Electrolyte, battery cell, battery, and electric device

Abstract

An electrolyte, a battery cell, a battery, and an electrical device are disclosed, belonging to the field of battery technology. The electrolyte includes: a solvent, including ethylene carbonate; and additives, including oxysilane compounds. Based on the total mass of the electrolyte, the mass content A of the oxysilane compound and the mass content B of the ethylene carbonate satisfy: 0.01 ≤ A: B ≤ 0.5. The oxysilane compound includes at least one compound having the following structures: [list of compounds]. The technical solutions of this application can improve the performance of the battery cell.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrolyte, a battery cell, a battery, and an electrical device. Background Technology

[0002] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within the new energy industry, battery technology is a crucial factor in its development.

[0003] The development of battery technology requires consideration of various design factors, such as capacity, energy density, cycle life, and reliability. As a crucial component of the battery cell, the electrolyte is vital to its performance. Therefore, developing an electrolyte that improves the performance of battery cells is a pressing technical challenge. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte to improve the performance of a battery cell.

[0005] To achieve the above objectives, this application provides an electrolyte, a battery cell, a battery, and an electrical device.

[0006] In a first aspect, an electrolyte is provided, comprising: a solvent comprising ethylene carbonate; an additive comprising an oxysilane compound; wherein, based on the total mass of the electrolyte, the mass content A of the oxysilane compound and the mass content B of the ethylene carbonate satisfy: 0.01 ≤ A: B ≤ 0.5; and the oxysilane compound comprises at least one compound having the following structure: , , , R includes at least one of the following: C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenyloxy, C1-C20 acyl, C2-C20 ether, C1-C20 silyl, or C6-C20 aromatic; R1, R2, R3, R4, R5, and R6 each independently include at least one of the following groups, substituted or unsubstituted: hydrogen, C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenyloxy, C2-C6 alkyl, C2-C20 alkyl, C2-C6 ... 20. Acynyl or alkynoxy group, C3-C20 cycloalkyl or epoxyalkyl group, C6-C20 aromatic group, C1-C20 cyano group, C1-C20 amino group, C1-C20 amino group, C2-C20 ether group, C1-C20 ureo group, C1-C20 carboxylic acid ester group, C1-C20 sulfonate group, C1-C20 isocyanate group, C1-C20 thiocyanate group, C4-C20 piperazine group, C1-C20 silyl group, and substituents include halogen elements.

[0007] This application provides an electrolyte comprising a solvent and an additive. The solvent includes ethylene carbonate, and the additive includes an oxygen-containing silane compound. The Si-O bonds in the oxygen-containing silane compound can eliminate protonated hydrogen produced by solvent decomposition, reducing the risk of reaction between protonated hydrogen and the positive electrode interface, thus providing some protection to the positive electrode interface and facilitating the formation of a uniform and dense electrolyte interface film. By setting the mass content A of the oxygen-containing silane compound and the mass content B of ethylene carbonate in the electrolyte to satisfy: 0.01 ≤ A: B ≤ 0.5, it is beneficial to improve the cycle stability of the battery cell, reduce the rate of increase of the DC internal resistance (DCR) during battery cell cycling, and suppress the damage to the positive electrode interface caused by solvent decomposition, reduce the gas produced by solvent decomposition, and improve the gas production of the battery cell.

[0008] In one possible implementation, based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound and the mass content B of the ethylene carbonate satisfy: 0.03 ≤ A: B ≤ 0.3.

[0009] When the ratio of A to B is not less than 0.03, the appropriate mass content of oxygen-containing silane compounds in the electrolyte is beneficial for forming a uniform, stable, and dense electrolyte interface film at the positive electrode, and for reducing the DCR growth of individual cells during long-term charge-discharge cycles; when the ratio is not more than 0.3, the appropriate mass content of ethylene carbonate in the electrolyte is beneficial for improving the conductivity of the electrolyte.

[0010] In one possible implementation, based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound satisfies: 0.3wt% ≤ A ≤ 2.5wt%. This allows for the effective formation of a dense and stable solid electrolyte membrane (CEI) at the positive electrode interface, reducing side reactions between the positive electrode and the electrolyte, facilitating improved cycle stability of the battery cell, reducing DCR growth during battery cell cycling, and improving gas generation during battery cell storage, especially at high temperatures.

[0011] In one possible implementation, based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound satisfies: 1wt% ≤ A ≤ 1.5wt%. This is beneficial for further reducing the rate of increase of the DCR of the battery cell during cycling and improving the gas production of the battery cell.

[0012] In one possible implementation, based on the total mass of the electrolyte, the mass content B of ethylene carbonate satisfies: 5wt% ≤ B ≤ 30wt%. Ethylene carbonate (EC) has a high dielectric constant and is beneficial for lithium ion dissociation, thus improving the conductivity of the electrolyte. Furthermore, during the charging and discharging process of the battery cell, ethylene carbonate undergoes localized decomposition on the surface of the negative electrode, forming a solid electrolyte interface film that provides some protection to the negative electrode.

[0013] In one possible implementation, based on the total mass of the electrolyte, the mass content B of ethylene carbonate satisfies: 5wt% ≤ B ≤ 16wt%. This provides a suitable mass content of ethylene carbonate, allowing for the inclusion of more oxygen-containing silane compounds in the electrolyte, thereby reducing side reactions between the cathode and the electrolyte.

[0014] In one possible implementation, the electrolyte further includes an electrolyte salt, wherein, based on the total mass of the electrolyte, the mass content B of the ethylene carbonate and the mass content C of the electrolyte salt satisfy: 1.2 ≤ B:C ≤ 2.5; alternatively, 1.5 ≤ B:C ≤ 2.2.

[0015] When the mass content of ethylene carbonate and the mass content of the electrolyte salt meet the above-mentioned ranges, EC molecules can be attracted to the electrolyte salt molecules, thereby reducing the risk of EC oxidation. For example, if the electrolyte salt is LiPF6, the dissociated Li... + It tends to coordinate with ECs that have a higher dielectric constant, typically a Li + It will coordinate with 2-4 ECs, thereby reducing the risk of EC molecules being oxidized at the positive electrode.

[0016] In one possible implementation, based on the total mass of the electrolyte, the mass content C of the electrolyte salt satisfies: 8wt%≤C≤17wt%; alternatively, 10wt%≤C≤17wt%. This results in a electrolyte with suitable ionic conductivity and individual battery cells with suitable internal resistance.

[0017] In one possible implementation, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate, or lithium difluorooxalato)borate. This allows for flexible selection of the electrolyte salt.

[0018] In one possible implementation, the electrolyte salt comprises lithium hexafluorophosphate.

[0019] In one possible implementation, the oxygen-containing silane compound includes: chloro(dimethyl)methoxysilane, divinyltetramethyldisiloxane, diethoxymethylvinylsilane, dimethoxymethylvinylsilane, trimethoxysilane, n-hexadecyltrimethoxysilane, 3-chloroisobutyltrimethoxysilane, (3-aminopropyl)trimethoxysilane, 3-piperazinylpropyltrimethoxysilane, triethoxysilane, propyltriethoxysilane, n-octyltriethoxysilane, (3-epoxypropoxypropyl)triethoxysilane, phenyl At least one of the following oxygen-containing silanes: triethoxysilane, 2-cyanoethyltriethoxysilane, diethylaminomethyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-ureopropyltriethoxysilane, 3-isocyanopropyltriethoxysilane, 3-thiocyanopropyltriethoxysilane, vinyltris(trimethylsiloxy)silane, vinyltris((1-methylvinyl)oxy)silane, vinyltris(2-methoxyethoxy)silane, triacetoxyethylsilane, methyltriacetoxysilane, tetramethoxysilane, and tetraphenoxysilane. These oxygen-containing silane compounds exhibit suitable solubility in solvents, facilitating the exertion of their effects.

[0020] In one possible implementation, the oxygen-containing silane compound includes at least one of vinyltris(trimethylsiloxy)silane, vinyltris[(1-methylvinyl)oxy]silane, and vinyltris(2-methoxyethoxy)silane. The above-mentioned oxygen-containing silane compound exhibits good synergistic effects with EC, resulting in high cycle capacity retention and low gas production in the battery cell.

[0021] In one possible implementation, the HF mass content D in the electrolyte satisfies: D ≤ 150 ppm. This is beneficial for improving the cycle life of the battery cells.

[0022] In one possible implementation, the water content E in the electrolyte satisfies: E ≤ 20 ppm. This is beneficial for improving the integrity of the CEI membrane, reducing the occurrence of side reactions, and improving the cycle performance of the battery cells.

[0023] In one possible implementation, the solvent also includes ethyl methyl carbonate. The solvent can be a blend of ethylene carbonate and ethyl methyl carbonate. Based on the total mass of the electrolyte, the sum of the mass contents of ethylene carbonate, ethyl methyl carbonate, additives, and electrolyte salts is 100 wt% or close to 100 wt%.

[0024] In a second aspect, a battery cell is provided, comprising the electrolyte of the first aspect and any possible implementation thereof.

[0025] In one possible implementation, the battery cell further includes a positive electrode sheet containing a positive electrode active material, wherein the positive electrode active material includes a lithium transition metal oxide. Battery cells prepared using lithium transition metal oxides as positive electrode active materials exhibit high capacity.

[0026] In one possible implementation, the lithium transition metal oxide has the chemical formula Li. a Ni b Co c M d N e O f A g Wherein, 0.8≤a≤1.3, 0.1≤b≤0.98, 0.01≤c≤0.3, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, M includes at least one of Mn or Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce or Te, and A includes at least one of S, N, P, F, Cl, Br or I. In one possible implementation, the volume average particle size Dv50 of the positive electrode active material satisfies: 3μm ≤ Dv50 ≤ 15μm, optionally, 5μm ≤ Dv50 ≤ 10μm. When the average particle size of the positive electrode active material is not less than 3μm, the positive electrode active material has a suitable specific surface area and appropriate surface energy, making it less prone to agglomeration and reducing the risk of side reactions with the electrolyte. This reduces the risk of increased internal resistance in the battery cell, thereby reducing the risk of excessive energy accumulation leading to temperature rise during charging and discharging, which is beneficial to improving the reliability of the battery cell. When the volume average particle size of the positive electrode active material does not exceed 15μm, the positive electrode active material has a suitable specific surface area, and the bond between the positive electrode active material and the current collector is relatively strong, reducing the risk of the positive electrode active material detaching from the current collector. This reduces the risk of local short circuits in the battery cell caused by the positive electrode active material floating in the electrolyte and contacting the negative electrode active material.

[0027] In one possible implementation, the mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material satisfy the following: 0.03wt% / μm ≤ A: Dv50 ≤ 0.8wt% / μm; alternatively, 0.05wt% / μm ≤ A: Dv50 ≤ 0.3wt% / μm. Limiting this relationship effectively protects the positive electrode interface, reduces side reactions between the solvent and the positive electrode interface, and helps reduce the gas production of the battery.

[0028] Thirdly, a battery is provided, comprising the battery cell of the second aspect and any possible implementation thereof.

[0029] Fourthly, an electrical device is provided, comprising the battery described in the third aspect. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a battery cell according to an embodiment of this application; Figure 2 This is a schematic diagram of a battery according to an embodiment of this application; Figure 3 This is a schematic diagram of an electrical device according to an embodiment of this application. Detailed Implementation

[0032] Embodiments of the electrolyte, battery cell, battery, and electrical device of this application have been specifically disclosed in detail with reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] 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 a 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 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Currently, lithium-ion battery technology is developing rapidly, and its application areas are constantly expanding. Lithium-ion batteries are not only used in electronic devices such as mobile phones and laptops, but also widely used in transportation vehicles such as electric motorcycles and electric vehicles, and have also expanded their applications to multiple fields such as military equipment and aerospace. Market demand has placed higher requirements on various aspects of lithium-ion batteries, including cycle performance and safety performance. Currently, most commercially available lithium-ion batteries use ethylene carbonate (EC), which has a high dielectric constant, as the main component of the non-aqueous electrolyte. However, EC has poor oxidation resistance and is easily oxidized and decomposed, producing gas, which leads to significant expansion of the battery cell volume. Adding appropriate additives to the electrolyte can help improve gas production in the battery cells, reduce cell expansion, and improve cycle performance. However, the type of additive added and the method of setting the additive content in the electrolyte are crucial to battery performance.

[0038] In view of this, embodiments of this application provide an electrolyte comprising a solvent and an additive. The solvent comprises ethylene carbonate, and the additive comprises an oxygen-containing silane compound. By rationally setting the mass ratio of the oxygen-containing silane compound to ethylene carbonate, the cycle performance of the battery cell can be improved, and the gas generation phenomenon of the battery cell can be mitigated.

[0039] The battery cell in this embodiment can be considered as a minimum unit of a battery. A battery cell includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0040] Electrolyte This application provides an electrolyte comprising a solvent and an additive, wherein the solvent comprises ethylene carbonate and the additive comprises an oxysilane compound.

[0041] In the embodiments of this application, the oxygen-containing silane compound refers to a compound that includes Si-O bonds and at least one organic group is directly bonded to a silicon atom. The organic group can refer to the portion remaining after an organic compound has had an atom or group of atoms removed.

[0042] Ethylene carbonate (EC) has a high dielectric constant, which is beneficial for the dissociation of metal ions, such as lithium ions, thereby improving the conductivity of the electrolyte. Furthermore, EC can decompose or partially decompose on the surface of the negative electrode, forming a solid electrolyte interface (SEI) film, which can provide some protection for the negative electrode.

[0043] During charging, as the voltage increases, the positive electrode active material in the battery cell will produce oxidizing substances (for example, ternary cathode materials will release oxygen atoms and produce highly oxidizing Ni). 4+This process leads to the dehydrogenation reaction (i.e., oxidative decomposition) of EC on the cathode surface, generating EC with one hydrogen atom removed. This removed EC then adsorbs onto the surface of the cathode active material. As delithiation progresses, the driving force for solvent decomposition on the cathode surface continuously increases, causing EC to further remove a hydrogen atom, generating vinylene carbonate (VC). Simultaneously, EC may also undergo ring-opening, generating oligomers such as C6H8O6 and C9H... 14 O8, C7H 10 Solvents such as O6 may eventually have their dehydrogenation products oxidized to CO and CO2. This results in significant gas production within the battery cell, causing it to expand and negatively impacting its performance. Furthermore, these reactions generate protons, leading to the decomposition of LiPF6 and the production of HF and Li. x PF y O z Products such as PF3O affect the cycle stability of lithium-ion batteries. The Si-O in oxygen-containing silane compounds can, to some extent, remove protonated hydrogen produced by solvent decomposition, suppressing HF generation and reducing HF damage to the positive electrode, thus improving the cycle performance of individual battery cells. On the other hand, oxygen-containing silane compounds can form a uniform and dense positive electrode-electrolyte interface (CEI) film at the positive electrode interface, thereby protecting the positive electrode and reducing the amount of anionic oxygen (e.g., O2) generated by the positive electrode active material. - O - This reduces the risk of solvent being oxidized by anionic oxygen, thereby reducing gas production.

[0044] Oxysilane compounds include at least one compound having the following structure: , , , .

[0045] R includes at least one of the following: C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenyloxy, C1-C20 acyl, C2-C20 ether, C1-C20 silyl or C6-C20 aromatic.

[0046] For the same structural formula, R represents the same functional group. For different structural formulas, R can be the same functional group or different functional groups. For example, for In this context, the two R groups are identical groups. and In general, the R group in the first structural formula and the R group in the second structural formula can be the same or different.

[0047] C1 alkyl indicates that it contains 1 carbon atom, and C20 alkyl indicates that it contains 20 carbon atoms. Similarly, n in Cn represents the number of carbon atoms.

[0048] The alkyl group is a saturated hydrocarbon group. As an example, the C1 alkyl group is -CH3, and the C2 alkyl group is -CH2CH3.

[0049] An alkoxy group consists of an alkyl group and an oxygen atom. As an example, the C1 alkoxy group is -OCH3.

[0050] An alkenyl group can be considered as a hydrocarbon group formed by removing one or more hydrogen atoms from an olefin molecule. As an example, a C2 alkenyl group is CH2=CH-.

[0051] An olefinic group consists of an alkenyl group and an oxygen atom. As an example, the C2 olefinic group is -OCH=CH2.

[0052] The acyl group is -(C=O)-. As an example, the C2 acyl group is an acetyl group CH3-CO-.

[0053] R1, R2, R3, R4, R5, and R6 each independently include at least one of the following groups, substituted or unsubstituted: hydrogen, C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenoxy, C2-C20 alkynyl or alkynoxy, C3-C20 cycloalkyl or epoxyalkyl, C6-C20 aromatic, C1-C20 cyano, C1-C20 amino, C1-C20 amino, C2-C20 ether, C1-C20 urea, C1-C20 carboxylic acid ester, C1-C20 sulfonate, C1-C20 isocyanate, C1-C20 thiocyanate, C4-C20 piperazine, and C1-C20 silyl, with substituents including halogen elements.

[0054] The Si-O bonds in oxygen-containing silane compounds can eliminate protonated hydrogen produced by solvent decomposition, reducing the risk of reaction between protonated hydrogen and the positive electrode interface, thus providing some protection to the positive electrode interface and facilitating the formation of a uniform and dense electrolyte interface film. This, in turn, helps improve the cycle life of individual battery cells, reduces the increase in internal resistance during long-term charge-discharge cycles, and minimizes gas production within the battery cells.

[0055] Optionally, the groups in R6 do not include phosphine groups, or in other words, the groups in R6 do not include the P element.

[0056] The alkyl, alkoxy, acyl, amino, amino, isocyanate groups, etc., in the embodiments of this application have common interpretations in the art and will not be elaborated further here.

[0057] Based on the total mass of the electrolyte, the mass content A of the oxysilane compound and the mass content B of ethylene carbonate satisfy the condition: 0.01 ≤ A:B ≤ 0.5. For example, A:B can be 0.01, 0.02, 0.05, 0.1, 0.3, 0.5, or any value within the above range.

[0058] When the ratio of A to B is not less than 0.01, the appropriate mass content of oxygen-containing silane compounds in the electrolyte is beneficial for forming a uniform, stable, and dense electrolyte interface film at the positive electrode. This helps reduce the DCR growth of individual cells during long-term charge-discharge cycles, thereby improving the cycle life of individual cells and reducing gas production within the cells. In other words, it reduces the risk that an excessively low mass content (A) of oxygen-containing silane compounds will not significantly improve gas production and cycle performance, and reduces the risk of deterioration in gas production due to an excessively high mass content (B) of ethylene carbonate.

[0059] When the ratio of A to B does not exceed 0.5, the appropriate mass content of ethylene carbonate in the electrolyte is beneficial for improving the electrolyte conductivity. Simultaneously, it can form a more uniform and dense SEI film, improving the cycle performance of the battery cells. In other words, it can reduce the risk of increased interfacial impedance due to an excessively thick CEI film caused by an excessively high mass content of oxygen-containing silane compounds (A), and reduce the risk of poor electrolyte conductivity and increased impedance of the battery cells caused by an excessively low mass content of ethylene carbonate (B).

[0060] Therefore, by setting 0.01≤A:B≤0.5, the battery cell has a lower internal resistance growth rate, a higher cycle life, and a lower gas production.

[0061] In some embodiments, based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound and the mass content B of the ethylene carbonate satisfy the condition: 0.03 ≤ A:B ≤ 0.3. For example, A:B can be 0.03, 0.04, 0.05, 0.08, 0.1, 0.2, 0.3, or any value within the above range. This is beneficial for reducing the DCR growth rate of the battery cell, improving the gas generation of the battery cell, and increasing the cycle life of the battery cell.

[0062] In some embodiments, based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound satisfies: 0.3wt% ≤ A ≤ 2.5wt%, optionally 1wt% ≤ A ≤ 1.5wt%. This allows for the effective formation of a dense and stable solid electrolyte membrane (CEI) at the positive electrode interface, reducing side reactions between the positive electrode and the electrolyte, facilitating improved battery cycle stability, reducing DCR growth during battery cycling, and mitigating gas generation during high-temperature storage.

[0063] A can be 0.3wt%, 0.4wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, or any value within the above range.

[0064] In some embodiments, based on the total mass of the electrolyte, the mass content B of ethylene carbonate satisfies: 5wt% ≤ B ≤ 30wt%, preferably 5wt% ≤ B ≤ 16wt%. Ethylene carbonate has a high dielectric constant and is beneficial for lithium ion dissociation, thus improving the conductivity of the electrolyte. Furthermore, during the charging and discharging process of the battery cell, ethylene carbonate undergoes localized decomposition on the surface of the negative electrode, forming a solid electrolyte interface film on the negative electrode surface, protecting the negative electrode and improving battery cycle performance.

[0065] B can be 5wt%, 8wt%, 10wt%, 16wt%, 20wt%, 30wt%, or any value within the above range.

[0066] In some embodiments, the electrolyte further includes an electrolyte salt, and based on the total mass of the electrolyte, the mass content of ethylene carbonate B and the mass content of the electrolyte salt C satisfy: 1.2 ≤ B:C ≤ 2.5; optionally, 1.5 ≤ B:C ≤ 2.2.

[0067] For example, B:C is 1.2, 1.4, 1.5, 1.6, 1.8, 2.1, 2.2, 2.3, 2.4, 2.5 or any value within the above range.

[0068] The electrolyte salt can be a lithium salt, in which case the electrolyte is the electrolyte in a lithium-ion battery cell.

[0069] Electrolyte salt molecules can form solvated structures with solvent molecules, meaning that a certain number of solvent molecules can attract the electrolyte salt molecule. For example, if the electrolyte salt is LiPF6 and the solvent is ethylene carbonate (EC), the dissociated Li... + It tends to coordinate with ECs that have a higher dielectric constant, typically a Li + It will coordinate with 2-4 ECs, thereby reducing the risk of EC molecules being oxidized at the positive electrode.

[0070] In this embodiment, when the mass content of ethylene carbonate B and the mass content of electrolyte salt C meet the above-mentioned ranges, EC molecules can be attracted to the electrolyte salt molecules, thereby reducing the risk of EC being oxidized at the positive electrode.

[0071] In some embodiments, based on the total mass of the electrolyte, the mass content C of the electrolyte salt satisfies: 8wt%≤C≤17wt%; optionally, 10wt%≤C≤17wt%. This results in a electrolyte with suitable ionic conductivity and a battery cell with suitable internal resistance.

[0072] C can be 8wt%, 9wt%, 10wt%, 12wt%, 16wt%, 17wt%, or any value within the above range.

[0073] In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate, or lithium difluorooxalato)borate. This allows for flexible selection of the electrolyte salt.

[0074] In electrolytes, electrolyte salts exist in the form of cations and anions. The type of electrolyte salt can be determined by detecting the form of the anion. For example, lithium hexafluorophosphate exists in electrolytes as PF6. - and Li + It exists in the form of.

[0075] In some embodiments, the electrolyte salt comprises lithium hexafluorophosphate. The chemical formula of lithium hexafluorophosphate is LiPF6.

[0076] In some embodiments, the oxygen-containing silane compound includes: chloro(dimethyl)methoxysilane, divinyltetramethyldisiloxane, diethoxymethylvinylsilane, dimethoxymethylvinylsilane, trimethoxysilane, n-hexadecyltrimethoxysilane, 3-chloroisobutyltrimethoxysilane, (3-aminopropyl)trimethoxysilane, 3-piperazinylpropyltrimethoxysilane, triethoxysilane, propyltriethoxysilane, n-octyltriethoxysilane, (3-epoxypropoxypropyl)triethoxysilane, phenyltriethoxysilane, etc. At least one of the following: methylsilane, 2-cyanoethyltriethoxysilane, diethylaminomethyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-ureopropyltriethoxysilane, 3-isocyanopropyltriethoxysilane, 3-thiocyanopropyltriethoxysilane, vinyltris(trimethylsiloxy)silane, vinyltris[(1-methylvinyl)oxy]silane, vinyltris(2-methoxyethoxy)silane, triacetoxyethylsilane, methyltriacetoxysilane, tetramethoxysilane, and tetraphenoxysilane.

[0077] The aforementioned oxygen-containing silane compounds have suitable solubility in solvents, which facilitates the application of their functions.

[0078] In some embodiments, the oxygen-containing silane compound includes at least one of vinyltris(trimethylsiloxy)silane, vinyltris[(1-methylvinyl)oxy]silane, and vinyltris(2-methoxyethoxy)silane.

[0079] The aforementioned oxygen-containing silane compounds exhibit good synergistic effects with EC solvents, resulting in high cycle capacity retention and low gas production in the battery cells.

[0080] In some embodiments, the solvent in the electrolyte may include, in addition to ethylene carbonate (EC), one or more of the following: propylene carbonate (PC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0081] In some embodiments, the additives in the electrolyte may include other additives besides oxygen-containing silane compounds, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0082] In some embodiments, the mass content D of HF in the electrolyte satisfies: D ≤ 150 ppm. For example, D is 150 ppm, 100 ppm, 50 ppm, or any value within the above range.

[0083] HF can adversely affect the cathode-electrolyte interface (CEI) film, leading to the decomposition or corrosion of the cathode active material, which is detrimental to improving the cycle life of the battery cell. Setting the HF mass content D to less than or equal to 150 ppm is beneficial to improving the cycle life of the battery cell.

[0084] In some embodiments, the water content E in the electrolyte satisfies the following condition: E ≤ 20 ppm. For example, E is 20 ppm, 10 ppm, or any value within the above range.

[0085] The electrolyte in this embodiment is a non-aqueous electrolyte. However, during the preparation of the electrolyte, it comes into contact with H2O in the air, resulting in a small amount of water in the electrolyte.

[0086] In this embodiment, controlling the water content in the electrolyte can improve the integrity of the CEI membrane, reduce the occurrence of side reactions, and improve the cycle performance of the battery cell.

[0087] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector.

[0088] The positive electrode current collector can be a metal foil or a composite current collector. For example, the positive electrode current collector can be an aluminum foil.

[0089] Composite current collectors may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] The positive electrode film layer includes a positive electrode active material. The positive electrode active material may be a known positive electrode active material for batteries.

[0091] The positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0092] The positive electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] [Negative electrode plate] The negative electrode includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0094] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. Composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0096] The negative electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] [Isolation membrane] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0098] The material of the separator membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0099] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0100] [Battery cell] This application provides a battery cell including the electrolyte described in the above embodiments.

[0101] In some embodiments, the battery cell further includes a positive electrode sheet containing a positive electrode active material, which includes a lithium transition metal oxide.

[0102] In some embodiments, the chemical formula of the lithium transition metal oxide is Li. a Ni b Co c M d N e O f A gWherein, 0.8≤a≤1.3, 0.1≤b≤0.98, 0.01≤c≤0.3, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, M includes at least one of Mn or Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce or Te, and A includes at least one of S, N, P, F, Cl, Br or I.

[0103] In some embodiments, b+c+d+e=1, f+g=2. For example, when A is S, f+g=2. In other embodiments, f+g may also be less than 2.

[0104] A can be a dopant element, which can occupy the position of an O element. N can be a dopant element, which can occupy the position of an M element.

[0105] a can be 0.8, 1, 1.2, 1.3 or any value within the above range; b can be 0.1, 0.2, 0.4, 0.6, 0.98 or any value within the above range; c can be 0.01, 0.1, 0.2, 0.3 or any value within the above range; d can be 0.01, 0.05, 0.1, 0.3, 0.5, 0.6 or any value within the above range; e can be 0, 0.2, 0.4, 0.5 or any value within the above range; f can be 0, 0.5, 0.8, 1, 1.2, 2 or any value within the above range; g can be 0, 0.5, 0.8, 1, 1.2, 2 or any value within the above range.

[0106] As an example, lithium transition metal oxides are ternary materials, such as LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 O2; Lithium transition metal oxides can also be doped ternary materials, such as LiNi. 0.5 Co 0.3 Mn 0.1 Ti 0.1 O2, etc.

[0107] In some embodiments, the lithium transition metal oxide is a lithium-rich manganese-based material, and the chemical formula of the lithium-rich manganese-based material is nLi₂MnO₃·(1-n)LiM 3 O2, M 3 Includes at least one of Co, Ni, and Mn, where 0 < n < 1. For example, the transition metal oxide of lithium is Li[Li].0.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0108] It should be noted that during the charging and discharging process, Li undergoes insertion / extraction and consumption in the positive electrode, battery cell, or electrical device. The molar content of Li differs when a battery cell is discharged to different states. In the examples of positive electrode materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the positive electrode material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0109] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate. Therefore, the measured oxygen content f in the cathode active material may be less than or equal to 2.

[0110] In some embodiments, the volume average particle size Dv50 of the positive electrode active material satisfies: 3μm≤Dv50≤15μm, and optionally, 5μm≤Dv50≤10μm. For example, Dv50 is 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, 15μm or any value within the above range.

[0111] As an example, the positive electrode active material is a ternary material, and the volume average particle size Dv50 of the ternary material satisfies: 3μm≤Dv50≤15μm.

[0112] When the average particle size of the positive electrode active material is not less than 3 μm, the positive electrode active material has a suitable specific surface area and surface energy, is less prone to agglomeration, and has a reduced risk of side reactions with the electrolyte. This reduces the risk of increased internal resistance in the battery cell, thereby reducing the risk of excessive energy accumulation during charging and discharging leading to temperature rise, which is beneficial to improving the reliability of the battery cell. When the volume average particle size of the positive electrode active material does not exceed 15 μm, the positive electrode active material has a suitable specific surface area, and the bonding between the positive electrode active material and the current collector is relatively strong. This reduces the risk of the positive electrode active material detaching from the current collector, thereby reducing the risk of local short circuits in the battery cell caused by the positive electrode active material being free in the electrolyte and coming into contact with the negative electrode active material.

[0113] In some embodiments, the mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material satisfy the following: 0.03wt% / μm≤A:Dv50≤0.8wt% / μm, optionally, 0.05wt% / μm≤A:Dv50≤0.3wt% / μm.

[0114] By defining the relationship between the mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material, the positive electrode active material can have a suitable specific surface area while the mass content of the oxygen-containing silane compound A is also suitable. This can further reduce the side reactions between the positive electrode active material and the solvent, reduce the gas production of the battery cell, reduce the internal resistance growth rate of the battery cell, and thus effectively protect the positive electrode interface and improve the cycle performance of the battery cell.

[0115] Compared to simply setting the volume average particle size Dv50 of the positive electrode active material or the mass content A of the oxygen-containing silane compound, setting the mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material, for a unit volume of positive electrode active material, setting an appropriate mass content of oxygen-containing silane compound is beneficial for allowing the oxygen-containing silane compound to play its full role, inhibiting solvent oxidation, and reducing the risk of excessive CEI film thickness, thereby further improving the cycle performance of the battery cell.

[0116] In some embodiments, the battery cell is a lithium-ion battery cell.

[0117] In some embodiments, the upper limit operating voltage of a single battery cell is 4.5V. That is, the battery cell can operate at a voltage of 4.5V, and the battery cell has good cycle performance and less gas production.

[0118] The embodiments of this application do not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0119] Figure 1 This is a schematic diagram of a battery cell according to an embodiment of this application. For example, such as... Figure 1 As shown, the battery cell 3 is a square battery cell. The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31, with electrolyte immersed in the electrode assembly 33.

[0120] The electrode assembly 33 can be made from a positive electrode, a negative electrode, and a separator through a winding process or a stacking process.

[0121] End cap assembly 32 includes electrode terminals 322, such as... Figure 1 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0122] The battery cell 3 also includes a current collector 34, which is used to connect the tabs 331 and the electrode terminals 322 of the electrode assembly 33.

[0123] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0124] [Battery] This application provides a battery, including the battery cell described in the above embodiments. Figure 2 This is a schematic diagram of a battery according to an embodiment of this application. Figure 2 As shown, battery 5 may include multiple battery cells (not shown in the figure).

[0125] Battery cells 3 can be directly assembled into battery 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into battery 5.

[0126] [Electrical appliances] This application provides an electrical device, including the battery described in the above embodiments.

[0127] Figure 3 This is a schematic diagram of an electrical device according to an embodiment of this application. Figure 3 As shown, this application provides an electrical device 6, which includes the battery in the above embodiment.

[0128] Alternatively, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., as is the case in the embodiments of this application.

[0129] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0130] [Example] Example 1 In Example 1, the electrolyte comprises ethylene carbonate solvent, an oxygen-containing silane compound additive, and an electrolyte salt. The additive is vinyltris(2-methoxyethoxy)silane, and the electrolyte salt is LiPF6. Based on the total mass of the electrolyte, the mass content of vinyltris(2-methoxyethoxy)silane (A) is 1 wt%, the mass content of ethylene carbonate (B) is 15 wt%, and the mass content of LiPF6 (C) is 10 wt%.

[0131] Examples 2-4 The difference between Examples 2-4 and Example 1 is that the mass content A of the oxygen-containing silane compound additive is different; correspondingly, the A:B ratio is different.

[0132] Examples 5-7 The difference between Examples 5-7 and Example 1 is that the mass content B of the ethylene carbonate solvent is different; correspondingly, the values ​​of A:B and B:C are different.

[0133] Examples 8-11 The difference between Examples 8-11 and Example 1 is that the mass content A of the oxygen-containing silane compound additive and the mass content B of the ethylene carbonate solvent are different; correspondingly, the values ​​of A:B and B:C are different.

[0134] Examples 12-14 The difference between Examples 12-13 and Example 6 is that the mass content C of the electrolyte salt is different; correspondingly, the B:C ratio is different. The difference between Examples 14 and Example 7 is that the mass content C of the electrolyte salt is different; correspondingly, the B:C ratio is different.

[0135] Examples 15-17 The difference between Examples 15-17 and Example 1 is that the specific types of oxygen-containing silane compounds in the additives are different.

[0136] Example 18 The difference between Example 18 and Example 1 is that the specific types of electrolyte salts are different.

[0137] Examples 19-21 The difference between Examples 19-21 and Example 4 is that the volume average particle size Dv50 of the positive electrode active material is different.

[0138] Example 22 The difference between Example 22 and Example 1 is that the mass content A of the oxygen-containing silane compound additive, the mass content B of the ethylene carbonate solvent, the mass content C of the electrolyte salt, and the volume average particle size Dv50 of the positive electrode active material are all different. Accordingly, the values ​​of A:B, B:C, and A:Dv50 are different.

[0139] In Examples 1-22, the positive electrode active material is LiNi. 0.6 Co 0.2 Mn 0.2 O2.

[0140] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the electrolyte does not contain oxygen-containing silane compound additives. The solvent EC has a mass content of 15 wt%, and the electrolyte salt has a mass content of 10 wt%.

[0141] Comparative Examples 2-3 The difference between Comparative Examples 2-3 and Example 1 is that A and B are different.

[0142] Table 1. Experimental parameters of the examples and comparative examples

[0143]

[0144] Table 2 Test results of the examples and comparative examples

[0145]

[0146] [Preparation of battery cells] (1) Preparation of positive electrode sheet: The positive electrode active material, binder polyvinylidene fluoride (PVDF) and conductive agent (acetylene black) are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:2:1. After thorough stirring and mixing, a positive electrode slurry is prepared. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed and cut to obtain the positive electrode sheet.

[0147] (2) Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a mass ratio of 96:1.5:1.5:1.0 and thoroughly stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold pressed and cut to obtain the negative electrode sheet.

[0148] (3) Separation membrane: Polypropylene membrane is used.

[0149] (4) Preparation of electrolyte: In a vacuum glove box (argon atmosphere, H2O < 0.1 ppm, O2 < 0.1 ppm), oxygen-containing silane compound additives and electrolyte salts are dissolved in a mixed solvent of ethylene carbonate EC and ethyl methyl carbonate EMC in the appropriate proportions, and stirred evenly to obtain electrolyte.

[0150] (5) Preparation of lithium-ion battery: The above positive electrode sheet, separator and negative electrode sheet are stacked and wound in sequence to obtain electrode assembly; the electrode assembly is placed in outer packaging, the electrolyte prepared above is added, and after encapsulation, standing, formation and aging processes, a lithium-ion battery cell is obtained.

[0151] It should be noted that the mass content of each component in the electrolyte (e.g., the mass content of additives, the mass content of electrolyte, and the mass content of solvent), the volume average particle size, the DC internal resistance of the battery cell, the gas generation performance of the battery cell, and the cycle performance of the battery cell in the embodiments of this application are common knowledge in the art and have the meaning of common knowledge in the art. They can be measured by test methods and instruments known in the art.

[0152] [Battery cell cycle performance testing] At 25°C, the prepared lithium-ion battery cells were left to rest for 5 minutes, then charged at a constant current rate of 0.5C to 4.5V, followed by constant voltage charging until the current was less than or equal to 0.05C. After resting for 5 minutes, they were discharged at a constant current rate of 1C to 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as the discharge capacity of the lithium-ion battery cell in the first cycle. The lithium-ion battery cells were subjected to 600 charge-discharge cycles using the above method, and the discharge capacity of each cycle was recorded.

[0153] The capacity retention rate of a single lithium-ion battery cell after 600 cycles at 25°C and 0.5C / 1C = discharge capacity of the 600th cycle / discharge capacity of the 1st cycle × 100%.

[0154] [Testing the DCR growth rate of individual battery cells] In this embodiment of the application, the internal resistance of the battery is represented by the direct current internal resistance (DCR). The test method of DCR is described below.

[0155] At 25℃, charge the battery cell at a constant current of 0.33C to 4.5V, then charge it at a constant voltage of 4.5V to a current of 0.05C, then discharge it at 0.5C for 1 hour, and discharge it at a current of 4C for 30 seconds. Record the initial voltage V1 at the start of discharge and the voltage V2 after 30 seconds of discharge. The initial DCR = (V1-V2) / I1, where I1 is the current corresponding to 4C.

[0156] Then, the battery cell is charged at a constant current of 0.5C to 4.5V, then charged at a constant voltage of 4.5V to the cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle. This cycle is repeated for the same battery cell.

[0157] After 600 cycles, the battery cell is charged at a constant current of 0.33C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C, then discharged at 0.5C for 1 hour, and discharged at a current of 4C for 30 seconds. The initial voltage V3 at the start of discharge and the voltage V4 after 30 seconds of discharge are recorded. The DCR of the 600th cycle is calculated as (V3-V4) / I2, where I2 is the current corresponding to 4C.

[0158] Cyclic DCR growth rate (%) = (DCR at 600th cycle - Initial DCR) / Initial DCR × 100%.

[0159] [Testing the gas generation performance of individual battery cells] In this embodiment of the application, the gas generation performance of a single battery cell is reflected by the volume expansion rate of the single battery cell. The test method for the volume expansion rate is described below.

[0160] The battery cells were fully charged to 4.5V at 1C and then left to stand in a 70℃ constant temperature chamber for 30 days. The volume expansion rate of the battery cells was obtained by measuring the initial volume and the volume after 30 days of standing using the water displacement method.

[0161] The volume expansion rate (%) of a single battery cell = [(volume after 30 days of standing / initial volume) - 1] × 100%. [Testing of components in the electrolyte] Solvents and additives can be determined by gas chromatography, with quantitative analysis of composition and content based on standard GB / T9722-2006. Electrolyte salts can be quantitatively analyzed by ion chromatography based on standard JY / T020-1996 to determine the concentration of inorganic components / lithium salts in the electrolyte.

[0162] [Test of HF content in electrolyte] Hydrofluoric acid content was analyzed by acid-base titration (SYA); reference standard HG / T4067-2015, Lithium Hexafluorophosphate electrolyte, 5.10 Determination of free acid content; under dry conditions, the free acid in the electrolyte was titrated with triethylamine standard solution, and the result was calculated as HF content. HF(ppm)=(V2-V1) / 1000*C*20 / m*1000000=(V2-V1)*C / m*20,000; In the formula: C—concentration of SYA standard solution, 0.02 mol / L; V1—The volume reading of the burette before the start of titration, in mL; V2—The volume reading of the burette, in mL, when the electrolyte sample is added and titration reaches the endpoint; 20 — Molar molecular weight of HF, g / mol; m — the amount of electrolyte weighed, in grams; 20000 — the coefficient for converting to μg / g.

[0163] [Test of H2O content in electrolyte] The Karl Fischer coulometric method was used for determination.

[0164] The electrolyte is injected into the balanced electrolytic cell. After the indicator electrode detects H2O, electrode oxidation occurs. -The water content is calculated by generating a quantitative chemical reaction between I2 and H2O; refer to standard HG / T4067-2015 Lithium Hexafluorophosphate Electrolyte 5.9 Determination of Moisture; the quantitative chemical reaction formula of I2 and H2O is: I2 + H2O + SO2 + 3C5H5N = 2C5H5N·HI + C5H5N·SO3; the water content is calculated by the amount of iodine consumed.

[0165] [Test of volume average particle size] Dv50: 50% of the total volume of particles have a diameter greater than this value, and another 50% of the total volume of particles have a diameter smaller than this value. Dv50 represents the median particle size of the powder. Unless otherwise specified, Dv50 in this application is determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions.

[0166] As shown in Examples 1-22 and Comparative Example 1, adding oxygen-containing silane compounds to the electrolyte is beneficial to improving the cycle life of battery cells and reducing the volume expansion rate of battery cells during long-term charge-discharge cycles.

[0167] As shown in Examples 1-22 and Comparative Examples 2-3, when the ratio of the mass content of oxygen-containing silane compounds to the mass content of ethylene carbonate is greater than 0.5, the battery cell exhibits a high internal resistance growth rate and poor cycle performance; conversely, when the ratio is less than 0.01, the battery cell exhibits a large volume expansion rate and poor cycle performance. Therefore, by setting the ratio of the mass content of oxygen-containing silane compounds to the mass content of ethylene carbonate to be between 0.01 and 0.5, the battery cell exhibits a lower internal resistance growth rate and a smaller volume expansion rate, while also maintaining a higher cycle capacity retention rate.

[0168] As shown in Examples 1, 3-4, and 2, by appropriately setting the mass content of the oxygen-containing silane compound additive in the electrolyte, such that the ratio of the mass content of the oxygen-containing silane compound to the mass content of ethylene carbonate is greater than or equal to 0.03, the battery cell exhibits a smaller DCR growth rate and a lower volume expansion rate. As shown in Examples 1, 6, 5, and 7, by appropriately setting the mass content of ethylene carbonate, ethylene carbonate and electrolyte salt form a solvated structure, which helps reduce the risk of ethylene carbonate oxidation at the positive electrode, thus reducing the occurrence of side reactions and improving the cycle performance of the battery cell. As shown in Examples 6 and 12-13, or Examples 14 and 7, by appropriately setting the mass content of electrolyte salt, such that the ratio of the mass content of ethylene carbonate to the mass content of electrolyte salt is within the range of 1.5 to 2.2, it helps reduce the capacity decay and DCR growth rate during battery cell cycling, while also suppressing the volume expansion of the battery cell at high temperatures.

[0169] As shown in Examples 1, 3, and 11, when the mass content of additive A is 0.4wt%~1.5wt%, the mass content of solvent EC B is 5wt%~16wt%, the mass content of electrolyte salt C is 10wt%~16wt%, and the volume average particle size Dv50 of the positive electrode active material is 5μm~10μm, the battery cells corresponding to the examples that simultaneously meet all ranges have high cycle capacity retention, low DCR growth rate, and small volume expansion rate, thus the battery cells have good overall performance.

[0170] As shown in Examples 15-17, the embodiments of this application are applicable to various oxygen-containing silane compounds; as shown in Examples 1 and 18, the embodiments of this application are applicable to various electrolyte salts. As shown in Examples 19-22, when the volume average particle size of the positive electrode active material and the mass content of the additive meet appropriate ranges, it is beneficial to suppress the occurrence of side reactions, and the battery cell has a higher cycle life. Specifically, as shown in Examples 1 and 2, or as shown in Examples 7 and 8, compared to only setting the volume average particle size of the positive electrode active material, while simultaneously setting the relationship between the mass content of the additive and the volume average particle size of the positive electrode active material, the battery cell has better cycle and gas generation performance. As shown in Examples 4, 21, and Examples 19-20, compared to only setting the mass content of the additive, while simultaneously adjusting the relationship between the mass content of the additive and the volume average particle size of the positive electrode active material to make it fall within the corresponding range, the battery cell has better cycle performance and a lower volume expansion rate.

[0171] In the embodiments of this application, the content of HF and water in the electrolyte is related to the environment in which the electrolyte is prepared, and has little correlation with the mass content of additives, solvent EC, and electrolyte salts.

[0172] It should be noted that other solvents may be added to the electrolyte in the embodiments of this application, and the electrolyte may also be applicable to other positive electrode active materials.

[0173] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: A positive electrode sheet containing a positive active material, wherein the positive active material includes a lithium transition metal oxide; Electrolyte, the electrolyte comprising: Solvent, including ethylene carbonate; Additives, including oxygen-containing silane compounds; Based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound satisfies: 0.3wt% ≤ A ≤ 2.5wt%, and the mass content B of the ethylene carbonate satisfies: 5wt% ≤ B ≤ 16wt%. The oxygen-containing silane compound includes at least one compound having the following structure: ， ， ， ， Wherein, R includes at least one of the following: C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenoxy, C1-C20 acyl, C2-C20 ether bond, C1-C20 silyl or C6-C20 aromatic group; R1, R2, R3, R4, R5, and R6 each independently include at least one of the following groups, substituted or unsubstituted: hydrogen, C1-C20 alkyl or alkoxy, C2-C20 alkenyl or alkenoxy, C2-C20 alkynyl or alkynoxy, C3-C20 cycloalkyl or epoxyalkyl, C6-C20 aromatic, C1-C20 cyano, C1-C20 amino, C1-C20 amino, C2-C20 ether, C1-C20 urea, C1-C20 carboxylic acid ester, C1-C20 sulfonate, C1-C20 isocyanate, C1-C20 thiocyanate, C4-C20 piperazine, and C1-C20 silyl, with substituents including halogen elements.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound and the mass content B of the ethylene carbonate satisfy the following: 0.03 ≤ A: B ≤ 0.

3.

3. The battery cell according to claim 2, characterized in that, Based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound satisfies: 1wt%≤A≤1.5wt%.

4. The battery cell according to claim 1, characterized in that, The electrolyte also includes an electrolyte salt. Based on the total mass of the electrolyte, the mass content of the ethylene carbonate B and the mass content of the electrolyte salt C satisfy the following: 1.2 ≤ B: C ≤ 2.

5.

5. The battery cell according to claim 4, characterized in that, Based on the total mass of the electrolyte, the mass content B of the ethylene carbonate and the mass content C of the electrolyte salt satisfy the following: 1.5 ≤ B:C ≤ 2.

2.

6. The battery cell according to claim 4, characterized in that, Based on the total mass of the electrolyte, the mass content C of the electrolyte salt satisfies: 8wt%≤C≤17wt%.

7. The battery cell according to claim 6, characterized in that, Based on the total mass of the electrolyte, the mass content C of the electrolyte salt satisfies: 10wt%≤C≤17wt%.

8. The battery cell according to claim 4, characterized in that, The electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate, lithium bis(oxalate)borate, or lithium difluorooxalateborate.

9. The battery cell according to claim 8, characterized in that, The electrolyte salt includes lithium hexafluorophosphate.

10. The battery cell according to claim 1, characterized in that, The oxygen-containing silane compounds include: chloro(dimethyl)methoxysilane, divinyltetramethyldisiloxane, diethoxymethylvinylsilane, dimethoxymethylvinylsilane, trimethoxysilane, n-hexadecyltrimethoxysilane, 3-chloroisobutyltrimethoxysilane, (3-aminopropyl)trimethoxysilane, 3-piperazinylpropyltrimethoxysilane, triethoxysilane, propyltriethoxysilane, n-octyltriethoxysilane, (3-epoxypropoxypropyl)triethoxysilane, and phenyltriethoxysilane. At least one of the following: 2-cyanoethyltriethoxysilane, diethylaminomethyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-ureopropyltriethoxysilane, 3-isocyanopropyltriethoxysilane, 3-thiocyanopropyltriethoxysilane, vinyltris(trimethylsiloxy)silane, vinyltris[(1-methylvinyl)oxy]silane, vinyltris(2-methoxyethoxy)silane, triacetoxyethylsilane, methyltriacetoxysilane, tetramethoxysilane, and tetraphenoxysilane.

11. The battery cell according to claim 10, characterized in that, The oxygen-containing silane compounds include at least one of vinyltris(trimethylsiloxy)silane, vinyltris[(1-methylvinyl)oxy]silane, and vinyltris(2-methoxyethoxy)silane.

12. The battery cell according to claim 1, characterized in that, The mass content D of HF in the electrolyte satisfies: D≤150ppm.

13. The battery cell according to any one of claims 1-12, characterized in that, The mass content E of water in the electrolyte satisfies: E≤20ppm.

14. The battery cell according to any one of claims 1-12, characterized in that, The chemical formula of the lithium transition metal oxide is Li. a Ni b Co c M d N e O f A g Wherein, 0.8≤a≤1.3, 0.1≤b≤0.98, 0.01≤c≤0.3, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, M includes at least one of Mn or Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce or Te, and A includes at least one of S, N, P, F, Cl, Br or I.

15. The battery cell according to any one of claims 1-12, characterized in that, The volume average particle size Dv50 of the positive electrode active material satisfies: 3μm≤Dv50≤15μm.

16. The battery cell according to claim 15, characterized in that, The volume average particle size Dv50 of the positive electrode active material satisfies: 5μm≤Dv50≤10μm.

17. The battery cell according to claim 16, characterized in that, The mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material satisfy the following: 0.03wt% / μm≤A:Dv50≤0.8wt% / μm.

18. The battery cell according to claim 17, characterized in that, The mass content A of the oxygen-containing silane compound and the volume average particle size Dv50 of the positive electrode active material satisfy the following: 0.05wt% / μm≤A:Dv50≤0.3wt% / μm.

19. The battery cell according to any one of claims 1-12, characterized in that, Based on the total mass of the additives, the mass content of the oxygen-containing silane compound is 99%-100%.

20. The battery cell according to any one of claims 1-12, characterized in that, Based on the total mass of the additives, the mass content of dioxane is 0%.

21. The battery cell according to any one of claims 1-12, characterized in that, Based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound and the mass content B of the ethylene carbonate satisfy: 5.4% ≤ A + B ≤ 17.5%.

22. The battery cell according to claim 21, characterized in that, Based on the total mass of the electrolyte, the mass content A of the oxygen-containing silane compound and the mass content B of the ethylene carbonate satisfy: 6% ≤ A + B ≤ 16.5%.

23. A battery, characterized in that, Includes the battery cell as described in any one of claims 1-22.

24. An electrical appliance, characterized in that, Includes the battery as described in claim 23.

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