Silicon-based material, negative electrode sheet, secondary battery, and device

Abstract

A silicon-based material, comprising: SiOx, wherein x is 0.5 to 1.6; and a carbon layer covering the surface of SiOx. The silicon-based material satisfies the following conditions: 0.2≤S1≤1.5, and / or 0.02≤ISi / ID≤0.5, wherein S1 refers to a standard deviation value of an ID / IG value of the carbon layer, the ID / IG value refers to the area ratio of a peak D to a peak G, and ISi / ID refers to the area ratio of a peak Si to the peak D.

Description

Silicon-based material, negative electrode sheet, secondary battery and device

[0001] The present application claims priority to Chinese Patent Application No. CN202410704230.X, filed on May 31, 2024, entitled “Silicon-based material, negative electrode sheet, secondary battery and device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to a silicon-based material, in particular to a silicon-based material, negative electrode sheet, secondary battery and device, belonging to the field of battery materials. BACKGROUND

[0003] Silicon material is a promising negative active material for the next generation of electrochemical devices due to its high specific capacity. However, pure silicon material has a volume expansion of 300% during charging and discharging, which leads to phenomena such as sheet pulverization, affecting the calendar life of the battery and restricting the application of silicon material.

[0004] Silicon-oxygen negative electrode material is a branch of silicon-based material. Due to the mixed phase structure of silicon and oxide, it can effectively alleviate the volume effect of silicon during charging and discharging, and the volume expansion is greatly reduced compared to pure silicon, making it easier to achieve commercial application. However, the silicon-oxygen negative electrode material has an unstable interface during high-temperature storage, which not only affects the rupture and regeneration of the SEI film, but also causes the active particles to pulverize themselves and cause the active material to fall off from the current collector, shortening the calendar life of the battery.

[0005] Therefore, there is an urgent need to develop a novel silicon-based material that can improve the high-temperature storage performance of the battery when applied to power batteries. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a silicon-based material, negative electrode sheet, secondary battery and device. The present application adjusts the average variance value of the ID / IG value of the carbon layer and the area ratio of the Si peak to the D peak in the silicon-based material to improve the uniformity and integrity of the carbon coating, effectively improving the high-temperature storage performance (calendar life) of the secondary battery.

[0007] The first aspect of the present application provides a silicon-based material, which comprises SiOx, wherein x is 0.5 to 1.6; and a carbon layer coated on the surface of SiOx, wherein the silicon-based material satisfies: 0≤S1≤1.5, and / or 0≤ISi / ID≤0.5; wherein the S1 refers to the standard deviation value of the ID / IG value of the carbon layer, the ID / IG value refers to the area ratio of the D peak and the G peak, and the ISi / ID refers to the area ratio of the Si peak and the D peak. The smaller the S1, the more uniform the surface coating, which is more conducive to the uniform film formation of the material during lithiation, and the better the storage performance; the smaller the ISi / ID, the lower the exposure degree of silicon, which reduces the direct contact with the electrolyte and in turn reduces the side reaction, and thus the better the electrochemical storage performance.

[0008] The second aspect of the present application provides a negative electrode tab, which comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises the silicon-based material of the first aspect.

[0009] The third aspect of the present application provides a secondary battery, which comprises the negative electrode tab of the second aspect and a positive electrode tab.

[0010] The fourth aspect of the present application provides a device, which comprises the secondary battery of the third aspect.

[0011] The present application improves the uniformity and integrity of carbon coating, reduces the exposure degree of active silicon, stabilizes the interface SEI film, reduces the electrochemical side reaction with the electrolyte, and thus improves the high-temperature storage performance of the secondary battery containing silicon. DETAILED DESCRIPTION

[0012] For the sake of brevity, the present application discloses only some numerical ranges specifically. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. Furthermore, each individual point or single numerical value, by itself, can be combined with any other point or single numerical value, or with other lower limits or upper limits, to form a range not explicitly recited.

[0013] Unless otherwise defined, the terms used in the present application have the common meanings generally understood by those skilled in the art. Unless otherwise specified, the values of each parameter mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the examples of the present application).

[0014] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0015] The term "ID / IG value" refers to the area ratio of the D peak to the G peak, where the D peak refers to the area at 1300 cm⁻¹. -1 up to 1420cm -1 The peak in the wavenumber range, G peak refers to 1540 cm⁻¹. -1 up to 1620cm -1 The peak of the wavenumber range.

[0016] The term "ISi / ID" refers to the area ratio of the Si peak to the D peak, where the Si peak refers to the peak area at 510 cm⁻¹. -1 up to 530cm -1 The peak area within the wavenumber range, D peak refers to the peak area at 1300 cm⁻¹. -1 up to 1420cm -1 The peak area within the wavenumber range.

[0017] The term "standard deviation S1" can be expressed as: Where n represents the Raman test data points, Xi represents the ID / IG value of a certain point in the silicon-based material imaging, and X represents the average value of the total ID / IG values ​​in the imaging area. The standard deviation S1 reflects the uniformity of the carbon layer in the silicon-based material (i.e., the uniformity of the coating).

[0018] The term "standard deviation S2" can be expressed as: Where n represents the Raman test data point, Yi represents the ISi / ID value of a point in the image, and Y represents the average ISi / ID value of the imaging region. The standard deviation S2 reflects the standard deviation of silicon exposure in the silicon-based material (i.e., the standard deviation of coating integrity).

[0019] I. Silicon-based materials

[0020] The silicon-based material provided in this application includes SiOx, where x is 0.5 to 1.6; and a carbon layer coated on the surface of SiOx, wherein the silicon-based material satisfies: 0.2 ≤ S1 ≤ 1.5, and / or 0.02 ≤ ISi / ID ≤ 0.5; wherein S1 refers to the standard deviation of the ID / IG value of the carbon layer; the ID / IG value refers to the area ratio of the D peak to the G peak; and the ISi / ID refers to the area ratio of the Si peak to the D peak. A smaller S1 indicates a more uniform surface coating, which is more conducive to uniform film formation during the lithiation process and better storage performance; a smaller ISi / ID indicates lower silicon exposure, reducing direct contact with the electrolyte and thus reducing side reactions, thereby improving electrochemical storage performance.

[0021] In some implementations, S1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or any value between them; in some implementations, 0.55 ≤ S1 ≤ 1.4.

[0022] In some embodiments, ISi / ID is 0.02, 0.03, 0.04, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any value between them; in some embodiments, 0.05 ≤ ISi / ID ≤ 0.4. ISi / ID accurately represents the integrity of carbon coating in silicon-based materials. The smaller the ISi / ID, the lower the degree of silicon exposure and the more complete the surface carbon coating, and vice versa.

[0023] In some embodiments, 1 ≤ ID / IG ≤ 3.66; in some embodiments, ID / IG is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 3.66, or any value between them; in some embodiments, 2 ≤ ID / IG ≤ 3.66. The ID / IG value is directly proportional to the disorder of the carbon material structure. It can accurately express the disorder of the carbon layer structure in silicon-based materials. The smaller the ID / IG value, the more the structure tends to be like ideal graphite; the larger the ID / IG value, the higher the structural disorder and the more defects.

[0024] In some embodiments, 0.01 ≤ S2 ≤ 0.6; in some embodiments, S2 is 0.01, 0.03, 0.06, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or any value between them; in some embodiments, 0.03 ≤ S2 ≤ 0.45; when S2 is small, the silicon exposure is more uniformly distributed and closer to the average value ISi / ID; when S2 is large, the silicon exposure is more discrete and farther from the average value ISi / ID.

[0025] In some embodiments, the carbon layer comprises a mass percentage C of 2% ≤ C ≤ 5% of the silicon-based material. If the mass percentage of the carbon layer is too low, it is difficult to achieve coating; if the mass percentage of the carbon layer is too high, defective carbon will undergo further side reactions, which is also undesirable.

[0026] In some embodiments, the SiOx comprises a pre-lithium silicon oxide compound (Li-SiOx).

[0027] According to an embodiment of this application, the preparation of the silicon-based material includes the following steps: (1) heating silicon oxide (SiO₂x) to approximately 200°C to 1500°C in an inert gas atmosphere; (2) injecting a carbon source gas and heating the gas at approximately 200°C to 1500°C for approximately 30 to 120 minutes to obtain a solid; (3) pulverizing and sieving the solid, wherein x is 0.5 to 1.5. Of course, the preparation method of this silicon-based material is not limited to this, but can also be carried out using other methods well known in the art.

[0028] In some embodiments, the positive electrode active material layer includes a positive electrode active material, which includes at least one of nickel-cobalt ternary materials and phosphate-based materials.

[0029] In some embodiments, the nickel-cobalt ternary material includes LiNi. m Co n At least one of the following materials: A(1-mn)O2, wherein A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver and niobium, and 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

[0030] In some implementations, m is a range of 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or any combination of these values. In some implementations, n is a range of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or any combination of these values.

[0031] In some embodiments, the nickel-cobalt ternary material includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, and Ni95.

[0032] In some embodiments, the phosphate-based material includes LiMn k B (1-k)At least one of PO4, wherein 0 ≤ k ≤ 1, and element B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead. In some embodiments, k is a range of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or any combination of these values. In some embodiments, the phosphate-based material includes lithium iron phosphate, LiMn... 0.6 Fe 0.4 PO4 and LiMn 0.8 Fe 0.2 At least one of PO4.

[0033] In some embodiments, the positive electrode active material includes at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

[0034] In some embodiments, the positive electrode active material layer further includes a binder and optionally a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0035] In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0036] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0037] In some embodiments, the positive electrode further includes a positive current collector, which may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0038] In some embodiments, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from carbon-based materials, tin-based materials, phosphorus-based materials and metallic lithium.

[0039] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0040] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0041] In some embodiments, the negative electrode further includes a negative electrode current collector, which includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0042] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. In some embodiments, the separator may be selected from polyethylene film, polypropylene film, polyvinylidene fluoride film, and their multilayer composite films.

[0043] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer includes at least one selected from polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0044] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0045] The inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0046] The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0047] When the secondary battery is a lithium-ion secondary battery, a lithium salt solution dissolved in an organic solvent is usually used as the non-aqueous electrolyte. The lithium salt can be an inorganic lithium salt (e.g., LiClO4, LiPF6, LiBF4, LiAsF6, LiSbF6) or an organic lithium salt (e.g., LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiN(CF3SO2)2, LiC(CF3SO2)3, LiCnF2n+1SO3 (n≥2)). Organic solvents used in non-aqueous electrolytes include cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, butene carbonate, or vinylene carbonate), chain carbonates (e.g., dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate), (chain esters, such as methyl propionate), cyclic esters (e.g., γ-butyrolactone), dimethoxyethane, chain ethers (e.g., diethyl ether, diethylene glycol dimethyl ether, or triethylene glycol dimethyl ether), cyclic ethers (e.g., tetrahydrofuran or 2-methyltetrahydrofuran), acetonitrile, propionitrile, or combinations thereof.

[0048] A lithium-ion rechargeable battery consists of a negative electrode, a positive electrode, a separator, and an electrolyte. The positive and negative electrodes are immersed in the electrolyte, and lithium ions move between them via the electrolyte, enabling the battery to charge and discharge. To prevent short circuits between the positive and negative electrodes through the electrolyte, a separator is used to separate them. Lithium-ion rechargeable batteries can be cylindrical (square or cylindrical) with an aluminum or steel casing, or they can be pouch batteries with an aluminum-plastic film casing.

[0049] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0050] In some embodiments, the secondary battery may include an outer packaging, which may be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch. The soft pack may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0051] In some embodiments, the shape of the secondary battery is not particularly limited; it can be cylindrical, square, or any other arbitrary shape.

[0052] In some embodiments, this application also provides a battery module. This battery module includes the aforementioned secondary battery. The battery module of this application uses the aforementioned secondary battery, and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of this application can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0053] In some embodiments, this application also provides a battery pack that includes the aforementioned battery modules. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0054] II. Apparatus

[0055] This application also provides an apparatus comprising at least one of the above-described secondary battery, battery module, and battery pack.

[0056] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. To meet the device's requirements for high power and high energy density in secondary batteries, battery packs or battery modules may be used.

[0057] In other embodiments, the device can be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a rechargeable battery as its power source.

[0058] Examples and Comparative Examples

[0059] To make the objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. However, it should be understood that the embodiments of this application are merely for illustrative purposes and not for limiting the application, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0060] The artificial graphite and silicon-based materials used in the following examples and comparative examples are all commercially available.

[0061] Example 1

[0062] Preparation of the positive electrode sheet:

[0063] LiNi, the positive electrode active material 0.9 Co 0.03 Mn 0.07 O2, conductive agent Super P / multi-walled carbon nanotubes and binder PVDF are dispersed in an appropriate amount of NMP at a mass ratio of 97.5:0.9 / 0.5:1.1 to form a uniform positive electrode slurry; the positive electrode slurry is coated on aluminum foil, and after drying, rolling and other processes, a positive electrode sheet is obtained.

[0064] Preparation of negative electrode sheet:

[0065] Artificial graphite and the silicon-based material of this application are premixed at a certain mass ratio to obtain a composite negative electrode active material. The composite negative electrode active material, conductive agent carbon black / carbon nanotubes, thickener CMC, binder SBR and PAA are homogenized at a mass ratio of 96:0.9 / 0.1:0.6:1.2:1.2 to obtain a uniformly dispersed slurry. The above slurry is coated on a 6μm or 8μm copper foil, dried at 100℃, and then rolled to obtain a negative electrode sheet.

[0066] Electrolyte preparation:

[0067] LiPF6 was dissolved in a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1), and 10 wt% fluoroethylene carbonate was added as a film-forming additive to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0068] Separator: Polyethylene separator.

[0069] Outer packaging: aluminum-plastic film.

[0070] Preparation of lithium-ion batteries

[0071] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The resulting battery cell is then wound to obtain a bare cell. This bare cell is placed in an outer packaging shell, and the prepared electrolyte is injected into the dried cell. After vacuum sealing, settling, formation, and shaping processes, a lithium-ion secondary battery is obtained.

[0072] Examples 2-8 and Comparative Example 1 were achieved by adjusting the ID / IG value and ISi / ID of the silicon-based material based on Example 1. The specific adjustment measures and detailed data are shown in Table 1.

[0073] Test methods

[0074] 1. Determination of ID / IG value

[0075] Raman spectroscopy was used to perform a precise scan of 2000 points within a 100μm × 100μm area, and the silicon-based material was measured at 1300 cm⁻¹ at each point. -1 ~1420cm -1 Peak area ID in the wavenumber range and at 1540 cm⁻¹ -1 ~1620cm -1 The ratio of peak area IG over the wavenumber range is ID / IG.

[0076] 2. Determination of ISi / ID value

[0077] Raman spectroscopy was used to perform a precise scan of 2000 points within a 100μm × 100μm area, and the silicon-based material was measured at 510 cm⁻¹ at each point. -1 ~530cm -1 Peak area ISi in the wavenumber range and at 1300 cm⁻¹ -1 ~1420cm -1 The ratio of peak area ID within the wavenumber range is ISi / ID.

[0078] 3. Determination of carbon layer content

[0079] The sample (silicon-based material) was burned in an oxygen stream, during which carbon was converted into carbon monoxide and / or carbon dioxide. The carbon monoxide was then catalytically oxidized to carbon dioxide at high temperature. The percentage of carbon in the sample was calculated by detecting the infrared absorption spectrum (characteristic absorption peak at 4260 nm) of carbon dioxide in the oxygen stream and applying the Lambert-Beer law.

[0080] 4. Determination of high-temperature storage performance (60℃, 7 days)

[0081] At room temperature (25℃), fresh soft-pack battery cells (lithium-ion batteries) were charged at a constant current of 0.5C, with a cutoff voltage of 4.2V. Then, they were discharged at a constant current of 0.5C, with a cutoff voltage of 2.5V. The capacity of the first discharge was recorded as the calculation baseline. Next, the cells were fully charged at a constant current of 0.5C, with a cutoff voltage of 4.2V. The fully charged batteries were then stored in a 60℃ constant temperature chamber for 7 days without being opened. After 7 days, the batteries were removed and left at room temperature (25℃) for 6-8 hours until the temperature returned to 25℃. A discharge test was then performed at a constant current of 0.5C, with a cutoff voltage of 2.3V. The discharge capacity of this test was recorded as the discharge capacity after 7 days of storage at 60℃. The formula for calculating the 7-day calendar life capacity retention rate at 60℃ is as follows:

[0082] The test results are shown in Table 1.

[0083] Table 1

[0084] As shown in Table 1, with ID / IG < 4, a lower S1 indicates a more uniform carbon coating on the silicon-based material, which is more beneficial for high-temperature storage. With S2 < 1, a lower ISi / ID indicates a more complete carbon coating on the silicon-based material, which is also more beneficial for high-temperature storage. Therefore, the silicon-based material of this application has the lowest carbon mass and the most uniform and complete coating layer, effectively improving the high-temperature storage performance (calendar life) of the secondary battery.

[0085] While some exemplary embodiments of this application have been described and illustrated, this application is not limited to the disclosed embodiments. Rather, those skilled in the art will recognize that modifications and changes can be made to the described embodiments without departing from the spirit and scope of this application as described in the appended claims.

Claims

1. A silicon-based material, characterized in that, comprises SiOx and a carbon layer coated on the surface of SiOx, wherein the silicon-based material satisfies: 0.2≤S1≤1.5, S1 refers to a standard variance value of ID / IG value of the carbon layer, wherein, x is 0.5 to 1.6; the ID / IG value refers to an area ratio of D peak and G peak.

2. The silicon-based material of claim 1, wherein, 0.55≤S1≤1.4。 3. The silicon-based material of claim 1 or 2, wherein, 1≤ID / IG≤3.

66.

4. The silicon-based material according to any one of claims 1 to 3, wherein, 2≤ID / IG≤3.

66.

5. The silicon-based material according to any one of claims 1 to 4, wherein, 0.02≤ISi / ID≤0.5, wherein the ISi / ID refers to an area ratio of Si peak and D peak.

6. The silicon-based material according to any one of claims 1 to 5, wherein, 0.05≤ISi / ID≤0.

4.

7. The silicon-based material according to any one of claims 1 to 6, wherein 0.01≤S2≤0.6, wherein S2 refers to a standard variance value of the ISi / ID.

8. The silicon-based material according to any one of claims 1 to 7, wherein, 0.03≤S2≤0.45。 9. The silicon-based material according to any one of claims 1 to 8, wherein, a mass percentage content C of the carbon layer in the silicon-based material satisfies 2%≤C≤5%.

10. The silicon-based material of any one of claims 1-8, wherein, the SiOx comprises a pre-lithium silicon oxide compound.

11. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector, the negative electrode active material layer comprising the silicon-based material according to any one of claims 1-10.

12. A secondary battery comprising the negative electrode sheet of claim 11 and a positive electrode sheet.

13. An apparatus comprising the secondary battery of claim 12.

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