Electrochemical device and electronic device

Abstract

The application provides an electrochemical device, which comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material; the negative electrode active material comprises a silicon-based active material, and the mass ratio of the silicon-based active material to the negative electrode active material is X%; the electrolyte contains metal ions, and the mass percentage of the metal ions in the electrolyte is A ppm based on the mass of the electrolyte; and the relationship between X and A satisfies the formula: 0X / A≤8. In the charging process of the electrochemical device, the metal ions can be reduced at the negative electrode and form a stable Si-metal binary alloy phase or a Si-O-metal ternary alloy phase with silicon in the silicon-based active material, effectively inhibits the lithium intercalation expansion of the silicon-based active material, reduces the consumption of the electrolyte, and effectively improves the cycle performance of the electrochemical device.

Description

[0001] The present application is a divisional application of the original invention patent application (application date: March 22, 2022, application number: 202210281888.5, and invention name: Electrochemical device and electronic device). TECHNICAL FIELD

[0002] The present application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. BACKGROUND

[0003] Lithium ion batteries have the advantages of high energy density, long cycle life, good safety, etc., and are widely used in various fields such as portable energy storage, electronic devices, electric vehicles, etc. With the rapid development of the technology society, higher requirements are put forward for the comprehensive performance of lithium ion batteries in various industries, such as higher energy density and better cycle performance, etc.

[0004] Silicon-based materials have high specific capacity, and can significantly improve the energy density of lithium ion batteries when used as negative electrode active materials. However, during the deintercalation of lithium ions, silicon-based materials will produce a large volume expansion, which will cause the thickness of the battery to increase during the cycle process, the destruction of the negative electrode SEI film, the instability of the electrode interface, and the consumption of electrolyte caused by the reformation of the SEI film, etc. These problems will worsen the cycle life of lithium ion batteries. SUMMARY

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

[0006] In order to achieve the above-mentioned purpose, the present application provides an electrochemical device, which comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material; the negative electrode active material contains a silicon-based active material, and the mass ratio of the silicon-based active material to the negative electrode active material is X%; the electrolyte contains metal ions, wherein the mass percentage of the metal ions in the electrolyte is A ppm based on the mass of the electrolyte, and the relationship between X and A satisfies the following relationship: 0 < X / A ≤ 8. In some embodiments, the relationship between X and A satisfies the following relationship: 0.001 ≤ X / A ≤ 4.

[0007] In some embodiments, the metal ions include at least one of 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 in the electrolyte is Appm based on the mass of the electrolyte, and 10 ≤ A ≤ 8000.

[0009] In some embodiments, the electrolyte can further comprise at least one of anions NO3 2- , SO4 2- , SO3 2- , CO3 2- , SiO3 2- .

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

[0011] In some embodiments, the electrolyte can further comprise an additive; the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, butanedinitrile, hexanedinitrile, 1,3,6-hexanetricarbonitrile.

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

[0013] In some embodiments, the negative electrode active material comprises silicon-based active particles, a square area of 200μm 2 is selected on a cross section of the negative electrode active material layer, the square area contains N silicon-based active particles, 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 / cm 3 , 1≤M≤2.5.

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

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

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

[0018] (3) the mass percentage of the 1,3-propane sultone is 0.5%-3%, based on the mass of the electrolyte;

[0019] (4) the mass percentage of the butanedinitrile is 0.5%-3%, based on the mass of the electrolyte;

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

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

[0022] In some embodiments, the present application also provides an electronic device comprising the above-mentioned electrochemical device.

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

[0024] The metal ions added in the electrochemical device of the present application can undergo reduction reaction at the negative electrode during charging and form stable Si-metal binary alloy phase or Si-O-metal ternary alloy phase with silicon elements in the silicon-based active material, effectively inhibiting the lithium intercalation expansion of the silicon-based active material, reducing the rupture of the negative electrode interface SEI film and the consumption of the electrolyte, and effectively improving the cycle performance of the electrochemical device. DETAILED DESCRIPTION

[0025] It will be understood that the disclosed embodiments are merely examples of the present application, and the present application can be implemented in various forms, therefore, the specific details disclosed herein should not be interpreted as limiting, but only as a basis for the claims and as a representative basis for teaching those of ordinary skill in the art to implement the present application in various ways.

[0026] [Electrochemical device]

[0027] The electrochemical device of the present application is not particularly limited, and it can include any device that undergoes electrochemical reaction. In some embodiments, the electrochemical device can include but is not limited to a lithium ion battery.

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

[0029] [Negative electrode sheet]

[0030] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer 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 active material layer further comprises a conductive agent. The specific kind of the conductive agent is not limited and can be selected according to the needs. As an example, the conductive agent includes, but is not limited to, at least one of conductive graphite, super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0036] In some embodiments, the negative active material layer further comprises a thickening agent. The specific kind of the thickening agent is not limited and can be selected according to the needs. As an example, the thickening agent includes, but is not limited to, sodium carboxymethyl cellulose (CMC).

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

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

[0039] The negative electrode sheet in the present application can be prepared according to the conventional method in the art. The negative active material and optionally the conductive agent, the binder, and the thickening agent are dispersed in a solvent to form a uniform negative electrode slurry, the negative electrode slurry is coated on the negative current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing. The solvent can be N-methyl pyrrolidone (NMP) or deionized water, but the present application is not limited thereto.

[0040] The negative electrode sheet in the present application does not exclude other additional functional layers in addition to the negative film layer. For example, in some embodiments, the negative electrode sheet of the present application further comprises a conductive primer layer (for example, composed of a conductive agent and a binder) disposed on the surface of the negative current collector and sandwiched between the negative current collector and the negative film layer.

[0041] [Electrolyte]

[0042] In some embodiments, the electrolyte comprises metal ions, which include at least one of magnesium ions, aluminum ions, zinc ions, calcium ions, titanium ions, cesium ions, molybdenum ions.

[0043] In some embodiments, the metal ions are from a bis-trifluorosulfonimide metal salt, a trifluorosulfonimide metal salt, or other salts known in the art containing the metal ions, such as magnesium sulfate, zinc sulfate, or aluminum sulfate.

[0044] In some embodiments, the mass percentage of the metal ions is A ppm, 10≤A≤8000, based on the mass of the electrolyte. 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 the interaction between the metal ions and silicon elements at the negative electrode cannot effectively inhibit the expansion of the silicon-based active material. When the mass percentage of the metal ions is too high, the excess metal elements will be deposited at the negative electrode, which is prone to cause side reactions with the electrolyte, adversely affecting the cycle performance of the electrochemical device.

[0045] In some embodiments, the electrolyte can further comprise at least one of anions NO3 2- , 804 2- , 803 2- , CO3 2- , SiO3 2- . In some embodiments, the mass percentage of the anions is B ppm, 5≤B≤10000, based on the mass of the electrolyte. In some embodiments, 100≤B≤10000. The addition of the anions in the electrolyte can further improve the cycle performance of the electrochemical device, because the anion groups participate in the formation of a low-impedance SEI film at the negative electrode interface, which helps to accelerate the conduction of lithium ions and effectively improves the cycle performance of the electrochemical device. In some embodiments, the anions are from lithium salt compounds, such as lithium sulfate, lithium nitrate, lithium sulfite, lithium silicate, or lithium carbonate, etc., or other substances known in the art containing the above-mentioned anions.

[0046] In some embodiments, the electrolyte can further comprise an additive; in some embodiments, the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, butanedinitrile, hexanedinitrile, 1,3,6-hexanetricarbonitrile. In some embodiments, the mass percentage of the additive is C%, 0.5≤C≤40, based on the total weight of the electrolyte. The additive can act as a positive and negative electrode interface protective agent, stabilize the electrode structure, reduce the side reactions between the positive and negative active materials and the electrolyte, and further improve the cycle stability of the electrochemical device.

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

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

[0049] In some embodiments, the mass percentage of the 1,3-propane sultone is 0.5%-3%.

[0050] In some embodiments, the mass percentage of the butanedinitrile is 0.5%-3%.

[0051] In some embodiments, the mass percentage of the adiponitrile is 0.5% to 3%.

[0052] In some embodiments, the mass percentage of the 1,3,6-hexanetricarbonitrile is 0.5% to 3%.

[0053] In some embodiments, the electrolyte further comprises an organic solvent and a lithium salt, wherein neither the organic solvent nor the kind of the lithium salt is particularly limited and can be selected as desired.

[0054] In some embodiments, the lithium salt includes, by way of example but not limitation, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB). The above lithium salt can be used alone or in combination of two or more.

[0055] In some embodiments, the organic solvent can include at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, a sulfone compound. By way of 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), cyclobutane sulfone (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), 1,3-dioxolane (DOL), dimethyl ether (DME). The above organic solvent can be used alone or in combination of two or more. Alternatively, the above organic solvent can be used in combination of two or more.

[0056] The electrolyte can be prepared according to a method conventional in the art. For example, the organic solvent, the lithium salt, and optionally the additive can be mixed uniformly to obtain the electrolyte. The order of adding each material is not particularly limited, for example, the lithium salt and optionally the additive can be added to the organic solvent and mixed uniformly to obtain the electrolyte.

[0057] In the present application, the additive in the electrolyte and its content can be determined according to the conventional method in the art. For example, the additive in the electrolyte and its content can be detected by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), inductively coupled plasma spectrometer (ICP), etc.

[0058] It should be noted that when the electrolyte in the present application is tested, the fresh prepared electrolyte can be directly taken, or the electrolyte can be obtained from the electrochemical device. An exemplary method for obtaining the electrolyte from the electrochemical device includes the following steps: discharging the electrochemical device to the discharge cut-off voltage, then performing centrifugal treatment, and then taking an appropriate amount of the liquid obtained by the centrifugal treatment as the electrolyte.

[0059] [Positive electrode sheet]

[0060] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film arranged on at least one surface of the positive electrode current collector. The positive electrode film generally comprises a positive electrode active material and optionally a positive electrode binder and a conductive agent.

[0061] In some embodiments, the positive electrode current collector can be a metal foil or a porous metal plate, for example, a foil or a porous plate using a metal such as aluminum, copper, nickel, titanium, silver, or an alloy thereof. As an example, the positive electrode current collector can be an aluminum foil.

[0062] In some embodiments, the positive electrode active material can 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-containing phosphate with olivine structure, etc., such as lithium cobaltate or lithium manganate, but the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials can also be used.

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

[0064] In some embodiments, the conductive agent comprises 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 the binder and the conductive agent are dissolved and dispersed in a solvent to form a uniform positive electrode slurry, the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained through processes such as drying, cold pressing, etc. The solvent is a solvent known in the art that can be used as a solvent for the positive electrode active material layer, for example, but not limited to, N-methyl pyrrolidone (NMP).

[0066] [Separator]

[0067] The separator includes polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer composite film thereof. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of 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 layer. In some embodiments, the coating layer comprises at least one of an organic coating layer and an inorganic coating layer, wherein the organic coating layer 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, acrylate-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, sodium carboxymethyl cellulose; and the inorganic coating layer is selected from at least one of SiO2, Al2O3, CaO, TiO2, ZnO2, MgO, ZrO2, SnO2.

[0070] The present application does not have specific limitations on the morphology and thickness of the separator, such as a porous structure. The preparation method of the separator is a method known in the art that can be used to prepare a separator for an electrochemical device.

[0071] [Shell]

[0072] The shell is used to package the electrode assembly. In some embodiments, the shell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.; or a soft package, such as a bag-type soft package, the material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS).

[0073] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process, the electrode assembly is placed in the shell, the electrolyte is injected, and after processes such as vacuum packaging, standing, formation, shaping, and capacity distribution, an electrochemical device can be obtained.

[0074] (Electronic device)

[0075] The electronic device of the present application is any electronic device such as, but not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a home-use large storage battery, a lithium ion capacitor. Note that the electrochemical device of the present application is applicable not only to the above-mentioned electronic devices but also to energy storage power stations, sea-borne vehicles, air-borne vehicles. The air-borne vehicles include air-borne vehicles within the atmosphere and air-borne vehicles outside the atmosphere.

[0076] In some embodiments, the electronic device comprises the electrochemical device of the present application.

[0077] [Tests]

[0078] Some specific examples and comparative examples are listed below to better illustrate the present application. In the following examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0079] The examples and comparative examples of the present application are all exemplified by lithium ion batteries and are all prepared according to the following method:

[0080] (1) Preparation of the positive electrode sheet

[0081] The positive electrode active material lithium cobaltate (molecular formula LiCoO2), polyvinylidene fluoride (PVDF) and conductive carbon black (Super-P) are mixed in a mass ratio of 96:2:2 in N-methyl pyrrolidone (NMP) to form a positive electrode slurry. The positive electrode slurry is uniformly coated on a positive electrode current collector aluminum foil with a thickness of 12 μm, baked at 120°C for 1 h, and then compressed and cut to obtain the positive electrode sheet.

[0082] (2) Preparation of the negative electrode sheet

[0083] The negative electrode active material, sodium carboxymethyl cellulose (CMC) and butadiene rubber are mixed in deionized water in a mass ratio of 85:2:13, and the mixture is stirred to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a negative electrode current collector copper foil with a thickness of 12 μm, baked at 120°C for 1 h to obtain a negative electrode film, and then compressed and cut to obtain the negative electrode sheet. The negative electrode active material is a mixture of a silicon-based active material and graphite, and the proportion of the silicon-based active material in the negative electrode active material is 15%.

[0084] (3) Preparation of the separator

[0085] A polypropylene film with a thickness of 12 μm was used as the separator.

[0086] (4) Preparation of the electrolyte

[0087] Ethylene carbonate and diethyl carbonate were mixed in a mass ratio of 3:7 to obtain a base solvent, and dry lithium hexafluorophosphate (LiPF6) was added to the base solvent to obtain an electrolyte, wherein the mass percentage of LiPF6 was 12.5%. The electrolyte containing the additive of the present application was obtained by adding a certain amount of the additive to the electrolyte.

[0088] (5) Preparation of the lithium ion battery

[0089] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive and negative electrodes to play a separating role, and then wound into a square bare cell. The bare cell was placed in an aluminum plastic packaging bag, and after drying at 80°C, a dry cell was prepared. The dry cell was injected with the corresponding electrolyte, and after vacuum packaging, standing, formation, and shaping, the lithium ion battery was prepared.

[0090] The lithium ion batteries of the examples and the comparative examples of the present application were prepared according to the above method, and the battery performance was tested. The types and amounts of the substances or additives used in the examples and the comparative examples, and the performance test results of the lithium ion batteries are shown in Tables 1 to 4, wherein the amount of each additive is the weight percentage calculated based on the mass of the electrolyte.

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

[0092] The cold-pressed negative electrode sheet was cut into a sample of 6 mm x 6 mm in size, and the sample stage was heated on a heater at a temperature of 150°C to 160°C. Paraffin was then applied to the sample stage, and after the paraffin melted, the negative electrode sheet sample was placed on the paraffin, with the sample slightly protruding from the edge of the sample stage. An ion polishing instrument was then used to cut the sample in the thickness direction, and a scanning electron microscope (SEM) was used to observe the cross section obtained by the cutting, and an X-ray energy spectrum analyzer (EDS) was used to detect the element Si to mark the silicon-based active particles. A square area of 200 μm 2 on the cross section was selected at any position, and the number of silicon-based active particles falling within the square area (any position of the particles falling within the square area was counted) was observed, i.e., the number of silicon-based active particles contained in a square area of 200 μm 2 .

[0093] Next, the performance of the lithium ion battery was tested.

[0094] (1) High temperature cycle performance test

[0095] The battery was charged at 45℃ to 4.45V at a constant current of 0.5C, rested for 30min, discharged to 3.0V at 0.5C, and cycled for 300 times;

[0096] Cycle capacity retention rate (%) = 300th discharge capacity / first discharge capacity x 100%

[0097] (2) Normal temperature cycle performance test

[0098] The battery was charged at 25℃ to 4.45V at a constant current of 0.5C, rested for 30min, discharged to 3.0V at 0.5C, and cycled for 300 times;

[0099] Cycle capacity retention rate (%) = 300th discharge capacity / first discharge capacity x 100%

[0100] (3) Compaction density of negative electrode sheet

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

[0102] The electrical performance test data are shown as follows:

[0103] In the examples of Table 1, the positive electrode active material used is LiCoO2, the negative electrode active material includes a mixture of silicon-based active material and graphite, the compaction density of the negative electrode sheet is 1.2g / cm 3 , and the metal salt added in Table 1 is a bis-trifluorosulfonimide metal salt.

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

[0105]

[0106] As can be seen from the data in Table 1, by adjusting the mass percentage content A ppm of magnesium ions in the electrolyte and the mass ratio of silicon-based active material to negative electrode active material X%, and making both satisfy the relationship: 0X / A≤8, further 0.001X / A≤4, the cycle performance of the lithium ion battery can be effectively improved; when the mass percentage content A ppm of the metal ions satisfies 10A≤8000, the electrochemical device has a more optimal 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, on the basis of Example 3-7, when 1≤N≤50, the cycle performance of the electrochemical device can be further improved; when the compaction density Mg / cm3of the negative electrode sheet is 1.5≤M≤2.5, the electrochemical device has better cycle performance. 3 When 1≤M≤2.5 is satisfied, the electrochemical device has better cycle performance.

[0120] The above disclosed features are not intended to limit the scope of the present disclosure, and equivalent changes made to the content described in the claims of the present disclosure should be included within the scope of the claims of the present 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 comprises 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 metal ions include at least one of magnesium ions, aluminum ions, zinc ions, calcium ions, titanium ions, cesium ions, and molybdenum ions; The negative electrode active material includes silicon-based active particles. The cross section of the negative electrode active material layer includes a square region with an area of 200 μm 2 2, the number of the silicon-based active particles contained in the square region is N, and 1 ≤ N ≤ 50. The cross section of the negative electrode active material layer is parallel to the thickness direction of the negative electrode active material layer.

2. The electrochemical device of claim 1, 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.

3. The electrochemical device according to claim 1, wherein, The electrolyte further comprises at least one of anions NO3 2- , SO4 2- , SO3 2- , CO3 2- , SiO3 2- .

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, wherein, The electrolyte also contains additives; The additives include at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonyl lactone, succinate, adiponitrile, or 1,3,6-hexanetrionitrile. 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 claim 1, wherein, The compacted density of the negative electrode sheet is M g / cm 3 , 1≤M≤2.

5.

7. The electrochemical device of claim 1, wherein, 0.001≤X / A≤4.

8. The electrochemical device according to claim 5, 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%.

9. An electronic device comprising the electrochemical device according to any one of claims 1-8.

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