Sodium-ion battery negative plate and preparation method thereof

Abstract

The invention relates to a sodium-ion battery negative electrode plate and a preparation method thereof, and belongs to the field of new energy batteries, and the specific scheme is as follows: the sodium-ion battery negative electrode plate comprises a current collector, a negative electrode coating a and a negative electrode coating b; at least one surface of the current collector is coated with the negative electrode coating a, the surface of the negative electrode coating a is coated with the negative electrode coating b, a negative electrode active substance of the negative electrode coating a is coal-based hard carbon, a negative electrode active substance of the negative electrode coating b is biomass hard carbon, the capacity ratio R1 of the coal-based hard carbon above 0.2 V is larger than or equal to 20% and smaller than or equal to 27%, and the capacity ratio R2 of the biomass hard carbon above 0.2 V is larger than or equal to 23% and smaller than or equal to 35%. The biomass hard carbon is arranged on one side far away from the current collector, the slope capacity proportion is high, the sodium precipitation risk is low, the surface density of the negative electrode can be improved, and the energy density is improved while the negative electrode dynamics is considered.

Description

Technical Field

[0001] The present invention belongs to the field of new energy batteries and relates to sodium ion batteries, and in particular to a sodium ion battery negative electrode sheet and a preparation method thereof. Background Art

[0002] In recent years, the cost of lithium-ion batteries has increased significantly. In comparison, low-cost sodium-ion batteries have become more advantageous. The working principle and production process of sodium-ion batteries are similar to those of lithium batteries, but sodium ore resources are extensive and the cost is low. For sodium-based hard carbon negative electrode materials, they are mainly divided into biomass hard carbon and coal-based hard carbon. Coal-based hard carbon has many advantages such as low cost, wide source, and high compaction density, but its potential for sodium is low, which is closer to the potential of sodium metal, and its rate performance is worse than that of biomass hard carbon. Anthracite particles are more easily broken, and small particles on the surface of the pole piece are easy to peel off, which may lead to problems such as low Hipot pass rate of the battery and high self-discharge rate. Summary of the invention

[0003] In order to solve the problems existing in the background technology, the present invention combines the characteristics of biomass hard carbon and coal-based hard carbon, and adopts a layered coating method to coat the coal-based hard carbon on the side close to the current collector, and the biomass hard carbon is coated on the surface of the coal-based hard carbon, which effectively improves the Hipot pass rate, reduces self-discharge, and can increase the negative electrode surface density while taking into account the negative electrode dynamics.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A sodium ion battery negative electrode sheet comprises a current collector, a negative electrode coating a and a negative electrode coating b; the negative electrode coating a is coated on at least one surface of the current collector, the negative electrode coating b is coated on the surface of the negative electrode coating a, the negative electrode active material of the negative electrode coating a is coal-based hard carbon, the negative electrode active material of the negative electrode coating b is biomass hard carbon, the capacity proportion R1 of the coal-based hard carbon above 0.2V satisfies 20%≤R1≤27%, the capacity proportion R2 of the biomass hard carbon above 0.2V satisfies 23%≤R2≤35%, and R1<R2 is satisfied.

[0006] Furthermore, the negative electrode coating a and the negative electrode coating b also include a conductive agent and a binder.

[0007] Furthermore, the weight ratio of the total negative electrode active material to the conductive agent and the binder in the negative electrode sheet is (90-98):(0.5-5.0):(1.5-5.0).

[0008] Furthermore, the conductive agent includes one or a combination of conductive carbon black, carbon nanotubes, conductive graphite, graphene, carbon fiber, acetylene black, and Ketjen black.

[0009] Furthermore, the binder includes one or a combination of styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, polyimide, polytetrafluoroethylene, and polyethylene oxide.

[0010] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0011] Step 1: coating a negative electrode slurry A on at least one surface of a current collector to obtain a negative electrode coating a, wherein the negative electrode active material in the negative electrode slurry A is coal-based hard carbon;

[0012] Step 2: coating the negative electrode slurry B on the negative electrode coating a to obtain the negative electrode coating b, wherein the negative electrode active material in the negative electrode slurry B is biomass hard carbon;

[0013] Step 3: After coating, the negative electrode sheet of the sodium ion battery is obtained by baking, rolling and die-cutting.

[0014] Furthermore, the negative electrode slurry A and the negative electrode slurry B also include a conductive agent and a binder.

[0015] Furthermore, the single-sided surface density of the negative electrode coating a is m1, and the single-sided surface density of the negative electrode coating b is m2, satisfying m2≤0.5m1, m1+m2≤110g / m 2 .

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The surface powder shedding of biomass hard carbon is better than that of coal-based hard carbon. This double-layer coating method can effectively reduce the surface damage of the negative electrode sheet, improve the pass rate of the Hipot test of the battery cell, and reduce the self-discharge rate of the battery cell.

[0018] (2) The biomass hard carbon is set on the side away from the current collector, with a high slope capacity ratio and a low risk of sodium precipitation, which can help increase the negative electrode surface density and improve the energy density while taking into account the negative electrode dynamics.

[0019] (3) The compaction density of biomass hard carbon is low. The coating is on the outer layer of the negative electrode. The voids in the coating are high, which ensures sufficient ion paths. The coal-based hard carbon is coated on the side close to the current collector. The compaction density of the coal-based hard carbon coating is high, and the voids in the coating are small, which ensures sufficient paths for electrons to be transferred from the current collector to the coating. The coating of the present invention takes into account both electron dynamics and ion dynamics. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the first sodium insertion curve of the negative electrode;

[0021] Figure 2 Schematic diagram of the negative electrode structure of the present invention;

[0022] In the figure, 1. negative electrode coating a, 2. negative electrode coating b, 3. current collector. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Comparative Example 1:

[0025] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0026] Step 1: Use hard carbon A (coal-based hard carbon, 0.2V capacity accounts for 21%) as the negative electrode active material, and prepare negative electrode slurry A by homogenization according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt, and coat the negative electrode with a surface density of 100g / m 2 After baking, rolling and die cutting, the compacted density is 1.0g / cm 3 ;

[0027] Step 2: prepare positive electrode slurry by homogenizing positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0028] Step 3: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division before testing.

[0029] Comparative Example 2:

[0030] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0031] Step 1: Use hard carbon B (biomass hard carbon, 0.2V capacity accounting for 28%) as the negative electrode active material, and prepare negative electrode slurry B by homogenizing according to the weight ratio of negative electrode active material, conductive carbon black, binder = 96%wt: 1%wt: 3%wt, and apply negative electrode surface density 100g / m 2 After baking, rolling and die cutting, the compacted density is 0.90g / cm 3 ;

[0032] Step 2: prepare positive electrode slurry by homogenizing positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0033] Step 3: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division before testing.

[0034] Embodiment 1:

[0035] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0036] Step 1: Use hard carbon A (coal-based hard carbon, 0.2V capacity accounts for 21%) as the negative electrode active material, and prepare negative electrode slurry A by homogenization according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. The negative electrode slurry A is coated on the current collector 3 to obtain a negative electrode coating a1, and the coating surface density is 70g / m 2 ;

[0037] Step 2: Use hard carbon B (biomass hard carbon, 0.2V capacity accounting for 28%) as the negative electrode active material, and prepare negative electrode slurry B by homogenizing according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. Apply the negative electrode slurry B on the negative electrode coating a1 to obtain a negative electrode coating b2 with a coating surface density of 30g / m 2 , complete baking and roller pressing (overall compaction density 0.95g / cm 3 ), die cutting;

[0038] Step 3: prepare positive electrode slurry by homogenizing the positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0039] Step 4: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division, and wait for testing.

[0040] Embodiment 2:

[0041] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0042] Step 1: Use hard carbon A (coal-based hard carbon, 0.2V capacity accounting for 21%) as the negative electrode active material, and prepare negative electrode slurry A by homogenization according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. The negative electrode slurry A is coated on the current collector 3 to obtain a negative electrode coating a1, and the coating surface density is 75g / m 2 ;

[0043] Step 2: Use hard carbon B (biomass hard carbon, 0.2V capacity accounting for 28%) as the negative electrode active material, and prepare negative electrode slurry B by homogenizing according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. Apply the negative electrode slurry B on the negative electrode coating a1 to obtain a negative electrode coating b2 with a coating surface density of 25g / m 2 , complete baking and roller pressing (overall compaction density 0.95g / cm 3 ), die cutting;

[0044] Step 3: prepare positive electrode slurry by homogenizing the positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0045] Step 4: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division, and wait for testing.

[0046] Embodiment 3:

[0047] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0048] Step 1: Use hard carbon A (coal-based hard carbon, 0.2V capacity accounting for 21%) as the negative electrode active material, and prepare negative electrode slurry A by homogenization according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. The negative electrode slurry A is coated on the current collector 3 to obtain a negative electrode coating a1, and the coating surface density is 80g / m 2 ;

[0049] Step 2: Use hard carbon B (biomass hard carbon, 0.2V capacity accounting for 30%) as the negative electrode active material, and prepare negative electrode slurry B by homogenizing according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. Apply the negative electrode slurry B on the negative electrode coating a1 to obtain the negative electrode coating b2, with a coating surface density of 25g / m 2 , complete baking and roller pressing (overall compaction density 0.95g / cm 3 ), die cutting;

[0050] Step 3: prepare positive electrode slurry by homogenizing the positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0051] Step 4: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division, and wait for testing.

[0052] Embodiment 4:

[0053] A method for preparing a negative electrode sheet for a sodium ion battery comprises the following steps:

[0054] Step 1: Use hard carbon A (coal-based hard carbon, 0.2V capacity accounting for 21%) as the negative electrode active material, and prepare negative electrode slurry A by homogenization according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. The negative electrode slurry A is coated on the current collector 3 to obtain a negative electrode coating a1, and the coating surface density is 85g / m 2 ;

[0055] Step 2: Use hard carbon B (biomass hard carbon, 0.2V capacity accounting for 30%) as the negative electrode active material, and prepare negative electrode slurry B by homogenizing according to the weight ratio of negative electrode active material, conductive carbon black, and binder = 96%wt: 1%wt: 3%wt. Apply the negative electrode slurry B on the negative electrode coating a1 to obtain the negative electrode coating b2, with a coating surface density of 25g / m 2 , complete baking and roller pressing (overall compaction density 0.95g / cm 3 ), die cutting;

[0056] Step 3: prepare positive electrode slurry by homogenizing the positive electrode Prussian blue, conductive agent and binder in a weight ratio of 92%wt:4%wt:4%wt in N-methylpyrrolidone system, and complete coating, baking and die cutting;

[0057] Step 4: Stack the positive and negative electrodes, and complete the processes of baking, liquid injection, packaging, formation, and capacity division, and wait for testing.

[0058] Battery Assembly:

[0059] The positive electrode sheet / separator / hard carbon negative electrode are stacked in sequence, injected with electrolyte, and then formed to prepare a battery.

[0060] Test method:

[0061] 25℃ cycle test: Under 25℃ environment, leave it for 10min, charge it with 1C constant current and constant voltage to 3.65V; leave it for 10min, discharge it with 1C constant current to 2.0V, leave it for 10min;

[0062] Case Hi-pot pass rate 1000T capacity retention rate 1000T sodium analysis ED(Wh / kg) Comparative Example 1 96％ 94.7％ yes 130 Comparative Example 2 100％ 95.6％ no 125 Example 1 100％ 95.7％ no 128 Example 2 100％ 95.7％ no 128 Example 3 100％ 95.6％ no 132 Example 4 100％ 95.6％ no 132

[0063] in conclusion:

[0064] Compared with Comparative Examples 1 and 2, Examples 1 and 2 can ensure high Hi-pot pass rate and high cycle retention rate, high negative electrode kinetics, and take into account energy density and kinetics under the condition of constant total surface density. In Examples 3 and 4, while coating biomass carbon (biomass carbon 0.2V capacity improvement), the overall surface density of the negative electrode sheet can be further improved, ensuring kinetics and cycle retention rate, while effectively improving energy density.

[0065] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A negative electrode sheet for a sodium ion battery, comprising a current collector, a negative electrode coating a and a negative electrode coating b; the negative electrode coating a is coated on at least one surface of the current collector, and the negative electrode coating b is coated on the surface of the negative electrode coating a, characterized in that: The negative electrode active material of the negative electrode coating a is coal-based hard carbon, and the negative electrode active material of the negative electrode coating b is biomass hard carbon. The capacity proportion R1 of the coal-based hard carbon above 0.2V satisfies 20%≤R1≤27%, and the capacity proportion R2 of the biomass hard carbon above 0.2V satisfies 23%≤R2≤35%, and R1<R2.

2. The negative electrode sheet for a sodium ion battery according to claim 1, characterized in that: The negative electrode coating a and the negative electrode coating b further include a conductive agent and a binder.

3. The negative electrode sheet for a sodium ion battery according to claim 2, characterized in that: The weight ratio of the total negative electrode active material to the conductive agent and the binder in the negative electrode sheet is (90-98):(0.5-5.0):(1.5-5.0).

4. The negative electrode sheet for a sodium ion battery according to claim 2, characterized in that: The conductive agent includes one or a combination of conductive carbon black, carbon nanotubes, conductive graphite, graphene, carbon fiber, acetylene black, and Ketjen black.

5. The negative electrode sheet for a sodium ion battery according to claim 2, characterized in that: The binder includes one or a combination of styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, polyacrylonitrile, polyimide, polytetrafluoroethylene, and polyethylene oxide.

6. A method for preparing a negative electrode sheet for a sodium ion battery according to claims 1-5, characterized in that: The following steps are involved: Step 1: coating a negative electrode slurry A on at least one surface of a current collector to obtain a negative electrode coating a, wherein the negative electrode active material in the negative electrode slurry A is coal-based hard carbon; Step 2: coating the negative electrode slurry B on the negative electrode coating a to obtain the negative electrode coating b, wherein the negative electrode active material in the negative electrode slurry B is biomass hard carbon; Step 3: After coating, the negative electrode sheet of the sodium ion battery is obtained by baking, rolling and die-cutting.

7. The preparation method according to claim 6, characterized in that: The negative electrode slurry A and the negative electrode slurry B further include a conductive agent and a binder.

8. The preparation method according to claim 6, characterized in that: The single-sided surface density of the negative electrode coating a is m1, and the single-sided surface density of the negative electrode coating b is m2, satisfying m2≤0.5m1, m1+m2≤110g / m 2 .

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