Battery

Abstract

The embodiment of the invention relates to the technical field of batteries, and provides a battery which comprises a positive plate, a negative plate and a diaphragm arranged between the positive plate and the negative plate, the negative plate comprises a negative current collector and an active coating coated on at least one surface of the negative current collector, and the active coating comprises a silicon-based material and a piezoelectric material; the diaphragm comprises a porous base material and a coating layer coated on the surface of the porous base material, and the coating layer facing one side of the negative plate is an oil coating layer; the particle size of the silicon-based material and the particle size of the piezoelectric material meet the condition that 20 < = L1 / L2 < = 100; wherein L1 is the particle size D50 of the silicon-based material, and L2 is the particle size D50 of the piezoelectric material. According to the battery, by regulating and controlling the particle size of the piezoelectric material and the particle size of the silicon material and improving the dispersion performance between the piezoelectric material and the silicon-based material, the dispersion degree of the negative electrode binder is improved, and the adhesion and stability between the negative electrode and the diaphragm are improved, so that the cycle performance of the battery is effectively improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a battery. Background Art

[0002] Currently, the negative electrode sheet of a lithium-ion battery is mainly made of a silicon-based material. However, the silicon-based material expands in volume during the cycling process, which easily causes the material to pulverize, resulting in poor cycling performance of the lithium-ion battery.

[0003] In related technologies, a piezoelectric material is added to the silicon-based material to improve the current distribution density of the negative electrode sheet and thus enhance the cycling performance of the lithium-ion battery. However, when an oil-based coating is applied to one side of the separator of the lithium-ion battery facing the negative electrode sheet, during the battery cycling process, the addition of the piezoelectric material will cause the bonding between the separator and the negative electrode sheet to deteriorate, resulting in phenomena such as lithium deposition and deformation, thereby affecting the cycling performance of the battery. Summary of the Invention

[0004] An embodiment of this application provides a battery, including: a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet;

[0005] The negative electrode sheet includes a negative current collector and an active coating coated on at least one surface of the negative current collector, and the active coating includes a silicon-based material and a piezoelectric material;

[0006] The separator includes a porous substrate and a coating coated on the surface of the porous substrate, and the coating on the side facing the negative electrode sheet is an oil-based coating;

[0007] The particle size of the silicon-based material and the particle size of the piezoelectric material satisfy the following formula:

[0008] 20 ≤ L1 / L2 ≤ 100;

[0009] wherein, L1 is the D50 particle size of the silicon-based material, and L2 is the D50 particle size of the piezoelectric material.

[0010] Optionally, the D50 particle size of the silicon-based material is 2 μm to 15 μm;

[0011] and / or,

[0012] the D50 particle size of the piezoelectric material is 0.1 μm to 1 μm.

[0013] Optionally, the mass percentage content A of the piezoelectric material in the active coating is 0.2 - 5, and the unit of A is wt%;

[0014] and / or,

[0015] the thickness T of the separator is 4 - 10, and the unit of T is μm.

[0016] Optionally, A and T satisfy the formula shown below:

[0017] 0.04 ≤ A / T ≤ 1.25.

[0018] Optionally, the piezoelectric material and the silicon-based material are mixed and doped in the active coating;

[0019] The density of the piezoelectric material distributed within a range of 1 μm 2 to 2 μm 2 around the silicon-based material particles is 0.5 - 10 times.

[0020] Optionally, the compaction density B of the negative electrode sheet is 0.2 - 5.0, and the unit of B is g / cm 3 .

[0021] Optionally, the mass percentage content A of the piezoelectric material in the coating and the compaction density B of the negative electrode sheet satisfy the formula shown below:

[0022] 0.11 ≤ A / B ≤ 4.55.

[0023] Optionally, the active coating includes a first region and a second region;

[0024] The first region is located on at least one side in the width direction of the negative electrode sheet, and the second region is adjacent to the first region;

[0025] And / or,

[0026] The mass percentage content A2 of the piezoelectric material in the second region is less than the mass percentage content A1 of the piezoelectric material in the first region;

[0027] And / or,

[0028] The width ratio of the second region to the first region is 100:(1 - 3).

[0029] Optionally, 0.3% ≤ A1 ≤ 5.1%;

[0030] And / or,

[0031] 0.2% ≤ A2 ≤ 5.0%;

[0032] And / or,

[0033] A2:A1 = 0.7 - 0.9:1.

[0034] Optionally, the piezoelectric material is selected from one or more of the following:

[0035] Quartz (SiO2), PZT (lead zirconate titanate, Pb[Zr x Ti1-x O3), lithium niobate (LiNbO3), barium titanate (BaTiO3), sodium niobate (NaNbO3), gallium nitride (GaN), zirconium titanium alloy (ZT).

[0036] The battery provided by the embodiment of the present application includes: a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and an active coating coated on at least one surface of the negative electrode current collector. The active coating includes a silicon-based material and a piezoelectric material; the separator includes a porous substrate and a coating coated on the surface of the porous substrate. The coating on the side facing the negative electrode sheet is an oil-based coating; the particle size of the silicon-based material and the particle size of the piezoelectric material satisfy: 20 ≤ L1 / L2 ≤ 100; where L1 is the D50 particle size of the silicon-based material, and L2 is the D50 particle size of the piezoelectric material. In the above battery, by regulating the particle size of the piezoelectric material and the silicon material, the dispersion performance between the piezoelectric material and the silicon-based material is improved, the dispersion degree of the negative electrode binder is increased, the electrode sheet is smoother after rolling, the adhesion and its stability between the negative electrode and the oil-based separator are improved, and the function of the piezoelectric material to inhibit the expansion of the silicon-based negative electrode can be effectively exerted, effectively improving the cycle performance of the battery. Description of the Drawings

[0037] Figure 1 It is a schematic diagram of a negative electrode sheet provided by an embodiment of the present application. Detailed Embodiments

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0039] In the embodiments of the present application, terms such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and effects, and do not limit their order. Those skilled in the art can understand that terms such as "first" and "second" do not limit the quantity and execution order, and terms such as "first" and "second" do not necessarily limit being different.

[0040] It should be noted that in the embodiments of the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "for example" in the present application should not be construed as being more preferred or having more advantages than other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0041] As described above, in a lithium-ion battery constructed with a negative electrode sheet prepared using a silicon-based material, during the cycling process of the battery, the addition of a piezoelectric material will cause the adhesion between the separator and the negative electrode sheet to deteriorate, resulting in phenomena such as lithium deposition and deformation, thereby affecting the cycling performance of the battery.

[0042] To address the above problems, the present application provides a battery, including: a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0043] The negative electrode sheet includes a negative electrode current collector and an active coating coated on at least one surface of the negative electrode current collector, and the active coating includes a silicon-based material and a piezoelectric material.

[0044] The separator includes a substrate and a coating coated on the surface of the substrate, and the coating on the side facing the negative electrode sheet is an oil-based coating;

[0045] The particle size of the silicon-based material and the particle size of the piezoelectric material satisfy the following formula:

[0046] 20 ≤ L1 / L2 ≤ 100;

[0047] Wherein, L1 is the D50 particle size of the silicon-based material, and L2 is the D50 particle size of the piezoelectric material.

[0048] Piezoelectric materials are a class of materials that can convert mechanical energy and electrical energy into each other. When a mechanical stress is applied to a piezoelectric material, it generates an electric charge, and this phenomenon is called the piezoelectric effect. Conversely, when an electric field is applied to it, it undergoes mechanical deformation, which is called the inverse piezoelectric effect.

[0049] By adding a piezoelectric material to the active coating of the negative electrode sheet and using the electromechanical coupling strategy to improve the cycling performance of the lithium-ion battery. When the battery is loaded with an external power source and Li+ is embedded in the material, the piezoelectric material is polarized due to the piezoelectric effect, causing the dipole moments to align, and the piezoelectric material particles are charged and separated, thereby forming a local microelectric field. The piezoelectric material will adsorb the free charges on the surface to eliminate this polarization, thereby acting as a driving force to promote the rapid transport of Li+, thus improving the rapid lithium insertion / extraction ability of the silicon-based material and suppressing the volume change of the silicon-based material, thereby improving the cycling performance of the lithium-ion battery.

[0050] However, the excessive hardness of the piezoelectric material itself will affect the flatness of the negative electrode sheet, which in turn affects the adhesion between the negative electrode sheet and the separator, and the improvement of the battery cycle performance is limited. Moreover, when the separator is coated with an oil-based coating on the negative electrode side, due to the full coating, the stability of the bonding interface between the separator and the negative electrode sheet is greatly affected by the change in the particle size relationship between the silicon-based material and the piezoelectric material. Therefore, by adjusting the particle size of the piezoelectric material and the silicon material, the dispersion performance between the piezoelectric material and the silicon-based material can be improved, the dispersion degree of the negative electrode binder can be increased, and the electrode sheet becomes flatter after rolling. Thus, the adhesion and its stability between the negative electrode and the separator are improved. However, the change in the particle size of the piezoelectric material will affect the exertion of its piezoelectric effect, and in turn, affect the battery cycle performance. When the particle size D50 of the silicon-based material and the particle size D50 of the piezoelectric material are adjusted to satisfy the above relationship, the adhesion performance between the negative electrode and the separator and the battery cycle performance can be taken into account, making the overall performance of the battery reach the optimum. Otherwise, if the ratio of the particle size D50 of the silicon-based material to the particle size D50 of the piezoelectric material is too small, it means that the particle size of the silicon-based material is too small or the particle size of the piezoelectric material is too large, and the adhesion between the negative electrode and the separator is interfered by the piezoelectric material, resulting in poor battery cycle performance; if the ratio of the particle size D50 of the silicon-based material to the particle size D50 of the piezoelectric material is too large, it means that the particle size of the silicon-based material is too large or the particle size of the piezoelectric material is too small, and the limiting effect of the piezoelectric material on the expansion of the silicon-based material is limited, and the battery cycle performance is also poor.

[0051] In one embodiment, the piezoelectric material may be selected from one or more of quartz (SiO2), PZT (lead zirconate titanate, Pb[Zr x Ti 1-x O3), lithium niobate (LiNbO3), barium titanate (BaTiO3), sodium niobate (NaNbO3), gallium nitride (GaN), zirconium titanium alloy (ZT).

[0052] In one embodiment, the silicon-based material includes at least one of silicon oxide particles and silicon carbide particles. The silicon oxide particles are silicon-containing oxide particles, and the silicon carbide particles are mixture particles of silicon and carbon.

[0053] In one embodiment, the particle size (D50) L1 of the silicon-based material is 2 - 15 μm. For example, L1 can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or the range composed of any two of the above values. If the particle size of the silicon-based material is too small, the increase in the specific surface area of the material will lead to an increase in side reactions during charge and discharge, especially a decrease in the first efficiency of the first charge and discharge, and finally affect the energy density of the battery. If the particle size of the silicon-based material is too large, it will affect the compaction density of the negative electrode sheet and weaken the negative electrode kinetics, affecting the fast charging performance of the overall battery.

[0054] In one embodiment, the particle size (D50) L2 of the piezoelectric material is 0.1 - 1 μm. For example, L2 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or the range composed of any two of the above values. If the particle size of the piezoelectric material is too small, it will cause an excessive increase in the liquid retention coefficient of the battery, resulting in battery swelling, affecting the battery thickness, and reducing the energy density of the battery. If the particle size of the piezoelectric material is too large, it cannot be evenly distributed on the surface of the silicon-based material, resulting in the inability to fully exert the expected effect of the piezoelectric material.

[0055] It should be noted that the method for testing the particle size of the piezoelectric material is as follows: Take 1 g of the sample and dissolve it in 99 g of ethanol, perform ultrasonic dispersion, the ultrasonic dispersion power is 100%, and the time is 5 h; then place it in a laser particle size analyzer, and read the data after the test is completed.

[0056] It should be noted that the method for testing the particle size of the silicon-based material is as follows: Take 1 g of the sample and dissolve it in 99 g of ethanol, perform ultrasonic dispersion, the ultrasonic dispersion power is 100%, and the time is 5 h; then place it in a laser particle size analyzer, and read the data after the test is completed.

[0057] In one embodiment, the mass percentage content A (wt%) of the piezoelectric material in the active coating is 0.2 - 5. For example, A can be 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or the range composed of any two of the above values. If the mass percentage content of the piezoelectric material in the active coating is too low, it will cause the inability to fully exert the effect of the piezoelectric material. If the mass percentage content of the piezoelectric material in the active coating is too high, it will cause too many non-active substances, affecting the capacity of the negative electrode and the overall energy density of the battery.

[0058] In one embodiment, the separator includes a porous substrate and a coating coated on the surface of the porous substrate. Among them, the coating on the side facing the negative electrode is an oil-based coating. The coating plays a bonding role. For example, the coating on the side facing the negative electrode is an oil-based coating, and the coating on the side facing the positive electrode is an aqueous coating. Or, the coatings on the sides facing the negative electrode and the positive electrode are both oil-based coatings, and the embodiments of the present application do not limit this.

[0059] In some embodiments, the separator further includes a ceramic coating, and the ceramic coating is coated on one side of the porous substrate.

[0060] For example, one side of the porous substrate facing the negative electrode sheet is coated with a ceramic coating, and the oil-based coating can be coated on top of the ceramic coating. Alternatively, one side of the porous substrate facing the positive and negative electrode sheets is coated with a ceramic coating, and the oil-based coating can be coated on the other side of the porous substrate.

[0061] In some embodiments, the thickness (μm) of the ceramic coating is 0.5 - 2μm. For example, it can be 0.5μm, 1μm, 1.5μm, 2μm, or any range formed by any two of the above values.

[0062] In some embodiments, the ceramic coating includes ceramic particles and a binder.

[0063] In some embodiments, the ceramic particles are selected from one or more of inert substances such as boehmite, alumina, silica, etc.

[0064] In some embodiments, the thickness of one side of the oil-based coating is 0.5 - 2μm. For example, it can be 0.5μm, 1μm, 1.5μm, 2μm, or any range formed by any two of the above values.

[0065] In some embodiments, the oil-based coating includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polymethyl methacrylate (PMMA).

[0066] In one embodiment, the thickness T (μm) of the separator is 4 - 10. For example, T can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any range formed by any two of the above values. If the separator is too thick, it will lead to a decrease in the battery energy density. At the same time, it will also affect the migration rate of lithium ions, resulting in a decrease in the battery kinetics, and thus situations such as too slow charging speed, overheating, and even lithium plating may occur. If the separator is too thin, the sharp particles of the positive and negative electrodes may pierce the separator and short-circuit with the opposite positive and negative electrodes, resulting in safety problems such as internal short-circuit and even thermal runaway.

[0067] In one embodiment, A and T satisfy the following formula:

[0068] 0.04 ≤ A / T ≤ 1.25.

[0069] If the ratio of A to T is greater than the above ratio range, it indicates that the content of the piezoelectric material is too much or the separator thickness is too low. The separator cannot fit well with the negative electrode sheet, resulting in a decrease in the peeling force between the separator and the negative electrode sheet, affecting the battery interface. When the interface adhesion is not tight, it may cause the lithium ion path to be blocked and finally lead to lithium plating. If the ratio of A to T is less than the ratio range, it indicates that the piezoelectric content is too little or the separator thickness is too large, and the battery energy density will be affected.

[0070] It should be noted that the test method for the content of the piezoelectric material is as follows: disassemble the 0% SOC battery, take a negative electrode sheet with a size of 2 cm × 2 cm, place it in an oven and dry it at 100 °C for 24 h, and then take it out; dissolve 1 g of the sample in 99 g of ethanol, perform ultrasonic dispersion, the ultrasonic dispersion power is 100%, and the time is 5 h; then use ICP to test the concentration of Ba ions, and calculate back the content of the piezoelectric material.

[0071] It should be noted that the test method for the diaphragm thickness is as follows: disassemble the 0% SOC battery, take a diaphragm with a size of 5 cm × 5 cm, let it stand for 12 h to dry, use a micrometer to measure the thickness, take 10 points, and finally obtain the average value as the diaphragm thickness.

[0072] In one embodiment, the piezoelectric material and the silicon-based material are mixed and doped in the active coating; the density of the piezoelectric material distributed within a range of 1-2 μm around the silicon-based material particles is 0.5-10 times / μm 2 . For example, the piezoelectric material within a range of 1 μm 2 or 2 μm 2 around any silicon-based material particle can have a distribution area of 0.5 times, 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, or any range composed of any two of the above values.

[0073] Adding a piezoelectric material to the active coating of the negative electrode sheet can improve the negative electrode current density distribution and enhance the cycling performance by using the piezoelectric material. However, the piezoelectric material does not have the function of lithium deintercalation / insertion. Therefore, if too much piezoelectric material is added, it will affect the negative electrode capacity design. So, a higher areal density is required to match the positive electrode, which will increase the negative electrode thickness, and finally the energy density of the battery will be lost. Otherwise, if the distribution of the piezoelectric material is too small, it means that the characteristics of the piezoelectric material cannot be properly exerted, which will instead affect the performance of the battery, and the energy density and cycling performance of the battery will be poor. Therefore, when the density of the piezoelectric material distributed on the surface of the silicon-based material satisfies the above relationship, the energy density and cycling performance can be taken into account, making the overall performance of the battery reach the optimal.

[0074] It should be noted that the test method for the distribution of the piezoelectric material: disassemble the 0% SOC battery, take a negative electrode sheet with a size of 2 cm × 2 cm, place it on the conductive adhesive, use SEM-EDS for testing, select a suitable position that can represent the overall distribution, with a magnification of about 100-500 times, and take a photo; then use image J software to analyze the distribution areas of Ba element and Si element, and obtain the proportion of the piezoelectric material distributed around the silicon-based material.

[0075] In one embodiment, the compaction density B (g / cm 3)is from 0.2 to 5.0. For example, the compaction density B of the negative electrode sheet is 0.2 g / cm 3 , 0.5 g / cm 3 , 1 g / cm 3 , 2 g / cm 3 , 3 g / cm 3 , 4 g / cm 3 , 5 g / cm 3 , or a range composed of any two of the above values. If the compaction density of the negative electrode sheet is too high, during charging, due to the excessive expansion of silicon carbide in the negative electrode, insufficient pores and excessive stress between particles, negative electrode demoulding, powdering, and even deformation of the battery body may occur. If the compaction density of the negative electrode sheet is too low, the pores are too large, resulting in insufficient electrical contact between particles, thereby affecting the conductivity of the negative electrode and the charge and discharge performance of the overall battery.

[0076] In one embodiment, the mass percentage content A of the piezoelectric material in the coating and the compaction density B of the negative electrode sheet satisfy the following formula:

[0077] 0.11 ≤ A / B ≤ 4.55.

[0078] If the ratio of A to B is too small, it means that there is too little piezoelectric material or the compaction density is too large, which will lead to a large cyclic expansion of the negative electrode sheet and a decline in cyclic performance. If the ratio of A to B is too large, it means that there is too much piezoelectric material or the compaction density is too small, and the energy density of the negative electrode sheet will be affected.

[0079] It should be noted that the method for testing the compaction density of the electrode sheet: Disassemble the 0% SOC battery, take 2 negative electrode sheets with a size of 5 cm × 5 cm. Scrape one of the sampled electrode sheets clean, then wash it 2 - 3 times with ethanol, place the sample in an 80°C oven for drying (protected by an argon or nitrogen atmosphere), then take it out and punch it into shape using a circular tool with a diameter of 2 cm, weigh it, and record it as Cu g , wash the other electrode sheet 2 - 3 times with dimethyl carbonate (DMC), place the sample in an 80°C oven for drying (protected by an argon or nitrogen atmosphere), then take it out and punch it into shape using a square tool with a length and width of 2 cm, weigh it, and record it as Anode g . The compaction density calculation formula is: P.D. (g / cm 3 ) = negative electrode areal density * 2 / (electrode sheet thickness - copper foil thickness)

[0080] In one embodiment, as Figure 1 shown, the active coating includes a first region 1 and a second region 2; the first region 1 is located on at least one side in the width direction of the negative electrode sheet, and the second region 2 is adjacent to the first region 1; the percentage content A2 of the piezoelectric material in the second region 2 is less than the percentage content A1 of the piezoelectric material in the first region 1.

[0081] In one embodiment, the mass percentage content A1 of the piezoelectric material in the first region is 0.3 wt% ≤ A1 ≤ 5.1 wt%. For example, A1 can be 0.3 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5.1 wt%, or a range composed of any two of the above values.

[0082] In one embodiment, the mass percentage content A2 of the piezoelectric material in the second region is 0.5 wt% ≤ A2 ≤ 5 wt%. For example, A2 can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a range composed of any two of the above values.

[0083] In one embodiment, A1 and A2 satisfy the following relationship:

[0084] A2 / A1 = 0.7 - 0.9:1;

[0085] For example, A2 / A1 can be 0.7:1, 0.8:1, 0.9:1, etc. If the ratio of A2 to A1 is too small, the energy density of the battery will be affected; if the ratio of A2 to A1 is too large, demolding of the negative electrode material area will occur.

[0086] In one embodiment, the width ratio of the second region to the first region is 100:(1 - 3);

[0087] For example, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, etc. When the ratio is too small, it indicates that the negative electrode capacity margin is small. If the negative electrode material fails during the cycling process, there will be more corresponding lithium sources in the positive electrode, resulting in lithium precipitation; when the ratio is too large, it means that there is less piezoelectric material in the second region and the lithium intercalation degree in the first region is relatively deep, then the stress will be large, and finally demolding will occur.

[0088] It should be noted that the test method for the content of the piezoelectric material in the active layer: Take the negative electrodes of the first region and the second region, scrape off the coating area, weigh it, take 0.1 g of the scraped powder, dissolve it in 99.9 mL of deionized water, add 9.9 ml of nitric acid solution with a nitric acid concentration of 50%, and shake well; then place the solution in a digestion furnace at 200 °C for 3 h. Take 1 mL of the prepared solution and use ICP to test the Ba ion concentration in the solution, and calculate back to obtain the content of the piezoelectric material.

[0089] In one embodiment, the dielectric constant of the piezoelectric material is 1000 - 20000. For example, 1000, 3000, 5000, 8000, 10000, 15000, 2000, or the range composed of any two of the above values. The electrolyte in the battery is usually an electrolyte solution in a liquid or gel state, and its dielectric constant determines the migration ability of ions in the electrolyte. In an electrolyte with a higher dielectric constant, the migration rate of ions under the action of an electric field is usually faster. This helps to improve the charge and discharge efficiency of the battery and may indirectly affect the output voltage and power of the battery. Therefore, the piezoelectric material can form a substance with a lower dielectric constant within the system, correspondingly reducing the dielectric constant of the overall system, so the overall electrochemical performance of the battery can be improved. If the dielectric constant of the piezoelectric material is too low, the internal resistance of the battery will be too large. If the dielectric constant of the piezoelectric material is too high, it will affect the charge storage and release efficiency of the electrode material, resulting in a decrease in energy density.

[0090] In one embodiment, the peeling force F between the separator and the negative electrode sheet is 4 N / m ≤ F ≤ 14 N / m. For example, F can be 4 N / m, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, or the range composed of any two of the above values.

[0091] In one embodiment, the Mohs hardness of the piezoelectric material is 3 - 7. For example, the Mohs hardness of the piezoelectric material is 3, 4, 5, 6, 7, or the range composed of any two of the above values. If the Mohs hardness of the piezoelectric material is too high, the volume expansion during the charge and discharge process is too large, which may lead to the problem of piercing the separator due to high hardness, thereby increasing the chemical self-discharge of the battery. If the Mohs hardness of the piezoelectric material is too low and it is too soft, it may not be able to effectively support the mechanical stress inside the battery and cause particle breakage, so it cannot balance the local lithium intercalation state inside the negative electrode and cannot exert the characteristics of the piezoelectric material.

[0092] In one embodiment, the active material layer further includes a conductive agent and a binder. The conductive agent includes one or more of carbon black, carbon fiber, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene. The binder includes one or more of polyacrylic acid, lithium polyacrylate, carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, and epoxy resin.

[0093] Hereinafter, the battery including the present application will be introduced in detail through specific examples.

[0094] Example 1

[0095] 1. Preparation of negative electrode sheet

[0096] Mix a silicon-based material (particle size D50≈10 μm), graphite, a piezoelectric material (BaTiO3; particle size D50≈0.3 μm), single-walled carbon nanotubes, polyacrylic acid, styrene-butadiene rubber, and deionized water in a mass ratio of 25:75:0.5:6:6:18:400 and stir evenly to obtain a first negative electrode slurry;

[0097] Mix a silicon-based material (particle size D50≈10 μm), graphite, a piezoelectric material (barium titanate; particle size D50≈0.3 μm), single-walled carbon nanotubes, polyacrylic acid, styrene-butadiene rubber, and deionized water in a mass ratio of 24.89:74.67:0.57:5.97:5.97:17.92:400 and stir evenly to obtain a second negative electrode slurry;

[0098] Apply the first negative electrode slurry evenly on both surface sides of a copper foil with a thickness of 6 μm at a surface density of 6.00 mg / cm 2 (coating width 97.6 mm). In the width direction of the negative electrode sheet, apply the second negative electrode slurry evenly on the two adjacent sides of the first negative electrode slurry coating area at a surface density of 6.00 mg / cm 2 (single-sided coating width 1.2 mm), and obtain a negative electrode sheet after drying;

[0099] Roll the negative electrode sheet containing the piezoelectric material until the compaction density of the negative electrode coating reaches 1.20 g / cm 3 , and then slit the electrode sheet and weld the tab to obtain a negative electrode sheet.

[0100] 2. Preparation of positive and negative electrode sheets

[0101] Mix the positive electrode active material, PVDF, and carbon black, and add N-methylpyrrolidone (NMP), and stir at high speed to obtain a uniformly dispersed positive electrode slurry; among them, the solid content of the positive electrode slurry is 72 wt%, the positive electrode active material is nickel-cobalt-manganese ternary material (NCM) and lithium iron phosphate, and the mass ratio of NCM to lithium iron phosphate is 19:1, and the mass ratio of NCM, PVDF, and carbon black is 97:1.5:1.5.

[0102] Apply the positive electrode slurry evenly on both the front and back sides of the aluminum foil. After drying and rolling, form a positive electrode active material layer on each of the front and back surfaces of the aluminum foil, and obtain a positive electrode sheet through die-cutting.

[0103] 3. Assembly of the battery

[0104] For the diaphragm progressive lamination, the negative electrode sheet, diaphragm, and positive electrode sheet are formed into a bare battery cell, and the aluminum pole ear (positive electrode ear) and nickel-plated copper pole ear (negative electrode ear) are turned out; then the bare battery cell is encapsulated with an aluminum-plastic film, and after processes such as baking, electrolyte injection (i.e., injecting electrolyte into the battery cell), formation, and aging, a soft-packaged battery is obtained. Among them, the diaphragm used includes a base film (polypropylene film), an adhesive layer on one side surface of the base film facing the negative electrode sheet, and an adhesive layer on one side surface of the base film facing the positive electrode sheet. The adhesive layer is formed by PVDF and PAN, and the porosity of the diaphragm is 40%.

[0105] Among them, the electrolyte is a mixed solution including EC, PC, PP, LiPF6, FEC, and PS with a mass ratio of 12:12:47:15:10:4.

[0106] The diaphragm is a polyethylene-coated diaphragm with a thickness of 4.2 μm; among them, the thickness of the polyethylene layer (porous substrate) is 2 μm, the thickness of the ceramic layer is 1 μm and is distributed in one layer (the ceramics selected are alumina (Al2O3) and silica (SiO2)), and the thickness of the oil-based coating on one side is 0.6 μm, with a total of 1.2 μm (the oil-based coating selected is polyvinylidene fluoride (PVDF)).

[0107] The preparation methods of the lithium-ion batteries in Examples 2 - 14 are basically the same as those in Example 1, except that the D50 particle sizes of the silicon-based material and the piezoelectric material are different. The specific adjustments are shown in Table 1.

[0108] The preparation methods of the lithium-ion batteries in Examples 15 - 34 are basically the same as those in Example 1, except that the mass percentage content of the piezoelectric material in the active coating, the thickness of the diaphragm, the compaction density of the negative electrode sheet, and the mass percentage content of the piezoelectric material in the first region and the second region are different. The specific adjustments are shown in Table 2.

[0109] Comparative Example 1, the preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the D50 particle size of the silicon-based material is adjusted to 20 μm and the D50 particle size of the piezoelectric material is adjusted to 0.05 μm.

[0110] Comparative Example 2, the preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the D50 particle size of the silicon-based material is adjusted to 1 μm and the D50 particle size of the piezoelectric material is adjusted to 1.5 μm.

[0111] Comparative Example 3, the preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the D50 particle size of the silicon-based material is adjusted to 20 μm and the D50 particle size of the piezoelectric material is adjusted to 0.2 μm.

[0112] Comparative Example 4. The preparation method of the lithium-ion battery in this comparative example is basically the same as that of Example 1, except that the particle size D50 of the silicon-based material is adjusted to 10 μm and the particle size D50 of the piezoelectric material is adjusted to 0.05 μm.

[0113] Experimental Example

[0114] The cycle performance, cycle expansion, lithium deposition situation, and deformation situation of the lithium-ion batteries in Examples 1 - [Example] and Comparative Examples 1 - 4 were tested, and the test results are shown in Table 2.

[0115] 1. Cycle performance and expansion test:

[0116] (1) Leave the lithium-ion battery standing at 25°C ± 2°C for 10 min; (2) Leave it standing at 0°C ± 2°C for 4 h; discharge at 0.2C to the lower limit voltage and leave it standing for 10 min; (3) Charge at 0.7C to the upper limit voltage, cut off at 0.05C, and leave it standing for 10 min; (4) Discharge at 0.2C to the lower limit voltage (for initial capacity test); (5) Leave it standing for 10 min; (6) Charge at 0.7C to the upper limit voltage, cut off at 0.05C, and measure the thickness; (7) Leave it standing at 0°C ± 2°C for 10 min; (8) Discharge at 0.5C to the lower limit voltage; leave it standing for 10 min; (9) Charge at 0.7C to the upper limit voltage, cut off at 0.05C, and leave it standing for 10 min. Steps 8 - 9 are repeated 800 times. For the first 200 times, measure the thickness every 50 times, and after 200 times, measure the thickness at full charge every 100 times during the test process; repeat steps (3) - (4) at 0°C every 100 times for capacity test. After cycling, measure the thickness in the fully charged state.

[0117] The cycle thickness expansion rate is calculated according to (PPG thickness after cycling - PPG thickness of the sample received) / PPG thickness of the sample received × 100%.

[0118] 2. Lithium deposition situation test

[0119] (1) Leave the lithium-ion battery standing at 0°C ± 2°C for 4 h; (2) Discharge at 0.2C to the lower limit voltage and leave it standing for 10 min; (3) Charge at 2C to the upper limit voltage, cut off at 0.05C, and leave it standing for 10 min; (4) Discharge at 0.5C to the lower limit voltage and leave it standing for 10 min. Steps (3) - (4) are repeated 20 times. After 20 cycles, dissect the battery in the fully charged state.

[0120] Determination of lithium deposition degree: It is determined according to the state of the fully charged and disassembled negative electrode sheet. When the overall negative electrode sheet shows golden yellow and the area showing gray is <2%, it is determined that there is no lithium deposition; when most of the negative electrode is golden yellow, but gray can be observed at some positions, and the gray area is between 2% and 20%, it is determined that there is slight lithium deposition; when part of the negative electrode is gray, but part of the golden yellow can still be observed, and the gray area is between 20% and 60%, it is determined that there is moderate lithium deposition; when most of the negative electrode shows gray and the gray area >60%, it is determined that there is severe lithium deposition.

[0121] 3. Deformation condition test

[0122] Place the battery on a stable test platform to ensure it is in a normal working state. Use a micrometer to accurately measure the initial thickness of the battery when no external force is applied, and record this data for reference. Place the battery flat on a horizontal table and use a PPG600g device for testing to obtain the battery thickness data. Calculate the degree of deformation according to the formula: Degree of deformation = PPG thickness / micrometer thickness - 1; when the degree of deformation is less than 1%, it is not deformed; when it is 1 - 2%, it is slightly deformed; when it is more than 2%, it is deformed.

[0123] Table 1

[0124]

[0125]

[0126] Table 2

[0127]

[0128]

[0129] Table 2 - continued

[0130]

[0131] 1. Referring to Table 1, for the lithium - ion batteries in Examples 1 - 14 compared with Comparative Examples 1 - 4, when the particle size D50 of the silicon - based material in the negative electrode sheet is adjusted to 2 μm - 15 μm, and the particle size D50 of the piezoelectric material is adjusted to 0.1 μm - 1 μm, during the cycling process of the lithium - ion battery, the capacity retention rate is relatively high. At the same time, during the cycling process, the lithium - ion battery does not deposit lithium, or only has slight lithium deposition, and the lithium - ion battery does not deform, or only has slight deformation, thus effectively improving the cycling performance of the lithium - ion battery.

[0132] Furthermore, as can be seen from Examples 1, 2, 4-7, 10, and 12, when the ratio between the particle size D50 of the silicon-based material in the negative electrode sheet and the particle size D50 of the piezoelectric material is limited to 20-100, during the cycling process, no lithium deposition and deformation occur in the lithium-ion battery, further improving the cycling performance of the lithium-ion battery.

[0133] 2. Referring to Table 2, compared with Example 1, for the lithium-ion batteries in Examples 15-18, when the content of the piezoelectric material is different and the content of the piezoelectric material is limited to 0.2-5, during the cycling process of the lithium-ion battery, the capacity retention rate is basically about 90%, and no lithium deposition and deformation occur, and the cycling performance of the battery is good. On the contrary, when the content of the piezoelectric material is outside the above range, during the cycling process of the lithium-ion battery, the capacity retention rate is basically about 88%, and lithium deposition and deformation occur, resulting in poor cycling performance of the battery.

[0134] Furthermore, as can be seen from Examples 19-22, when the thickness of the separator of the lithium-ion battery is too thick (Example 22), or the thickness of the separator is too thin (Example 21), during the cycling process of the lithium-ion battery, the capacity retention rate decreases significantly (compared with Examples 19 and 20, the thickness of the separator is within a moderate range), and lithium deposition and deformation occur, making the cycling performance of the battery poor.

[0135] Furthermore, as can be seen from Examples 23-25, when the compaction density of the negative electrode sheet is too high (Example 25), during the cycling process of the lithium-ion battery, the capacity retention rate decreases significantly compared with Examples 24 and 25, and lithium deposition and deformation occur, making the cycling performance of the battery poor.

[0136] As can be seen from Examples 26-27, when the content of the piezoelectric material is too small relative to the thickness of the separator, the ability of the piezoelectric material to limit the expansion of the silicon-based material decreases, so the battery cycling retention rate decreases, and lithium deposition and deformation also occur.

[0137] As can be seen from Examples 1, 2, 23, 26, 28, and 29, the content of the negative electrode piezoelectric material is closely related to the compaction density of the negative electrode. When the content of the piezoelectric material is too high or too low relative to the compaction density of the negative electrode, it will lead to a decrease in the battery cycling retention rate, accompanied by lithium deposition in the battery and prone to deformation.

[0138] As can be seen from Example 1 and Examples 31-34, when the content of the piezoelectric material in the second region is too much or too little relative to the content of the piezoelectric material in the first region, the probability of pole piece demoulding increases, which will lead to an increase in battery swelling, deterioration of cycling performance, and an increase in the chance of lithium deposition and deformation in the battery.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, comprising: A positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, characterized in that the negative electrode sheet includes a negative electrode current collector and an active coating coated on at least one surface of the negative electrode current collector, and the active coating includes a silicon-based material and a piezoelectric material; the separator includes a porous substrate and a coating coated on the surface of the porous substrate, and the coating on the side facing the negative electrode sheet is an oil-based coating; The particle size of the silicon-based material and the particle size of the piezoelectric material satisfy the following formula: 20 ≤ L1 / L2 ≤ 100; wherein, L1 is the D50 particle size of the silicon-based material, and L2 is the D50 particle size of the piezoelectric material.

2. The battery according to claim 1, wherein The D50 particle size of the silicon-based material is 2 μm to 15 μm; and / or the D50 particle size of the piezoelectric material is 0.1 μm to 1 μm.

3. The battery according to claim 1, characterized in that, The mass percentage content A of the piezoelectric material in the active coating is 0.2 - 5, and the unit of A is wt%; and / or the thickness T of the separator is 4 - 10, and the unit of T is μm.

4. The battery according to claim 3, wherein, A and T satisfy the following formula: 0.04 ≤ A / T ≤ 1.

25.

5. The battery according to any one of claims 1-4, characterized in that, The piezoelectric material and the silicon-based material are mixed and doped in the active coating; The density of the piezoelectric material distributed within a range of 1 μm 2 to 2 μm 2 around the silicon-based material particles is 0.5 to 10 times.

6. The battery according to any one of claims 1-4, characterized in that, The compaction density B of the negative electrode sheet is 0.2 - 5.0, and the unit of B is g / cm 3 .

7. The battery according to claim 6, wherein, The mass percentage content A of the piezoelectric material in the coating and the compaction density B of the negative electrode sheet satisfy the following formula: 0.11 ≤ A / B ≤ 4.

55.

8. The battery according to any one of claims 1-4, characterized in that, The active coating includes a first region and a second region; The first region is located on at least one side in the width direction of the negative electrode sheet, and the second region is adjacent to the first region; and / or the mass percentage content A2 of the piezoelectric material in the second region is less than the mass percentage content A1 of the piezoelectric material in the first region; and / or the width ratio of the second region to the first region is 100:(1 - 3).

9. The battery according to claim 8, characterized in that 0.3％≤A1≤5.1％； and / or 0.2％≤A2≤5.0％； and / or A2:A1 = 0.7 - 0.9:

1.

10. The battery according to any one of claims 1-4, characterized in that, The piezoelectric material is selected from one or more of the following: Quartz (SiO2), PZT (lead zirconate titanate, Pb[Zr x Ti 1-x O3), lithium niobate (LiNbO3), barium titanate (BaTiO3), sodium niobate (NaNbO3), gallium nitride (GaN), zirconium titanium alloy (ZT).

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