Electrolyte, secondary battery, and electric device

Abstract

This application provides an electrolyte, a secondary battery, and an electrical device. The lithium nitrate and additives in the electrolyte can co-form a film on the electrode surface, thus achieving a balance between battery cycle performance, high-temperature storage performance, and fast-charging performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to electrolytes, secondary batteries, and electrical devices. Background Technology

[0002] With the popularization and widespread application of digital smart products and new energy vehicles, the market has placed higher demands on the range and charging speed of lithium batteries used in these devices. Extensive research has revealed that the solid electrolyte interface (SEI) film on the surface of the negative electrode plays a crucial role in battery performance, and the composition of the electrolyte significantly affects the performance of the SEI film.

[0003] In related technologies, the strength and toughness of the battery SEI film are not good. During multiple battery cycles, the SEI film is prone to cracking, which seriously affects the cycle stability of the battery. In addition, if the ionic conductivity of the SEI film is not good, it is also not conducive to achieving the fast charging performance of the battery. Summary of the Invention

[0004] In view of this, this application provides an electrolyte in which lithium nitrate and additives can be co-formed on the surface of the electrode sheet, which can take into account the cycle performance, high temperature storage performance and fast charging performance of the battery.

[0005] The first aspect of this application provides an electrolyte comprising lithium nitrate and an additive as shown in formula (I);

[0006]

[0007] Wherein, at least one of R1, R2, R3 and R4 contains an unsaturated bond capable of undergoing an addition polymerization reaction, and at least one of R1, R2, R3 and R4 contains a -OC bond, which is connected to a silicon atom or a carbon atom.

[0008] The lithium nitrate and additives in the electrolyte can participate in the formation of the SEI film on the surface of the negative electrode. The additives undergo addition polymerization under electrochemical catalysis to form polymers. Because the additives contain both Si atoms and -OC bonds, and the -OC bonds are connected to silicon or carbon atoms, the polymers formed after addition polymerization are flexible, thereby improving the toughness of the SEI film to better adapt to the volume expansion / contraction of the negative electrode material during charging and discharging. This ensures the SEI film remains stable during battery charge-discharge cycles and improves the battery's storage stability. Furthermore, the Li3N generated from the lithium nitrate reaction can enhance the strength and ionic conductivity of the SEI film. Therefore, the electrolyte can form a stable, tough SEI film with high ionic conductivity on the negative electrode surface, optimizing the negative electrode interface and improving the battery's fast-charging performance and cycle stability.

[0009] In addition, the above-mentioned additives and lithium nitrate can also participate in the film formation on the positive electrode surface, forming a positive electrode electrolyte interface (CEI) film with strength, toughness and high ionic conductivity on the positive electrode surface. The CEI film and the above-mentioned SEI film synergistically improve the performance of the battery.

[0010] Optionally, the unsaturated bonds include carbon-carbon double bonds and / or carbon-carbon triple bonds.

[0011] Optionally, R1, R2, R3, and R4 are each independently selected from substituted or unsubstituted hydrocarbon groups containing the unsaturated bond and / or the -OC bond.

[0012] Optionally, one or two of R1, R2, R3, and R4 contain the unsaturated bonds.

[0013] Optionally, the -OC bond is connected to a Si atom.

[0014] Optionally, the number of carbon atoms in R1, R2, R3 and R4 is each an independent positive integer from 1 to 12.

[0015] Optionally, R1, R2, R3, and R4 are each independently a group other than H atoms and hydroxyl groups.

[0016] Optionally, the substituted or unsubstituted hydrocarbon group containing the unsaturated bond includes vinyl and / or ethynyl groups; the substituted or unsubstituted hydrocarbon group containing the -OC bond includes at least one of methoxy, ethoxy, 2-methoxyethoxy, and phenoxy.

[0017] Furthermore, the additive includes at least one of formulas (A)-(E).

[0018]

[0019] Optionally, the content of the additive is in the range of 0.1% to 5% based on the total mass of the electrolyte.

[0020] Optionally, the lithium nitrate in the electrolyte has a mass content in the range of 0.1% to 5%.

[0021] Optionally, the electrolyte further includes lithium bisfluorosulfonylimide. Further, the lithium bisfluorosulfonylimide in the electrolyte has a mass content in the range of 1% to 15.6%.

[0022] Optionally, the electrolyte further includes a fluorinated ether solvent as shown in formula (II).

[0023]

[0024] Wherein, R5 and R6 are fluoroalkyl groups, wherein the number of carbon atoms of the fluoroalkyl group is a positive integer from 1 to 12.

[0025] Optionally, the electrolyte further includes a carbonate solvent. Further, the mass ratio of the fluoroether solvent to the carbonate solvent is 1:(1-19).

[0026] Optionally, the electrolyte further includes an electrolyte salt; the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium sulfate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonate)imide, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium di(oxalate borate), and lithium perchlorate.

[0027] A second aspect of this application provides a secondary battery, including a negative electrode; at least the surface of the negative electrode has a solid electrolyte interface film.

[0028] The solid electrolyte interface membrane comprises a silicon-containing flexible polymer and Li3N.

[0029] The Li3N in the aforementioned solid electrolyte interphase (SEI) membrane can enhance the strength and ionic conductivity of the SEI membrane, while the silicon-containing flexible polymer can enhance the toughness of the SEI membrane. Therefore, the aforementioned solid electrolyte membrane has good toughness, high strength, and ionic conductivity, which can optimize the negative electrode interface of the battery and improve the fast charging performance and cycle stability of the battery.

[0030] Optionally, the silicon-containing flexible polymer comprises a polymerization product of at least one additive as shown in formula (I);

[0031]

[0032] Wherein, at least one of R1, R2, R3 and R4 contains an unsaturated bond capable of undergoing an addition polymerization reaction, and at least one of R1, R2, R3 and R4 contains a -OC bond, which is connected to a silicon atom or a carbon atom.

[0033] Optionally, the secondary battery includes the electrolyte provided in the first aspect of the embodiments of this application.

[0034] Optionally, the negative electrode includes a current collector and a negative electrode active material layer disposed on at least one side of the current collector, the negative electrode active material layer including a silicon-based negative electrode material.

[0035] A third aspect of this application provides an electrical device that includes the battery provided in the second aspect of this application. Because the device is powered by the battery provided in the second aspect of this application, it can achieve stable fast charging and has good market prospects.

[0036] Optionally, the electrical equipment includes consumer electronics and vehicles. Detailed Implementation

[0037] Extensive research has led to the consensus that the SEI film in lithium-ion batteries has a multi-layered structure. Generally, the SEI film comprises a bilayer structure: an outer layer (closer to the electrolyte) typically contains porous organic components, while the inner layer (closer to the active material) contains dense inorganic components. The performance of the SEI film plays a crucial role in the battery's stability and fast-charging performance. An ideal SEI film should possess high ionic conductivity, good electronic insulation, high strength and toughness, and high uniformity. However, typical SEI films are either brittle, exhibiting poor stability during repeated charge-discharge cycles and prone to breakage, potentially leading to safety incidents; or they have high impedance, failing to meet the demands of fast-charging performance. Furthermore, insufficient ionic conductivity also affects fast-charging performance. For example, during fast charging, the rate at which lithium ions pass through the SEI film is slower than the rate at which lithium deposits at the negative electrode, resulting in significant polarization at the negative electrode interface. This can lead to the continuous formation of lithium dendrites at the negative electrode, causing short circuits and even explosive combustion in the lithium-ion battery.

[0038] To address the above problems, embodiments of this application provide an electrolyte comprising lithium nitrate and an additive as shown in formula (I);

[0039]

[0040] Wherein, at least one of R1, R2, R3, and R4 contains an unsaturated bond capable of undergoing addition polymerization, and at least one of R1, R2, R3, and R4 contains a -OC bond, which is bonded to a silicon atom or a carbon atom. Specifically, this refers to the oxygen atom in the -OC bond being bonded to a silicon atom or a carbon atom.

[0041] In this application specification, "unsaturated bond" specifically refers to "unsaturated bond that can undergo addition polymerization," unless otherwise specified.

[0042] In the embodiments of this application, an additive molecule may contain Si-OC bonds but not COC bonds; it may contain COC bonds but not Si-OC bonds; or it may contain both Si-OC bonds and COC bonds.

[0043] In the embodiments of this application, the aforementioned unsaturated bonds and -OC bonds may coexist in one side chain (e.g., the aforementioned unsaturated bonds and -OC bonds coexist in R1); they may also coexist in two different side chains (e.g., the aforementioned unsaturated bonds are in R1 and the -OC bonds are in R2); or some unsaturated bonds and some -OC bonds may coexist in one side chain, while other unsaturated bonds and / or other -OC bonds coexist in different side chains (e.g., R1 contains both the aforementioned unsaturated bonds and -OC bonds, R2 is a hydrocarbon group containing the aforementioned unsaturated bonds, and R3 and R4 are hydrocarbon groups containing -OC bonds).

[0044] During battery charging, the components of the electrolyte (including additives, lithium nitrate, and solvent) react under electrochemical and temperature-catalyzed conditions, forming an SEI film on the surface of the negative electrode. The additives, containing unsaturated bonds capable of addition polymerization, can polymerize, primarily located on the side of the SEI film closest to the electrolyte. The additives also contain both Si atoms and -OC bonds, with the -OC bonds connected to either Si or C atoms. This results in a polymer with good flexibility, enhancing the SEI film's toughness. Consequently, during battery charging and discharging, the SEI film expands and contracts in tandem with the negative electrode material, mitigating SEI film rupture and exhibiting good stability, thus improving battery cycle stability. Simultaneously, lithium nitrate in the electrolyte, as an additive, reacts to generate inorganic substances with high ionic conductivity, such as Li3N, which mainly form on the side of the SEI film closest to the negative electrode, simultaneously improving both the SEI film's strength and ionic conductivity. Specifically, increasing the strength of the SEI film can reduce side reactions during battery cycling, giving the SEI film a "strong inside, flexible outside" effect. This helps improve the battery's high-temperature storage stability and extend its cycle life. Furthermore, Li3N can also increase the ionic conductivity of the SEI film, improving the battery's rate performance and thus its fast-charging performance. In other words, it enables sustained, stable, and safe fast charging. In summary, the above electrolytes can improve the fast-charging performance, storage, and cycle stability of batteries (especially high-energy-density battery systems).

[0045] In addition, the above-mentioned additives and lithium nitrate can also participate in the formation of the cathode electrolyte interface (CEI) film. The final CEI film can work together with the SEI film to improve the cycle performance and fast charging performance of the battery. Its function and principle are similar to those of the SEI film, and will not be elaborated here.

[0046] In some embodiments of this application, the unsaturated bonds capable of addition polymerization are selected from carbon-carbon double bonds and / or carbon-carbon triple bonds. Carbon-carbon double and triple bonds can undergo addition polymerization without introducing active functional groups into the electrolyte, reducing the risk of side reactions between electrolyte components and between the electrolyte and other substances in the battery cell. This results in more stable electrolyte performance and further ensures the normal operation of the battery.

[0047] In the embodiments of this application, R1, R2, R3, and R4 can each be independently selected from substituted or unsubstituted hydrocarbon groups containing -OC bonds and / or unsaturated bonds, substituted or unsubstituted ester groups containing -OC bonds and / or unsaturated bonds, substituted or unsubstituted aldehyde groups containing -OC bonds and / or unsaturated bonds, substituted or unsubstituted carboxyl groups containing -OC bonds and / or unsaturated bonds, substituted or unsubstituted amino groups containing -OC bonds and / or unsaturated bonds, substituted or unsubstituted amide groups containing -OC bonds and / or unsaturated bonds, etc. Furthermore, the above groups may also contain substituents, wherein the substituents include, but are not limited to, halogen atoms, such as F atoms, Cl atoms, etc.

[0048] In some embodiments of this application, R1, R2, R3, and R4 are each independently selected from substituted or unsubstituted hydrocarbon groups containing -OC bonds and / or unsaturated bonds. Further, the aforementioned hydrocarbon groups are substituted hydrocarbon groups.

[0049] In some embodiments of this application, R1, R2, R3, and R4 are each independently a substituted or unsubstituted hydrocarbon group containing an unsaturated bond capable of addition polymerization, or a substituted or unsubstituted hydrocarbon group containing a -OC bond. Thus, in the additive molecule, the unsaturated group and the -OC bond belong to different side chains, so the flexible segment acts as a side chain in the final polymer, which is more conducive to improving the flexibility of the SEI. Further, in some specific embodiments, two of R1, R2, R3, and R4 are substituted or unsubstituted hydrocarbon groups containing the aforementioned unsaturated bonds, and the other two are substituted or unsubstituted hydrocarbon groups containing -OC bonds. This better balances the crosslinking degree and flexibility of the additive polymer, that is, it balances the high strength and toughness of the polymer in the SEI film, further improving the continuous stability of the SEI during battery cycling. In some embodiments of this application, the aforementioned hydrocarbon groups containing -OC bonds include, but are not limited to, substituted or unsubstituted alkyl groups, substituted or unsubstituted phenyl groups (e.g., benzyl), etc. Furthermore, in some specific embodiments, the hydrocarbon group containing the -OC bond is an alkoxy group, which is more conducive to ensuring the high flexibility of the polymer.

[0050] In some embodiments of this application, one or two of R1, R2, R3, and R4 contain unsaturated bonds capable of addition polymerization. This allows control over the degree of crosslinking of the final polymer within a suitable range, further ensuring high polymer flexibility and facilitating the change of the SEI film with the volume change of the negative electrode active material, thus further improving the cycle performance of the battery. Here, for ease of description, R1, R2, R3, and R4 are collectively referred to as "side groups." When a single side group contains only one of the aforementioned unsaturated bonds, the number of unsaturated bonds capable of addition polymerization in one molecule of additive is less than or equal to two. When a single side group contains multiple of the aforementioned unsaturated bonds (e.g., a side group of -C=CCCC=C), only one or two side groups contain the aforementioned unsaturated bonds, and there is no limit to the total number of unsaturated bonds in one molecule of the first additive. Further, in some specific examples, when a single side group contains multiple unsaturated bonds, the side group is a non-conjugated system.

[0051] In some embodiments of this application, the aforementioned -OC bond is connected to Si atoms; that is, the additive with a 1-molecule structure contains Si-OC bonds. The bond length of the Si-O bond is greater than that of the Si-C bond, and the Si-O bond is more flexible, which is more conducive to improving the toughness of the SEI film, and therefore more conducive to the performance of the battery.

[0052] In some embodiments of this application, the additive with a single molecular structure may contain multiple -OC bonds. For ease of description, R1, R2, R3, and R4 are collectively referred to as "side groups". Specifically, multiple side groups may each contain -OC bonds, so that the additive with a single molecular structure contains multiple -OC bonds; alternatively, a single side group may contain multiple -OC bonds; or multiple side groups may simultaneously contain multiple -OC bonds. Increasing the number of -OC bonds is more beneficial to improving the toughness of the final SEI film. The -OC bonds have high reactivity. Controlling the number of -OC bonds in the additive with a single molecular structure within a suitable range can reduce the risk of side reactions with other substances in the battery cell, which is beneficial to the performance of the battery.

[0053] In some embodiments of this application, the number of carbon atoms in R1, R2, R3, and R4 is each an independent positive integer from 1 to 12. Controlling the number of carbon atoms in R1, R2, R3, and R4 within this range can improve the solubility of the additive in the electrolyte, thereby ensuring better performance of the SEI and CEI films and facilitating optimal battery performance. For example, the number of carbon atoms in R1, R2, R3, and R4 can each be independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12.

[0054] In some embodiments of this application, R1, R2, R3, and R4 are not hydrogen atoms or hydroxyl groups. That is, R1, R2, R3, and R4 are neither hydrogen atoms nor hydroxyl groups. This significantly reduces the risk that additives and the polymers formed by them may affect battery performance.

[0055] In some embodiments of this application, substituted or unsubstituted hydrocarbon groups containing unsaturated bonds capable of addition polymerization include, but are not limited to, vinyl and / or ethynyl groups; substituted or unsubstituted hydrocarbon groups containing -OC bonds include, but are not limited to, at least one of methoxy, ethoxy, 2-methoxyethoxy, and phenoxy. In some specific embodiments, the additive includes at least one of formulas (A) to (E).

[0056]

[0057]

[0058] The CAS number of the substance represented by formula (A) is 17985-63-6; the CAS number of the substance represented by formula (B) is 873703-35-6; the CAS number of the substance represented by formula (C) is 129762-81-8; the CAS number of the substance represented by formula (D) is 144967-39-5; and the CAS number of the substance represented by formula (E) is 67892-60-8.

[0059] In some specific embodiments, the above-mentioned additives include structures as shown in formula (E), namely, divinyldiethoxysilane. The above-mentioned substances with a molecular structure contain two carbon-carbon double bonds capable of addition polymerization, as well as two highly flexible ethoxy groups. The resulting SEI film exhibits suitable cross-linking and toughness, while reducing the risk of introducing side reactions that could degrade battery performance. This makes it easier to simultaneously improve both battery storage stability and cycle life.

[0060] In some embodiments of this application, the mass percentage of the additive is in the range of 0.1% to 5% based on the total mass of the electrolyte. Exemplarily, the mass percentage of the additive in the electrolyte can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, etc. Controlling its content within the above range allows for appropriate control of the total thickness of the SEI film, resulting in a lower interfacial impedance of the battery, which is beneficial for rapid charging and discharging; it also gives the SEI film better toughness, inhibiting SEI film rupture and improving battery cycle performance.

[0061] In some embodiments of this application, the mass percentage of lithium nitrate is within the range of 0.1% to 5% based on the total mass of the electrolyte. Exemplarily, the mass percentage of lithium nitrate in the electrolyte can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, etc. Controlling the mass content of lithium nitrate within the above range can effectively improve the strength and ionic conductivity of the SEI film, while avoiding waste caused by excessive insoluble lithium nitrate and controlling production costs.

[0062] In some embodiments of this application, the electrolyte further includes lithium bisfluorosulfonylimide (LiFSI). The addition of lithium bisfluorosulfonylimide not only improves the stability of the electrolyte salt but also helps reduce the impedance of the SEI film and improves the ionic conductivity of the SEI film. Preferably, in some specific embodiments, the mass content of lithium bisfluorosulfonylimide in the electrolyte is in the range of 1% to 15.6%. Understandably, LiFSI is also a common electrolyte salt. When its mass content in the electrolyte is high, a portion of it participates in the formation of the SEI film as an additive during battery formation, while the remaining LiFSI participates in subsequent charge-discharge cycles as an electrolyte salt. For example, the mass percentage of LiFSI in the electrolyte can be 1.0%, 1.2%, 1.5%, 2.0%, 2.2%, 2.5%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 15.5%, etc. Preferably, in some specific embodiments, the mass percentage of LiFSI in the electrolyte is in the range of 1% to 5%. This can improve the performance of the SEI film and significantly reduce the risk of corrosion of the positive electrode current collector, thereby further ensuring the performance of the battery.

[0063] In some embodiments of this application, the electrolyte further includes at least one fluoroether solvent as shown in formula (II). Wherein, R5 and R6 are fluoroalkyl groups; specifically, R5 and R6 can be perfluoroalkyl groups or partially fluoroalkyl groups. The number of carbon atoms in the fluoroalkyl group is a positive integer from 1 to 12. For example, the number of carbon atoms in the fluoroalkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. The aforementioned fluoroether solvents can reduce the viscosity of the electrolyte, increase the solubility of the electrolyte (e.g., the solubility of the electrolyte itself), increase the wettability of the electrolyte to the negative electrode, positive electrode, and separator, and improve the oxidation resistance of the electrolyte, thereby improving the overall electrochemical performance of the battery. In some specific embodiments, R5 and R6 can each be independently selected from one or two of monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, and trifluoroethyl.

[0064] In some embodiments of this application, the electrolyte further includes carbonate solvents. In some embodiments of this application, the carbonate solvents include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). In some specific embodiments, the above-mentioned carbonate solvents simultaneously include cyclic carbonates and linear carbonates, wherein the cyclic carbonates include ethylene carbonate, and the linear carbonates include at least one of diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. Cyclic carbonates have high dielectric constants, while linear carbonates have low viscosity; their combined use is beneficial for improving the ionic conductivity of the electrolyte. In some specific embodiments, the carbonate solvent includes EC:DEC:EMC in a mass ratio of (2-4):(2-3):(4-5). For example, the mass ratio of EC:DEC:EMC can be 2:(2-3):(4-5), 2.5:(2-3):(4-5), 3:(2-3):(4-5), 3.5:(2-3):(4-5), 4.0:(2-3):(4-5), (2-4):2:(4-5), (2-4):2.5:(4-5), (2-4):(2-3):4.5, etc.

[0065] In some specific embodiments of this application, the mass ratio of the fluorinated ether solvent to the carbonate solvent is 1:(1-19). Exemplarily, the mass ratio of the fluorinated ether solvent to the carbonate solvent can be 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:19, etc. Controlling the mass ratio within the above range allows the electrolyte to have a suitable viscosity, which better wets the electrode plates; simultaneously, an appropriate amount of carbonate solvent helps to increase the voltage window of the electrolyte, meeting the needs of high energy density batteries.

[0066] In some embodiments of this application, the electrolyte further includes an electrolyte salt; the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium sulfate (Li2SO4), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium bis(trifluoromethanesulfonate) imide (LiTFSI), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFA or LiOTF), and lithium perchlorate (LiClO4).

[0067] In some embodiments of this application, the molar concentration of the electrolyte salt in the electrolyte is 0.8 mol / L-1.2 mol / L. It should be noted that when the electrolyte also contains LiFSI, the following cases need to be considered: when the mass percentage of LiFSI in the electrolyte is less than or equal to 5.0%, LiFSI exists only as an additive and is not included in the calculation of the electrolyte salt concentration; while when the mass percentage of LiFSI in the electrolyte is greater than 5.0%, the LiFSI within 5.0% is considered an additive, and the portion exceeding 5.0% is counted as the electrolyte salt and included in the calculation of the electrolyte salt concentration. Furthermore, lithium nitrate is not included in the calculation of the electrolyte salt concentration.

[0068] This application also provides a battery, including a negative electrode; at least the surface of the negative electrode has a solid electrolyte interface film.

[0069] The solid electrolyte interface membrane comprises a silicon-containing flexible polymer and Li3N.

[0070] The Li3N in the aforementioned solid electrolyte interphase (SEI) membrane can enhance the strength and ionic conductivity of the SEI membrane, while the silicon-containing flexible polymer can enhance the toughness of the SEI membrane. Therefore, the aforementioned solid electrolyte membrane has good toughness, high strength, and ionic conductivity, which can optimize the negative electrode interface of the battery and improve the fast charging performance and cycle stability of the battery.

[0071] Of course, in some embodiments, the battery also includes a positive electrode with a positive electrolyte interface (CEI) film on its surface. The CEI film includes both the aforementioned silicon-containing flexible polymer and Li3N. The modification principle of the silicon-containing flexible polymer and Li3N on the CEI film is similar to that of the SEI film, and will not be repeated here. The aforementioned CEI film can synergistically improve the battery's cycle and storage stability and fast charging performance.

[0072] In some embodiments of this application, the silicon-containing flexible polymer comprises a polymeric product of at least one additive as shown in formula (I);

[0073]

[0074] Among them, at least one of R1, R2, R3 and R4 contains an unsaturated bond capable of undergoing addition polymerization reaction, and at least one of R1, R2, R3 and R4 contains an -O-C bond, and the -O-C bond is connected to a Si atom or a C atom. Thus, the silicon-containing flexible polymer has both certain strength and good flexibility.

[0075] In some embodiments of the present application, the secondary battery includes the electrolyte provided in the embodiments of the present application.

[0076] In some embodiments of the present application, the above-mentioned negative electrode can be any negative electrode well-known in the art. In some specific embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector. Among them, the negative electrode active material includes, but is not limited to, one or more of carbon-based negative electrodes, silicon-based negative electrodes, and tin-based negative electrodes. Among them, the carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, etc.; the silicon-based negative electrode can include silicon, silicon carbide, silicon oxide, silicon metal compound, etc.; the tin-based negative electrode can include tin, tin carbide, tin oxide, tin metal compound. In some specific embodiments, the above-mentioned negative electrode active material is selected from at least one of silicon monoxide, silicon carbide, and silicon-carbon composite. The above-mentioned negative electrode active material is not only more suitable for liquid lithium-ion batteries, and the main material of the above-mentioned silicon-based negative electrode is silicon. Under certain conditions, the improvement effect of the additive on the silicon-based negative electrode is better.

[0077] In the present application, the above-mentioned positive electrode is any positive electrode sheet well-known in the art. In some embodiments, the above-mentioned positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one side thereof. Among them, the positive electrode active material is any positive electrode active material well-known in the art. Exemplarily, it includes, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), lithium manganate (LiMnO2), binary material LiNi x A (1-k) O2 (where A is selected from one of Co and Mn, 0 < k < 1), ternary material LiNimEnM (1-m-n) O2 (where E and M are independently selected from at least one of Co, Al, and Mn, and E and M are different, 0 < m < 1, 0 < n < 1).

[0078] In some embodiments of this application, the negative electrode active material layer and the positive electrode active material layer each independently include a conductive agent and a binder. In this application, the binder and conductive agent are selected from any binder and conductive agent known in the art. In some embodiments, the conductive agent in the positive electrode sheet and the negative electrode sheet may be independently selected from at least one of acetylene black, SuperP, SuperS, graphene, carbon fiber, carbon nanotubes, and Ketjen black.

[0079] In some embodiments of this application, a separator is provided between the positive and negative electrodes. In this application, the separator can be any separator known in the art.

[0080] This application also provides an electrical device that includes the secondary battery provided in this application. Because the device is powered by the battery provided in the second aspect of this application, it can achieve stable fast charging and has good market prospects.

[0081] In some embodiments of this application, the aforementioned electrical equipment includes, but is not limited to, 3C electronic devices, new energy vehicles, electric bicycles, etc.

[0082] The technical solution of this application is further described below with reference to several embodiments.

[0083] Example 1

[0084] The electrolyte was prepared in a glove box filled with argon gas, where the water and oxygen contents were both less than 1 ppm. The electrolyte included a carbonate solvent, 0.5% by mass of an additive (specifically, diallyldiethoxysilane), 1.0% by mass of lithium nitrate, and an electrolyte salt (specifically, LiPF6), with a LiPF6 molar concentration of 1 mol / L. The carbonate solvent consisted of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a mass ratio of 30:30:40.

[0085] Example 2

[0086] The only difference from Example 1 is that the electrolyte also includes 3.0% LiFSI by mass.

[0087] Example 3

[0088] The difference from Example 1 is that the electrolyte also includes 3.0% LiFSI by mass, and the solvent of the electrolyte also includes a fluorinated ether solvent (specifically dimethyl ether). Specifically, the electrolyte formulation is as follows: a solvent with a mass ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate: dimethyl ether of 27:27:36:10, an additive of 0.5% by mass (specifically diallyldiethoxysilane, structure shown in formula (E)), lithium nitrate of 1.0% by mass, LiFSI of 3.0% by mass, and an electrolyte salt (specifically LiPF6) with a molar concentration of 1 mol / L.

[0089] Example 4

[0090] The difference from Example 3 is that dimethyl ether is replaced with an equal mass of di(trifluoromethyl) ether, and the electrolyte does not contain LiFSI.

[0091] Example 5

[0092] The difference from Example 3 is that the mass percentage of LiFSI in the electrolyte is 6%, and the content of LiPF6 is slightly adjusted so that the molar concentration of the electrolyte salt in the electrolyte is 1 mol / L (the portion of LiFSI with a mass percentage exceeding 5% is calculated as the electrolyte salt, that is, based on the total mass of the electrolyte, 1 wt.% of LiFSI is calculated as the electrolyte salt).

[0093] Example 6

[0094] The only difference from Example 3 is that dimethyl ether is replaced with an equal mass of di(trifluoromethyl) ether.

[0095] Example 7

[0096] The difference from Example 3 is that dimethyl ether is replaced with an equal mass of di(trifluoromethyl) ether, and the mass percentage of lithium nitrate is increased to 2.0%.

[0097] Example 8

[0098] The difference from Example 7 is that the mass percentage of lithium nitrate in the electrolyte is 0.1%.

[0099] Example 9

[0100] The difference from Example 7 is that the mass percentage of lithium nitrate in the electrolyte is 5.0%.

[0101] Example 10

[0102] The difference from Example 7 is that the mass percentage of the additive in the electrolyte is 0.1%.

[0103] Example 11

[0104] The difference from Example 7 is that the mass percentage of the additive in the electrolyte is 3.0%.

[0105] Example 12

[0106] The difference from Example 7 is that the mass percentage of the additive in the electrolyte is 5.0%.

[0107] Example 13

[0108] The difference from Example 7 is that the mass percentage of the additive in the electrolyte is 7.0%.

[0109] Example 14

[0110] The difference from Example 7 is that the additive is replaced by a structure as shown in Formula (A) instead of diallyl diethoxysilane.

[0111]

[0112] Example 15

[0113] The difference from Example 7 is that the additive is replaced with the structure shown in (B).

[0114] Example 16

[0115] The difference from Example 7 is that the additive is replaced with the structure shown in (C).

[0116] Example 17

[0117] The difference from Example 7 is that the additive is replaced with the structure shown in (D).

[0118] Example 18

[0119] The difference from Example 7 is that the additive is replaced with

[0120] Example 19

[0121] The difference from Example 7 is that the additive is replaced with

[0122] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0123] Comparative Example 1

[0124] The electrolyte was prepared in a glove box filled with argon gas, where the water and oxygen contents were both less than 1 ppm. The electrolyte consisted of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a mass ratio of 30:30:40, 3.0% LiFSI, and LiPF6 as the electrolyte salt at a concentration of 1 mol / L.

[0125] Comparative Example 2

[0126] The electrolyte was prepared in a glove box filled with argon gas, where the water and oxygen contents were both less than 1 ppm. The electrolyte consisted of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a mass ratio of 30:30:40, 3.0% LiFSI by mass, 0.1% lithium nitrate by mass, and LiPF6 as the electrolyte salt at a concentration of 1 mol / L.

[0127] Comparative Example 3

[0128] The electrolyte was prepared in a glove box filled with argon gas, where the water and oxygen contents were both less than 1 ppm. The electrolyte consisted of ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate: di(trifluoromethyl) ether in a mass ratio of 27:27:36:10, 3.0% LiFSI by mass, 1.0% additive (specifically, diallyldiethoxysilane), and LiPF6 as the electrolyte salt at a concentration of 1 mol / L.

[0129] Performance testing

[0130] (1) Preparation of test batteries containing the electrolytes of the examples and comparative examples: Prepare a positive electrode sheet, a negative electrode sheet, and a separator (specifically a polypropylene separator). The positive electrode sheet includes a positive current collector (specifically an aluminum foil) and a positive active material layer. The positive active material layer includes a positive active material (specifically LiNi) with a mass ratio of 97.00:1.45:1.55. 0.8 Co 0.1 Mn 0.1The battery cell consists of O2 (i.e., NCM811), a conductive agent (specifically Super P), and a binder (specifically polyvinylidene fluoride, PVDF). The negative electrode includes a negative current collector (specifically copper foil) and a negative active material layer, which comprises a negative active material (specifically graphite), a conductive agent (specifically Super P), and a binder (specifically 1 part by weight of sodium carboxymethyl cellulose (CMC) + 1.6 parts by weight of styrene-butadiene rubber (SBR)) in a mass ratio of 96.00:1.40:2.60. A separator is placed between the positive and negative electrode to separate them, thus obtaining a battery cell. The battery cell is filled with the electrolytes of each embodiment and comparative example, and formed to obtain a pouch battery. The operating voltage range of the pouch battery is 2.5V-4.25V. Batteries containing the electrolytes of each embodiment are designated as S1-S19, and batteries containing the electrolytes of each comparative example are designated as DS1-DS3.

[0131] Additionally, a supplementary test example battery S20 is provided. The difference between battery S20 and battery S7 is that the negative electrode active material of battery S20 is replaced with SiOx. A supplementary comparative example battery DS4 is provided. The difference between battery DS4 and battery DS1 is only that the negative electrode active material of battery DS4 is replaced with SiOx.

[0132] (2) Test the battery's room temperature cycle performance:

[0133] At room temperature (specifically 25℃±1℃), each test battery was charged to 4.25V using a constant current of 0.33C; then discharged to 2.5V using a constant current of 0.33C. The discharge capacity at this point was marked as C0. A charge-discharge cycle was performed using 1C0 / 1C0 (i.e., charging to 4.25V with a constant current of 1C0 and discharging to 2.5V with a constant current of 1C0 constitutes one cycle). The number of charge-discharge cycles when the battery capacity retention rate reached 80% was recorded as the battery's cycle life. The results are summarized in Table 1.

[0134] (3) High-temperature cycle performance test of the battery:

[0135] At 25℃, each test battery was charged to 4.25V using a constant current of 0.33C; then discharged to 2.5V using a constant current of 0.33C, at which point the discharge capacity was marked as C0. Subsequently, at 45℃, charge-discharge cycles were performed at 1C0 / 1C0 (i.e., charging to 4.25V with a constant current of 1C0 and discharging to 2.5V with a constant current of 1C0 constitutes one cycle). The number of charge-discharge cycles when the battery capacity retention rate was 80% was recorded as the cycle life of the battery at high temperature. The results are summarized in Table 1.

[0136] (4) Test the battery's 50% DCIR (DC internal resistance).

[0137] After adjusting the state of charge (SOC) of each test battery to 50%, the battery voltage U1 was recorded. Then, the batteries were discharged at 1.5C for 30 seconds, and the final discharge voltage U2 was recorded. The 50% DCIR of each battery was then calculated according to 50% DCIR = (U1-U2) / 1.5C. The results are summarized in Table 1.

[0138] (5) Storage test at 60℃

[0139] At 25℃, each test battery was charged to 4.25V using a constant current of 0.33C, and then kept at a constant voltage of 4.25V until 0.05C was cut off. It was then discharged to 2.5V using a constant current of 0.33C, at which point the discharge capacity was recorded as C0. Each test battery was fully charged, and its volume was measured. The batteries were then stored in a 60℃ oven. After 30 days of storage, the batteries were taken out, cooled to room temperature, and their volume changes compared to before storage were measured. On the 30th day, the batteries were removed, cooled to room temperature, and then discharged to 2.5V using a constant current of 0.3C, recording the discharge capacity C1. The batteries were then charged to 4.25V using a constant current of 0.3C, kept at a constant voltage of 4.25V until 0.05C was cut off, and after resting for 30 minutes, discharged to 2.5V using a constant current of 0.3C, recording the discharge capacity C2.

[0140] High-temperature storage residual capacity retention rate (%) = C1 / C0 × 100%;

[0141] High-temperature storage capacity retention rate (%) = C2 / C0 × 100%. The results are summarized in Table 1.

[0142] (6) Room temperature fast charging capability test

[0143] Take the three-electrode cells of each of the above test cells and perform the following tests at room temperature:

[0144] ① Connect the Blue Electric test cabinet according to the standard test procedure. At the same time, use a 3-channel Agilent data acquisition instrument to collect the voltage between the positive and negative electrodes, between the positive electrode and the copper wire reference electrode, and between the negative electrode and the copper wire reference electrode. Before the test, the copper wire reference electrode is also lithium plated. Specifically, lithium is plated in the forward direction for 4 hours with a current of 20μA (connecting the positive electrode and the copper wire reference electrode), and lithium is plated in the reverse direction for 4 hours with a current of 20μA (connecting the negative electrode and the copper wire reference electrode).

[0145] ② Charge at a constant current of 0.5C to the upper limit voltage of 4.25V, let stand for 1 hour, discharge at a constant current of 1 / 3C to the lower limit voltage of 2.5V, and let stand for 1 hour;

[0146] ③ Charge at a constant current of 1C to the upper limit voltage of 4.25V, let stand for 1 hour, discharge at a constant current of 1 / 3C to the lower limit voltage of 2.5V, and let stand for 1 hour;

[0147] ④ Charge at a constant current of 1.5C to the upper limit voltage of 4.25V, let stand for 1 hour, discharge at a constant current of 1 / 3C to the lower limit voltage of 2.5V, and let stand for 1 hour;

[0148] ⑤ Charge at a constant current of 2C to the upper limit voltage of 4.25V, let stand for 1 hour, then discharge at a constant current of 1 / 3C to the lower limit voltage of 2.5V, and let stand for 1 hour;

[0149] ⑥ Charge at 3C constant current to the upper limit voltage of 4.25V, let stand for 1 hour, discharge at 1 / 3C constant current to the lower limit voltage of 2.5V, and let stand for 1 hour;

[0150] ⑦ Take the battery's SOC at each charging rate when the negative electrode potential reaches 0mV relative to the reference electrode, and calculate the charging time required to go from 10% SOC to 80% SOC. Specifically, using a copper wire reference electrode, determine the battery's SOC at each charging rate when it reaches 0mV. First, charge at 0.5C to 10% SOC, then charge at 3C until the negative electrode potential reaches 0mV. Record the time as t1, corresponding to an SOC of a%. Then charge at 2.5C until the negative electrode potential reaches 0mV. The time is denoted as t2, corresponding to a SOC of b%. Then, charging at 2C until the negative electrode potential reaches 0mV, the charging time is t3, corresponding to a SOC of c%. Next, charging at 1.5C until the negative electrode potential reaches 0mV, the charging time is t4, corresponding to a SOC of d%. Finally, charging at 1C until the negative electrode potential reaches 0mV, the charging time is t5, corresponding to a SOC of 80%. The charging time from 10% SOC to 80% SOC is t1 + t2 + t3 + t4 + t5. The results are summarized in Table 1.

[0151] (7) Fast charging cycle performance test

[0152] At 25℃, each test battery was charged and discharged according to the following cycle strategy: 0.5C for 12 min, 3C constant current for 8.9 min, 2.5C constant current for 1.2 min, 2C constant current for 1.8 min, 1.5C constant current for 2.4 min, 1.5C constant current for 5 min, then 0.3C constant current to 4.25V and constant voltage to 0.05C, rested for 30 min, and then discharged at 1C constant current to 2.5V. This constitutes one cycle. The number of fast charging cycles at which the capacity retention rate decreased to 80% is summarized in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] Based on the parameters of each test battery and the data in Table 1, it can be found that among the batteries using graphite as the negative electrode active material, compared with the comparative batteries (DS1-DS3), the example batteries S1-S19 can balance cycle performance, high-temperature storage performance, and rate performance (specifically reflected in DCIR and fast charging performance).

[0157] Comparing the performance of batteries S1-S19 in Examples reveals that, in S1-S3, with other parameters remaining constant, adding LiFSI to the electrolyte improves the battery's cycle life, high-temperature storage, and fast-charging performance. Further addition of fluorinated ether solvents promotes the dissolution of lithium nitrate and enhances electrolyte wetting of the battery, resulting in superior cycle life and fast-charging performance. Comparing the data from batteries S4-S6 shows that when the LiFSI content is within the range further suggested in this application, the battery's overall performance is better (S6). High temperatures exacerbate the effect of LiFSI on the positive electrode current collector, thus slightly reducing high-temperature storage performance, but improving rate performance. Comparing the performance of batteries S10-S13 shows that when the additive content is within the range suggested in this application, it is more conducive to achieving optimal rate performance. Comparing the performance of batteries S7 and S14-S17 shows that dipylenyldiethoxysilane can better balance improving both cycle life and rate performance simultaneously. Comparing the performance of S7 and S18, it can be seen that the modification effect is better when the ether oxygen atom is directly connected to the Si atom.

[0158] In batteries using silicon-based anode materials, battery S20 using the electrolyte provided in the embodiments of this application is superior to the comparative battery DS4.

[0159] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. An electrolyte, characterized in that, Including lithium nitrate and additives as shown in formula (I); Wherein, at least one of R1, R2, R3 and R4 contains an unsaturated bond that can undergo addition polymerization, and at least one of R1, R2, R3 and R4 contains a -OC bond, which is connected to a silicon atom or a carbon atom; the unsaturated bond includes a carbon-carbon double bond and / or a carbon-carbon triple bond.

2. The electrolyte according to claim 1, characterized in that, R1, R2, R3, and R4 are each independently selected from substituted or unsubstituted hydrocarbon groups containing the unsaturated bond and / or the -OC bond.

3. The electrolyte according to claim 1, characterized in that, One or two of R1, R2, R3, and R4 contain the unsaturated bonds.

4. The electrolyte according to any one of claims 1-3, characterized in that, The -OC bond is connected to the Si atom.

5. The electrolyte according to any one of claims 1-3, characterized in that, The number of carbon atoms in R1, R2, R3, and R4 are each an independent positive integer from 1 to 12.

6. The electrolyte according to any one of claims 1-3, characterized in that, R1, R2, R3, and R4 are each independently a group other than H atoms and hydroxyl groups.

7. The electrolyte according to claim 2, characterized in that, The substituted or unsubstituted hydrocarbon groups containing the unsaturated bonds include vinyl and / or ethynyl groups; the substituted or unsubstituted hydrocarbon groups containing the -OC bonds include at least one of methoxy, ethoxy, 2-methoxyethoxy, and phenoxy.

8. The electrolyte according to claim 7, characterized in that, The additive includes at least one of formulas (A)-(E).

9. The electrolyte according to any one of claims 1-3, characterized in that, Based on the total mass of the electrolyte, the content of the additive is in the range of 0.1% to 5%.

10. The electrolyte according to any one of claims 1-3, characterized in that, The lithium nitrate in the electrolyte has a mass content in the range of 0.1% to 5%.

11. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte also includes lithium bis(fluorosulfonyl)imide.

12. The electrolyte according to claim 11, characterized in that, The lithium difluorosulfonylimide in the electrolyte has a mass content in the range of 1% to 15.6%.

13. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte also includes fluorinated ether solvents as shown in formula (II). Wherein, R5 and R6 are fluoroalkyl groups, wherein the number of carbon atoms of the fluoroalkyl group is a positive integer from 1 to 12.

14. The electrolyte according to claim 13, characterized in that, The electrolyte also includes carbonate solvents.

15. The electrolyte according to claim 14, characterized in that, The mass ratio of the fluoroether solvent to the carbonate solvent is 1:(1-19).

16. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte also includes an electrolyte salt; the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium sulfate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonate)imide, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium di(oxalate borate), and lithium perchlorate.

17. A secondary battery, characterized in that, It includes a negative electrode; the surface of the negative electrode has a solid electrolyte interface film, the solid electrolyte interface film comprising a silicon-containing flexible polymer and Li3N; The silicon-containing flexible polymer comprises a polymer product of at least one additive as shown in formula (I); Wherein, at least one of R1, R2, R3 and R4 contains an unsaturated bond that can undergo addition polymerization, and at least one of R1, R2, R3 and R4 contains a -OC bond, which is connected to a silicon atom or a carbon atom; the unsaturated bond includes a carbon-carbon double bond and / or a carbon-carbon triple bond.

18. The secondary battery according to claim 17, characterized in that, The secondary battery includes the electrolyte as described in any one of claims 1-16.

19. The secondary battery according to claim 17 or 18, characterized in that, The negative electrode includes a current collector and a negative electrode active material layer disposed on at least one side of the current collector, the negative electrode active material layer including a silicon-based negative electrode material.

20. An electrical appliance, characterized in that, The electrical equipment includes a secondary battery as described in any one of claims 17-19.

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