Secondary battery and electronic device comprising same

Abstract

Provided is a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte solution, wherein the negative electrode sheet comprises a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer, the negative electrode active material layer comprising a silicon-oxygen compound coated with a carbon layer; and the electrolyte solution comprises a fluorine-containing compound and a nitrogen-containing compound. In magic angle spin solid state nuclear magnetic lithium spectrum 7Li MAS ssNMR analysis of the solid electrolyte interface film, the lithium element peak area of LiF at the position of -1.4±0.2 ppm is SLiF, and the lithium element peak area of Li3N at the position of 8.1 ppm is SLi3N. The silicon-oxygen compound coated with a carbon layer has a graphitization degree G, where 1＜G×SLiF / SLi3N＜5.

Description

Secondary battery and electronic device including the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 20, 2023, with application number 202311766980.1 and application name “Secondary battery and electronic device including the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage technology, and in particular to a secondary battery and an electronic device including the same. Background Art

[0003] Secondary batteries, such as lithium-ion batteries, have taken over the fields of mobile phones, laptops, and even become a key component of various electric vehicles due to their many advantages. However, due to the theoretical specific capacity of the positive and negative electrode materials, the energy density of existing commercial lithium-ion batteries is difficult to exceed 300Wh kg -1 , which limits its application in pure electric vehicles, aerospace, 5G and other fields. Therefore, technicians are committed to developing batteries with high capacity and high energy ratio to meet the needs of future society.

[0004] The theoretical specific capacity of silicon material is as high as 4200mAh g -1 (Li 4.4 Si), which is more than 10 times that of graphite, and silicon has a moderate electrode potential (~0.3V vs Li / Li + ) and extremely rich crustal reserves, it is considered to be one of the most promising negative electrode materials. However, during the battery cycle, the silicon material itself will undergo significant volume changes, which will accelerate the mechanical fracture and loss of electrical contact of the silicon electrode and form "dead silicon", which will eventually lead to the continuous consumption of electrolyte, the decrease of negative electrode capacity and the deterioration of battery performance. In addition, the negative electrode interface passivation film SEI formed on the surface of the silicon material by the electrolyte commonly used in industry is loose and porous, and cannot prevent the continuous decomposition of the electrolyte. These will lead to problems such as low coulombic efficiency of the battery, rapid capacity decay and short cycle life.

[0005] Therefore, there is a need in the art for a high capacity secondary battery with improved electrochemical and kinetic properties.

[0006] Application Contents

[0007] In a first aspect of the present application, the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material layer and a solid electrolyte interface membrane located on the surface of the negative electrode active material layer, the negative electrode active material layer comprises a silicon oxide compound coated with a carbon layer, the electrolyte comprises a fluorine-containing compound and a nitrogen-containing compound, wherein the solid electrolyte interface membrane is subjected to magic angle spinning solid-state nuclear magnetic lithium spectroscopy. 7 The peak area of ​​lithium in LiF at -1.4±0.2ppm in Li MAS ssNMR analysis is S LiF , and the lithium element peak area in Li3N at 8.1ppm is S Li3N , wherein the carbon layer-coated silicon oxide compound has a graphitization degree G, and wherein, 1 <G×S LiF / S Li3N <5.

[0008] According to one embodiment of the present application, the fluorine-containing compound and the nitrogen-containing compound in the electrolyte are the same compound, which contains both fluorine and nitrogen.

[0009] In some embodiments, in addition to the compound containing both fluorine and nitrogen, the electrolyte further comprises other fluorine-containing compounds or nitrogen-containing compounds.

[0010] According to one embodiment of the present application, the fluorine-containing compound and the nitrogen-containing compound in the electrolyte are different compounds, that is, the electrolyte contains both nitrogen-containing and fluorine-free compounds and fluorine-containing and nitrogen-free compounds.

[0011] By adding fluorine-containing compounds and nitrogen-containing compounds to the electrolyte, a solid electrolyte interface film SEI containing LiF and Li3N can be formed on the surface of the negative electrode active material layer during the battery cycle. Among them, LiF can effectively alleviate the breakage of particles, especially silicon material particles, thereby inhibiting the contact between the electrolyte and the negative electrode material and continuously causing side reactions, which will bring about negative effects such as low coulombic efficiency and rapid consumption of the electrolyte. Li3N itself is an excellent conductor of lithium ions and electrons, which helps to improve the problems of reduced capacity and decreased battery dynamics caused by the lack of electrical contact between silicon particles during the cycle. Surprisingly, when 1 <G×S LiF / S Li3N <5, especially 1.8≤G×S LiF / S Li3NWhen ≤4.3, the graphitization degree of the carbon-coated silicon oxide compound and the solid electrolyte interface film SEI on the surface of the negative electrode active material layer achieve excellent matching. Therefore, the secondary battery according to the present invention can not only effectively alleviate the adverse effects of low coulombic efficiency and continuous consumption of electrolyte caused by volume expansion of the silicon-containing negative electrode, but also improve the loss of electrical contact of the silicon oxide compound particles during the cycle, thereby extending the cycle life of the battery and improving the battery's dynamic performance. In some preferred embodiments, 2.9≤G×S LiF / S Li3N ≤4.1.

[0012] The degree of graphitization is a measure of the degree to which the crystal structure of a carbon material approaches perfect graphite after rearrangement from an amorphous carbon structure, that is, the degree of order. The closer the carbon material is to ideal graphite, the fewer lattice defects, the smaller the electron migration resistance, the better the battery kinetics, and the more thoroughly the electrolyte is reduced on the surface of the material. For example, when LiFSI is included in the electrolyte, as the degree of graphitization of the negative electrode active material increases, the Li3N generated by LiFSI on the surface of the negative electrode active material will increase and affect S LiF / S Li3N ratio.

[0013] When the graphitization is too high, the reactivity of the electrode material with the electrolyte is too high, and the material will be very brittle and easily cracked during rolling. These will increase the side reactions of the electrolyte and shorten the battery life. In addition, when the graphitization is too low, the kinetics of the electrode material are poor and the capacity cannot be properly exerted, resulting in low battery capacity. Therefore, in some embodiments, 60≤G≤95 is set, thereby obtaining a negative electrode active material that can match the electrolyte of the present application. In some preferred embodiments, 75%≤G≤90%.

[0014] In some embodiments, since LiF is a poor conductor of lithium ions and electrons, when the content of LiF in the SEI film is too high, it will make it difficult to fully utilize the capacity of the electrode and deteriorate the dynamic performance of the battery. When the content of Li3N in the SEI film is too high, the active sites on the electrode surface will increase, which will lead to a decrease in the first coulombic efficiency of the battery and cause serious high-temperature cycle gas generation, thereby reducing the energy density and cycle life of the battery. Therefore, set 1≤S LiF / S Li3N ≤6, especially 2≤S LiF / S Li3N ≤5.

[0015] In some embodiments, the electrolyte comprises a compound of formula I,

[0016] X is Li, Na, K, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C1-C4 alkoxy group, or a substituted or unsubstituted C1-C4 alkenyl group; and R is F or a C1-C4 alkyl group substituted with F.

[0017] The compound of formula I contains N and F. With the help of the compound of formula I, the secondary battery according to the present application can form a solid electrolyte interface film SEI containing LiF and Li3N on the surface of the negative electrode active material layer during cycling, and optimize the electrochemical performance of the battery by adjusting the ratio of LiF and Li3N therein.

[0018] In some embodiments, the compound of formula I comprises at least one of LiFSI, LiFTFSI, NAFSI, and MeFSI,

[0019] In some embodiments, the content of the compound of formula I is 1 wt % to 10 wt % based on the total weight of the electrolyte.

[0020] In some embodiments, the negative electrode active material layer further includes graphite, and the graphite includes at least one of artificial graphite and natural graphite.

[0021] In some embodiments, the silicon oxide compound coated by the carbon layer has an amount of 5 wt % to 35 wt % based on the total weight of the negative electrode active material layer.

[0022] In some embodiments, the carbon layer of the carbon-layer-coated silicon oxide compound contains 5 wt % to 30 wt % based on the total weight of the carbon-layer-coated silicon oxide compound.

[0023] In some embodiments, the graphite is artificial graphite or natural graphite.

[0024] In some embodiments, the electrolyte further comprises fluoroethylene carbonate.

[0025] In some embodiments, the electrolyte further comprises methylene methanedisulfonate.

[0026] In some embodiments, the electrolyte further comprises fluoroethylene carbonate and methylene methanedisulfonate, wherein, based on the total weight of the electrolyte, the content of the compound of formula I is 2 wt % to 8 wt %, the content of the fluoroethylene carbonate is 1 wt % to 5 wt %, and the content of the methylene methanedisulfonate is 0.1 wt % to 2 wt %.

[0027] When the LiF content in the solid electrolyte interface (SEI) is too low, LiF cannot effectively mitigate the fragmentation of silicon oxide material particles and inhibit the continuous reaction between the electrolyte and the negative electrode active material. When the LiF content is too high, since LiF is a poor conductor of lithium ions and electrons, the high content of LiF in the SEI film makes it difficult to fully utilize the electrode capacity and degrades the battery's kinetic performance. In addition, when the Li3N content in the SEI film is too low, it will be difficult to ensure the efficient migration of lithium ions in the SEI. When the Li3N content in the SEI film is too high, the active sites on the electrode surface increase, resulting in a decrease in the battery's initial coulombic efficiency and severe high-temperature cycling gassing, thereby reducing the battery's energy density and cycle life.

[0028] In this regard, in some preferred embodiments according to the present invention, by using fluoroethylene carbonate (FEC) and methylene methanedisulfonate (MMDS) in the electrolyte at the content defined by the present invention, the content of LiF and Li3N can be effectively adjusted and the reaction between the electrolyte and the negative electrode active material and the migration efficiency of lithium ions can be further balanced. In some embodiments, fluoroethylene carbonate can be used to maintain the content of LiF in SEI. In some embodiments, since methyl methanedisulfonate has a higher priority for reduction and decomposition on the negative electrode surface than FEC, LiFSI, EC, etc., when methyl methanedisulfonate preferentially decomposes to form an SEI film, the decomposition of other components of the electrolyte can be reduced, thereby reducing the thickness of SEI and obtaining the desired kinetic performance.

[0029] In some embodiments, the secondary battery is a lithium ion secondary battery, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes a LiNi m Co n A (1-m-n) The lithium nickel transition metal oxide shown in O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0030] In a second aspect of the present application, the present application provides an electronic device, which includes the secondary battery according to the second aspect of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the scope of protection claimed in the present application. Unless otherwise clearly indicated, the following terms used herein have the meanings indicated below.

[0032] As used herein, the term "about" is used to describe and illustrate small variations. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely as well as an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such range formats are for convenience and brevity and should be flexibly understood to include not only the numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0033] In the detailed description and claims, a list of items linked by the term "one of" can mean any of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, the phrase "one of A, B, and C" means only A; only B; or only C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0034] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" or "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" or "at least one of A, B, or 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 element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0035] In the detailed description and claims, the number following the capital letter "C" is used in the description of the carbon number, such as "C1-C 10 ”, “C3-C 10 ”, etc., the number after “C”, such as “1”, “3” or “10”, represents the number of carbon atoms in the specific functional group. That is, the functional group may include 1-10 carbon atoms and 3-10 carbon atoms, respectively. For example, “C1-C4 alkyl” or “C1-4 "Alkyl" refers to an alkyl group having 1 to 4 carbon atoms, for example, CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, CH3CH2CH(CH3)- or (CH3)3C-.

[0036] As used herein, the term "alkyl" refers to a straight chain saturated hydrocarbon structure having 1 to 10 carbon atoms. "Alkyl" also contemplates branched or cyclic hydrocarbon structures having 3 to 10 carbon atoms. For example, an alkyl group may be an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 8 carbon atoms, an alkyl group having 1 to 6 carbon atoms, or an alkyl group having 1 to 4 carbon atoms. When an alkyl group having a specific carbon number is specified, all geometric isomers having that carbon number are contemplated; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; and "propyl" includes n-propyl, isopropyl, and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc. Additionally, the alkyl group may be optionally substituted.

[0037] The term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight or branched and has at least one and typically 1, 2 or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 10 carbon atoms, for example, 2 to 8 carbon atoms, 2 to 6 carbon atoms, or 2 to 4 carbon atoms. Representative alkenyl groups include, for example, vinyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, etc. In addition, the alkenyl group can be optionally substituted.

[0038] Primary and secondary batteries

[0039] The secondary battery of the present application is, for example, a lithium secondary battery or a sodium secondary battery. The secondary battery of the present application can especially include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, a sodium ion secondary battery, a sodium polymer secondary battery or a sodium ion polymer secondary battery.

[0040] In some embodiments, the secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0041] electrolyte

[0042] The electrolyte according to the present application includes a fluorine-containing compound and a nitrogen-containing compound.

[0043] In some embodiments, the fluorine-containing compound and the nitrogen-containing compound are the same compound.

[0044] In some embodiments, the electrolyte comprises a compound of formula I,

[0045] X is Li, Na, K, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C1-C4 alkoxy group, or a substituted or unsubstituted C1-C4 alkenyl group; and R is F or a C1-C4 alkyl group substituted with F.

[0046] In some embodiments, based on the total weight of the electrolyte, the content of the compound of formula I is 1 wt % to 10 wt %, for example, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt % or any interval thereof.

[0047] Positive electrode

[0048] In some embodiments, the positive electrode sheet includes a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0049] The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments of the present application, the positive electrode active material includes a lithium-containing transition metal oxide. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0050] The positive electrode active material layer also 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.

[0051] In some embodiments, the current collector may be aluminum, but is not limited thereto.

[0052] The positive electrode can be prepared by methods known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone.

[0053] In some embodiments, the positive electrode active material includes at least one selected from lithium nickel transition metal oxides. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: LiNi m Co n A (1-m-n)O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0054] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM523, NCM622, NCM811, Ni90 (ie, NCM90), Ni92 (ie, NCM92), or Ni95 (ie, NCM900).

[0055] In some embodiments, the chemical formula of the lithium nickel transition metal oxide is LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.7≤m≤1, 0≤n≤0.3, m+n≤1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, 0.7≤m≤1, 0≤n≤0.3, and m+n≤1.

[0056] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM811, Ni90, Ni92, or Ni95.

[0057] Negative electrode

[0058] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0059] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector, such as 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.

[0060] In some embodiments, the negative electrode active material comprises a material that reversibly intercalates / deintercalates lithium ions. In some embodiments, the material that reversibly intercalates / deintercalates lithium ions comprises a carbon material. In some embodiments, the carbon material can be any carbon-based negative electrode active material commonly used in lithium-ion rechargeable batteries.

[0061] In some embodiments, the negative electrode active material includes a carbon layer-coated silicon oxide and graphite.

[0062] In some embodiments, based on the total weight of the negative electrode active material layer, the content of the silicon oxide compound coated by the carbon layer is 5 weight % to 35 weight %, for example, 5 weight %, 8 weight %, 10 weight %, 12 weight %, 15 weight %, 18 weight %, 20 weight %, 22 weight %, 25 weight %, 28 weight %, 30 weight %, 32 weight %, 35 weight % or any range thereof.

[0063] In some embodiments, based on the total weight of the carbon-layer-coated silicon oxide compound, the content of the carbon layer in the carbon-layer-coated silicon oxide compound is 5 wt % to 30 wt %, for example, 5 wt %, 8 wt %, 10 wt %, 12 wt %, 15 wt %, 18 wt %, 20 wt %, 22 wt %, 25 wt %, 28 wt %, 30 wt % or any range thereof.

[0064] In some embodiments, the graphite is artificial graphite or natural graphite.

[0065] In some embodiments, the carbon material includes, but is not limited to, crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon can be amorphous, flaky, platelet-shaped, spherical, or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or the like. The specific type of negative electrode active material is not particularly limited and can be selected according to needs.

[0066] In some embodiments, the negative electrode active material layer further includes a binder, which includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0067] In some embodiments, the negative electrode active material layer further includes a conductive agent, which 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.

[0068] diaphragm

[0069] In some embodiments, the electrochemical device of the present application includes a separator between the positive electrode and the negative electrode to prevent short circuits. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited and may be any known prior art technology. In some embodiments, the separator comprises a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.

[0070] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.

[0071] In some embodiments, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. In some embodiments, the separator comprises a porous substrate and a coating layer, wherein the coating layer comprises inorganic particles and a binder. In some embodiments, the coating layer has a thickness of about 0.5 microns to about 10 microns, about 1 micron to about 8 microns, or about 3 microns to about 5 microns.

[0072] 2. Electronic Devices

[0073] The electronic device of the present application may be any device using the electrochemical device of the present application.

[0074] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0075] In some embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0076] In order to achieve the above-mentioned purpose and enable technical personnel in this technical field to understand the application scheme, the following examples are given of the specific implementation plans adopted in this application. It should be stated that the described embodiments are only part of the embodiments of this application, not all of the embodiments.

[0077] 3. Test Method

[0078] 1. Graphitization degree G test of carbon layer coated silicon oxide compound

[0079] The graphite (002) interlayer spacing d002 is determined by XRD testing and then substituted into the Mering–Maire formula (also known as the Franklin formula) to calculate:

[0080] G=(0.3440–d002) / (0.3440–0.3354)×100%

[0081] Where: G is the degree of graphitization (%); 0.3440 is the interlayer spacing of non-graphitized carbon (nm); 0.3354 is the interlayer spacing of ideal graphite crystal (nm), which is also 1 / 2 of the c-axis lattice constant of hexagonal graphite; d002 is the carbon material

[0082] The interlayer spacing of the crystal plane (nm).

[0083] 2.S LiF / S Li3N Ratio test

[0084] After the battery is divided into capacities, it is charged to 3.8V at 0.01C, and then discharged to 2.5V at 0.1C. The battery can be disassembled in an argon-filled glove box, 500mg of the active material layer is scraped and soaked in a low-boiling-point dimethyl carbonate DMC solvent for half an hour. After it is completely dried, it is fully ground with a mortar and pestle, and finally filled into a nuclear magnetic resonance tube and sealed for storage. The measurement is performed without exposure to the atmosphere. Select a 700M nuclear magnetic resonance instrument and select 7 The Li spectrum was collected 24 times, and two peaks at -1.4ppm and 8.1ppm were selected. The peak areas were integrated to obtain the ratio of the two peak areas, i.e., S LiF / S Li3N .

[0085] 3. First Coulombic efficiency test

[0086] At 25°C, charge the prepared lithium-ion secondary battery at a constant current rate of 1C to 4.25V. Then, charge it at a constant voltage until the current is less than 0.05C. Record the initial charge capacity. After 5 minutes of rest, discharge it at a rate of 1C to 2.5V. Record the initial discharge capacity. The initial coulombic efficiency performance test of the lithium-ion secondary battery = initial discharge capacity / initial charge capacity × 100%.

[0087] 4. Cycle capacity retention test

[0088] 25°C 1C / 1C 1000 Cycles: At 25°C, the above-mentioned lithium-ion batteries were charged at 1C constant current and constant voltage to 4.25V, and then discharged at 1C constant current to 2.5V. After 1000 charge and discharge cycles, the capacity retention after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after 500th cycle / discharge capacity after first cycle × 100%.

[0089] 25°C 2C / 2C 500 Cycles: At 25°C, the above-mentioned lithium-ion batteries were charged at 2C constant current and constant voltage to 4.25V, and then discharged at 2C constant current to 2.5V. After 500 charge and discharge cycles, the capacity retention after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after 500th cycle / discharge capacity after first cycle × 100%.

[0090] 45°C 1C / 1C 500 Cycles: At 25°C, the above-mentioned lithium-ion battery was charged at 1C constant current and constant voltage to 4.25V, and then discharged at 1C constant current to 2.5V. After 500 charge and discharge cycles, the capacity retention after the 500th cycle at 25°C was calculated according to the following formula: discharge capacity after the 300th cycle / discharge capacity at the first cycle × 100%.

[0091] Example 1

[0092] Preparation of the negative electrode: The negative electrode active material (a composite of a carbon layer-coated silicon oxide compound and artificial graphite, wherein the weight ratio of artificial graphite to the carbon layer-coated silicon oxide compound is 86:14, and the weight content of the carbon layer in the carbon layer-coated silicon oxide compound is 10%), the conductive agent acetylene black, the binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose CMCNa, and the polyacrylic acid PAA are mixed in a weight ratio of 95:2:1.5:1:0.5, and deionized water is added and stirred to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on an 8μm negative electrode current collector copper foil; the coated copper foil is dried at 85°C, and then cold pressed, cut, and slit, and then dried under vacuum conditions at 120°C for 12 hours to obtain the negative electrode.

[0093] Preparation of positive electrode: LiNi 0.9 Co 0.05 Mn 0.05O2, conductive material carbon nanotubes, acetylene black, and adhesive polyvinylidene fluoride are mixed in a mass ratio of 95:2:1:2, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on a 12μm positive electrode current collector aluminum foil; the coated aluminum foil is dried at 85°C, and then cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode.

[0094] Preparation of electrolyte: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium salt LiPF6 and solvent EC / DEC / EMC = 25 / 20 / 55 were mixed in a certain proportion to prepare a 1 M solution. Finally, the compound of formula I and additives in Table 1 were added and stirred to obtain the electrolyte.

[0095] Preparation of diaphragm: PP / PE / PP three-layer composite diaphragm.

[0096] Assembly of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator being between the positive and negative electrode sheets. Then, after winding and welding the tabs, they are placed in an outer packaging foil aluminum-plastic film and injected with the above-mentioned electrolyte. The injection coefficient (injection coefficient=quality of electrolyte / capacity of battery design) is selected according to Table 1. After being left at 45°C for 48h, high-temperature fixture formation is carried out (formation conditions: pressure 210kgf, 0.05C current is charged to 4.2V, and then 0.1C is charged to 4.2V and then 0.2C is discharged to 3.0V, repeated twice, and the formation temperature is provided in Table 1). Then, after secondary sealing, conventional capacity separation is carried out.

[0097] Examples 2-17 and Comparative Examples 1-11

[0098] Examples 2-17 and Comparative Examples 1-11 were carried out with reference to Example 1, wherein the electrolyte components and formation temperatures used in Examples 2-17 and Comparative Examples 1-11 are shown in Table 1.

[0099] Table 1

[0100] The Chinese names of the abbreviations in Table 1 are as follows:

[0101] LiFTFSI: lithium fluorosulfonyl (trifluoromethanesulfonyl) imide;

[0102] LiFSI: lithium bis(fluorosulfonyl)imide;

[0103] MeFSI: methylbis(fluorosulfonyl)imide;

[0104] MMDS: methylene methanedisulfonate;

[0105] PS: 1,3-propane sultone;

[0106] PES: 1,3-propene sultone;

[0107] LiPO2F2: lithium difluorophosphate;

[0108] D2: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0109] FEC: Fluoroethylene carbonate.

[0110] The lithium ion batteries obtained from Examples 1-17 and Comparative Examples 1-11 were subjected to graphitization degree G test, S test, and LiF / S Li3N The test results of the battery performance test are shown in Table 2.

[0111] Table 2

[0112] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application, and that these changes, substitutions and modifications also fall within the scope of protection of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer, the negative electrode active material layer comprises a silicon oxide compound coated with a carbon layer, and the electrolyte comprises a fluorine-containing compound and a nitrogen-containing compound. The solid electrolyte interface film is subjected to magic angle spinning solid-state nuclear magnetic spectroscopy. 7 The peak area of ​​lithium in LiF at -1.4±0.2ppm in Li MAS ssNMR analysis is S LiF , and the peak area of ​​lithium in Li3N at 8.1ppm is S Li3N , Wherein, the silicon oxide compound coated with the carbon layer has a graphitization degree G, And among them, 1 <G×S LiF / S Li3N <5.

2. The secondary battery according to claim 1, characterized in that: 60%≤G≤95%, preferably 75%≤G≤90%.

3. The secondary battery according to claim 1 or 2, characterized in that: 1≤S LiF / S Li3N ≤6, preferably 2≤S LiF / S Li3N ≤5.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: 1.8≤G×S LiF / S Li3N ≤4.3, preferably 2.9≤G×S LiF / S Li3N ≤4.

1.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The electrolyte comprises a compound of formula I, X is selected from Li, Na, K, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C1-C4 alkoxy and substituted or unsubstituted C1-C4 alkenyl, and R is F or C1-C4 alkyl substituted with F.

6. The secondary battery according to claim 5, characterized in that: The compound of formula I includes at least one of LiFSI, LiFTFSI, NAFSI and MeFSI, 7. The secondary battery according to claim 5 or 6, characterized in that: Based on the total weight of the electrolyte, the content of the compound of formula I is 1 wt % to 10 wt %.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: At least one of the following conditions is met: (i) the negative electrode active material layer further comprises graphite, wherein the graphite comprises at least one of artificial graphite and natural graphite, (ii) based on the total weight of the negative electrode active material layer, the content of the silicon oxide compound coated by the carbon layer is 5 wt % to 35 wt %, wherein based on the total weight of the silicon oxide compound coated by the carbon layer, the content of the carbon layer of the silicon oxide compound coated by the carbon layer is 5 wt % to 30 wt %.

9. The secondary battery according to any one of claims 5 to 7, characterized in that: The electrolyte further comprises fluoroethylene carbonate and methylene methanedisulfonate, wherein, based on the total weight of the electrolyte, the content of the compound of formula I is 2 wt % to 8 wt %, the content of the fluoroethylene carbonate is 1 wt % to 5 wt %, and the content of the methylene methanedisulfonate is 0.1 wt % to 2 wt %.

10. The secondary battery according to any one of claims 1 to 9, characterized in that: The secondary battery is a lithium ion secondary battery, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a LiNi m Co n A (1-m-n) The lithium nickel transition metal oxide shown in O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

11. An electronic device, characterized in that: The electronic device includes the secondary battery according to any one of claims 1 to 10.

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