Anode sheet and battery

Abstract

In order to overcome the problem of liquid storage performance of the negative pole piece in the prior art, the application provides a negative pole piece and a battery. The negative pole piece comprises a current collector, an active material layer and a ceramic layer. The active material layer is arranged on at least one side of the current collector, and the ceramic layer is arranged on the side of the active material layer away from the current collector. The ceramic layer comprises ceramic particles. The ceramic particles have a porous structure. The porosity of the ceramic particles is greater than 50%. The pore size is 2-50 nm. The ceramic particles have carboxyl functional groups. In the application, the ceramic layer is arranged on the surface of the active material layer. The ceramic particles with the porous structure in the ceramic layer increase the electrolyte storage capacity of the negative pole piece, so that the liquid storage rate of the battery is increased, the ion conductivity is improved, and the cycle performance of the battery is improved. The carboxyl functional groups loaded on the ceramic particles are combined with the surface hydroxyl groups of the negative electrode material in the active material layer, so that the adhesion between the active material layer and the ceramic layer is enhanced, and the ceramic particles are prevented from falling off.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a negative electrode sheet and a battery. BACKGROUND

[0002] Lithium ion batteries, as a chemical energy storage medium, are widely used in the fields of electronic consumer goods, E-bike, EV and other new energy fields due to their low self-discharge rate, good cycle performance and other characteristics. With the gradual perfection of the lithium ion battery industry, the market demand tends to be rational, and lithium ion batteries with high safety and electrochemical performance gradually become the research focus and key point in the field of new energy.

[0003] With the continuous improvement of the energy density of lithium ion batteries, the compaction of the negative electrode sheet is also increasing, which leads to the decline of the liquid retention performance of the negative electrode sheet to the electrolyte, aggravates the capacity attenuation of the battery, and greatly affects the long cycle life of the lithium ion battery.

[0004] Therefore, there is an urgent need for a negative electrode sheet with high liquid retention performance. SUMMARY

[0005] The technical problem to be solved by the application is the problem of the decline of the liquid retention performance of the existing negative electrode sheet. The application provides a negative electrode sheet and a battery.

[0006] To solve the above technical problem, the application provides a negative electrode sheet, which comprises a current collector, an active material layer and a ceramic layer, the active material layer is arranged on at least one side of the current collector, and the ceramic layer is arranged on the side of the active material layer away from the current collector.

[0007] The ceramic layer comprises ceramic particles, the ceramic particles have a porous structure, the porosity of the ceramic particles is greater than 50%, the pore size is 2-50 nm, and the ceramic particles have carboxyl functional groups.

[0008] Preferably, the content of the carboxyl functional groups in the ceramic particles is 0.2-0.5 mmol / g.

[0009] Preferably, the specific surface area of the ceramic particles is 100-360 m 2 / g.

[0010] Preferably, the D50 of the ceramic particles is 1.0-2.0 pm, and the D90 is 1.8-5.5 pm.

[0011] Preferably, the density of the ceramic particles is 1.0-2.0 g / cm 3 .

[0012] Preferably, the thickness of the ceramic layer is 4-7 pm.

[0013] Preferably, the ceramic layer further comprises a lithium salt additive, the lithium salt additive comprising at least one of lithium carboxymethyl cellulose, hydroxypropyl methyl cellulose modified to contain a lithium salt.

[0014] Preferably, the ceramic layer further comprises a dispersant, a negative electrode binder, and a separator binder; and a mass ratio of the ceramic particles, the lithium salt additive, the dispersant, the negative electrode binder, and the separator binder is 100: (0.8-1.2): (0.3-0.5): (5-10): (5-10).

[0015] Preferably, the active material layer comprises a negative electrode active material, a surface of the negative electrode active material having a hydroxyl group.

[0016] In a second aspect, the present application provides a battery comprising the negative electrode sheet as described above.

[0017] In the present application, by arranging the ceramic layer on the surface of the active material layer, the ceramic particles with a porous structure in the ceramic layer, and the porosity of the ceramic particles being greater than 50% and the pore size being 2-50 nm, the electrolyte storage amount of the negative electrode sheet is increased, the liquid retention rate of the battery is increased, the ion conductivity is improved, and the cycle performance of the battery is improved; at the same time, the carboxyl functional groups on the surface of the ceramic particles are combined with the surface hydroxyl groups of the negative electrode material in the active material layer, and the adhesion between the active material layer and the ceramic layer is enhanced. DETAILED DESCRIPTION

[0018] In order to make the technical problems solved by the present application, the technical solutions and beneficial effects more clearly understood, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0019] An embodiment of the present application provides a negative electrode sheet, comprising a current collector, an active material layer, and a ceramic layer, the active material layer being arranged on at least one side of the current collector, and the ceramic layer being arranged on a side of the active material layer away from the current collector; the ceramic layer comprises ceramic particles, the ceramic particles having a porous structure, the porosity of the ceramic particles being greater than 50% and the pore size being 2-50 nm, and the ceramic particles having carboxyl functional groups thereon.

[0020] In the present application, by arranging the ceramic layer on the surface of the active material layer, the ceramic particles with a porous structure in the ceramic layer, and the porosity of the ceramic particles being greater than 50% and the pore size being 2-50 nm, the electrolyte storage amount of the negative electrode sheet is increased, the liquid retention rate of the battery is increased, the ion conductivity is improved, and the cycle performance of the battery is improved; at the same time, the carboxyl functional groups on the surface of the ceramic particles are combined with the surface hydroxyl groups of the negative electrode material in the active material layer, and the adhesion between the active material layer and the ceramic layer is enhanced.

[0021] In some embodiments, the content of carboxyl functional groups in the ceramic particles is 0.2-0.5 mmol / g. By adjusting the content of carboxyl functional groups in the ceramic particles, the adhesion between the ceramic particles and the active material layer and the ceramic layer is adjusted, thus preventing the ceramic particles from detaching.

[0022] In some embodiments, the porosity of the ceramic particles is 50%-70%, and the pore size is 2-50 nm. Within this range, the porosity and pore size of the ceramic particles can store more electrolyte, improve ionic conductivity, and do not affect the thermal conductivity of the ceramic layer, thereby improving the electrical performance of the battery.

[0023] And / or, the specific surface area of ​​the ceramic particles is 100-360 m². 2 / g. Within this range, the specific surface area of ​​the ceramic particles allows the binder in the ceramic layer to come into more contact with the ceramic particles or to wrap around the surface of the ceramic particles during the drying process of the ceramic layer slurry, increasing the adhesive area and improving the bonding strength.

[0024] Specifically, the porosity of the ceramic particles includes, but is not limited to, 50%, 55%, 60%, 65%, or 70%.

[0025] The pore sizes of ceramic particles include, but are not limited to, 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm.

[0026] The specific surface area of ​​ceramic particles includes, but is not limited to, 150 m². 2 / g、160 m 2 / g、170 m 2 / g、190 m 2 / g、200m 2 / g、220 m 2 / g、240 m 2 / g or 250 m 2 / g.

[0027] In some embodiments, the ceramic particles have a D50 of 1.0-2.0 μm and a D90 of 1.8-5.5 μm. If the ceramic particle size is too small, the ceramic layer density is high, reducing the battery's energy density; if the ceramic particle size is too large, the ceramic layer thickness is uneven, with protrusions, affecting the adhesion between the ceramic layer and the active material layer. By limiting the D50 and D90 particle sizes of the ceramic particles to within this range, the peel strength of the negative electrode sheet and the battery's energy density are ensured.

[0028] Specifically, the D50 of the ceramic particles includes, but is not limited to, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2.0μm.

[0029] The D90 of ceramic particles includes, but is not limited to, 1.8μm, 2.0μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 3.0μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 4.0μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5.0μm, 5.2μm, or 5.5μm.

[0030] In some embodiments, the density of the ceramic particles is 1.0-2.0 g / cm³. 3 The lower the density of ceramic particles, the larger the corresponding specific surface area and porosity. By controlling the density of ceramic particles within the above range, their specific surface area and porosity can be controlled, further reducing the weight of the negative electrode sheet and increasing the energy density of the battery.

[0031] Specifically, the density of the ceramic particles includes, but is not limited to, 1.0 g / cm³. 3 1.1 g / cm 3 1.2 g / cm 3 1.3 g / cm 3 1.4 g / cm 3 1.5 g / cm 3 1.6 g / cm 3 1.7 g / cm 3 1.8 g / cm 3 1.9 g / cm 3 Or 2.0 g / cm 3 .

[0032] In a preferred embodiment, the density of the ceramic particles is 1.0-1.5 g / cm³. 3 .

[0033] In some embodiments, the thickness of the ceramic layer is 4-7 μm. By controlling the thickness of the ceramic layer within this range, micro-short circuits caused by burrs at the edge of the negative electrode are reduced.

[0034] Specifically, the thickness of the ceramic layer includes, but is not limited to, 4μm, 4.3μm, 4.6μm, 4.9μm, 5.2μm, 5.5μm, 5.8μm, 6.1μm, 6.4μm, 6.7μm or 7.0μm.

[0035] In some embodiments, the ceramic layer further includes a lithium salt additive, which includes at least one of lithium carboxymethyl cellulose and modified hydroxypropyl methyl cellulose containing lithium salt. By introducing the lithium salt additive into the ceramic layer, the lithium salt additive can provide some lithium ions during battery charging and discharging, thereby improving ionic conductivity.

[0036] In some embodiments, the ceramic layer further includes a dispersant, a negative electrode binder, and a separator binder;

[0037] The mass ratio of the ceramic particles, lithium salt additive, dispersant, negative electrode binder, and separator binder is 100:(0.8-1.2):(0.3-0.5):(5-10):(5-10). The separator binder bonds the separator, making the separator and electrode a single unit, increasing the structural stability of the battery, reducing powder shedding from the negative electrode, and improving the problem of active material shedding during battery cycling.

[0038] Specifically, the negative electrode binder includes at least one of styrene-butadiene rubber and polyacrylic acid.

[0039] The diaphragm binder includes room temperature ceramic binder HD2126; the dispersant includes at least one of polyvinyl alcohol and sodium hexametaphosphate.

[0040] Specifically, the mass ratio of ceramic particles, lithium salt additives, dispersants, negative electrode binders, and separator binders includes, but is not limited to, 100:0.8:0.3:5:5, 100:1.2:0.5:10:10, 100:1.2:0.3:5:5, 100:1:0.3:5:5, 100:0.8:0.4:5:5, 100:0.8:0.5:5:5, 100:0.8:0.3:7:5, 100:0.8:0.3:10:5, 100:0.8:0.3:5:7, or 100:0.8:0.3:5:10.

[0041] In some embodiments, the ceramic particles are boehmite. The boehmite used in this application is obtained custom-made.

[0042] In some embodiments, the active material layer comprises a negative electrode active material, the surface of which has hydroxyl groups. The negative electrode active material is modified by chemical oxidation (Hummers method, nitric acid oxidation) or plasma treatment (water vapor plasma) to give the surface of the negative electrode active material hydroxyl groups.

[0043] Specifically, the negative electrode active material includes at least one of graphite and silicon carbon;

[0044] Based on the mass of the active material layer as 100%, the active material layer comprises 96.7% negative electrode active material, 1.0% conductive agent, 1.5% binder and 0.8% thickener.

[0045] The conductive agent includes at least one of Ketjen black, graphite, hard carbon, soft carbon, carbon nanotubes, graphene, porous carbon, superconducting carbon black (Super P), acetylene black, furnace black, and whisker carbon nanotubes (VGCF).

[0046] The adhesive includes at least one of styrene-butadiene rubber and polyacrylic acid.

[0047] The thickener includes at least one of (lithium-containing / sodium-containing) carboxymethyl cellulose.

[0048] Furthermore, one embodiment of this application provides a method for preparing boehmite with carboxyl functional groups, taking 5 kg of powder particles as an example, including the following steps:

[0049] S1. Take 5±0.1 kg of 0.4~0.5 mol / L dilute hydrochloric acid solution, add 5 kg of boehmite powder in batches, adjust the pH to an acidic environment (pH<2), and stir at a medium speed of 6~7 m / s.

[0050] S2. Stir for 240±10 minutes, controlling the temperature below 40℃. The acid reacts with the aluminum hydroxyl groups on the surface of the boehmite to form soluble aluminum salts (such as Al). 3+ And release OH - .

[0051] S3. Use a stainless steel screen to filter the stirred slurry and wash the boehmite multiple times with deionized water until the pH is 6.5-7.

[0052] S4. Disperse the acid-washed and activated boehmite particles in a 0.5-1 mol / L formic acid solution and mix them at a mass ratio of 1:1-1:1.1.

[0053] S5. Stir at a linear speed of 6~7 m / s, heating temperature of 50±3℃, medium speed for 3-10h. The carboxyl groups (-COOH) in the formic acid molecules are attached to the surface of boehmite through physical adsorption, thus obtaining boehmite with different carboxyl content.

[0054] S6. Use a sieve to filter and wash with deionized water to remove excess formic acid until the pH value is 7-8.

[0055] S7. Place the sample in an oven and dry at 60-80℃ for 6-12 hours. After drying, activated boehmite particles with carboxyl groups on the surface are obtained. Boehmite with different carboxyl contents was prepared under the reaction conditions shown in Table 1.

[0056] Table 1

[0057]

[0058] Carboxyl content test

[0059] 1. Dry the boehmite sample at 100℃ to constant weight, ensuring the sample is free of moisture or other volatile impurities. Crush and sieve to ensure uniform particle size. Weigh 10mg of the sample (usually 5-10mg), accurate to 0.1mg.

[0060] 2. The content of surface carboxyl groups is determined in an inert nitrogen atmosphere to avoid oxidation or other interference.

[0061] 3. The temperature range for the thermal decomposition test is set to 200-500℃, and the heating rate is 10℃ / min.

[0062] 4. Record the mass change curve (TGA curve) of the sample during the heating process, and calculate the mass loss (Δm) of the sample in the carboxyl decomposition temperature range.

[0063] The mass loss is directly proportional to the carboxyl group content. The molar mass of the carboxyl group is 46 g / mol. Calculate the molar content of the carboxyl group based on the mass loss (Δm) and the sample mass (m).

[0064] Increasing the carboxyl content of boehmite significantly enhances its hydrophilicity, acidity, reactivity, and adsorption properties, while also affecting its thermal stability.

[0065] One embodiment of this application also provides a battery, including the negative electrode sheet as described above.

[0066] The present invention will be further illustrated by the following examples.

[0067] The present invention specifically describes the negative electrode sheet and battery disclosed herein.

[0068] Example 1

[0069] 1) Preparation of negative electrode sheet

[0070] Graphite anode, conductive agent conductive carbon black, anode binder styrene-butadiene rubber, and sodium carboxymethyl cellulose were added to deionized water at a mass ratio of 96.7:1.0:1.5:0.8 to adjust the viscosity. Then, the mixture was dispersed at high speed at 3200 rpm for 120 min and vacuumed at 1000 rpm for 30 min to obtain the active material layer slurry.

[0071] A solution of lithium carboxymethyl cellulose (CMC-Li) additive was prepared by adding water. Boehmite was then added to the solution and dispersed using a high-speed disperser for 1 hour. The dispersed slurry was then ground using a sand mill. Sodium hexametaphosphate dispersant was then added and dispersed at high speed for 20 minutes. SBR binder and diaphragm binder SWA610 were then added to the slurry and dispersed at a linear speed V = 6 m / s for 40 minutes. The solid content of the ceramic layer slurry was 35%, and the viscosity was less than 200 cp. The mass ratio of boehmite, CMC-Li, dispersant, SBR binder, and diaphragm binder was 100:1.0:0.4:7:7.

[0072] The prepared active material layer slurry is coated onto copper foil using a coating machine, and the ceramic layer slurry is coated onto the active material layer using a coating machine. After drying, the mixture is rolled to obtain the negative electrode sheet.

[0073] The boehmite contained 0.4 mmol / g of carboxyl functional groups, had a porosity of 60%±3, a pore size of 30±3 nm, and a specific surface area of ​​260±20 m². 2 The particle size distribution is 1.3 ± 0.1 g / cm³, with a D50 of 1.5 ± 0.2 μm, a D90 of 3.5 ± 0.3 μm, and a density of 1.3 ± 0.1 g / cm³. 3 The thickness of the ceramic layer is 5±0.2μm.

[0074] 2) Preparation of the positive electrode:

[0075] 97.8% of the positive electrode active material lithium cobalt oxide, 1% of the positive electrode conductive agent conductive carbon black, and 1.2% of the binder PVDF were added to N-methylpyrrolidone and stirred to prepare a positive electrode slurry. The positive electrode slurry was then coated on both surfaces of the positive electrode current collector Al foil, and after drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0076] 3) Lithium-ion battery manufacturing:

[0077] The separator, positive electrode, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator, thus forming an electrode assembly. The electrode assembly is then placed in an outer package, injected with commercially available electrolyte, and sealed. After processes such as electrolyte injection, formation, and degassing, a lithium-ion battery is obtained.

[0078] Examples 2 to 17

[0079] Examples 2 through 17 are largely the same as Example 1, except that they use the formulas in Table 2.

[0080] Table 2

[0081]

[0082] Comparative Example 1

[0083] Most of the steps in Comparative Example 1 and Example 1 are the same, except that the boehmite does not have a carboxyl functional group.

[0084] Comparative Example 2

[0085] Comparative Example 2 and Example 1 follow most of the same steps, except that the negative electrode does not contain a ceramic layer.

[0086] Comparative Examples 3 to 4

[0087] Most of the steps in Comparative Example 3 and Example 1 are the same, except that the formulation in Table 2 is used.

[0088] Comparative Example 5

[0089] Comparative Example 5 and Example 1 follow most of the same steps, except that the ceramic layer does not contain lithium salt additive lithium carboxymethyl cellulose (which cannot be made into an electrode).

[0090] Electrical performance testing:

[0091] The negative electrode sheets and batteries prepared in the above embodiments and comparative examples were tested as follows.

[0092] 1. Battery liquid retention rate:

[0093] Test method: The battery was designed with a capacity of 2000mAh. Positive and negative electrode sheets were coated according to the standard areal density. In the example, the negative electrode sheet was coated with a 4~7μm ceramic layer. The weight of the electrode sheets was recorded and numbered. The weight before liquid injection, the weight after liquid injection, and the weight after sealing were recorded. The following can be calculated: Battery liquid injection volume = weight after sealing - weight before liquid injection, Battery liquid retention rate = battery liquid injection volume / battery weight.

[0094] 2. Test on the adhesion of the ceramic layer to the separator in the negative electrode sheet:

[0095] Test method: The ceramic material layer contains a separator adhesive. After the battery is shaped, the separator will adhere to the ceramic layer negative electrode sheet, while the negative electrode sheet without a ceramic layer will not adhere to the separator.

[0096] 3. Heat resistance test:

[0097] Test method: After fully charging the battery, perform a nail penetration test.

[0098] 4. 25℃ Cyclic Test:

[0099] After placing the battery in a constant temperature test chamber at 25℃±2℃ for 1 hour, charge it to 4.2V with a constant current and constant voltage of 1C and cut off the current at 0.05C; discharge it to 2.5V with a constant current of 1C and record the discharge capacity; repeat the above steps 500 times and calculate the capacity retention rate.

[0100] The test results obtained from the examples and comparative examples are entered into Table 3.

[0101] Table 3

[0102]

[0103] As can be seen from the test results in Table 3, the negative electrode sheet in this application has a better liquid absorption capacity, and the battery made using the negative electrode sheet in this application has better cycle performance.

[0104] The test results of Examples 1-4 and Comparative Example 1 show that the presence of carboxyl functional groups in the ceramic particles can improve the cycle performance of the battery. The test results of Examples 1, 5-7, and Comparative Example 3 show that when the porosity of the ceramic particles decreases, the liquid retention rate of the battery decreases, the ionic conductivity within the battery decreases, and thus the cycle performance of the battery declines. The test results of Examples 1, 8-9, and Comparative Example 4 show that when the pore size of the ceramic particles decreases, their specific surface area increases, their density increases, the energy density of the battery decreases, and the cycle performance of the battery declines. When the pore size of the ceramic particles is too large, their specific surface area decreases, the contact area with the binder in the ceramic layer decreases, and the ceramic particles are more likely to detach, thus reducing the cycle performance of the battery. The test results of Examples 1 and 10-13 show that when the particle size of the ceramic particles is too small, the density of the ceramic layer is high, the energy density of the battery decreases, and the cycle performance of the battery declines. When the particle size of ceramic particles is too large, the ceramic layer thickness is uneven and there are bumps, which affects the adhesion between the ceramic layer and the active material layer, and the cycle performance of the battery decreases. As can be seen from the test results of Examples 1, Examples 14 to 17, and Comparative Example 2, when no ceramic layer is provided on the negative electrode, the heat resistance of the battery decreases and it is prone to ignition and combustion.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a current collector, an active material layer, and a ceramic layer, wherein the active material layer is disposed on at least one side of the current collector, and the ceramic layer is disposed on the side of the active material layer opposite to the current collector; The ceramic layer comprises ceramic particles, which have a porous structure, a porosity greater than 50%, a pore size of 2-50 nm, and carboxyl functional groups on the ceramic particles. The content of carboxyl functional groups in the ceramic particles is 0.2-0.5 mmol / g; The ceramic particles have a D50 of 1.0-2.0 μm and a D90 of 1.8-5.5 μm. The active material layer includes a negative electrode active material, and the surface of the negative electrode active material has hydroxyl groups.

2. The negative electrode sheet according to claim 1, characterized in that, The specific surface area of ​​the ceramic particles is 100-360 m². 2 / g.

3. The negative electrode sheet according to claim 1, characterized in that, The density of the ceramic particles is 1.0-2.0 g / cm³. 3 .

4. The negative electrode sheet according to claim 3, characterized in that, The thickness of the ceramic layer is 4-7 μm.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The ceramic layer further includes lithium salt additives, which include at least one of lithium carboxymethyl cellulose and modified lithium-containing hydroxypropyl methyl cellulose.

6. The negative electrode sheet according to claim 5, characterized in that, The ceramic layer further includes a dispersant, a negative electrode binder, and a separator binder; the mass ratio of the ceramic particles, lithium salt additive, dispersant, negative electrode binder, and separator binder is 100:(0.8-1.2):(0.3-0.5):(5-10):(5-10).

7. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-6.

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