Electrochemical devices and electronic devices

Abstract

This application provides an electrochemical device comprising a negative electrode and an electrolyte. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer comprises a negative active material. The negative active material contains a silicon-based active material, and the mass percentage of the silicon-based active material in the negative active material is X%. The electrolyte contains metal ions, and based on the mass of the electrolyte, the mass percentage of the metal ions is A ppm, where X and A satisfy the relationship: 0 < X / A ≤ 8. During the charging process of the electrochemical device, the metal ions can undergo a reduction reaction at the negative electrode and form a stable Si-metal binary alloy phase or Si-O-metal ternary alloy phase with the silicon element in the silicon-based active material. This effectively suppresses the lithium intercalation expansion of the silicon-based active material, reduces electrolyte consumption, and effectively improves the cycle performance of the electrochemical device.

Description

[0001] This application is a divisional application of the original invention patent application (filed on March 22, 2022, application number 202210281888.5, invention title "electrochemical device and electronic device"). Technical Field

[0002] This application relates to the field of electrochemistry, and more particularly to an electrochemical device and an electronic device. Background Technology

[0003] Lithium-ion batteries have advantages such as high energy density, long cycle life, and good safety, and are widely used in various fields such as portable energy storage, electronic devices, and electric vehicles. With the rapid development of science and technology, all industries are placing higher demands on the overall performance of lithium-ion batteries, such as higher energy density and better cycle performance.

[0004] Silicon-based materials possess high specific capacity, and when used as negative electrode active materials in lithium-ion batteries, they can significantly improve the energy density of lithium-ion batteries. However, during the lithium-ion insertion and extraction process, silicon-based materials experience significant volume expansion, leading to increased battery thickness during cycling, damage to the negative electrode SEI film resulting in electrode interface instability, and electrolyte consumption due to SEI film regeneration. These problems all deteriorate the cycle life of lithium-ion batteries. Summary of the Invention

[0005] In view of the problems existing in the background art, the purpose of this application is to provide an electrochemical device and an electronic device.

[0006] To achieve the above objectives, this application provides an electrochemical device comprising a negative electrode and an electrolyte; the negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector; the negative active material layer includes a negative active material; the negative active material contains a silicon-based active material, and the mass percentage of the silicon-based active material in the negative active material is X%; the electrolyte contains metal ions, wherein, based on the mass of the electrolyte, the mass percentage of the metal ions is A ppm, and X and A satisfy the following relationship: 0 < X / A ≤ 8. In some embodiments, X and A satisfy the following relationship: 0.001 ≤ X / A ≤ 4.

[0007] In some embodiments, the metal ions include at least one selected from magnesium ions, aluminum ions, zinc ions, calcium ions, titanium ions, cesium ions, and molybdenum ions.

[0008] In some embodiments, the mass percentage of the metal ions is Appm, 10 ≤ A ≤ 8000, based on the mass of the electrolyte.

[0009] In some embodiments, the electrolyte may further contain anions NO3-. 2- SO4 2- SO3 2- CO3 2- SiO3 2- At least one of them.

[0010] In some embodiments, the mass percentage of the anion is B ppm based on the mass of the electrolyte, where 5 ≤ B ≤ 10000.

[0011] In some embodiments, the electrolyte may further contain additives; the additives include at least one selected from fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonyl lactone, succinic acid, adiponitrile, and 1,3,6-hexanetrionitrile.

[0012] In some embodiments, the mass percentage of the additive is C%, based on the total weight of the electrolyte, and 0.5 ≤ C ≤ 40%.

[0013] In some embodiments, the negative electrode active material comprises silicon-based active particles, with an area of ​​200 μm selected on the cross-section of the negative electrode active material layer. 2 The square region contains N silicon-based active particles, where 1 ≤ N ≤ 50, and the cross-section of the negative electrode active material layer is parallel to the thickness direction of the negative electrode active material layer.

[0014] In some embodiments, the compaction density of the negative electrode sheet is M g / cm³. 3 , 1≤M≤2.5.

[0015] In some embodiments, the electrochemical device described in this application satisfies at least one of the following conditions:

[0016] (1) Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 5%-30%;

[0017] (2) Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is 0.5%-3%;

[0018] (3) Based on the mass of the electrolyte, the mass percentage of 1,3-propanesulfonyl lactone is 0.5%-3%;

[0019] (4) Based on the mass of the electrolyte, the mass percentage of the succinic anion is 0.5%-3%;

[0020] (5) Based on the mass of the electrolyte, the adiponitrile mass percentage is 0.5%-3%;

[0021] (6) Based on the mass of the electrolyte, the mass percentage of the 1,3,6-hexanetrionitrile is 0.5%-3%.

[0022] In some embodiments, this application also provides an electronic device, which includes the electrochemical device described above.

[0023] This application includes at least the following beneficial effects:

[0024] The metal ions added to the electrochemical device of this application can undergo a reduction reaction at the negative electrode during the charging process, and form a stable Si-metal binary alloy phase or Si-O-metal ternary alloy phase with the silicon element in the silicon-based active material. This effectively inhibits the lithium intercalation expansion of the silicon-based active material, reduces the rupture of the SEI film at the negative electrode interface and the consumption of electrolyte, and effectively improves the cycle performance of the electrochemical device. Detailed Implementation

[0025] It will be understood that the disclosed embodiments are merely examples of this application, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this application in various ways.

[0026] [Electrochemical device]

[0027] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium-ion battery.

[0028] The electrochemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0029] [Negative electrode plate]

[0030] The negative electrode sheet includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0031] In some embodiments, the negative electrode active material layer comprises a negative electrode active material. In some embodiments, the negative electrode active material comprises a silicon-based active material, and the silicon-based active material accounts for X% of the mass of the negative electrode active material; in some embodiments, the electrolyte contains metal ions, wherein the mass percentage of the metal ions is A ppm based on the mass of the electrolyte, and X and A satisfy the following relationship: 0 < X / A ≤ 8, and in some embodiments, 0.001 ≤ X / A ≤ 4. During the charging process of the electrochemical device, the metal ions can undergo a reduction reaction at the negative electrode and form a stable Si-metal binary alloy phase or Si-O-metal ternary alloy phase with the silicon element in the silicon-based active material, effectively suppressing the expansion of the silicon-based active material caused by the intercalation of active ions (e.g., lithium ions), reducing the rupture of the SEI film at the negative electrode interface and the consumption of electrolyte, and effectively improving the cycle performance of the electrochemical device (e.g., lithium-ion battery).

[0032] In some embodiments, the negative electrode active material layer comprises silicon-based active particles, and the cross-section of the negative electrode active material layer has an area of ​​200 μm. 2 The square region contains N silicon-based active particles, where 1 ≤ N ≤ 50. The cross-section of the negative electrode active material layer is parallel to its thickness direction; that is, the cross-section of the negative electrode active material layer is obtained by cutting the negative electrode active material layer along its thickness direction. When 1 ≤ N ≤ 50, the electrolyte wetting effect on the negative electrode is better, and the impedance of active ions during insertion and extraction within the negative electrode sheet is lower, resulting in superior cycle performance of the electrochemical device.

[0033] In some embodiments, the compaction density of the negative electrode sheet is Mg / cm³. 3 1≤M≤2.5. When the compaction density of the negative electrode is too low, it affects the connection between the active material particles. After the active ions (such as lithium ions) embedded in the negative electrode expand, it is easy to cause the active material to fall off and become deactivated, resulting in electrical connection failure. When the compaction density of the negative electrode is too high, it is easy to cause some active particles to be crushed and reduce the wetting effect of the electrolyte on the negative electrode, which has an adverse effect on the cycle performance of the electrochemical device.

[0034] In some embodiments, the negative electrode active material layer further includes a negative electrode binder. In some embodiments, the negative electrode binder comprises at least one of the following: ethylene difluoropropylene-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0035] In some embodiments, the negative electrode active material layer further includes a conductive agent. The specific type of conductive agent is not limited and can be selected as needed. As examples, the conductive agent includes, but is not limited to, at least one of conductive graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0036] In some embodiments, the negative electrode active material layer further includes a thickener. The specific type of thickener is not limited and can be selected as needed. As an example, thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC).

[0037] The negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0038] The negative electrode current collector can be a metal foil or a porous metal plate, such as a foil or porous plate of metals or alloys thereof, such as copper, nickel, titanium, or iron. As an example, the negative electrode current collector is copper foil.

[0039] The negative electrode sheet in this application can be prepared according to conventional methods in the art. Typically, the negative electrode active material, along with optional conductive agents, binders, and thickeners, are dispersed in a solvent to form a uniform negative electrode slurry. This slurry is then coated onto a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but this application is not limited to these.

[0040] The negative electrode sheet in this application does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoating (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.

[0041] Electrolyte

[0042] In some embodiments, the electrolyte contains metal ions, including at least one selected from magnesium ions, aluminum ions, zinc ions, calcium ions, titanium ions, cesium ions, and molybdenum ions.

[0043] In some embodiments, the metal ion is derived from bis(trifluorosulfonyl)imide metal salt, trifluorosulfonylimide metal salt, or other salts containing the metal ion known in the art, such as magnesium sulfate, zinc sulfate, or aluminum sulfate.

[0044] In some embodiments, based on the mass of the electrolyte, the mass percentage of the metal ions is Appm, where 10 ≤ A ≤ 8000; in some embodiments, 100 ≤ A ≤ 5000. When the mass percentage of the metal ions is too low, the binary or ternary alloy phase formed by its interaction with silicon at the negative electrode cannot effectively suppress the expansion of the silicon-based active material. Conversely, when the mass percentage of the metal ions is too high, excessive metal elements will deposit at the negative electrode, easily causing side reactions with the electrolyte and adversely affecting the cycle performance of the electrochemical device.

[0045] In some embodiments, the electrolyte may further contain anions NO3-. 2- SO4 2- SO3 2- CO3 2- SiO3 2- At least one of the following. In some embodiments, the mass percentage of the anion is B ppm based on the mass of the electrolyte, where 5 ≤ B ≤ 10000, and in some embodiments, 100 ≤ B ≤ 10000. Adding the anion to the electrolyte can further improve the cycle performance of the electrochemical device, as the anionic groups participate in the formation of a low-resistance SEI film at the negative electrode interface, which helps accelerate lithium-ion conduction and effectively improves the cycle performance of the electrochemical device. In some embodiments, the anion is derived from lithium salt compounds, such as lithium sulfate, lithium nitrate, lithium sulfite, lithium silicate, or lithium carbonate, or other substances known in the art containing the aforementioned anions.

[0046] In some embodiments, the electrolyte may further comprise additives; in some embodiments, the additives include at least one selected from fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonyl lactone, succinic acid, adiponitrile, and 1,3,6-hexanetrionitrile. In some embodiments, the mass percentage of the additives is C%, 0.5 ≤ C ≤ 40, based on the total weight of the electrolyte. The additives can act as interface protectants for the positive and negative electrodes, stabilizing the electrode structure, reducing side reactions between the active materials of the positive and negative electrodes and the electrolyte, and further improving the cycle stability of the electrochemical device.

[0047] In some embodiments, the fluoroethylene carbonate has a mass percentage content of 5%-30%.

[0048] In some embodiments, the mass percentage of the vinylene carbonate is 0.5%-3%.

[0049] In some embodiments, the 1,3-propanesulfonyl lactone has a mass percentage content of 0.5%-3%.

[0050] In some embodiments, the succinic anionylene content is 0.5%-3% by mass.

[0051] In some embodiments, the adiponitrile content is 0.5%-3% by mass.

[0052] In some embodiments, the 1,3,6-hexanetrionitrile has a mass percentage content of 0.5%-3%.

[0053] In some embodiments, the electrolyte further includes an organic solvent and a lithium salt, wherein the types of the organic solvent and the lithium salt are not specifically limited and can be selected as needed.

[0054] In some embodiments, as examples, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), and lithium dioxalate borate (LiBOB). One of the above lithium salts may be used alone, or two or more may be used simultaneously.

[0055] In some embodiments, the organic solvent may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, and sulfone compounds. For example, the organic solvent includes, but is not limited to, at least one of propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), 1,3-dioxolane (DOL), and dimethyl ether (DME). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0056] The electrolyte can be prepared according to conventional methods in the art. For example, the organic solvent, the lithium salt, and optionally the additives can be mixed evenly to obtain the electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the lithium salt and optionally the additives can be added to the organic solvent and mixed evenly to obtain the electrolyte.

[0057] In this application, the additives and their content in the electrolyte can be determined using methods conventional in the art. For example, the additives and their content in the electrolyte can be detected by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), inductively coupled plasma atomic emission spectrometry (ICP), etc.

[0058] It should be noted that, during the electrolyte testing of this application, freshly prepared electrolyte can be used directly, or electrolyte can be obtained from an electrochemical device. An exemplary method for obtaining electrolyte from an electrochemical device includes the following steps: discharging the electrochemical device to the discharge cutoff voltage and then centrifuging it; subsequently, a suitable amount of the centrifuged liquid is taken as the electrolyte.

[0059] [Positive electrode tablets]

[0060] The positive electrode includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. The positive electrode film typically includes a positive active material and optionally a positive binder and a conductive agent.

[0061] In some embodiments, the positive current collector may be a metal foil or a porous metal plate, such as a foil or porous plate made of metals or alloys thereof, such as aluminum, copper, nickel, titanium, or silver. As an example, the positive current collector may be an aluminum foil.

[0062] In some embodiments, the positive electrode active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium phosphate with olivine structure, such as lithium cobalt oxide or lithium manganese oxide. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0063] In some embodiments, the positive electrode binder includes at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0064] In some embodiments, the conductive agent includes at least one of conductive graphite, superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] The positive electrode sheet can be prepared according to methods known in the art. In some embodiments, in the preparation of the positive electrode slurry, the positive electrode active material and optionally a binder and conductive agent are typically dissolved and dispersed in a solvent to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and the positive electrode sheet is obtained through processes such as drying and cold pressing. The solvent is a solvent known in the art that can be used as the positive electrode active material layer, such as, but not limited to, N-methylpyrrolidone (NMP).

[0066] [Isolation membrane]

[0067] The separator membrane comprises polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer composite membrane thereof. The separator membrane is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through.

[0068] In some embodiments, the separator is a single-layer separator or a multi-layer separator.

[0069] In some embodiments, the separator is coated with a coating. In some embodiments, the coating comprises at least one of an organic coating and an inorganic coating, wherein the organic coating is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, acrylic-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, and sodium carboxymethyl cellulose; and the inorganic coating is selected from at least one of SiO2, Al2O3, CaO, TiO2, ZnO2, MgO, ZrO2, and SnO2.

[0070] This application does not impose any particular limitations on the morphology and thickness of the separator; for example, the separator may have a porous structure. The method for preparing the separator is a well-known method in the art and can be used to prepare separators for electrochemical devices.

[0071] [case]

[0072] The housing is used to encapsulate the electrode assembly. In some embodiments, the housing may be a rigid housing, such as a rigid plastic housing, an aluminum housing, a steel housing, etc.; or it may be a flexible package, such as a pouch-type flexible package, the material of which may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0073] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process. The electrode assembly is placed in a housing, the electrolyte is injected, and after vacuum sealing, settling, formation, shaping, and capacity separation, an electrochemical device can be obtained.

[0074] (Electronic devices)

[0075] The electronic device covered by this application is any electronic device, such as, but not limited to, laptops, pen-based 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, large household batteries, and lithium-ion capacitors. It should be noted that the electrochemical device covered by this application is applicable not only to the electronic devices listed above, but also to energy storage power stations, maritime transport vehicles, and air transport vehicles. Air transport vehicles include both intra-atmosphere and extra-atmosphere air transport vehicles.

[0076] In some embodiments, the electronic device includes the electrochemical device described above in this application.

[0077] [test]

[0078] The following specific embodiments and comparative examples are provided to better illustrate this application. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments are commercially available.

[0079] The embodiments and comparative examples in this application all use lithium-ion batteries as examples and are prepared according to the following methods:

[0080] (1) Preparation of positive electrode

[0081] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), and conductive carbon black (Super-P) were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 12 μm thick aluminum foil for the positive electrode current collector and baked at 120 °C for 1 hour. After that, it was compacted and slit to obtain the positive electrode sheet.

[0082] (2) Preparation of negative electrode

[0083] The negative electrode active material, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber were dissolved in deionized water at a mass ratio of 85:2:13 and thoroughly mixed to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil with a thickness of 12 μm for the negative electrode current collector and baked at 120°C for 1 hour to obtain a negative electrode film. After compaction and slitting, a negative electrode sheet was obtained. The negative electrode active material was a mixture of silicon-based active material and graphite, with the silicon-based active material accounting for 15% of the negative electrode active material.

[0084] (3) Preparation of the separating membrane

[0085] A 12μm thick polypropylene film was used as the separator.

[0086] (4) Preparation of electrolyte

[0087] Ethylene carbonate and diethyl carbonate are mixed uniformly at a mass ratio of 3:7 to obtain a base solvent. Dry lithium hexafluorophosphate (LiPF6) is added to the base solvent and mixed uniformly to obtain an electrolyte, wherein the mass percentage of LiPF6 is 12.5%. Adding a certain amount of the additives described in this application to the above electrolyte can yield an electrolyte containing the additives.

[0088] (5) Preparation of lithium-ion batteries

[0089] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound into a square bare cell. The bare cell is placed in an aluminum-plastic packaging bag and baked at 80°C to remove moisture, resulting in a dry cell. The appropriate electrolyte is then injected, and the process involves vacuum sealing, settling, formation, and shaping to complete the preparation of the lithium-ion battery.

[0090] The lithium-ion batteries of the examples and comparative examples in this application were prepared according to the above method, and their performance was tested. The types and contents of substances or additives used in the examples and comparative examples, as well as the performance test results of the lithium-ion batteries, are shown in Tables 1 to 4. The contents of each additive are weight percentages calculated based on the mass of the electrolyte.

[0091] 200μm on the cross-section of the negative electrode active material layer 2 Test of the number of silicon-based active particles contained in the square region:

[0092] The cold-pressed negative electrode sheet was cut into 6mm × 6mm samples. The sample stage was placed on a heater and heated to a temperature between 150℃ and 160℃. Paraffin wax was then applied to the sample stage. After the paraffin wax melted, the negative electrode sheet sample was placed on it, slightly protruding from the edge of the sample stage. The sample was then cut along its thickness using an ion polisher. The resulting cross-section was observed using a scanning electron microscope (SEM), and elemental Si was detected using an X-ray energy dispersive spectroscopy (EDS) instrument to label the silicon-based active particles. A 200μm area was selected at any location on the resulting cross-section. 2 Within a square area, observe the number of silicon-based active particles falling within that area (any particle falling within the square area is counted). This number represents the area of ​​a 200μm region. 2 The number of silicon-based active particles contained in the square region.

[0093] Next, the performance of the lithium-ion battery will be tested.

[0094] (1) High-temperature cycling performance test

[0095] The battery was charged to 4.45V at a constant current of 0.5C at 45℃, left to rest for 30 minutes, and then discharged to 3.0V at 0.5C for 300 charge-discharge cycles.

[0096] Cycle capacity retention (%) = (Capacity after 300 discharge cycles / Initial discharge capacity) × 100%

[0097] (2) Room temperature cycling performance test

[0098] The battery was charged to 4.45V at a constant current of 0.5C at 25℃, left to rest for 30 minutes, and then discharged to 3.0V at 0.5C for 300 charge-discharge cycles.

[0099] Cycle capacity retention (%) = (Capacity after 300 discharge cycles / Initial discharge capacity) × 100%

[0100] (3) Compacted density of the negative electrode

[0101] The compaction density of the negative electrode sheet = the mass of the negative electrode active layer per unit area (g / cm³) 2 The mass of the negative electrode active material layer per unit area can be measured using a standard balance, and the thickness of the negative electrode active material layer can be measured using a micrometer.

[0102] The electrical performance test data is shown below:

[0103] In the embodiments listed in Table 1, the positive electrode active material used is LiCoO2, and the negative electrode active material includes a mixture of silicon-based active material and graphite. The compaction density of the negative electrode sheet is 1.2 g / cm³. 3 The metal salts added in Table 1 are all bis(trifluorosulfonyl)imide metal salts.

[0104] Table 1. Parameters of Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-4

[0105]

[0106] As can be seen from the data in Table 1, by adjusting the mass percentage of magnesium ions (A ppm) in the electrolyte and the mass ratio of silicon-based active material to negative electrode active material to X%, the two can satisfy the following relationship: 0 < X / A ≤ 8, and further, 0.001 ≤ X / A ≤ 4, which can effectively improve the cycle performance of lithium-ion batteries. When the mass percentage of metal ions (A ppm) satisfies 10 ≤ A ≤ 8000, the electrochemical device has even better cycle performance.

[0107] In the embodiments listed in Table 2, the positive electrode active material used in Examples 2-1 to 2-11 is LiCoO2, the negative electrode active material includes a mixture of silicon-based active material and graphite, and the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 The electrolyte contains 1000 ppm of magnesium ions, and silicon-based active materials account for 15% of the negative electrode active materials.

[0108] Table 2 Parameters of Examples 2-1 to 2-11 and Examples 1-4

[0109]

[0110]

[0111] As can be seen from Table 2, adding different amounts and types of anions based on Examples 1-4 can further improve the cycle performance of the electrochemical device. This is because the anionic groups can participate in the formation of a low-resistance SEI film at the negative electrode interface, which can accelerate the conduction of lithium ions and improve the cycle performance of the electrochemical device. When the mass percentage content B ppm of the anions meets the requirement of 5 ≤ B ≤ 10000, the electrochemical device has better cycle performance.

[0112] In the embodiments listed in Table 3, the positive electrode active material used in Examples 3-1 to 3-8 is LiCoO2, the negative electrode active material includes a mixture of silicon-based active material and graphite, and the compaction density of the negative electrode sheet is 1.2 g / cm³. 3 The electrolyte contains 1000 ppm of magnesium ions and NO3. 2- The content is 500ppm, and silicon-based active materials account for 15% of the negative electrode active materials.

[0113] Table 3 Parameters of Examples 3-1 to 3-8 and Examples 2-5

[0114]

[0115] As can be seen from Table 3, adding different types and amounts of additives based on Examples 2-5 can further improve the cycle performance of the electrochemical device. When the mass percentage C% of the additive satisfies 0.5≤C≤40, the electrochemical device has better cycle performance.

[0116] In Table 4, the positive electrode active material used in Examples 4-1 to 4-4 was LiCoO2, the negative electrode active material was a mixture of silicon-based active material and graphite, the magnesium ion content in the electrolyte was 1000 ppm, and NO3- was... 2- The content was 500 ppm.

[0117] Table 4. Parameters of Examples 3-7 and Examples 4-1 to 4-8

[0118]

[0119] As can be seen from Table 4, based on Examples 3-7, when 1 ≤ N ≤ 50, the cycle performance of the electrochemical device can be further improved; when the compaction density of the negative electrode sheet is Mg / cm 3 When 1≤M≤2.5, the electrochemical device has better cycle performance.

[0120] The above-described features are not intended to limit the scope of this disclosure. Therefore, any equivalent changes made to the content described in the claims of this disclosure should be included within the scope of the claims of this disclosure.

Claims

1. An electrochemical device, comprising a negative electrode and an electrolyte: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector; The negative electrode active material layer includes a negative electrode active material; The negative electrode active material contains silicon-based active material, and the silicon-based active material accounts for X% of the mass of the negative electrode active material. The electrolyte contains metal ions, wherein... Based on the mass of the electrolyte, the mass percentage of the metal ions is A ppm, 10 ≤ A ≤ 8000, and the following relationship exists between X and A: 0 <X / A≤8; The negative electrode active material includes silicon-based active particles. The cross-section of the negative electrode active material layer includes an area of ​​200 μm. 2 A square region, wherein the number of silicon-based active particles contained in the square region is N, 1≤N≤50, and the cross section of the negative electrode active material layer is parallel to the thickness direction of the negative electrode active material layer; The electrolyte also contains additives, including at least one selected from fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonyl lactone, succinate, adiponitrile, or 1,3,6-hexanetrionitrile.

2. The electrochemical device according to claim 1, wherein, The metal ions include at least one of magnesium ions, aluminum ions, zinc ions, calcium ions, titanium ions, cesium ions, and molybdenum ions.

3. The electrochemical device according to claim 1, wherein, The electrolyte also contains anions NO3-. 2- SO4 2- SO3 2- CO3 2- SiO3 2- At least one of them.

4. The electrochemical device according to claim 3, wherein, Based on the mass of the electrolyte, the mass percentage of the anion is B ppm, where 5 ≤ B ≤ 10000.

5. The electrochemical device according to claim 1 or 3, wherein, Based on the total weight of the electrolyte, the mass percentage of the additive is C%, 0.5 ≤ C ≤ 40.

6. The electrochemical device according to any one of claims 1-3, wherein, The compaction density of the negative electrode sheet is M g / cm³. 3 , 1≤M≤2.

5.

7. The electrochemical device according to any one of claims 1-3, wherein, 0.001≤X / A≤4.

8. The electrochemical device according to any one of claims 1-3, wherein, During the charging process of the electrochemical device, the metal ions undergo a reduction reaction on the negative electrode and form a stable Si-metal binary alloy phase or Si-O-metal ternary alloy phase with the silicon element in the silicon-based active material.

9. The electrochemical device according to any one of claims 1-3, wherein at least one of the following conditions is satisfied: (1) Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 5%-30%; (2) Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is 0.5%-3%; (3) Based on the mass of the electrolyte, the mass percentage of the 1,3-propanesulfonyl lactone is 0.5%-3%; (4) Based on the mass of the electrolyte, the mass percentage of the succinic anion is 0.5%-3%; (5) Based on the mass of the electrolyte, the adiponitrile mass percentage is 0.5%-3%; (6) Based on the mass of the electrolyte, the mass percentage of the 1,3,6-hexanetrionitrile is 0.5%-3%.

10. An electronic device comprising the electrochemical device according to any one of claims 1-9.

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