A lithium-ion battery negative electrode sheet, preparation method and lithium-ion battery thereof

Abstract

The present invention discloses a lithium ion battery negative electrode sheet, a preparation method and a lithium ion battery thereof. The negative electrode sheet comprises a current collector and an electrode layer, wherein the electrode layer is laid on the current collector; the electrode layer comprises a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose and a ‑ The negative electrode additive A accounts for 0.01%-0.5% of the total mass of the negative electrode active material, the conductive agent, and the sodium carboxymethyl cellulose; the structural formula of the negative electrode additive A is: #imgabs0#, wherein, in the above formula, R is ‑NH2, ‑OH, or ‑SiH3.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronic devices such as mobile phones and laptops, as well as electric vehicles and large energy storage devices. Since the solid phase diffusion coefficient of lithium in graphite is relatively small (usually only about 10-10cm 2 / s), which makes the solid-phase diffusion of lithium within the graphite easily the controlling step of the entire electrode reaction. We often reduce the particle size of the negative electrode material graphite and increase its granulation level to reduce the diffusion path of lithium ions, thereby reducing the diffusion impedance of lithium ions and improving the fast charging performance of the battery. However, reducing the particle size and increasing the granulation level will increase the amount of dispersant and adhesive consumed between particles. This will lead to a decrease in the peel strength between the negative electrode slurry and the foil, resulting in severe powder loss during battery cell cycling and ultimately the risk of short circuit.

[0003] In other words, if the graphite particle size is larger, the lithium ion diffusion time is longer, affecting the fast charging performance. When the graphite particle size is reduced, the specific surface area is too large, resulting in excessive consumption of dispersant-grade adhesive between the particles, affecting the peel strength between the particles and the foil, and causing serious powder loss during the battery cycle. However, if the proportion of dispersant and adhesive is increased, it is equivalent to indirectly reducing the proportion of the negative electrode main material, which will reduce the energy density of the battery cell, making the fast charging capability of the negative electrode incompatible with the energy density.

[0004] Therefore, there is an urgent need for a negative electrode sheet that can effectively solve the problem of easy powder loss while ensuring good fast charging cycle performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium ion battery negative electrode sheet, a preparation method and a lithium ion battery thereof, which can effectively solve the problem of easy powder loss while ensuring good fast charging cycle performance.

[0006] The present invention discloses a negative electrode sheet for a lithium ion battery, wherein the negative electrode sheet comprises a current collector and an electrode layer, wherein the electrode layer is laid on the current collector; the electrode layer comprises a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose and a conductive agent containing OH. - The negative electrode additive A accounts for 0.01%-0.5% of the total mass of the negative electrode active material, the conductive agent, and the sodium carboxymethyl cellulose; the structural formula of the negative electrode additive A is:

[0007]

[0008] Wherein, in the above formula, R is -NH2, -OH or -SiH3.

[0009] Optionally, the negative electrode additive A accounts for 0.5% of the total mass of the negative electrode active material, the conductive agent, and sodium carboxymethyl cellulose.

[0010] Optionally, the negative electrode active material is graphite, the conductive agent is acetylene black, and the mass ratio of graphite, acetylene black and sodium carboxymethyl cellulose is 97.5:2.5:1.

[0011] Optionally, the electrode layer of the negative electrode sheet includes a single-sided area and a double-sided area, the thickness of the single-sided area is W1, the thickness of the double-sided area is W2, W1 / W2=X; the mass ratio of the negative electrode additive A is Y, and X and Y satisfy the following relationship:

[0012] 0.04≤Y / (X-0.5)≤9

[0013] Among them, 0.5<X<0.75, 0≤Y≤0.1, and both X and Y are rounded to two decimal places.

[0014] Y represents the amount of negative electrode additive A added during the negative electrode sheet batching process, while X represents the ratio of the single-sided area to the double-sided area. Due to the different pressures on the single and double-sided areas during the rolling stage, their thicknesses vary. Negative electrode additive A strengthens the bonding strength within the negative electrode sheet. The degree of internal bonding within the electrode sheet is correlated to the thickness difference between the single and double-sided areas after rolling.

[0015] The present invention also discloses a method for preparing a negative electrode sheet for a lithium ion battery, which is applicable to the above-mentioned method for preparing a negative electrode sheet, specifically comprising the steps of:

[0016] Mixing the negative electrode active material, the conductive agent, the solvent and the negative electrode additive A to obtain a negative electrode slurry;

[0017] The negative electrode slurry is coated on the current collector, and then baked and dried to obtain a negative electrode sheet;

[0018] In the rolling process, the single-side area and double-side area of the negative electrode sheet pass through the rolling process and are subjected to different pressures. The ratio of the thickness W1 of the single-side area to the thickness W2 of the double-side area after rolling is X = W1 / W2. The mass ratio of the negative electrode additive A is Y. X and Y satisfy the following relationship:

[0019] 0.04≤Y / (X-0.5)≤9

[0020] Where 0.5<X<0.75, 0≤Y≤0.1, and both X and Y are rounded to two decimal places.

[0021] The present invention also discloses a lithium-ion battery, specifically comprising the negative electrode sheet as described above.

[0022] Optionally, the lithium-ion battery further comprises an electrolyte, and the electrolyte lithium salt of the electrolyte is selected from at least one of an organic lithium salt or an inorganic lithium salt.

[0023] Optionally, the lithium-ion battery further comprises an electrolyte, and the electrolyte lithium salt of the electrolyte is selected from at least one of compounds containing fluorine and lithium.

[0024] Optionally, the lithium-ion battery further comprises an electrolyte, and the electrolyte lithium salt of the electrolyte is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bisfluoroimide sulfonate lithium.

[0025] Optionally, the electrolyte lithium salt concentration is 0.5M to 1.5M.

[0026] The negative electrode sheet of the lithium ion battery of the present invention, the negative electrode additive A contains OH - , can form a chemical bond with the carboxyl group in sodium carboxymethyl cellulose, thereby enhancing the bonding force, and no binder such as styrene-butadiene rubber is needed in the negative electrode sheet, reducing the mass ratio of the conductive agent and binder in the electrode layer of the negative electrode sheet, effectively solving the problem of easy powder loss of the negative electrode sheet, while ensuring the high energy density and good fast charge cycle performance of the battery cell. Moreover, when R is -NH2, the negative electrode additive A will undergo self-polymerization reaction at a certain temperature, further enhancing the OH - The bonding is further enhanced, which reduces the mass proportion of the conductive agent and the binder in the electrode layer of the negative electrode sheet, effectively solving the problem of easy powder loss of the negative electrode sheet, while ensuring the high energy density of the battery cell and good fast charging cycle performance. DETAILED DESCRIPTION

[0027] It should be understood that the terms used herein, the specific structures and functional details disclosed are only for describing specific embodiments and are representative. However, the present invention can be implemented in many alternative forms and should not be construed as being limited to only the embodiments described herein.

[0028] The present invention will be described in detail below with reference to optional embodiments.

[0029] As an embodiment of the present invention, a negative electrode sheet of a lithium ion battery is disclosed, the negative electrode sheet includes a current collector and an electrode layer, the electrode layer is laid on the current collector; the electrode layer includes a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose and a - The negative electrode additive A accounts for 0.01%-0.5% of the total mass of the negative electrode active material, the conductive agent, and the sodium carboxymethyl cellulose; the structural formula of the negative electrode additive A is:

[0030]

[0031] Wherein, in the above formula, R is -NH2, -OH or -SiH3.

[0032] The negative electrode sheet of the lithium ion battery of the present invention, the negative electrode additive A contains OH - , can form a chemical bond with the carboxyl group in sodium carboxymethyl cellulose, thereby enhancing the bonding force, and no binder such as styrene-butadiene rubber is needed in the negative electrode sheet, reducing the mass ratio of the conductive agent and binder in the electrode layer of the negative electrode sheet, effectively solving the problem of easy powder loss of the negative electrode sheet, while ensuring the high energy density and good fast charge cycle performance of the battery cell. Moreover, when R is -NH2, the negative electrode additive A will undergo self-polymerization reaction at a certain temperature, further enhancing the OH - The bonding is further enhanced, which reduces the mass proportion of the conductive agent and the binder in the electrode layer of the negative electrode sheet, effectively solving the problem of easy powder loss of the negative electrode sheet, while ensuring the high energy density of the battery cell and good fast charging cycle performance.

[0033] Furthermore, when R is -NH2, the negative electrode additive A undergoes the following self-polymerization reaction at a certain temperature:

[0034]

[0035] Furthermore, the negative electrode additive A used in the negative electrode sheet of the present invention has multiple hydroxyl functional groups (3), has better compatibility with solvents, and contains branched amino groups (-NH2) that can form unsaturated bonds with benzene rings under electrocatalytic conditions, thereby allowing polymerization reactions to occur.

[0036] Specifically, the negative electrode additive A may account for 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, or 0.5% of the total mass of the negative electrode active material, the conductive agent, and the sodium carboxymethyl cellulose. Preferably, the negative electrode additive A accounts for 0.5% of the total mass of the negative electrode active material, the conductive agent, and the sodium carboxymethyl cellulose.

[0037] Specifically, the negative electrode active material is graphite, the conductive agent is acetylene black, and the mass ratio of graphite, acetylene black and sodium carboxymethyl cellulose is 97.5:2.5:1.

[0038] Specifically, the electrode layer of the negative electrode sheet includes a single-sided area and a double-sided area. The thickness of the single-sided area is W1, and the thickness of the double-sided area is W2. W1 / W2=X; the mass ratio of the negative electrode additive A is Y, and X and Y satisfy the following relationship:

[0039] 0.04≤Y / (X-0.5)≤9

[0040] Among them, 0.5<X<0.75, 0≤Y≤0.1, and both X and Y are rounded to two decimal places.

[0041] The present invention also discloses a method for preparing a negative electrode sheet for a lithium ion battery, which is applicable to the method for preparing the negative electrode sheet as described above, and comprises the steps of:

[0042] Mixing the negative electrode active material, the conductive agent, the solvent and the negative electrode additive A to obtain a negative electrode slurry;

[0043] The negative electrode slurry is coated on the current collector, and then baked and dried to obtain a negative electrode sheet;

[0044] In the rolling process, the single-side area and double-side area of the negative electrode sheet pass through the rolling process and are subjected to different pressures. The ratio of the thickness W1 of the single-side area to the thickness W2 of the double-side area after rolling is X = W1 / W2. The mass ratio of the negative electrode additive A is Y. X and Y satisfy the following relationship:

[0045] 0.04≤Y / (X-0.5)≤9

[0046] Where 0.5<X<0.75, 0≤Y≤0.1, and both X and Y have two decimal places.

[0047] The present invention also discloses a lithium ion battery comprising the above-mentioned negative electrode sheet. The lithium ion battery comprises an electrolyte, which is composed of an organic solvent, an electrolyte lithium salt and an additive.

[0048] Specifically, the lithium-ion battery further comprises an electrolyte, wherein the electrolyte lithium salt of the electrolyte is selected from at least one of an organic lithium salt or an inorganic lithium salt. Specifically, the lithium-ion battery further comprises an electrolyte, wherein the electrolyte lithium salt of the electrolyte is selected from at least one of a compound containing fluorine and lithium.

[0049] Specifically, the lithium-ion battery also includes an electrolyte, and the electrolyte lithium salt of the electrolyte is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bisfluoroimide sulfonate lithium.

[0050] Specifically, the electrolyte lithium salt concentration is 0.5M to 1.5M. If the lithium salt concentration is too low, the electrolyte conductivity will be low, affecting the rate and cycle performance of the entire battery system. If the lithium salt concentration is too high, the electrolyte viscosity will be too high, also affecting the rate of the entire battery system. More preferably, the lithium salt concentration is 0.8M to 1.3M.

[0051] Specifically, the organic solvent of the electrolyte is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0052] Specifically, a lithium-ion battery also includes a positive electrode sheet and a separator, which will not be described in detail here.

[0053] The following is further explained in detail through specific examples.

[0054] Preparation of the electrolyte: The following steps are used to prepare the electrolyte: EC / PC / DEC / PP (by mass ratio = 1 / 1 / 2 / 6) are mixed as the organic solvent. Anode additives PS and FEC, as well as nitrile compounds SN, ADN, and HTCN, are added to the organic solvent and mixed thoroughly. LiPF6 is then added to obtain a mixed solution with a LiPF6 concentration of 1.1 mol / L. PS stands for 1,3-propane sultone, FEC stands for fluoroethylene carbonate, SN stands for succinonitrile, ADN stands for adiponitrile, and HTCN stands for 1,3,6-hexanetricarbonitrile.

[0055] The electrolyte formula is as follows:

[0056] EC PC DEC PP LiPF6 PS FEC SN DNA HTCN 7 7 14 42 13.8 4 8 1 1 2

[0057] To prepare the positive electrode sheet, the positive electrode active material LCO, the conductive agent CNT, and the binder polyvinylidene fluoride were thoroughly mixed in N-methylpyrrolidone at a ratio of 97:1.5:1.5 by weight to form a uniform positive electrode slurry. This slurry was applied to the positive electrode current collector Al foil, dried, and cold-pressed to produce the positive electrode sheet.

[0058] Negative electrode sheet preparation: Graphite (the negative electrode active material), acetylene black (the conductive agent), and sodium carboxymethyl cellulose (the thickener) were thoroughly mixed in a suitable amount of deionized water at a mass ratio of 97.5:2.5:1. Anode additive A was then added to form a uniform negative electrode slurry. This slurry was then mixed with the silicon-based material at 1200 rpm for 3 hours to obtain a mixed slurry. The mass ratio of hectorite to silicon-based material in the mixed slurry was 0.008:1. The ethanol solvent was then removed by evaporation to obtain the negative electrode material. This slurry was coated onto a Cu foil negative electrode current collector, dried, and cold pressed to obtain the negative electrode sheet. The amount of negative electrode additive A added is shown in the table below.

[0059] Negative electrode ingredients list:

[0060]

[0061]

[0062] In the above table, the mass ratios of graphite, acetylene black and sodium carboxymethyl cellulose are shown, and the negative electrode additive A is the percentage of the total mass of graphite, acetylene black and sodium carboxymethyl cellulose.

[0063] The negative electrode sheets of each embodiment and comparative example were prepared according to the negative electrode sheet ingredient list in the above table.

[0064] Lithium-ion battery production: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The process is then wound into a bare cell. The bare cell is placed in an outer packaging bag, and the aforementioned electrolyte is injected into the dried cells. After vacuum packaging, resting, formation, and shaping, the lithium-ion battery is completed.

[0065] Normal temperature cycle test of battery:

[0066] Test method: Place the battery in an environment of 25±2 degrees, follow the standard charge and discharge cycle, cycle rate 5C, charging voltage 3.0-4.5V, and calculate the capacity retention rate of the battery after the cycle.

[0067] The calculation formula is as follows:

[0068] nth cycle capacity retention rate (%) = (nth cycle discharge capacity) / (first cycle discharge capacity) * 100%

[0069] The test results are shown in Table 1 below:

[0070]

[0071]

[0072] It can be seen from the examples and comparative example 1 in Table 1 that the cycle performance of Example 2 is the best and no powder falls off during the cycle, that is, the negative electrode additive A can improve the adhesion between the negative electrode material and the current collector, and the best effect is achieved when the dosage is 0.5%.

[0073] It should be noted that the limitations on the various steps involved in this solution do not limit the order of the steps without affecting the implementation of the specific solution. The steps written in front can be executed first, later, or even simultaneously. As long as this solution can be implemented, it should be regarded as falling within the scope of protection of the present invention.

[0074] The above is a further detailed description of the present invention in conjunction with specific optional embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A lithium-ion battery negative electrode sheet, characterized in that: The negative electrode sheet includes a current collector and an electrode layer, wherein the electrode layer is laid on the current collector; the electrode layer includes a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose and a - The negative electrode additive A is a mixture of the negative electrode active material, the conductive agent, the solvent and the negative electrode additive A; the negative electrode additive A accounts for 0.01% to 0.5% of the total mass of the negative electrode active material, the conductive agent and the sodium carboxymethyl cellulose; the structural formula of the negative electrode additive A is: Wherein, in the above formula, R is -NH2, -OH or -SiH3; The electrode layer of the negative electrode sheet includes a single-sided area and a double-sided area. The thickness of the single-sided area is W1, the thickness of the double-sided area is W2, and W1 / W2=X. The mass ratio of the negative electrode additive A is Y, and X and Y satisfy the following relationship: 1≤Y / (X-0.5)≤9 Among them, 0.51≤X≤0.53, 0.01≤Y≤0.07, and both X and Y are rounded to two decimal places.

2. The lithium-ion battery negative electrode sheet according to claim 1, wherein: The negative electrode additive A accounts for 0.5% of the total mass of the negative electrode active material, the conductive agent, and sodium carboxymethyl cellulose.

3. The lithium-ion battery negative electrode sheet according to claim 1, wherein: The negative electrode active material is graphite, the conductive agent is acetylene black, and the mass ratio of the graphite, acetylene black and sodium carboxymethyl cellulose is 97.5:2.5:

1.

4. A method for preparing a negative electrode sheet for a lithium-ion battery, applied to the method for preparing a negative electrode sheet according to any one of claims 1 to 3, characterized in that: Including steps: Mixing the negative electrode active material, the conductive agent, the solvent and the negative electrode additive A to obtain a negative electrode slurry; The negative electrode slurry is coated on the current collector, and then baked and dried to obtain a negative electrode sheet; In the rolling process, the single-side area and double-side area of the negative electrode sheet pass through the rolling process and are subjected to different pressures. The ratio of the thickness W1 of the single-side area to the thickness W2 of the double-side area after rolling is X = W1 / W2. The mass ratio of the negative electrode additive A is Y. X and Y satisfy the following relationship: 0.04≤Y / (X-0.5)≤9 Where 0.5<X<0.75, 0≤Y≤0.1, and both X and Y have two decimal places.

5. A lithium-ion battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 3.

6. The lithium-ion battery according to claim 5, wherein The lithium-ion battery further comprises an electrolyte, wherein the electrolyte lithium salt of the electrolyte is selected from at least one of an organic lithium salt or an inorganic lithium salt.

7. The lithium-ion battery according to claim 5, wherein The lithium-ion battery further includes an electrolyte, wherein the electrolyte lithium salt of the electrolyte is selected from at least one compound containing fluorine and lithium.

8. The lithium-ion battery according to claim 5, wherein The lithium-ion battery further comprises an electrolyte, wherein the electrolyte lithium salt of the electrolyte is selected from at least one of hexafluorophosphate, hexafluoroarsenate, perchlorate, trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tris(trifluoromethylsulfonyl)methyl lithium, and bisfluoroimide sulfonate lithium.

9. The lithium-ion battery according to any one of claims 6 to 8, wherein The electrolyte lithium salt concentration is 0.5M to 1.5M.

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