Battery and electric device

Abstract

The present application discloses a battery and an electric device. The battery comprises a cell and an electrolyte, wherein the cell comprises a negative electrode sheet and a separator, the negative electrode sheet comprises a current collector and a negative electrode active material layer, the negative electrode active material layer comprises a silicon-based material, and the separator comprises a base film and a coating; the mass percentage of a silicon element in the negative electrode active material layer is a; the viscosity of the electrolyte is b, in units of cp; the percentage of the thickness of the coating relative to the thickness of the separator is c; and 0.037≤a*b / c≤5.625. In the present application, by controlling the value of a*b / c within the range of 0.037-5.625, the wettability of the electrolyte on the negative electrode and the fast charging performance of the battery can be effectively improved while ensuring the energy density of the battery.

Description

A battery and an electrical device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411600580.8, filed on November 11, 2024, entitled “A Battery and an Electric Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of batteries, specifically to a battery and an electrical device. Background Technology

[0004] A lithium battery consists of a cell composed of a positive electrode, a negative electrode, and a separator, an electrolyte filling the cell, and a battery casing that encloses the cell and electrolyte. The negative electrode of a conventional battery consists of a current collector and a layer of negative electrode active material coated on the current collector.

[0005] The negative electrode active material in the negative electrode active material layer is usually graphite or carbon with a similar graphite structure. In order to improve the energy density of the battery, silicon can be doped into the conventional negative electrode active material layer. However, when the silicon content in the negative electrode increases, it will lead to increased negative electrode expansion, poor electrolyte wetting effect, and poor battery fast charging performance. Summary of the Invention

[0006] Therefore, the technical problem to be solved by this application is to overcome the defect that the fast charging performance of batteries deteriorates when the silicon content in the negative electrode is increased in the prior art, thereby providing a battery and power device that solves the above problem.

[0007] To achieve the above objectives, this application provides a battery, including a cell and an electrolyte. The cell includes a negative electrode and a separator. The negative electrode includes a current collector and a negative electrode active material layer, the negative electrode active material layer including a silicon-based material. The separator includes a base film and a coating. The mass percentage of silicon in the negative electrode active material layer is a; the viscosity of the electrolyte is bcp; the percentage of the thickness of the coating to the thickness of the separator is c; 0.037≤a*b / c≤5.625.

[0008] This application also provides an electrical device comprising the above-described electrochemical device.

[0009] The beneficial effects of this application are as follows:

[0010] This application improves the wetting effect of the electrolyte on the negative electrode and the fast charging performance of the battery by adjusting the mass percentage (a) of silicon in the negative electrode active material layer, the electrolyte viscosity (bcp), and the coating thickness / separator thickness (c). By comprehensively controlling the value of a*b / c within the range of 0.037-5.625, the application can improve the wetting effect of the electrolyte on the negative electrode and the fast charging performance of the battery. Detailed Implementation

[0011] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0012] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0013] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 50%-90% and 60%-80% are listed for a specific parameter, it is expected that ranges of 50%–80% and 60%–90% would also be understood.

[0014] A battery includes a cell and an electrolyte. The cell includes a negative electrode and a separator. The negative electrode includes a current collector and a negative electrode active material layer, the negative electrode active material layer including a silicon-based material. The separator includes a base film and a coating. The mass percentage of silicon in the negative electrode active material layer is 'a'. The viscosity of the electrolyte is 'bcp'. The percentage of coating thickness to separator thickness is 'c'. The value of a*b / c is 0.037 ≤ a*b / c ≤ 5.625. That is, the value of a*b / c can be any value between 0.037 and 5.625, such as: 0.037, 0.05, 0.1, 0.15, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.625, etc.

[0015] This application improves the electrolyte's wetting effect on the negative electrode and the battery's fast-charging performance by adjusting the silicon content (a), electrolyte viscosity (bcp), and the coating thickness / separator thickness percentage (c%). By comprehensively controlling the value of a*b / c within the range of 0.037-5.625, the application aims to achieve this. Specifically, during battery charging and discharging, a high silicon content leads to significant volume expansion of the active material layer and increased porosity within the electrode. These pores require electrolyte filling. If the electrolyte viscosity is too high, it results in poor electrode wetting, hindering lithium-ion transport and reducing fast-charging performance. Therefore, a lower electrolyte viscosity is needed to quickly and fully fill the pores and wet the negative electrode. Thus, when the silicon content is high, the electrolyte viscosity (bcp) should be lower. The viscosity (cp) should not be too high. Furthermore, the diaphragm coating has a certain liquid retention capacity. When the electrode expands, it squeezes the diaphragm, causing the electrolyte to be squeezed out. During the expansion of the negative electrode, more pores can absorb the electrolyte squeezed out by the diaphragm, facilitating electrolyte entry into the electrode. Therefore, the coating thickness in the diaphragm cannot be too small; that is, the percentage (c) of coating thickness / diaphragm thickness cannot be too small. Simultaneously, the electrolyte viscosity cannot be too low. The electrolyte includes solvent and solute; the higher the viscosity, the stronger the interaction between the solute and solvent, and vice versa. The weaker the solvent-solvent transport rate, the lower the viscosity, which leads to a mismatch between the solute and solvent transport rates, resulting in poorer wetting of the electrode. Furthermore, the coating thickness in the separator cannot be too thick. Since the electrolyte filling volume in a battery is generally fixed, a thicker coating results in a higher electrolyte absorption by the separator, leaving less electrolyte for the electrode. Although some electrolyte can be released to the negative electrode during subsequent charging expansion, this still results in a low initial electrolyte volume on the negative electrode side. In summary, this application improves the wetting of the negative electrode by comprehensively controlling the mass percentage of silicon in the negative electrode active material layer (a), the electrolyte viscosity (b), and the percentage of coating thickness to separator thickness (c), ensuring that 0.037 ≤ a*b / c ≤ 5.625, thereby improving the fast-charging performance of the battery.

[0016] Adding silicon to the negative electrode active material can improve the battery energy density. The silicon in the negative electrode active material layer can be derived from silicon-carbon materials and / or silicon-oxygen materials. The silicon content refers to the mass percentage 'a' of silicon in the negative electrode active material layer, and the silicon content 'a' is controlled between 0.5% and 30%. For example, 'a' can be controlled to be 0.5%, 1%, 2%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, etc.

[0017] In an optional embodiment, the silicon content 'a' in the negative electrode active material layer is preferably controlled to be 2%-16%. Specifically, in this application, a negative electrode with a higher silicon content is preferred, as it can improve the energy density of the battery. However, the silicon content cannot be too high, as this would cause increased expansion of the negative electrode, leading to increased porosity and a greater demand for electrolyte wetting. Therefore, the silicon content 'a' in the negative electrode active material layer of this application is preferably controlled to be 2%-16%.

[0018] The viscosity b of the electrolyte affects the wetting effect of the electrolyte. In this application, the electrolyte viscosity is controlled within the range of 1.5-3.7 cp; for example, the viscosity b is controlled to be 1.5, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.7, etc.

[0019] In one optional embodiment, the electrolyte viscosity is preferably controlled within the range of 2.1-2.8 cp. Specifically, in this application, a lower viscosity electrolyte is preferred, which can improve the fluidity of the electrolyte and enhance the wetting effect of the electrolyte on the electrode. However, the electrolyte viscosity cannot be too low, as this will cause a serious mismatch between the solvent and solute transport rates in the electrolyte, which will result in a poorer wetting ability on the electrode. Therefore, the electrolyte viscosity is preferably controlled within the range of 2.1-2.8 cp to improve the wetting effect of the electrolyte on the electrode.

[0020] The diaphragm includes a base membrane and a coating, with the coating disposed on the surface of the base membrane. The coating generally includes inorganic and organic components. The coating has a porous structure and liquid absorption capacity, which is related to the coating thickness. The liquid absorption capacity of the diaphragm can be adjusted by controlling the percentage c between the coating thickness and the diaphragm thickness. In this application, the percentage c between the coating thickness and the diaphragm thickness can be controlled to be 8%-50%. For example, c can be controlled to be 8%, 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0021] In one optional embodiment, the percentage c of coating thickness / separator thickness is preferably controlled within the range of 13%-32%. Specifically, in this application, a higher percentage c of coating thickness / separator thickness is preferred to improve the coating's liquid absorption capacity. However, the percentage c of coating thickness / separator thickness should not be too high. If it is too high, the coating's liquid absorption capacity will be too large. When the electrolyte injection amount is certain, most of the electrolyte will be absorbed by the separator, resulting in less electrolyte absorbed by the negative electrode initially, poor lithium-ion transport rate, and poor battery fast charging performance. Therefore, in this application, it is preferred to control c to 13%-32%, which is more conducive to the separator having a more appropriate amount of electrolyte, which is released and wets the electrode during the subsequent electrode expansion process.

[0022] Furthermore, by controlling the value of a*b / c within a more preferred range, the negative electrode wetting and fast charging performance of this application are even better. For example, the value of a*b / c is controlled between 0.165 and 2.585.

[0023] When the silicon-based material includes silicon-carbon material, the silicon-carbon material includes a porous carbon matrix and silicon particles. The silicon particles are pure silicon crystals. The silicon particles are embedded in the porous carbon matrix. The porous carbon can alleviate expansion by utilizing its own pores, thereby reducing electrode expansion, appropriately increasing electrolyte viscosity, and appropriately reducing the amount of electrolyte absorbed by the diaphragm. Therefore, the value of a*b / c is preferably 0.431-1.05.

[0024] The energy density of a battery is related to the compaction density of the negative electrode. Appropriately increasing the compaction density can improve the contact between particles, increase the electronic conductivity of the negative electrode, and thus improve the battery's energy density. In this application, the compaction density of the negative electrode is 1.25-1.8 g / cm³. 3 For example: 1.25g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 wait.

[0025] Increasing compaction density is beneficial for improving battery energy density; however, higher compaction density results in smaller electrode pores, reducing the initial electrolyte storage capacity. This allows for a reduction in electrolyte viscosity (b), further controlling the range of a*b / c to ensure sufficient electrolyte wetting within the pores. Additionally, appropriately increasing the percentage (c) of coating thickness / separator thickness can improve the separator's electrolyte retention capacity, facilitating the subsequent back-wetting of the electrode by electrolyte squeezed out from the separator. Specifically, when the negative electrode compaction density is 1.45-1.8 g / cm³... 3 When the value of a*b / c is preferably 0.333-0.820, the negative electrode wetting and fast charging performance are better.

[0026] The electrolyte comprises a solvent and a lithium salt;

[0027] The solvent is selected from carbonates, carboxylic acid esters, ethers, sulfones, nitriles, phosphate esters, or fluorides of the above solvents;

[0028] The lithium salt is selected from lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0029] To reduce the viscosity of the electrolyte, the solvent contains at least 10% to 60% carbonate solvent and 0% to 50% carboxylic acid ester solvent;

[0030] And / or, the lithium salt concentration in the electrolyte is 0.8-2.5M; for example: 0.8M, 0.9M, 1.0M, 1.2M, 1.5M, 1.8M, 2.0M, 2.3M, 2.5M.

[0031] For the diaphragm, the coating contains inorganic components, which have good electrolyte retention capacity. The coating thickness should not be too large, as this would result in the diaphragm absorbing a large amount of electrolyte, leaving less electrolyte available for the negative electrode. Conversely, the coating thickness should not be too small, as it retains some electrolyte and can be used to replenish the negative electrode electrolyte during subsequent long-cycle processes. Therefore, the preferred coating thickness is 1-7 μm; for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, etc.

[0032] The inorganic components contained in the coating are selected from alumina, boehmite, silicon dioxide, zirconium oxide, titanium dioxide, cerium oxide, and magnesium aluminate, etc.

[0033] An electrical device includes the battery described above; the battery includes a positive electrode plate, wherein the positive electrode active material in the positive electrode plate includes LiNi. x Co y Mn z O2, where 1>x≥0.5, x+y+z=1.

[0034] The following detailed description discloses embodiments of the battery and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0035] [Battery]

[0036] The battery described in this application is a secondary battery, also known as a rechargeable battery or a storage battery, which refers to a battery that can be used again after being discharged by recharging to activate the active materials.

[0037] Typically, a battery consists of a cell, an electrolyte, and an outer casing; the cell includes a positive electrode, a negative electrode, and a separator. During charging and discharging, active ions (such as lithium ions) move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, mainly serves to conduct active ions.

[0038] As an example, the battery manufacturing process is as follows: the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum sealing, standing, formation, and shaping processes, a secondary battery is obtained.

[0039] [Positive electrode tablets]

[0040] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material can be any conventionally used positive electrode material.

[0041] The above-mentioned positive electrode sheet preparation method is as follows: the positive electrode active material, conductive agent, binder and any other components are dispersed in a solvent and stirred under the action of a vacuum stirrer until the system is homogeneous to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil, dried at room temperature and then transferred to an oven for further drying, and then cold-pressed and slit to obtain a positive electrode sheet.

[0042] In this application, the positive electrode active material is a conventional positive electrode active material in the battery field, such as the ternary positive electrode material LiNi. x Co y Mn z O2, etc., where 1 > x ≥ 0.5, x + y + z = 1.

[0043] Conductive agents are used to improve the electrical conductivity between particles of positive electrode active material. In this application, the conductive agent can be a conventional choice in the battery field, such as carbon nanotubes, carbon black, or graphene.

[0044] The binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. In this application, the binder can be a conventional choice in the battery field. For example, the binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate.

[0045] The solvent used in this application is used to achieve uniform dispersion among the positive electrode active material, conductive agent, and binder. It can be a common type of solvent in the battery field, such as: N,N dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, dimethyl carbonate, N,N dimethylformamide, etc.

[0046] This application does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0047] [Negative electrode plate]

[0048] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes conventional silicon-based materials in the battery field and other negative electrode active materials. The silicon-based materials include silicon-carbon materials and / or silicon-oxygen materials. Other negative electrode active materials include artificial graphite, natural graphite, etc.

[0049] This application does not limit the preparation method of silicon-carbon materials. Specifically, they can be prepared by chemical vapor deposition (CVD). Specifically, through the adsorption force of porous carbon, silane is gradually decomposed to produce elemental silicon at 450-500℃, which is then deposited into the carbon framework. Acetylene carbon coating (500-550℃) forms a stable coated carbon layer on the silicon-carbon surface, ultimately yielding the silicon-carbon material. Further details are omitted here. This application allows for the control of the number of silicon particles deposited in the porous carbon by adjusting the silane flow rate and deposition time.

[0050] In some embodiments, a conductive agent is used to improve the conductivity between particles of the negative electrode active material. The negative electrode active material layer may also optionally include a conductive agent. In this application, the conductive agent can be a conventional choice in the battery field. As an example, the conductive agent may be selected from carbon nanotubes, carbon black, or graphene.

[0051] The binder is used to improve the adhesion between particles of the negative electrode active material and the adhesion between the negative electrode active material and the current collector. In this application, the binder can be a conventional choice in the battery field. For example, the binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate.

[0052] In some implementations, as an example, the negative current collector is copper foil.

[0053] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, rolling, cutting and other processes.

[0054] Electrolyte

[0055] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte comprises a solvent and a solute. This application does not impose specific limitations on the type of solute in the electrolyte, and it can be selected according to requirements. As an example, the electrolyte of this application can be any electrolyte suitable for electrochemical energy storage devices in the art. The solute typically includes lithium salts, and the solvent is an organic solvent.

[0056] Specifically, the lithium salt concentration in the electrolyte is 0.8-2.5M, and the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium dioxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium trifluoromethanesulfonate (LiTFS), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0057] Specifically, the solvent is selected from carbonates, carboxylic acid esters, ethers, sulfones, nitriles, phosphate esters, or fluorides of the above solvents; the solvent contains at least 10% to 60% carbonate solvent and 0% to 50% carboxylic acid ester solvent. For example, the solvent includes at least one of fluoroethylene carbonate (FEC), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propionate (EP), ethyl acetate (EA), acetonitrile (AN), and trifluoroethanol (TFEA).

[0058] [Septum]

[0059] The membrane used in this application has a base film and a coating.

[0060] This application does not impose any particular restrictions on the type of base membrane. Any well-known porous base membrane with good chemical and mechanical stability can be selected. In some embodiments, as an example, the base membrane is either PP or PE.

[0061] The coating in this application includes an inorganic component; the inorganic component is selected from alumina, boehmite, silica, zirconium oxide, titanium dioxide, cerium oxide, and magnesium aluminate, etc.; in some embodiments, it also includes an organic component, the organic component being selected from polyvinylidene fluoride, polymethyl methacrylate, aramid, etc.

[0062] Example 1

[0063] A battery includes a cell and an electrolyte. The cell includes a negative electrode and a separator. The negative electrode includes a current collector and a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, which is a silicon-based material, specifically a silicon-carbon material. The separator includes a base film and a coating.

[0064] 1. Preparation of positive electrode sheet

[0065] The specific preparation process of the positive electrode is as follows: The positive electrode active material LiNi... x Co y Mn z O2 (x = 0.92, y = 0.05, z = 0.03), conductive agent acetylene black, and binder PVDF are mixed in a mass ratio of 92:4:4. NMP solvent is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0066] 2. Preparation of negative electrode sheet

[0067] The specific preparation process is as follows: The negative electrode active material, conductive agent carbon black, thickener CMC, and binder SBR are mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous, obtaining a negative electrode slurry. The negative electrode slurry is uniformly coated onto both surfaces of the negative electrode current collector copper foil, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, negative electrode sheets are obtained. The compacted density of the negative electrode sheets after cold pressing is shown in Table 1. In this embodiment, the compacted density of the negative electrode sheet is 1.6 g / cm³. 3 .

[0068] In this application, the negative electrode active material is obtained by mixing artificial graphite and silicon-carbon material at a mass ratio of (40-99):(1-60). In this embodiment, the artificial graphite and silicon-carbon material are mixed at a mass ratio of 65.2:34.8 as shown in Table 1. The silicon-carbon material is prepared by chemical vapor deposition (CVD). Specifically, through the adsorption force of porous carbon, silane decomposes at a deposition temperature of 450°C to produce gaseous silicon and hydrogen. The gaseous silicon will be deposited in the carbon matrix, that is, under this condition, the gaseous silicon gradually permeates into the carbon skeleton. After the silicon matrix is ​​deposited, a carbon coating layer is required to prevent pure silicon from contacting air. That is, acetylene carbon is coated on the surface of silicon-carbon at a carbon coating temperature of 550°C to form a stable silicon-carbon material. In the preparation of silicon-carbon material in this application, the silane decomposition and deposition process occurs simultaneously at high temperature. The silane flow rate is controlled at 18 L / min, and the deposition time is controlled at 15 h to prepare a silicon-carbon material with a silicon content of 50%.

[0069] 3. Acquisition of the diaphragm

[0070] The diaphragm in this embodiment is a commercially available product, comprising a base membrane and a coating. The diaphragm parameters are shown in Table 1. In this embodiment, the base membrane is made of PP with a thickness of 12 mm, and the inorganic component in the coating is alumina with a thickness of 1.5 mm.

[0071] 4. Preparation of electrolyte

[0072] The specific preparation process is as follows: Various solvents are mixed in an argon-filled glove box to obtain an organic solvent. In this embodiment, fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and propylene carbonate (PC) are mixed in a mass ratio of 15:20:60:5. Then, fully dried lithium salt (LiPF6) is dissolved in the mixed organic solvent. Next, 0.5% of 1,3-propanesulfonyl lactone, 0.5% of tris(trimethylsilyl)phosphate, and 1% of vinyl sulfate are added to the electrolyte. The mixture is stirred until completely dissolved to prepare an electrolyte with a lithium salt concentration of 2.5M as shown in Table 1.

[0073] 5. Battery assembly

[0074] The specific process is as follows: the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and volume adjustment, a lithium-ion battery is obtained.

[0075] Examples 2-12 and Comparative Examples 1-2

[0076] A secondary battery differs from Example 1 in that the parameters and conditions in the preparation of the negative electrode, the acquisition of the separator, and the preparation of the electrolyte are different. The different parameters are shown in Table 1 below. Everything else is exactly the same as in Example 1.

[0077] Table 1

[0078] The batteries of the above embodiments and comparative examples were tested in steps a, b, and c.

[0079] The detection of 'a': This refers to the detection of the mass percentage 'a' of silicon element in the negative electrode active material layer. The detection process is as follows:

[0080] Pretreatment: The negative electrode sheet was cleaned with DMC solvent, dried at 60°C, and then scraped off with powder.

[0081] Weigh the sample and place it in a nickel crucible pre-filled with potassium hydroxide. Add a small amount of potassium hydroxide to cover the sample surface, add two drops of ethanol, and heat on an electric furnace until the potassium hydroxide melts and dehydrates. Then transfer the crucible to a muffle furnace at 1100℃ and maintain the molten state for 8 hours. Remove the nickel crucible and allow it to cool slightly. Place the crucible in a 300mL plastic beaker and add hot water for extraction. After the reaction, remove the crucible, add HCl to the beaker for acidification, add hydrogen peroxide, and after cooling, filter out other impurities. Transfer the filtered solution to a 100mL volumetric flask, dilute to volume, and mix well. After standing, transfer a portion of the solution to another 100mL volumetric flask, dilute to volume, mix well, and allow to stand until clear before analysis. Simultaneously prepare a blank solution (without the sample added) and follow the above steps to obtain the final solution. Then, based on the characteristics of the sample and the elements to be detected, set appropriate ICP instrument operating conditions, including a gas flow rate of 0.5 L / min and a power of 1150 W; a Si element measurement wavelength of 288.158 nm; and test the Si content of the elements by ICP.

[0082] The detection of b: that is, the detection of the viscosity b of the electrolyte. The detection process is as follows:

[0083] The battery was discharged completely, and the battery cell was disassembled and removed. The battery cell was sealed in an aluminum-plastic bag, and the remaining electrolyte was squeezed out using a tablet press. The electrolyte was then extracted by puncturing the cell with a syringe and tested using a Cambridge viscometer. The Cambridge viscometer is designed based on electromagnetic oscillation viscosity detection technology and uses a magnetically levitated probe for viscosity measurement. Specifically, the electrolyte was placed in a beaker, and the sample temperature was controlled at 25°C for testing. The reading was taken after the displayed value stabilized. In this embodiment, the viscosity b of the electrolyte is shown in Table 2.

[0084] The detection of c: This refers to the test of the percentage c of the coating thickness to the membrane thickness in the diaphragm. There are two test methods, including:

[0085] a. Use a micrometer to measure the thickness H1 of the diaphragm; after removing the coating on the diaphragm surface with tape, use a micrometer to measure the thickness H2 of the base film. The coating thickness is (H2-H1) / n, where n = 1 or 2.

[0086] b. Obtain a cross-sectional SEM image of the diaphragm and use a scanning electron microscope to measure the thickness of the coating and the base film.

[0087] In this embodiment, scanning electron microscopy was used to measure the thickness of the coating and the base film. The percentage c of the thickness of the coating and the diaphragm is shown in Table 2.

[0088] Test 1 - Fast charging capability @ 10-80% SOC:

[0089] a. Charge the battery at a constant current of 0.33C to the upper limit voltage of 4.25V, then charge it at a constant voltage until the cutoff current is less than or equal to 0.05C, and then discharge it;

[0090] Repeat the above steps 3 times, and use the discharge capacity of the third discharge as the discharge capacity of the battery.

[0091] b: Based on the battery capacity in a, charge the battery at 0.33C to 10% SOC; denoted as T0;

[0092] c: Then, charge the battery at 4C, 3.5C, 3.0C, 2.75C, 2.5C, 2.25C, 2.0C, 1.75C, 1.5C, 1.25C, 1C, and 0.33C respectively to the cutoff voltages of 3.95V, 3.97V, 3.985V, 3.996V, 4.005V, 4.015V, 4.025V, 4.045V, 4.067V, 4.091V, 4.11V, and 4.25V. Record the time taken to charge the battery to 80% SOC as T1. T1-T0 is the fast charging time, in minutes.

[0093] Test 2 - Energy Density Test:

[0094] a: Charge the battery at a constant current of 0.33C to the upper limit voltage of 4.25V, then charge it at a constant voltage until the cutoff current is less than or equal to 0.05C, and then discharge it;

[0095] Repeat the above steps 3 times, and use the discharge energy of the third discharge as the discharge energy E of the battery;

[0096] b: The battery weight M is obtained by weighing using an electronic balance;

[0097] c: Calculation of gravimetric energy density: E / M, unit Wh / Kg.

[0098] Test 3 - Cycle life test at 25℃:

[0099] The lithium-ion battery was left to stand at 25°C for 120 minutes, then charged at a constant current of 0.5C to the cutoff voltage of 4.25V, and charged at a constant voltage until the cutoff current was ≤0.05C. After standing for 10 minutes, it was discharged at a constant current of 0.5C to 2.5V. This constitutes one cycle. The above steps were repeated until 80% SOH was reached, and the number of cycles was recorded.

[0100] The test results are shown in Table 2 below.

[0101] Table 2

[0102] Table 3

[0103] Table 4

[0104] As shown in Tables 2-4, this application, by comprehensively adjusting the silicon content (a), electrolyte viscosity (b), and the coating thickness / base film thickness percentage (c), and controlling the value of a*b / c within the range of 0.037-5.625, can effectively improve negative electrode wetting while maintaining good battery energy density, thereby improving fast-charging performance. A comparison of the data in Tables 2-4, especially between Examples 1 and 8 in Table 2 and other examples, and between Example 10 in Table 4 and other examples, shows that when the value of a*b / c is further preferably between 0.165-2.585, it achieves better improvement in fast-charging and cycle performance while maintaining battery energy density.

[0105] When the value of a is further preferably 2%-16%, b is further preferably 2.1-2.8%, and c is further preferably 13%-32%, it can not only effectively improve the fast charging performance, but also significantly improve the cycle performance, and the number of cycles can reach more than 1000.

[0106] When a, b, and c are all within their preferred ranges, and the value of a*b / c is within the preferred range of 0.165-2.585, and the silicon-based material is silicon-carbon material, the value of a*b / c is further preferably 0.431-1.05, and the compaction density of the negative electrode is 1.45-1.8 g / cm³. 3 When the above-mentioned preferred setting conditions are met, see Examples 5 and 7 in Table 2 and Example 6 in Table 4. Comparison with data from other examples shows that it significantly improves cycle performance while improving fast charging performance.

[0107] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A battery, comprising a cell and an electrolyte, the cell comprising a negative electrode and a separator, the negative electrode comprising a current collector and a negative electrode active material layer, the negative electrode active material layer comprising a silicon-based material, and the separator comprising a base film and a coating; characterized in that, The mass percentage of silicon in the negative electrode active material layer is a; the viscosity of the electrolyte is b, in cp; the percentage of coating thickness to separator thickness is c; 0.037≤a*b / c≤5.

625.

2. The battery according to claim 1, characterized in that, The value of a is 0.5%-30%; And / or, the value of b is 1.5-3.7; And / or, the c is 8%-50%.

3. The battery according to claim 2, characterized in that, The percentage of a is 2%-16%; And / or, the value of b is 2.1-2.8; And / or, the c is 13%-32%.

4. The battery according to any one of claims 1-3, characterized in that, The value of a*b / c is 0.165-2.585; When the silicon-based material is silicon-carbon material, the value of a*b / c is 0.431-1.

05.

5. The battery according to claim 1, characterized in that, The compacted density of the negative electrode is 1.25-1.8 g / cm³. 3 .

6. The battery according to claim 5, characterized in that, When the compaction density of the negative electrode is 1.45-1.8 g / cm³ 3 When the time is right, the value of a*b / c is 0.333-0.

82.

7. The battery according to claim 1, characterized in that, The electrolyte comprises a solvent and a lithium salt; The solvent is selected from carbonates, carboxylic acid esters, ethers, sulfones, nitriles, phosphate esters, or fluorides of the above solvents; The lithium salt is selected from lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluorosulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

8. The battery according to claim 7, characterized in that, The solvent contains at least 10 wt% to 60 wt% of carbonate solvent and 0 wt% to 50 wt% of carboxylic acid ester solvent; And / or, the lithium salt concentration in the electrolyte is 0.8-2.5M.

9. The battery according to claim 1, characterized in that, The coating contains inorganic components, which are selected from alumina, boehmite, silicon dioxide, zirconium oxide, titanium dioxide, cerium oxide, and magnesium aluminate. The coating has a thickness of 1-7 μm.

10. An electrical device, characterized in that, The battery comprises any one of claims 1-9; the battery includes a positive electrode, wherein the positive electrode active material in the positive electrode includes LiNi. x Co y Mn z O2, where 1>x≥0.5, x+y+z=1.

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