composite conductive agent is formed by mixing multi-walled carbon nanotubes and carbon black conductive agent, and the mass ratio of multi-walled carbon nanotubes and carbon black conductive agent is 1:3-5.

The current collector is carbon-coated copper foil with a thickness of 4.5 μm, carbon-coated copper foil with a thickness of 6 μm, copper foil with a thickness of 4.5 μm or copper foil with a thickness of 6 μm.

A method for preparing a silicon-based negative electrode sheet for a high energy density lithium-ion battery, specifically comprising the following steps:

(1) Prepare the slurry for coating the inner coating: make the negative electrode by semi-dry mixing process of silicon oxide, single particle graphite, liquid inner layer conductive agent, powder inner layer conductive agent and inner layer binder slurry A;

(2), apply the negative electrode slurry A to both sides of the current collector to form a double-layer internal coating, place the current collector coated with a double-layer internal coating in an oven for low temperature and vacuum treatment, and set aside ;

(3), preparing the slurry for coating the middle coating: making negative electrode slurry B through wet process of mixing silicon oxide, single particle graphite, liquid middle layer conductive agent and middle layer binder;

(4), preparing the slurry for coating the external coating: making the negative electrode slurry C through the wet process of mixing single particle graphite, the liquid outer layer conductive agent, the powder outer layer conductive agent and the outer layer binder;

(5), coating the negative electrode slurry B on the surface of the double-layer internal coating to form a double-layer middle coating, coating the negative electrode slurry C on the surface of the double-layer middle coating, and finally moving to the oven Vacuum drying treatment to obtain the negative electrode material;

(6) The dried negative electrode material is processed by rolling and cutting to obtain a silicon-based negative electrode sheet.

In the described step (2), the temperature of the low temperature and vacuum treatment is 45°C, the vacuum pressure is -90Kpa, and the time is 12h; in the described step (5), the temperature of the vacuum drying treatment is 95°C, and the vacuum pressure is -90Kpa, the time is 24h.

In the step (6), the rolling compaction density is 1.35-1.55g/m ³ .

Advantages of the present invention:

(1), the present invention adopts a three-layer active material coating structure, the silicon content of the active material in the three-layer material coating structure is higher than 80%, so that the energy density of the prepared lithium-ion battery is greater than 380Wh/Kg, and the silicon-based negative electrode The full charge expansion rate of the lithium-ion battery and the lithium-ion battery is low, and the active material coating and the current collector are not easy to fall off, which greatly improves the cycle performance of the silicon-based negative electrode sheet;

(2), the inner coating of the present invention uses a high proportion of single particle graphite to match a low proportion of silicon oxide, and the inner layer binder includes a polyacrylic acid (PAA) type binder and a styrene-butadiene rubber (SBR) type binder , which improves the adhesion between the internal coating and the current collector, and at the same time increases the flexibility of the silicon-based negative electrode sheet. The single particle graphite with a small particle size can provide more particles and better distribution in the same mass. Between the particles of silicon oxide, it increases conductivity and buffers expansion;

(3), the middle coating of the present invention uses a high proportion of silicon oxide to match a low proportion of single particle graphite, and simultaneously matches a low proportion of polyacrylic acid (PAA) type binder and sodium carboxymethylcellulose (CMC) to bond agent, and the conductive agent in the middle layer of the liquid, so that the prepared lithium-ion battery takes into account the energy density, while ensuring the conductivity of the middle coating, so that it can match the resistivity of the inner coating and the outer coating;

(4), the outer coating of the present invention uses a high proportion of pure single particle graphite, the coating surface density is low, and the quality and flexibility of the surface of the silicon-based negative plate are improved;

(5), the single particle graphite of the inner coating and the outer coating of the present invention produce a synergistic effect to inhibit expansion. During the charge and discharge process, the middle coating shows high expansion, and the low proportion of silicon oxide in the inner coating shows low Expansion, the single particle graphite expansion rate of the outer coating is extremely low, therefore, the inner coating and the outer coating can well buffer the expansion of the middle coating with a high proportion of silicon oxide, compared with the traditional single-layer and double-layer designs , showing a buffer expansion phenomenon, so that the overall expansion of the silicon-based negative plate is low expansion;

(6), the low expansion rate of the silicon-based negative electrode sheet made by the present invention makes the expansion rate of the lithium-ion battery low, thereby greatly improving the cycle performance of the lithium-ion battery, and the silicon-based negative electrode sheet after the cycle is still not active The shedding of the material coating is of great significance to the future large-scale promotion of high-silicon negative electrodes for lithium-ion batteries.

Description of drawings

Fig. 1 is a cross-sectional view of a silicon-based negative electrode sheet of the present invention.

Fig. 2 is a diagram of the surface state of the silicon-based negative electrode sheet after 400 cycles of the battery cell in Example 1 of the present invention.

3 is a diagram of the surface state of the silicon-based negative electrode sheet after 400 cycles of the cell in Comparative Example 1 of the present invention.

Reference numerals: 01 - current collector, 02 - inner coating, 03 - middle coating, 04 - outer coating.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

As shown in Figure 1, a method for preparing a silicon-based negative electrode sheet for a high-energy-density lithium-ion battery includes the following steps:

(1) Prepare the slurry for coating the inner coating: make the negative electrode by semi-dry mixing process of silicon oxide, single particle graphite, liquid inner layer conductive agent, powder inner layer conductive agent and inner layer binder Slurry A; Wherein, the mass ratio of the main material of the inner layer in the negative electrode slurry A is silicon oxide and single particle graphite is 30:70, and the mass ratio of the main material of the inner layer, the conductive agent of the inner layer and the binder of the inner layer is 92:3:5, the inner conductive agent is an aqueous solution of single-walled carbon nanotubes (SWCNT), superconducting carbon black SP, and carbon nanofibers (VGCF), and the mass ratio of SWCNT, SP, and VGCF is 1:15:10. Layer binder includes PAA type binder and SBR type binder, the mass ratio of PAA type binder and SBR type binder is 7:1, the solid content of negative electrode slurry A is 34.5%, the viscosity is 3854mpas;

(2), transfer the negative electrode slurry A to an extrusion coating transfer tank, circulate and defoam, and apply the negative electrode slurry A to both sides of the current collector 01 (a carbon-coated copper foil with a thickness of 6 μm), Form a double-layer internal coating 02, place the current collector 01 coated with a double-layer internal coating 02 in an oven for 12 hours at a temperature of 45°C and a vacuum pressure of -90Kpa, and wait for use; among them, the internal coating 02 The total surface density of both sides is 30g/m ² , and the dry film thickness after drying treatment is 28μm;

(3), prepare the slurry for coating the middle part of the coating: make negative electrode slurry B through wet process of mixing silicon oxide, single particle graphite, liquid middle layer conductive agent and middle layer binder; wherein, negative electrode slurry The mass ratio of the main material in the middle part of B, that is, silicon oxide and single particle graphite, is 92:8, the mass ratio of the main material in the middle layer, the conductive agent in the middle layer, and the binder in the middle layer is 86:4:10, and the conductive agent in the middle layer is SWCNT and composite The mixed aqueous solution of conductive agent, the mass ratio of SWCNT and composite conductive agent is 1:3, the composite conductive agent is formed by mixing multi-walled carbon nanotubes and superconducting carbon black, the mass of multi-walled carbon nanotubes and superconducting carbon black The ratio is 1:3-5, the middle layer binder includes PAA binder and CMC binder, the mass ratio of PAA binder and CMC binder is 8:1, and the solid content of negative electrode slurry B It is 22.5%, and the viscosity is 2269mpas;

(4), preparation is coated with the slurry of external coating: single-grain graphite, outer layer conductive agent and outer layer binding agent are made into negative electrode slurry C through wet method slurry mixing process; Wherein, in the negative electrode slurry C The mass ratio of single particle graphite, outer layer conductive agent and outer layer binder is 95.0:1.5:3.5, the outer layer conductive agent is an aqueous solution of SWCNT and superconducting carbon black SP, and the mass ratio of SWCNT and superconducting carbon black SP is 1:15, the outer layer binder includes PAA type binder and SBR type binder, the mass ratio of PAA type binder and SBR type binder is 3:1, and the solid content in negative electrode slurry C is 40.6%, viscosity is 1780mpas;

(5), transfer the negative electrode slurry B and the negative electrode slurry C to the double-layer extrusion coating transfer tank, circulate and defoam, and then apply the negative electrode slurry B on the surface of the double-layer inner coating 02, Form a double-layer middle coating 03, apply negative electrode slurry C on the surface of the double-layer middle coating 03 to form a double-layer outer coating 04, and finally move it to an oven at a temperature of 95°C and a vacuum pressure of -90Kpa After 24 hours of treatment, the negative electrode material was obtained; wherein, the total surface density of both sides of the middle coating was 68g/m ² , the total surface density of both sides of the outer coating was 18g/m ² , and the dry film thickness of the negative electrode material was 122μm;

(6) The dried negative electrode material is subjected to rolling (compaction density: 1.45 g/m ² ) and cutting processes to obtain a silicon-based negative electrode sheet.

The prepared silicon-based negative electrode sheet and the ternary high-nickel positive electrode sheet with a Ni content of more than 85% were assembled into a soft-packed lithium-ion battery with a battery capacity of 28Ah, an electrochemical test cycle rate of 0.5C, and a voltage range of 2.75-4.25V.

Example 2

A method for preparing a silicon-based negative electrode sheet for a high energy density lithium-ion battery, specifically comprising the following steps:

(1) Prepare the slurry for coating the inner coating: make the negative electrode by semi-dry mixing process of silicon oxide, single particle graphite, liquid inner layer conductive agent, powder inner layer conductive agent and inner layer binder Slurry A; Wherein, the mass ratio of the main material of the inner layer in the negative electrode slurry A is silicon oxide and single particle graphite is 28:72, and the mass ratio of the main material of the inner layer, the conductive agent of the inner layer and the binder of the inner layer is 90.5:3.5:6, the inner conductive agent is an aqueous solution of single-walled carbon nanotube (SWCNT), superconducting carbon black SP and carbon nanofiber (VGCF) conductive agent, and the mass ratio of SWCNT, SP and VGCF is 1:15:10 , the inner layer binder includes PAA type binder and SBR type binder, the mass ratio of PAA type binder and SBR type binder is 9.5:1, the solid content of negative electrode slurry A is 33.6%, The viscosity is 3682mpas;

(2) Transfer negative electrode slurry A to an extrusion-type coating transfer tank, circulate and defoam, and apply negative electrode slurry A to both sides of a carbon-coated copper foil with a thickness of 4.5 μm to form a double-layer interior Coating, the current collector coated with double-layer internal coating is placed in an oven for 12 hours at a temperature of 45°C and a vacuum pressure of -90Kpa, and is ready for use; wherein, the total surface density of both sides of the internal coating is 30g/m ^2. The dry film thickness after drying treatment is 28μm;

(3), prepare the slurry for coating the middle part of the coating: make negative electrode slurry B through wet process of mixing silicon oxide, single particle graphite, liquid middle layer conductive agent and middle layer binder; wherein, negative electrode slurry The mass ratio of the main material in the middle part of B, that is, silicon oxide and single particle graphite, is 94:6, the mass ratio of the main material in the middle layer, the conductive agent in the middle layer, and the binder in the middle layer is 86:4:10, and the conductive agent in the middle layer is SWCNT and composite The mixed aqueous solution of conductive agent, the mass ratio of SWCNT and composite conductive agent is 1:3, the composite conductive agent is formed by mixing multi-walled carbon nanotubes and superconducting carbon black, the mass of multi-walled carbon nanotubes and superconducting carbon black The ratio is 1:3-5, the middle layer binder includes PAA binder and CMC binder, the mass ratio of PAA binder and CMC binder is 8:1, and the solid content of negative electrode slurry B It is 23.7%, and the viscosity is 2540mpas;

(4), preparation is coated with the slurry of external coating: single-grain graphite, outer layer conductive agent and outer layer binding agent are made into negative electrode slurry C through wet method slurry mixing process; Wherein, in the negative electrode slurry C The mass ratio of single particle graphite, outer layer conductive agent and outer layer binder is 95.0:1.5:3.5, the outer layer conductive agent is an aqueous solution of SWCNT and superconducting carbon black SP, and the mass ratio of SWCNT and superconducting carbon black SP is 1:15, the outer layer binder includes PAA type binder and SBR type binder, the mass ratio of PAA type binder and SBR type binder is 2:1, and the solid content in negative electrode slurry C is 42.1%, viscosity is 1970mpas;

(5), transfer the negative electrode slurry B and the negative electrode slurry C to the double-layer extrusion coating transfer tank, circulate and defoam, and then apply the negative electrode slurry B on the surface of the double-layer internal coating to form Double-layer middle coating, coating the negative electrode slurry C on the surface of the double-layer middle coating to form a double-layer outer coating, and finally moving it to an oven for 24 hours at a temperature of 95°C and a vacuum pressure of -90Kpa to obtain Negative electrode material; wherein, the total surface density of both sides of the middle coating is 72g/m ² , the total surface density of both sides of the outer coating is 22g/m ² , and the dry film thickness of the negative electrode material is 128μm;

(6) The dried negative electrode material is subjected to rolling (compacted density: 1.5 g/m ² ) and cutting processes to obtain a silicon-based negative electrode sheet.

The prepared silicon-based negative electrode sheet and the ternary high-nickel positive electrode sheet with a Ni content of more than 85% were assembled into a soft-packed lithium-ion battery with a battery capacity of 28Ah, an electrochemical test cycle rate of 0.5C, and a voltage range of 2.75-4.25V.

Example 3

A method for preparing a silicon-based negative electrode sheet for a high energy density lithium-ion battery, specifically comprising the following steps:

(1) Prepare the slurry for coating the inner coating: make the negative electrode by semi-dry mixing process of silicon oxide, single particle graphite, liquid inner layer conductive agent, powder inner layer conductive agent and inner layer binder Slurry A; wherein, the mass ratio of the main material of the inner layer in the negative electrode slurry A is silicon oxide and single particle graphite is 25:75, and the mass ratio of the main material of the inner layer, the conductive agent of the inner layer and the binder of the inner layer is 90.5:3.5:6, the inner layer conductive agent is SWCNT aqueous solution and VGCF conductive agent, the mass ratio of SWCNT and VGCF is 1:10, the inner layer binder includes PAA type binder and SBR type binder, PAA The mass ratio of the type binder and the SBR type binder is 10:1, the solid content of the negative electrode slurry A is 32.6%, and the viscosity is 3451mpas;

(2) Transfer the negative electrode slurry A to the extrusion coating transfer tank, circulate and defoam, and apply the negative electrode slurry A to both sides of the copper foil with a thickness of 6 μm to form a double-layer internal coating , put the current collector coated with double-layer internal coating in an oven for 12 hours at a temperature of 45°C and a vacuum pressure of -90Kpa, and wait for use; wherein, the total surface density of both sides of the internal coating is 32g/m ² , The dry film thickness after drying treatment is 29 μm;

(3), prepare the slurry for coating the middle part of the coating: make negative electrode slurry B through wet process of mixing silicon oxide, single particle graphite, liquid middle layer conductive agent and middle layer binder; wherein, negative electrode slurry The mass ratio of the main material in the middle part of B, that is, silicon oxide and single particle graphite, is 94:6, the mass ratio of the main material in the middle layer, the conductive agent in the middle layer, and the binder in the middle layer is 87:3.5:9.5, and the conductive agent in the middle layer is SWCNT and composite The mixed aqueous solution of conductive agent, the mass ratio of SWCNT and composite conductive agent is 1:4, the composite conductive agent is formed by mixing multi-walled carbon nanotubes and superconducting carbon black, the mass of multi-walled carbon nanotubes and superconducting carbon black The ratio is 1:3-5, the middle layer binder includes PAA binder and CMC binder, the mass ratio of PAA binder and CMC binder is 6:1, and the solid content of negative electrode slurry B It is 22.7%, and the viscosity is 2640mpas;

(4), preparation is coated with the slurry of external coating: single-grain graphite, outer layer conductive agent and outer layer binding agent are made into negative electrode slurry C through wet method slurry mixing process; Wherein, in the negative electrode slurry C The mass ratio of single particle graphite, outer layer conductive agent and outer layer binder is 94.5:2:3.5, the outer layer conductive agent is an aqueous solution of SWCNT and superconducting carbon black SP, and the mass ratio of SWCNT and superconducting carbon black SP is 1 :15, the outer layer binder includes PAA binder and SBR binder, the mass ratio of PAA binder and SBR binder is 3:1, and the solid content in negative electrode slurry C is 41.6 %, viscosity is 1870mpas;

(5), transfer the negative electrode slurry B and the negative electrode slurry C to the double-layer extrusion coating transfer tank, circulate and defoam, and then apply the negative electrode slurry B on the surface of the double-layer internal coating to form Double-layer middle coating, coating the negative electrode slurry C on the surface of the double-layer middle coating to form a double-layer outer coating, and finally moving it to an oven for 24 hours at a temperature of 95°C and a vacuum pressure of -90Kpa to obtain Negative electrode material; wherein, the total surface density of both sides of the middle coating is 68g/m ² , the total surface density of both sides of the outer coating is 23g/m ² , and the dry film thickness of the negative electrode material is 126μm;

(6) The dried negative electrode material is subjected to rolling (compacted density: 1.5 g/m ² ) and cutting processes to obtain a silicon-based negative electrode sheet.

The prepared silicon-based negative electrode sheet and the ternary high-nickel positive electrode sheet with a Ni content of more than 85% were assembled into a soft-packed lithium-ion battery with a battery capacity of 28Ah, an electrochemical test cycle rate of 0.5C, and a voltage range of 2.75-4.25V.

Comparative example 1

A preparation method of a double-layer coated lithium-ion battery silicon-based negative plate, the same as the steps (1)-(3) of Example 1, the difference is that the negative electrode slurry B is coated on the surface of the double-layer internal coating After being applied, the negative electrode slurry C is not coated, and directly moved to an oven for 24 hours at a temperature of 95°C and a vacuum pressure of -90Kpa to obtain the negative electrode material. The negative electrode material is rolled as in Example 1 (the compacted density is 1.45 g/m ² ), slitting process and other treatments to obtain the silicon-based negative electrode sheet.

The prepared silicon-based negative electrode sheet and the ternary high-nickel positive electrode sheet with a Ni content of more than 85% were assembled into a soft-packed lithium-ion battery with a battery capacity of 28Ah, an electrochemical test cycle rate of 0.5C, and a voltage range of 2.75-4.25V.

Comparative example 2

A method for preparing a single-layer coated lithium-ion battery silicon-based negative plate, according to the step (3) of Example 2 to prepare the negative electrode slurry B, and then the negative electrode slurry B is coated on the carbon-coated copper with a thickness of 4.5 μm After the both sides of the foil are double-sided, move it directly to an oven and treat it for 24 hours at a temperature of 95°C and a vacuum pressure of -90Kpa to obtain the negative electrode material. The total density of both sides of the negative electrode slurry B is 72g/m ² . Similar to Example 2, the silicon-based negative electrode sheet was obtained through rolling (compacted density: 1.45 g/m ² ), slitting, and other treatments.

The prepared silicon-based negative electrode sheet and the ternary high-nickel positive electrode sheet with a Ni content of more than 85% were assembled into a soft-packed lithium-ion battery with a battery capacity of 28Ah, an electrochemical test cycle rate of 0.5C, and a voltage range of 2.75-4.25V.

The lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to charge and discharge experiments, and the experimental results and data are shown in Table 1 below.

Table 1

From the experimental results data in Table 1, it can be seen that the silicon-based negative electrode sheets prepared in Examples 1-3 have a lower expansion rate, so that the cell expansion rate of the lithium-ion battery is low, and after 400 cycles of charging and discharging, the ACR growth rate Compared with the lithium-ion batteries prepared in Comparative Examples 1 and 2, the capacity retention rate is higher.

From the surface state diagrams of the silicon-based negative electrode sheet in Figure 2 and Figure 3, it can be seen that after the silicon-based negative electrode sheet prepared in Comparative Example 1 was charged and discharged for 400 cycles, the silicon-based negative electrode sheet had obvious powder separation from the current collector. However, the surface of the silicon-based negative electrode sheet prepared in Example 1 was basically unchanged.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (10)

1. A silicon-based negative plate of a high-energy-density lithium ion battery is characterized in that: the current collector comprises a current collector, an inner coating coated on the surface of the current collector, a middle coating coated on the surface of the inner coating and an outer coating coated on the surface of the middle coating; the inner coating and the middle coating both comprise the silica and the single-particle graphite, and the mass ratio of the silica to the single-particle graphite in the inner coating is 15-30:70-85, wherein the mass ratio of the silicon monoxide to the single-particle graphite in the middle coating is 88-95:5-12, and the outer coating is a single-particle graphite layer.

2. The silicon-based negative plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the particle size D50 of the single-particle graphite is 5-7 mu m; the double surfaces of the current collector are coated with internal coatings, the surface of each layer of internal coating is coated with a middle coating, and the surface of each layer of middle coating is coated with an external coating; the total surface density of the two surfaces of the internal coating is 25-35g/m ² The total surface density of the middle coating on both sides is 65-75g/m ² The total surface density of the two surfaces of the external coating is 15-23g/m ² 。

3. The silicon-based negative plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the inner coating further comprises an inner layer conductive agent and an inner layer adhesive, wherein the inner coating comprises silica and single-particle graphite as inner layer main materials, and the mass ratio of the inner layer main materials to the inner layer conductive agent to the inner layer adhesive is 89-94:1-5:3-6, wherein the inner layer conductive agent comprises a liquid inner layer conductive agent and a powder inner layer conductive agent, the liquid inner layer conductive agent is formed by mixing and dispersing one or more of a single-walled carbon nanotube, a multi-walled carbon nanotube and a composite conductive agent in water, the powder inner layer conductive agent is one or more of superconducting carbon black, a carbon nanofiber conductive agent and multilayer graphene powder, the inner layer binder comprises a polyacrylic binder and a styrene butadiene rubber binder, and the mass ratio of the polyacrylic binder to the styrene butadiene rubber binder is 6-10:1, the solid content of the slurry for coating the inner coating is 30-35%, and the viscosity is 2500-4000mpas.

4. The silicon-based negative plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the middle coating also comprises a middle layer conductive agent and a middle layer binder, wherein the middle layer coating contains silicon monoxide and single-particle graphite as middle layer main materials, and the mass ratio of the middle layer main materials to the middle layer conductive agent to the middle layer binder is 84-89:2-4:6-10, the middle layer conductive agent is a liquid middle layer conductive agent, the liquid middle layer conductive agent is formed by mixing and dispersing one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and a composite conductive agent in water, the middle layer binder comprises a polyacrylic acid binder and a sodium carboxymethyl cellulose binder, the mass ratio of the polyacrylic acid binder to the sodium carboxymethyl cellulose binder is 7-10.

5. The silicon-based negative plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the outer coating also comprises an outer layer conductive agent and an outer layer binder, and the mass ratio of the single-particle graphite in the outer coating to the outer layer conductive agent to the outer layer binder is 93-96:1-3:1-4, wherein the outer layer conductive agent comprises a liquid outer layer conductive agent and a powder outer layer conductive agent, the liquid outer layer conductive agent is formed by mixing and dispersing one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and a composite conductive agent in water, the powder outer layer conductive agent is one or more of superconducting carbon black, a carbon nanofiber conductive agent and multilayer graphene powder, the outer layer binder comprises a polyacrylic binder and a styrene butadiene rubber binder, the mass ratio of the polyacrylic binder to the styrene butadiene rubber binder is (2-4).

6. The silicon-based negative plate of the high-energy-density lithium ion battery according to any one of claims 3 to 5, wherein: the composite conductive agent is formed by mixing multi-wall carbon nanotubes and superconducting carbon black, wherein the mass ratio of the multi-wall carbon nanotubes to the superconducting carbon black is 1.

7. The silicon-based negative plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the current collector is made of a carbon-coated copper foil with the thickness of 4.5 micrometers, a carbon-coated copper foil with the thickness of 6 micrometers, a copper foil with the thickness of 4.5 micrometers or a copper foil with the thickness of 6 micrometers.

8. The preparation method of the silicon-based negative electrode plate of the high-energy-density lithium ion battery according to claim 1, characterized in that: the method specifically comprises the following steps:

(1) Preparing slurry for coating the inner coating: preparing silicon oxide, single-particle graphite, a liquid inner layer conductive agent, a powder inner layer conductive agent and an inner layer binder into negative electrode slurry A through a semidry method slurry mixing process;

(2) Coating the negative electrode slurry A on two sides of the current collector to form a double-layer internal coating, and placing the current collector coated with the double-layer internal coating in an oven for low-temperature and vacuum treatment for later use;

(3) Preparing slurry for coating the middle coating: preparing silicon monoxide, single-particle graphite, a liquid middle-layer conductive agent and a middle-layer binder into negative electrode slurry B through a wet slurry mixing process;

(4) Preparing slurry for coating the external coating: preparing single-particle graphite, a liquid outer-layer conductive agent, a powder outer-layer conductive agent and an outer-layer binder into cathode slurry C by a wet slurry mixing process;

(5) Coating the negative electrode slurry B on the surface of the double-layer internal coating to form a double-layer middle coating, coating the negative electrode slurry C on the surface of the double-layer middle coating, and finally moving the double-layer middle coating to a drying oven for vacuum drying treatment to obtain a negative electrode material;

(6) And rolling and slitting the dried negative electrode material to obtain the silicon-based negative electrode plate.

9. The method for preparing the silicon-based negative plate of the high-energy-density lithium ion battery according to claim 8, wherein the method comprises the following steps: in the step (2), the low-temperature and vacuum treatment temperature is 45 ℃, the vacuum pressure is-90 Kpa, and the time is 12h; in the step (5), the temperature of vacuum drying treatment is 95 ℃, the vacuum pressure is-90 Kpa, and the time is 24h.

10. A high energy product according to claim 8The preparation method of the silicon-based negative plate of the lithium ion battery with the mass density is characterized by comprising the following steps of: in the step (6), the compacted density of the rolling is 1.35 to 1.55g/m ³ 。

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