Electrochemical apparatus and electronic apparatus comprising electrochemical apparatus

Abstract

An electrochemical apparatus and an electronic apparatus comprising the electrochemical apparatus. The electrochemical apparatus comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprises silicon, and on the basis of the total mass of the negative electrode material layer, the mass percentage content A of the silicon is 1% to 20%; the electrolyte comprises a compound of formula I and fluoroethylene carbonate, and on the basis of the total mass of the electrolyte, the mass percentage content C of the compound of formula I is 3% to 50%. The negative electrode sheet and the electrolyte are simultaneously applied to the electrochemical apparatus, thereby improving the cycle performance of the electrochemical apparatus.

Description

An electrochemical device and an electronic device including the electrochemical device.

[0001] This application claims priority to Chinese Patent Application No. 202411207751.0, filed on August 30, 2024, entitled "An Electrochemical Device and an Electronic Device Including the Electrochemical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device including the electrochemical device. Background Technology

[0003] With the rapid development of electronic products, rechargeable batteries are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and power storage systems due to their advantages such as high energy density, miniaturization, and lightweight design. Especially in the 3C product sector, consumers still have a significant demand for improved battery life, thus placing higher demands on the energy density of rechargeable batteries. To further improve the energy density of rechargeable batteries, high-specific-capacity electrode materials are required. Silicon-based materials, as a type of alloyed anode material, can provide an ultra-high specific capacity of up to 4200 mAh / g, making them a highly promising material for improving energy density. However, after lithiation, silicon-based materials form lithium-silicon alloys. These alloys are highly reactive and readily attack solvent molecules in the electrolyte, leading to rapid electrolyte consumption and loss of active lithium, resulting in poor cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device that improve the cycle performance of the electrochemical device.

[0005] The first aspect of this application provides an electrochemical device comprising a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode material layer containing silicon, and the mass percentage A of silicon is 1% to 20% based on the total mass of the negative electrode material layer.

[0006] The electrolyte comprises a compound of formula I and fluoroethylene carbonate:

[0007] Wherein, R is selected from unsubstituted or fluorinated C2-C6 alkyl groups, unsubstituted or fluorinated C6-C6 alkyl groups. 12 Aryl;

[0008] Based on the total mass of the electrolyte, the mass percentage C of the compound of formula I is 3% to 50%.

[0009] In one embodiment of this application, the compound of formula I is selected from at least one of the following compounds:

[0010] In one embodiment of this application, the mass percentage B of fluoroethylene carbonate is 5% to 30% based on the total mass of the electrolyte.

[0011] In one embodiment of this application, the mass percentage content B of fluoroethylene carbonate and the mass percentage content A of silicon element satisfy 1≤B / A≤10.

[0012] In one embodiment of this application, the mass percentage C of the compound of formula I and the mass percentage A of silicon element satisfy 1≤C / A≤10.

[0013] In one embodiment of this application, the electrolyte further includes a non-fluorinated cyclic carbonate, which includes at least one of ethylene carbonate or propylene carbonate; the mass percentage of the non-fluorinated cyclic carbonate is 10% to 30% based on the total mass of the electrolyte.

[0014] In one embodiment of this application, the electrolyte comprises a linear carbonate, which includes at least one of methyl ethyl carbonate or diethyl carbonate; the mass percentage of the linear carbonate is 5% to 40% based on the total mass of the electrolyte.

[0015] In one embodiment of this application, the electrolyte further comprises a linear carboxylic acid ester, which includes at least one of ethyl propionate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the mass percentage of the linear carboxylic acid ester is 5% to 40% based on the total mass of the electrolyte.

[0016] In one embodiment of this application, the electrolyte includes a lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide; the lithium salt additive has a mass percentage content of 0.1% to 5% based on the total mass of the electrolyte.

[0017] In one embodiment of this application, the electrochemical device includes a separator. Along the direction of extension of the electrode tab of the electrochemical device, the separator extends beyond the positive electrode by a length of a μm and has a thickness of b μm, where 0.0008 ≤ b / a ≤ 0.018, and a satisfies the condition: 1000 ≤ a ≤ 5000.

[0018] A second aspect of this application provides an electronic device that includes the electrochemical device provided in the first aspect of this application.

[0019] The beneficial effects of this application are:

[0020] This application provides an electrochemical device comprising a negative electrode and an electrolyte. The negative electrode includes a negative electrode material layer containing silicon, with the silicon content A ranging from 1% to 20% based on the total mass of the negative electrode material layer. The electrolyte comprises a compound of formula I and fluoroethylene carbonate (FEC). FEC is a good electrolyte additive for electrochemical devices. During formation, FEC in the electrolyte can form a cross-linked, highly resilient polymer protective layer at the electrode interface, thereby significantly improving the cycle performance of the electrochemical device. However, FEC is consumed relatively quickly, resulting in a thick polymer layer that hinders lithium-ion transport. By adding the compound of formula I, a passivation layer of lithium-containing inorganic compounds rich in S and F elements is formed at the electrode interface, preventing excessive polymerization of FEC. This synergistically forms a thinner solid electrolyte interface (SEI) / cathode electrolyte interface (CEI), thereby improving the cycle performance of the electrochemical device.

[0021] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0022] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0023] To address the issues of rapid electrolyte consumption and active lithium loss in silicon-based batteries, existing technologies typically incorporate FEC (Fluorescent Electrolyte). FEC is an excellent film-forming additive used to repair damage to the SEI (Sediment Injection) film on the surface of silicon particles. However, FEC is consumed rapidly, and excessive FEC addition can lead to poor battery cycle performance. Therefore, this invention constructs an SEI film containing inorganic components such as Li2S and LiF on the surface of the silicon anode by adding compounds with the general formula SO2F-. This SEI film exhibits more stable inorganic phase formation and promotes ion transport, thereby enhancing the overall stability of the SEI film, reducing the FEC consumption rate, and improving the cycle stability of the electrochemical device.

[0024] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application. However, the electrochemical devices of this application are not limited to lithium-ion batteries. There are no particular limitations on the electrochemical devices of this application, and they may include any device in which an electrochemical reaction occurs.

[0025] The first aspect of this application provides an electrochemical device comprising a negative electrode and an electrolyte, wherein the negative electrode includes a negative electrode material layer containing silicon, and the silicon mass percentage A is 1% to 20% based on the total mass of the negative electrode material layer; the electrolyte comprises a compound of formula I and fluoroethylene carbonate.

[0026] Wherein, R is selected from unsubstituted or fluorinated C2-C6 alkyl groups, unsubstituted or fluorinated C6-C6 alkyl groups. 12 Aryl group; the mass percentage C of compound I is 3% to 50% based on the total mass of the electrolyte. Controlling the mass percentage A of silicon within this range ensures sufficient space for the expansion of nano-silicon particles during charging and discharging of the electrochemical device, effectively mitigating material breakage caused by particle expansion and improving the energy density and cycle performance of the electrochemical device. However, in electrochemical devices containing silicon-based materials, the highly reactive lithium alloy formed after lithiation of the silicon-based material leads to rapid electrolyte consumption, affecting the cycle performance. This application simultaneously adds compound I and FEC to the electrolyte, with the mass percentage C of compound I controlled within the above range. This forms a passivation layer at the electrode interface rich in S and F elements, containing lithium-containing inorganic compounds, preventing excessive polymerization of FEC. This synergistically forms a thinner SEI / CEI layer, reducing FEC consumption and active lithium loss, and improving the cycle performance of the electrochemical device.

[0027] The negative electrode material layer contains silicon. Based on the total mass of the negative electrode material layer, the mass percentage A of silicon is between 1% and 20%, for example, it can be 1%, 5%, 10%, 15%, 20%, or a range of any two of these values. The silicon is introduced from a silicon-based material, which can be selected from at least one of silicon-carbon materials, silicon-oxygen materials, or micron-sized silicon.

[0028] The negative electrode material layer also contains carbon material, which may include at least one of natural graphite, artificial graphite, hard carbon material, soft carbon material, or mesophase micro carbon spheres, and the content of carbon material ranges from 30% to 60%. For example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range of any two of these values.

[0029] Based on the mass of the electrolyte, the mass percentage C of compound I is 3% to 50%, for example, it can be 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination of two of these values. When the content of compound I is too low, the lithium-containing inorganic material rich in S and F elements formed at the electrode interface is insufficient to regulate the decomposition of FEC, resulting in insufficient strength. When the content of compound I is high, the content of lithium-containing inorganic material rich in S and F elements formed at the electrode interface is excessive, leading to excessive rigidity and brittleness of the SEI. By controlling the mass percentage C of compound I within the above range, the decomposition products of compound I are inorganic-rich phases, which can be matched with the organic phase formed by FEC, achieving an effect similar to polymer / inorganic composite solid electrolytes, exhibiting higher stability, thereby improving the cycle performance of the electrochemical device.

[0030] In one embodiment of this application, the compound of formula I is selected from at least one of the following compounds:

[0031] An electrolyte comprising at least one of the compounds of Formula I is applied to an electrochemical device. The decomposition products of the compounds of Formula I are rich in inorganic phase, which can be matched with the organic phase formed by FEC, achieving an effect similar to that of polymer / inorganic composite solid electrolytes. It has higher stability and reduces the consumption of FEC and the loss of active lithium without affecting other performance, thereby improving the cycle performance of the electrochemical device.

[0032] In one embodiment of this application, the mass percentage B of fluoroethylene carbonate (FEC) is 5% to 30% based on the total mass of the electrolyte. For example, B can be 5%, 10%, 15%, 20%, 25%, 30%, or a range of any two of these values. By controlling the mass percentage B of FEC within the above range, FEC can form a cross-linked, highly resilient polymer protective layer at the electrode interface during battery formation, thereby greatly improving the cycle performance of the lithium secondary battery. If the FEC content is too low, it is difficult to form a complete polymer layer, resulting in poor cycle performance of the electrochemical device; if the content is too high, an excessively thick polymer layer is formed at the electrode interface, leading to obstructed interfacial ion transport and poor low-temperature and high-rate discharge performance of the electrochemical device.

[0033] In one embodiment of this application, the mass percentage content B of fluoroethylene carbonate and the mass percentage content A of silicon satisfy the condition 1 ≤ B / A ≤ 10. For example, the value of B / A can be 1, 3, 5, 8, 10, or a range consisting of any two of these values. By controlling the ratio of the mass percentage content B of fluoroethylene carbonate and the mass percentage content A of silicon within the above range, the SEI film under Si volume expansion can be repaired, and the cycle performance of the electrochemical device can be improved.

[0034] In one embodiment of this application, the mass percentage C of the compound of formula I and the mass percentage A of silicon element satisfy 1 ≤ C / A ≤ 10. For example, the value of C / A can be 1, 3, 5, 8, 10, or a range consisting of any two of these values. By controlling the ratio of the mass percentage C of the compound of formula I and the mass percentage A of silicon element within the above range, the interface can be effectively passivated, thereby improving the cycle performance of the electrochemical device.

[0035] In one embodiment of this application, the electrolyte further includes a non-fluorinated cyclic carbonate, which includes at least one of ethylene carbonate or propylene carbonate; the mass percentage of the non-fluorinated cyclic carbonate is 10% to 30% based on the total mass of the electrolyte. For example, the mass percentage of the non-fluorinated cyclic carbonate can be 10%, 15%, 20%, 25%, 30%, or a range of any two of these values. By controlling the mass percentage of the non-fluorinated cyclic carbonate within the above range, the ion transport performance of the electrolyte, the interfacial impedance of the electrochemical device, and the cycle performance of the electrochemical device can be improved.

[0036] In one embodiment of this application, the electrolyte comprises a linear carbonate, which includes at least one of methyl ethyl carbonate or diethyl carbonate; the mass percentage of the linear carbonate is 5% to 40% based on the total mass of the electrolyte. By selecting at least one of the above materials, the mass percentage of the linear carbonate is controlled within the above range, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a range consisting of any two of these values. The linear carbonate has a low viscosity, and its addition to the electrolyte will improve the overall ionic conductivity.

[0037] In one embodiment of this application, the electrolyte further comprises a linear carboxylic acid ester, which includes at least one selected from ethyl propionate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the mass percentage of the linear carboxylic acid ester is 5% to 40% based on the total mass of the electrolyte. By selecting at least one of the above materials and controlling the mass percentage of the linear carboxylic acid ester within the above range, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a range consisting of any two of these values, the overall ionic conductivity and kinetic performance of the electrochemical device can be further improved.

[0038] In one embodiment of this application, the electrolyte includes a lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of the lithium salt additive is 0.1% to 5%. By selecting at least one of the above materials, the mass percentage of the lithium salt additive is controlled within the aforementioned range. For example, the mass percentage of the lithium salt additive can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range consisting of any two of these values. Combined with the LiPF6 main salt, the cycle performance of the electrochemical device can be improved.

[0039] In this application, the electrolyte also includes a non-aqueous solvent. Non-aqueous solvents include dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, caprolactone, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and combinations thereof.

[0040] This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, the mass percentage of non-aqueous solvents in the dry electrolyte can be 0% to 73.9%, such as 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 73.9%, or any range of two such values.

[0041] In this application, the electrolyte also contains a lithium salt. There are no particular limitations on the lithium salt; any lithium salt known in the art can be used, as long as it achieves the purpose of this application. For example, the lithium salt can be selected from at least one of LiPF6, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, and LiC(SO2CF3)3. For example, LiPF6 can be used as the lithium salt. Based on the mass of the electrolyte, the mass percentage of the lithium salt can be from 8% to 20%, for example, the mass percentage of the lithium salt can be 8%, 10%, 12%, 13%, 15%, 18%, 20%, or a range consisting of any two of these values.

[0042] In one embodiment of this application, the separator extends along the direction of the tab of the electrochemical device, with a length a μm beyond the positive electrode, and a thickness b μm, where 0.0008 ≤ b / a ≤ 0.018, and a satisfies the condition: 1000 ≤ a ≤ 5000. For example, the length a μm of the separator extending beyond the positive electrode can be 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, or any range of two such values; the ratio b / a of the separator thickness b μm and the length a μm of the separator extending beyond the positive electrode along the direction of the tab of the electrochemical device can be 0.0008, 0.001, 0.005, 0.01, 0.012, 0.015, 0.018, or any range of two such values. By controlling the length 'a' of the separator extending beyond the positive electrode within the aforementioned range, short circuits between the positive and negative electrodes are avoided, while also ensuring that space in the electrochemical device is not wasted, thus preventing a loss of the electrochemical device's energy density (ED). Controlling the ratio of the separator thickness 'b' μm to the length 'a' μm extending beyond the positive electrode within the aforementioned range can reduce the energy density loss of the electrochemical device while maintaining its mechanical properties. In the electrolyte, FEC itself enhances the separator's resistance to thermal shock; the addition of at least one compound of Formula I can further enhance this effect, reducing the temperature rise inside the electrochemical device under high-temperature abuse and minimizing separator shrinkage. In this application, the length 'a' μm of the separator extending beyond the positive electrode, and the ratio of the separator thickness 'b' μm to the length 'a' μm extending beyond the positive electrode, best meet the requirements for energy density and stability of the electrochemical device within the scope of protection of this application.

[0043] This application does not impose any other limitations on the separator membrane, as long as it can achieve the purpose of this application. For example, the separator membrane may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. Polyethylene and polypropylene can prevent short circuits and can also improve the stability of the electrochemical device through the turn-off effect. For example, polyethylene may include at least one of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. The surface of the separator membrane may include a porous layer disposed on at least one surface of the separator membrane. The porous layer may include at least one of inorganic particles or a binder. The porous layer can improve the heat resistance, oxidation resistance, and electrolyte wetting performance of the separator membrane, and enhance the adhesion between the separator membrane and the electrode. For example, inorganic particles may include at least one of the following: alumina (Al₂O₃), silicon dioxide (SiO), magnesium oxide (MgO), titanium dioxide (TiO₂), hafnium dioxide (HfO₂), tin oxide (SnO₂), cerium dioxide (CeO₂), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. For example, the binder for the porous layer may include at least one of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In this application, the thickness of the separator membrane is only required to achieve the purpose of this application; for example, the thickness of the separator membrane may be from 4 μm to 30 μm.

[0044] This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application, for example, it may include aluminum foil, aluminum alloy foil, or composite current collector (e.g., aluminum-carbon composite current collector). The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it achieves the purpose of this application, for example, the positive electrode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0045] The positive electrode material layer of this application may further include a conductive agent and a binder. This application does not particularly limit the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, sheet graphite, graphene, carbon nanotubes, carbon nanowires, or carbon fibers. The binder may include at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose (CMC-Na), polyvinyl acetate, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyaniline, polyimide, polyamide-imide, polysiloxane, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0046] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0047] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0048] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0049] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of conductive agents and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0050] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 150 μm.

[0051] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0052] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0053] The preparation process of electrochemical devices is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. Furthermore, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device. This application does not limit the packaging bag; those skilled in the art can choose one according to actual needs, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag may be used.

[0054] A second aspect of this application provides an electronic device that includes the electrochemical device provided in the first aspect of this application.

[0055] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0056] Example

[0057] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0058] Test methods and equipment:

[0059] Test for silicon elemental mass percentage:

[0060] A lithium-ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode sheet was removed. It was then soaked in dimethyl carbonate (DMC) for 20 minutes, followed by rinsing with DMC and acetone respectively. The negative electrode sheet was then placed in an oven and baked at 80℃ for 12 hours to obtain the negative electrode sheet. The negative electrode sheet was then placed in a vacuum oven and dried at 100℃ for 24 hours. One gram of powdered negative electrode material layer was scraped off from the negative electrode sheet with a blade, and the mass percentage of silicon in the negative electrode material layer was determined using an ICP (Inductively Coupled Plasma) analyzer.

[0061] Cyclic performance test:

[0062] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 0.5C to 4.45V, then charge it at a constant voltage to a current of 0.025C. Let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V. Record this as the initial discharge capacity C1. Repeat this process for 200 cycles and record the discharge capacity C2 after 200 cycles. Calculate the cycle capacity retention rate of the lithium-ion battery. Cycle capacity retention rate = C2 / C1 × 100%.

[0063] Cyclic thickness growth rate test:

[0064] Charge the battery to 4.45V at a constant current of 0.5C, then charge it to 0.025C at a constant voltage. Let it stand for 5 minutes and measure the thickness. This thickness is recorded as the thickness of the battery after the first full charge. Use the same charge and discharge process as in the above cycle capacity retention test, cycle 500 times, and measure the thickness. This thickness is recorded as the battery thickness after the 500th cycle.

[0065] The difference between the battery thickness after the 500th cycle and the thickness at the first full charge is divided by the thickness at the first full charge. The battery thickness is measured using a micrometer, and the average value is taken from five different locations. This average value is the cycle thickness growth rate. The smaller the cycle thickness growth rate, the better.

[0066] Example 1-1

[0067] <Preparation of the positive electrode>

[0068] Lithium cobalt oxide (LCO), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a slurry with a solid content of 75 wt%, which was stirred until homogeneous. The slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector and dried at 90°C to obtain a positive electrode sheet with a coating thickness of 110 μm. This completes the single-sided coating of the positive electrode sheet. The above steps were then repeated on the other surface of the positive electrode sheet to obtain a double-sided coated positive electrode sheet. After coating, the positive electrode sheet was cut to a size of 74 mm × 867 mm and tabs were welded on for later use.

[0069] <Preparation of Negative Electrode Sheets>

[0070] A Si / C composite material (carbon nanopore-loaded Si), artificial graphite, lithium polyacrylate (PAA-Li) anode binder, and carbon nanotubes anode conductive agent were mixed in a mass ratio of 20:70:7:3. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain an anode slurry with a solid content of 30 wt%. The anode slurry was uniformly coated onto one side of a 12 μm thick copper foil anode current collector and dried at 120 °C to obtain a single-sided coated anode sheet with a coating thickness of 143 μm. The above steps were repeated on the other side of the copper foil to obtain a double-sided coated anode sheet. After cold pressing and slitting, a 78 mm × 875 mm anode sheet was obtained. The mass percentage of Si element was 10% based on the total mass of the anode material layers. The thickness of the single-sided anode material layer after cold pressing was 80 μm.

[0071] <Preparation of Electrolyte>

[0072] In an argon-atmospheric glove box with a water content <10ppm, dimethyl carbonate and ethyl acetate were mixed at a mass ratio of 1:1 to obtain a base solvent. Then, fluoroethylene carbonate, compound I-2, and lithium hexafluorophosphate were added and mixed thoroughly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentages of lithium hexafluorophosphate were 12.5%, fluoroethylene carbonate 20%, and compound I-2 3%, with the remainder being the base solvent.

[0073] <Preparation of the separating membrane>

[0074] A 15μm thick polyethylene (PE) film (supplied by Celgard) was used.

[0075] <Preparation of Lithium-ion Batteries>

[0076] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation. The electrode assembly is then wound. Along the direction of the electrochemical device's tabs, the separator extends 5 mm beyond the positive electrode, and its thickness is 15 μm. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0077] Among them, based on the total mass of the negative electrode material layer, the mass percentage of silicon element is 10%; based on the total mass of the electrolyte, the mass percentage of compound I is 3%, and the mass percentage of fluoroethylene carbonate is 20%, as shown in Table 1. Any fraction less than 100% is made up with the basic solvent.

[0078] Examples 1-2 to Examples 1-8

[0079] Except for the preparation of the electrolyte, where the mass percentage of compound I-2 and fluoroethylene carbonate is adjusted according to Table 1, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0080] Examples 1-9 to Examples 1-10

[0081] Except for the adjustment of the relevant parameters of the mass percentage of silicon element in the negative electrode material layer according to Table 1 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Examples 1-3.

[0082] Examples 1-11 to Examples 1-14

[0083] Except for <Preparation of Electrolyte>, which adjusts the parameters related to the type of compound I according to Table 1, the rest is the same as in Examples 1-3.

[0084] Comparative Example 1

[0085] Except for <Preparation of Electrolyte>, which does not add compound I-2 according to Table 1, changes the mass percentage of the base solvent accordingly, and keeps the mass percentage of lithium salt unchanged, the rest is the same as in Examples 1-3.

[0086] Comparative Example 2

[0087] Except for <Electrolyte Preparation>, which follows Table 1 without the addition of FEC, the mass percentage of the base solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 1-3.

[0088] Comparative Examples 3 to 6

[0089] Except for the preparation of the electrolyte, where the mass percentage of compounds I-2 and fluoroethylene carbonate is adjusted according to Table 1, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-3.

[0090] Example 2-1

[0091] Except for <Preparation of Electrolyte> where the parameters related to propylene carbonate are added according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-7.

[0092] Examples 2-2 to 2-4

[0093] Except for <Preparation of Electrolyte> where the mass percentage of propylene carbonate is adjusted according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 2-1.

[0094] Examples 2-5 to Examples 2-6

[0095] Except for the <Preparation of Electrolyte>, which adjusts the parameters related to the type of non-fluorinated cyclic carbonate according to Table 2, the rest is the same as in Examples 2-3.

[0096] Examples 2-7

[0097] Except for <Electrolyte Preparation> where the relevant parameters for methyl ethyl carbonate are added according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-7.

[0098] Examples 2-8 to 2-10

[0099] Except for <Preparation of Electrolyte> where the mass percentage of methyl ethyl carbonate is adjusted according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 2-7.

[0100] Example 2-11

[0101] Except for <Preparation of Electrolyte>, which adjusts the type of linear carbonate according to Table 2, the rest is the same as in Examples 2-8.

[0102] Example 2-12

[0103] Except for <Electrolyte Preparation> where the parameters related to propyl propionate are added according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-7.

[0104] Examples 2-13 to 2-15

[0105] Except for <Preparation of Electrolyte> where the mass percentage of propyl propionate is adjusted according to Table 2, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 2-12.

[0106] Example 2-16

[0107] Except for the <Preparation of Electrolyte>, which adjusts the parameters related to the type of linear carboxylic acid ester according to Table 2, the rest is the same as in Examples 2-13.

[0108] Examples 2-17 to 2-20

[0109] Except for the preparation of the electrolyte, where the mass percentages of propylene carbonate, ethylene carbonate, methyl ethyl carbonate, and propyl propionate are adjusted according to Table 2, the mass percentages of the base solvent are changed accordingly, and the mass percentages of the lithium salt remain unchanged, the rest are the same as in Examples 1-7.

[0110] Examples 3-1 to 3-3

[0111] Except for the preparation of the electrolyte, where the mass percentage of lithium salt additives is adjusted according to Table 3, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-3.

[0112] Examples 3-4 to 3-5

[0113] Except for <Preparation of Electrolyte>, where the types and number of lithium salt additives and the corresponding mass percentage of lithium salt additives are adjusted according to Table 3, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-3.

[0114] Examples 3-6 to Examples 3-8

[0115] Except for <Electrolyte Preparation>, which adjusts the types and number of lithium salt additives and the mass percentage of lithium salt additives according to Table 3, and changes the mass percentage of the base solvent accordingly while keeping the mass percentage of lithium salts unchanged, the rest is the same as in Examples 2-17.

[0116] Examples 4-1 to 4-5

[0117] Except for adjusting the parameters related to the length a μm of the separator beyond the positive electrode and the thickness b μm as shown in Table 4 in the <Preparation of Lithium-ion Batteries>, and changing the ratio (b / a) of the separator thickness b μm to the length a μm beyond the positive electrode, the rest is the same as in Examples 1-3.

[0118] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0119] Table 1 Note: " / " in Table 1 indicates that there is no corresponding preparation parameter, substance or performance parameter.

[0120] As can be seen from Examples 1-1 to 1-14 and Comparative Examples 1 to 6, the examples selected compounds of Formula I within the scope of protection of this application and adjusted their mass percentages C, B, and A (e.g., fluoroethylene carbonate, silicon). The comparative examples did not simultaneously satisfy these characteristics. In the examples of this application, the lithium-ion battery exhibits higher capacity retention and lower cycle thickness growth rate, indicating that the lithium-ion battery has better cycle performance.

[0121] In the electrolyte, the mass percentage C of compound I typically affects the cycle performance of the electrochemical device. Examples 1-1 to 1-5, Comparative Examples 1, 3, and 4 show that when C is too large, as in Comparative Example 4, the lithium-ion battery exhibits low capacity retention and a high cycle thickness growth rate; when C is too small, as in Comparative Example 3, the lithium-ion battery exhibits low capacity retention and a high cycle thickness growth rate; and when compound I is not included, as in Comparative Example 1, the lithium-ion battery exhibits a high cycle thickness growth rate. This indicates that neither excessively large nor small values ​​of C can improve the cycle performance of the lithium-ion battery. Therefore, by adjusting the value of C within the scope of this application, the decomposition products of compound I are rich in inorganic phases, which can match the organic phase formed by FEC, reducing the gas production generated by the oxidation reaction. This results in a higher capacity retention and a lower cycle thickness growth rate for the lithium-ion battery, indicating better cycle performance.

[0122] In the electrolyte, the type of compound of formula I typically affects the cycle performance of the electrochemical device. As can be seen from Examples 1-11 to Examples 1-14, selecting compounds of formula I within the scope of protection of this application results in higher capacity retention and lower cycle thickness growth rate of the lithium-ion battery, indicating that the lithium-ion battery has better cycle performance.

[0123] In the electrolyte, the mass percentage (B) of FEC typically affects the cycle performance of the electrochemical device. Examples 1-3, 1-6 to 1-8, Comparative Examples 2 to 3, and 4 show that when B is too large, such as in Comparative Example 4, the lithium-ion battery exhibits poor cycle performance, with FEC oxidized on the positive electrode side to generate carbon dioxide, resulting in a high cycle thickness growth rate. Conversely, when B is too small, such as in Comparative Example 3, the lithium-ion battery also exhibits poor cycle performance and a low cycle thickness growth rate. When the electrolyte does not contain FEC, such as in Comparative Example 2, the lithium-ion battery's cycle performance is even worse, indicating that neither excessively large nor small B can improve the cycle performance of the lithium-ion battery. Therefore, by adjusting the value of B within the scope of this application, the lithium-ion battery can achieve higher capacity retention and a lower cycle thickness growth rate, demonstrating better cycle performance.

[0124] Table 2 Note: In Table 2, “\” indicates that there is no corresponding preparation parameter, substance or performance parameter.

[0125] The composition and content of the electrolyte typically affect the cycle performance of lithium-ion batteries. Through Examples 2-1 to 2-20, it was demonstrated that when the composition and content of the electrolyte are within the scope of protection of this application, the lithium-ion batteries exhibit better cycle performance.

[0126] In electrolytes, the type and mass percentage of non-fluorinated cyclic carbonates typically affect the cycle performance of electrochemical devices. Examples 2-1 to 2-4 demonstrate that, within the scope of this application, adding propylene carbonate to the electrolyte, with increasing mass percentage, improves interfacial ion transport, enhances interfacial film stability, improves capacity retention, and reduces the cycle thickness growth rate. In Examples 2-5 and 2-6, adding at least one of ethylene carbonate or propylene carbonate to the electrolyte improves ion transport performance, interfacial impedance, and capacity retention, while reducing the cycle thickness growth rate. By controlling the composition and content of the electrolyte within the scope of this application, it is demonstrated that lithium-ion batteries exhibit better cycle performance.

[0127] In electrolytes, the type and mass percentage of linear carbonates typically affect the cycle performance of electrochemical devices. Examples 2-7 to 2-10 demonstrate that, within the scope of this application, the addition of propyl propionate to the electrolyte, with increasing mass percentage, improves interfacial ion transport in the bulk phase, resulting in better capacity retention and a lower cycle thickness growth rate. In Examples 2-11, the addition of diethyl carbonate to the electrolyte enhances overall ionic conductivity, leading to better capacity retention and a lower cycle thickness growth rate. By controlling the composition and content of the electrolyte within the scope of this application, it is demonstrated that lithium-ion batteries exhibit better cycle performance.

[0128] In electrolytes, the type and mass percentage of linear carboxylic acid esters typically affect the cycle performance of electrochemical devices. Examples 2-12 to 2-15 demonstrate that, within the scope of this application, the addition of propylene carbonate to the electrolyte, with increasing mass percentage, improves interfacial ion transport in the bulk phase, resulting in better capacity retention and a lower cycle thickness growth rate. In Examples 2-16, the addition of propyl acetate to the electrolyte enhances overall ionic conductivity, leading to better capacity retention and a lower cycle thickness growth rate. By controlling the composition and content of the electrolyte within the scope of this application, it is demonstrated that lithium-ion batteries exhibit better cycle performance.

[0129] Table 3

[0130] The type and mass percentage of lithium salt additives typically affect the cycle performance of lithium-ion batteries. When lithium salt additives are further added to the electrolyte, and the type and content of the lithium salt additives are within the scope of this application, the resulting lithium-ion batteries exhibit higher cycle capacity retention and lower cycle thickness growth rate. For example, in Examples 3-1 to 3-3, LiBF4 can improve the battery interface, providing a boron-rich interface, constructing polygrain boundaries (grain boundary ion transport capacity is higher than bulk ion transport capacity), enhancing interface ion transport, and improving capacity retention. Simultaneously, it can improve cathode stability, suppress gas generation, and reduce the cycle thickness growth rate. Examples 3-1 to 3-5 demonstrate that the cycle performance of the lithium-ion batteries is further improved.

[0131] As can be seen from Examples 3-6 to 3-8, by adding propylene carbonate, ethylene carbonate, methyl ethyl carbonate and propyl propionate to the electrolyte, and simultaneously adding lithium salt additives, the electrochemical device exhibits a higher cycle capacity retention rate and a lower cycle thickness growth rate.

[0132] Table 4

[0133] The length of the separator extending beyond the positive electrode typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 4-1, 4-3, and 4-5, when the length of the separator extending beyond the positive electrode is within the range specified in this application, as the length of the separator extending beyond the positive electrode increases, the lithium-ion battery exhibits higher cycle capacity retention and a lower thickness growth rate. This is because increasing the length of the separator extending beyond the positive electrode increases the overall area of ​​the separator, enhancing heat absorption in the lithium-ion battery, lowering the overall battery temperature, improving the positive electrode gas generation problem, and reducing the cycle thickness growth rate, thereby further improving the cycle performance of the lithium-ion battery.

[0134] The thickness of the separator typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 4-2 to 4-4, when the separator thickness is within the range of this application, as the separator thickness decreases, the lithium-ion battery exhibits a higher cycle capacity retention rate, which can further improve the cycle performance of the lithium-ion battery.

[0135] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrochemical device comprising a negative electrode and an electrolyte, wherein, The negative electrode sheet includes a negative electrode material layer, the negative electrode material layer contains silicon element, and the mass percentage A of silicon element is 1% to 20% based on the total mass of the negative electrode material layer; The electrolyte comprises a compound of formula I and fluoroethylene carbonate: Wherein, R is selected from unsubstituted or fluorinated C2-C6 alkyl groups, unsubstituted or fluorinated C6-C6 alkyl groups. 12 Aryl; Based on the total mass of the electrolyte, the mass percentage C of the compound of formula I is 3% to 50%.

2. The electrochemical device according to claim 1, wherein, The compound of formula I is selected from at least one of the following compounds:

3. The electrochemical device according to claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage B of the fluoroethylene carbonate is 5% to 30%.

4. The electrochemical device according to claim 1, wherein, The mass percentage B of the fluoroethylene carbonate and the mass percentage A of the silicon element satisfy the condition 1 ≤ B / A ≤ 10.

5. The electrochemical device according to claim 1, wherein, The mass percentage C of the compound of Formula I and the mass percentage A of silicon element satisfy the relationship that 1 ≤ C / A ≤ 10.

6. The electrochemical device according to claim 1, wherein, The electrolyte also includes a non-fluorinated cyclic carbonate, which includes at least one of ethylene carbonate or propylene carbonate. Based on the total mass of the electrolyte, the mass percentage of the non-fluorinated cyclic carbonate is 10% to 30%.

7. The electrochemical device according to claim 1, wherein, The electrolyte comprises a linear carbonate, which includes at least one of methyl ethyl carbonate or diethyl carbonate; the linear carbonate has a mass percentage content of 5% to 40% based on the total mass of the electrolyte.

8. The electrochemical device according to claim 1, wherein, The electrolyte further comprises linear carboxylic acid esters, including at least one of ethyl propionate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the mass percentage of the linear carboxylic acid ester is 5% to 40% based on the total mass of the electrolyte.

9. The electrochemical device according to any one of claims 1 to 8, wherein, The electrolyte includes lithium salt additives, which include at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of the lithium salt additive is 0.1% to 5%.

10. The electrochemical device according to claim 1, wherein, The electrochemical device includes a separator. Along the direction of the tab of the electrochemical device, the separator extends beyond the positive electrode by a length of a μm and has a thickness of b μm, where 0.0008 ≤ b / a ≤ 0.018, and a satisfies the condition: 1000 ≤ a ≤ 5000.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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