Electrochemical device and electronic apparatus

Abstract

The invention discloses an electrochemical device and electronic equipment, the electrochemical device comprises a negative electrode piece and an electrolyte, the negative electrode piece comprises a negative electrode active material, the negative electrode active material contains a silicon-based material, based on the mass of the negative electrode active material, the mass percentage content of a silicon element in the silicon-based material is Z1%, 0.1 < Z1 < 15, the electrolyte comprises a compound shown in a formula I and a substance A, the substance A is selected from at least one of ethylene sulfite, ethylene sulfate, vinyl ethylene sulfite, trifluoromethyl phenyl sulfide or methylene methanedisulfonate, based on the mass of the electrolyte, the mass percentage content of the compound shown in the formula I is a%, the mass percentage content of the substance A is b%, a / b is larger than or equal to 0.5 and smaller than or equal to 20, and a is larger than or equal to 0.5 and smaller than or equal to 20. The electrochemical device provided by the invention has relatively small volume expansion and relatively low impedance increase in a normal-temperature cycle process.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high operating voltage, long cycle life and environmental friendliness. They are widely used in portable electronic devices such as mobile phones, laptops, and cameras. They are also the preferred power source for future electric vehicles and hybrid vehicles. At present, in order to improve the energy density of lithium-ion batteries, high-specific-capacity electrode materials are mainly used. Silicon-based materials, as a type of alloyed negative electrode materials, can provide ultra-high specific capacity of up to 4200mAh / g. However, silicon negative electrodes will experience drastic volume expansion and contraction during the lithium ion insertion / deinsertion process, resulting in increased impedance. Summary of the invention

[0003] In view of this, the present application provides an electrochemical device and an electronic device, wherein the negative electrode of the electrochemical device is a silicon-containing negative electrode and the electrolyte of the electrochemical device contains a compound of formula I and substance A, and the types and contents of the three are appropriately regulated so that the three cooperate with each other, thereby suppressing the volume expansion and impedance growth of the electrochemical device during normal temperature circulation.

[0004] In a first aspect, the present application provides an electrochemical device, the electrochemical device comprising a negative electrode plate and an electrolyte, the negative electrode plate comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material, based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, 0.1<Z1<15, and the electrolyte comprises a compound of formula I;

[0005]

[0006] R is selected from fluorine-substituted or unsubstituted C2-C6 alkyl, fluorine-substituted or unsubstituted C6-C 12 Nitrogen-containing heterocyclic group, fluorine-substituted or unsubstituted C6~C 12Aryl. The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide or methylene disulfonate. Based on the mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of substance A is b%, 0.5≤a / b≤20, 0.5≤a≤20. Preferably, substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide or methylene disulfonate and contains at least vinyl sulfate. The present application regulates the content of silicon in the silicon-based material within the above range, and at the same time coordinately regulates the electrolyte to include the compound of formula I and substance A, and the type and content of the compound of formula I and the type and content of substance A are also within the above range. As a result, the volume expansion and impedance growth of the silicon-containing negative electrode electrochemical device in normal temperature cycles can be improved. The inventors have found that by regulating the electrolyte to contain the compound of formula I and substance A and their content and ratio within the above range, a relatively stable interface layer can be formed between the electrolyte and the surface of the mixed silicon-carbon negative electrode, thereby reducing the side reactions of the electrolyte on the negative electrode surface during the cycle, thereby achieving the inhibition of volume expansion and impedance growth of the battery during normal temperature cycling.

[0007] In some embodiments, the compound of Formula I includes at least one of the following compounds:

[0008]

[0009] The above-mentioned compound of formula I, when combined with substance A and an appropriate amount of silicon, has a better effect of inhibiting the volume expansion and impedance growth of the battery during normal temperature cycling.

[0010] In some embodiments, at least one of the following conditions is satisfied: (1) 0.1≤a / Z1≤6, (2) 0.3≤b≤8. Preferably, 4≤Z1≤5, 0.5≤b≤4. More preferably, 1≤b≤3, 2≤a / Z1≤3. The present application further regulates the values ​​of the silicon content, the content of the compound of formula I, and the content of substance A within the above ranges, which can further improve the cycle performance of the electrochemical device at room temperature.

[0011] In some embodiments, the silicon-based material includes at least one of silicon, silicon monoxide, silicon carbon or silicon oxycarbon ceramic particles, the silicon carbon particles include a carbon skeleton, amorphous silicon dispersed in the carbon skeleton, and a protective layer located on at least a portion of the surface of the carbon skeleton, the material of the protective layer includes amorphous carbon, and the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon or hard carbon.

[0012] In some embodiments, the electrolyte includes fluoroethylene carbonate and / or vinylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is c1%, and the mass percentage of vinylene carbonate is c2%, satisfying: 12≤(c1+c2×60)≤25, 0.5≤(c1+c2×60) / Z1≤10. Preferably, 2.4≤(c1+c2×60) / Z1≤4.8. The electrolyte is regulated to also include fluoroethylene carbonate and / or vinylene carbonate, and their content relationship is within the above range. While taking into account the suppression of the normal temperature cycle volume expansion of the electrochemical device, its storage performance at high temperature can be further improved, especially the suppression of its storage volume expansion at high temperature.

[0013] In some embodiments, the electrolyte includes a dinitrile compound, the dinitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether or 1,4-dicyano-2-butene, and the mass percentage of the dinitrile compound is d%, 0.1≤d≤5 based on the mass of the electrolyte. By adding the dinitrile compound to the electrolyte, and the type and content of the dinitrile compound are within the scope of the present application, it is beneficial to further improve the storage performance of the electrochemical device at high temperature.

[0014] In some embodiments, the electrolyte includes a trinitrile compound, the trinitrile compound is selected from at least one of 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, 1,3,5-pentanetricarbonitrile or tricyanobenzene, and the mass percentage of the trinitrile compound is e%, 1≤d / e≤2 based on the mass of the electrolyte. Preferably, 1≤d≤5. The electrolyte is further regulated to include a trinitrile compound, and the content of the trinitrile compound is also within the above range, which has a better effect on improving the high temperature storage performance of the electrochemical device.

[0015] In some embodiments, the electrolyte further comprises substance B and ethylene carbonate, substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate or ethyl propionate, and based on the mass of the electrolyte, the mass percentage of substance B is f%, 25≤f≤50, and the mass percentage of ethylene carbonate is g%, 10≤g≤20. The electrolyte contains the above-mentioned substance B, and the content of substance B is also within the scope of the present application. Substance B and an appropriate amount of ethylene carbonate can further improve the comprehensive performance of the electrochemical device, especially the electrochemical device has a better room temperature and high temperature cycle capacity retention rate, and a lower high temperature storage volume expansion rate. Preferably, 0.5≤f / g≤3.

[0016] In a second aspect, the present application provides an electronic device, which includes the electrochemical device in any of the above embodiments. Therefore, the electronic device provided by the present application has good room temperature performance.

[0017] The electrochemical device provided in the first aspect of the present application has a small volume expansion and a low impedance growth under normal temperature cycles. Thus, the electronic device provided in the second aspect of the present application also has a small volume expansion and a low impedance growth under normal temperature cycles. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0019] It should be noted that in the specific embodiments of the present application, a lithium ion secondary battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium ion secondary battery.

[0020] Lithium-ion secondary battery

[0021] The invention comprises a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material comprises a silicon-based material, and based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1, 0.1<Z1<15, and the electrolyte comprises a compound of formula I;

[0022]

[0023] R is selected from fluorine-substituted or unsubstituted C2-C6 alkyl, fluorine-substituted or unsubstituted C6-C 12 Nitrogen-containing heterocyclic group, fluorine-substituted or unsubstituted C6~C 12Aryl. The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl sulfite, trifluoromethyl phenyl sulfide or methylene disulfonate. Based on the mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of substance A is b%, 0.5≤a / b≤20, 0.5≤a≤20, 0.1≤a / Z1≤6, 0.3≤b≤8. Preferably, substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl sulfite, trifluoromethyl phenyl sulfide or methylene disulfonate and contains at least vinyl sulfate. The present application can improve the volume expansion and impedance growth of the electrochemical device under normal temperature circulation by regulating the content of silicon element in the silicon-based material to be appropriate and regulating the electrolyte to include the compound of formula I and substance A, and the content of the compound of formula I and substance A is also within the above range. Exemplarily, the value of a can be 0.5, 1, 2, 5, 6, 8, 10, 12, 14, 15, 17, 18, 20, or a range consisting of any two of the above values. Exemplarily, the value of a / b can be 0.5, 1.3, 3.2, 4.4, 5.2, 7.2, 8.5, 9.9, 11.4, 13.9, 14.4, 16.1, 17.1, 19.4, 20, or a range consisting of any two of the above values. Exemplarily, the value of a / Z1 can be 0.1, 0.2, 0.8, 1.1, 1.4, 1.9, 2.0, 2.7, 2.8, 3, 3.4, 3.7, 4.1, 4.5, 4.7, 5, 6, or a range consisting of any two of the above values. Exemplarily, the value of b can be 0.3, 0.5, 1.0, 1.3, 1.6, 2.0, 2.5, 2.7, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.6, 4.9, 5, 5.5, 6, 6.5, 7.5, 8, or a range consisting of any two of the above values. Exemplarily, the value of Z1 can be 4, 4.3, 4.5, 4.6, 4.8, 5, or a range consisting of any two of the above values.

[0024] In some embodiments, the compound of Formula I includes at least one of the following compounds:

[0025]

[0026] The above-mentioned compounds of formula I are more conducive to synergistically improving the volume expansion and impedance growth of electrochemical devices during normal temperature cycles with other substances.

[0027] In some embodiments, the electrolyte includes fluoroethylene carbonate and / or vinylene carbonate, based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is c1%, and the mass percentage of vinylene carbonate is c2%, satisfying: 12≤(c1+c2×60)≤25, 2.4≤(c1+c2×60) / Z1≤4.8. The electrolyte contains fluoroethylene carbonate and / or vinylene carbonate, and the content of fluoroethylene carbonate and / or vinylene carbonate is in the above range, which can better improve the volume expansion of the electrochemical device at room temperature and take into account the lower impedance growth. Exemplarily, the value of (c1+c2×60) can be 12, 12.4, 13.4, 14.8, 16.0, 16.7, 17.0, 18.3, 19.7, 20.4, 21.6, 22.6, 23.0, 24.7, 25 or a range consisting of any two of the above values. Illustratively, the value of (c1+c2×60) / Z1 can be 0.5, 1.5, 2.4, 2.6, 2.8, 3, 3.2, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 6, 8.5, 10 or a range consisting of any two of the above values.

[0028] In some embodiments, the electrolyte includes a dinitrile compound, the dinitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether or 1,4-dicyano-2-butene, and the mass percentage of the dinitrile compound is d%, 0.1≤d≤5 based on the mass of the electrolyte. The electrolyte contains the above-mentioned types and contents of dinitrile compounds, which is beneficial to further improve the high temperature storage performance of the electrochemical device. Exemplarily, the value of d can be 0.1, 0.3, 0.6, 1.1, 1.3, 1.6, 2.2, 2.5, 2.8, 3.4, 3.6, 4, 4.4, 5 or a range consisting of any two of the above values.

[0029] In some embodiments, the electrolyte includes a trinitrile compound, the trinitrile compound is selected from at least one of 1,3,6-hexane trinitrile, 1,2,3-tris(2-cyano)propane, 1,3,5-pentane tricarbonitrile or tricyanobenzene, and the mass percentage of the trinitrile compound is e%, 1≤d / e≤2 based on the mass of the electrolyte. The electrolyte contains the above-mentioned types and contents of trinitrile compounds, and the effect of improving the high-temperature storage performance of the electrochemical device is better. Exemplarily, the value of d / e can be 1, 1.1, 1.3, 1.5, 1.8, 2 or a range consisting of any two of the above values.

[0030] In some embodiments, the electrolyte further includes substance B and ethylene carbonate, substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate or ethyl propionate, and based on the mass of the electrolyte, the mass percentage of substance B is f%, 25≤f≤50, and the mass percentage of ethylene carbonate is g%, 10≤g≤20. At this time, the comprehensive performance of the electrochemical device is better, that is, normal temperature cycle, high temperature cycle and high temperature storage are all better. Exemplarily, the value of f can be 25, 28, 30, 32, 35, 38, 40, 45, 50 or a range consisting of any two of the above values. Exemplarily, the value of g can be 10, 12, 13, 15, 18, 19, 20 or a range consisting of any two of the above values. Illustratively, the value of f / g can be 0.5, 0.6, 0.8, 0.9, 1.2, 1.3, 1.5, 1.8, 2.0, 2.1, 2.3, 2.4, 2.8, 2.9, 3, or a range consisting of any two of the above values.

[0031] The present application has no particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector, etc.

[0032] The negative electrode material layer may also include a binder and a thickener. The present application does not particularly limit the types of the binder and the thickener, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber or acrylic (ester) styrene-butadiene rubber; the thickener may include but is not limited to at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0033] The negative electrode material layer may also include a conductive agent. The present application does not particularly limit the type of the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials or conductive polymers. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder and thickener in the negative electrode active layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. Optionally, the negative electrode sheet may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application does not particularly limit the composition of the conductive layer, which may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, for example, it may be at least one of the conductive agent and binder in the above-mentioned negative electrode active layer.

[0034] other

[0035] The lithium-ion secondary battery also includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved, for example, it may include aluminum foil, aluminum alloy foil or a composite current collector (for example, a composite current collector with a metal layer disposed on the surface of a polymer layer).

[0036] The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 13 μm.

[0037] The positive electrode active material layer includes a positive electrode active material. The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include a composite metal oxide containing one or more selected from the group consisting of cobalt, manganese, and nickel and lithium, or an olivine-type phosphate containing one or more selected from iron, cobalt, nickel, and manganese. These positive electrode active materials can be used alone or in combination of two or more.

[0038] As such lithium composite metal oxides, for example, LiCoO2, LiMn2O4, LiNiO2, LiCo 1-x Ni x O2(0.01 <x<1)、LiNi x MnyCo z O2 (x+y+z=1), solid solution of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe, etc.), LiNi 1 / 2 Mn 3 / 2O4, LiFePO4, LiMnPO4, and LiMn 1-x Fe x PO4 (0.01 < x < 1), and more preferably two or more. A part of these composite metal oxides with lithium or olivine-type phosphates containing lithium can be replaced by other elements, or a part of cobalt, nickel, manganese, and iron can be replaced by one or two or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or coated with a compound containing these other elements or a carbon material. The present application has no particular limitation on the thickness of the positive electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0039] The positive electrode active material layer may further include a conductive agent and a binder. The present application has no particular limitation on the types of the conductive agent and the binder, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNT), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylates, acrylate polymers, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymer.

[0040] The present application has no particular limitation on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved.

[0041] The lithium ion secondary battery further includes a separator, which is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and does not affect the progress of the electrochemical charge and discharge process. The present application has no particular limitation on the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film.

[0042] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the present application has no particular restrictions on the above-mentioned inorganic particles, for example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the above-mentioned binder, for example, it may be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0043] The pore size of the diaphragm in the present application is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In some embodiments, the thickness of the diaphragm is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the diaphragm is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the diaphragm is within the above range, the insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0044] The electrochemical device of the present application also includes a packaging bag for containing a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in the electrochemical device, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0045] Lithium-ion secondary batteries can be prepared according to conventional methods in the art. For example, the positive electrode sheet, separator and negative electrode sheet are stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain an electrode assembly, or the electrode assembly can be obtained by winding; the electrode assembly is placed in a packaging shell, and the electrolyte is injected and sealed to obtain a secondary battery. There is no special limitation on the structure of lithium-ion secondary batteries, and coin-type batteries, cylindrical batteries, square batteries, or soft-pack batteries with single-layer or multi-layer separators can be used.

[0046] The purpose of the lithium ion secondary battery of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the lithium ion battery of the present application can be used for, but not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium ion capacitors, etc.

[0047] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Unless otherwise stated, the parts, percentages and ratios listed are all based on mass.

[0048] Example 1-1

[0049] (I) Preparation of lithium-ion batteries

[0050] <Preparation of negative electrode sheet>

[0051] Si / C composite material (carbon nanopore loaded Si), artificial graphite, negative electrode binder lithium polyacrylate (PAA-Li), and negative electrode conductive agent carbon nanotubes were mixed in a mass ratio of 20:70:7:3, deionized water was added, and mixed evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 30wt%. The negative electrode slurry was evenly coated on one side of a negative electrode current collector copper foil with a thickness of 12μm, and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer coated with a coating thickness of 143μm, and then the above steps were repeated on the other side of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer, and then cold pressed and cut to obtain a negative electrode sheet with a specification of 78mm×875mm, wherein the content of silicon in the silicon-based material based on the mass of the negative electrode active material is shown in Table 1.

[0052] <Preparation of positive electrode sheet>

[0053] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.4:1.6, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%. The positive electrode slurry is obtained after being stirred evenly by a vacuum mixer. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 85°C to obtain a positive electrode sheet with a single-sided positive electrode material layer coated with a coating thickness of 110μm. After that, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer coated. After coating, the positive electrode sheet is cold pressed and cut into a specification of 74mm×867mm for standby use. Among them, the compaction density of the positive electrode material layer after cold pressing is 4.15g / cm 3 .

[0054] <Preparation of Electrolyte>

[0055] In an argon atmosphere glove box with a water content of less than 10 ppm, propylene carbonate (PC), propyl propionate (PP) and diethyl carbonate (DEC) are mixed in a mass ratio of 2:3:5 to obtain a base solvent, and then formula I-1 (formula I compound), vinyl sulfate (substance A) and lithium hexafluorophosphate are added to the base solvent, and mixed evenly to obtain an electrolyte. Wherein, based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 12.5%, the contents of the formula I compound and substance A are shown in Table 1, and the balance is the base solvent.

[0056] <Diaphragm>

[0057] A polyethylene (PE) porous membrane with a thickness of 5 μm was used.

[0058] <Preparation of lithium-ion batteries>

[0059] The prepared positive electrode sheet, separator, negative electrode sheet and separator are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly. After welding the pole ear, the electrode assembly is placed in an aluminum plastic film packaging bag, placed in a vacuum oven at 85°C for 12 hours to remove moisture, and the prepared electrolyte is injected. After vacuum packaging, standing, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0060] Example 1-2 to Example 1-39

[0061] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0062] Example 2-1 to Example 2-7

[0063] Based on the electrolyte of Example 1-6, the substances in Table 2 are further added to the base solvent during the preparation process, and the balance is the base solvent. The rest is the same as that of Example 1-6.

[0064] Example 3-1 to Example 3-5

[0065] Based on the electrolyte of Example 2-7, the substances in Table 3 were further added to the base solvent during the preparation process, and the balance was the base solvent. The rest was the same as Example 1-1.

[0066] Comparative Examples 1 to 7

[0067] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0068] (II) Test methods

[0069] 1. Test of silicon content

[0070] The lithium-ion battery discharged at 0.5C to 3.0V was disassembled, the negative electrode plate was removed, and it was soaked in dimethyl carbonate (DMC) for 20 minutes, and then rinsed with DMC and acetone in turn. Then the negative electrode plate was placed in an oven and baked at 80°C for 12 hours to obtain the negative electrode plate. The negative electrode plate was placed in a vacuum oven and dried at 100°C for 24 hours, and 1g of the powdered sample of the negative electrode material layer on the negative electrode plate was scraped off with a blade, and then the mass percentage of silicon element in the negative electrode material layer was tested using an ICP (Inductively coupled plasma) analyzer.

[0071] 2. Cycle performance test

[0072] Place the lithium-ion battery in a 25℃ / 45℃ constant temperature test box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge it to 4.45V at a constant current of 0.5C, then charge it at a constant voltage to a current of 0.025C, let it stand for 5 minutes, and discharge it to 3.0V at a constant current of 0.5C. Record it as the initial discharge capacity C1, the initial thickness D1, and the initial impedance I1. Repeat this step for 500 cycles, record the discharge capacity C2 after 500 cycles, the thickness D2, and the impedance I2, and calculate the lithium-ion battery cycle capacity retention rate.

[0073] Normal temperature / high temperature cycle capacity retention rate = C2 / C1×100%

[0074] Normal temperature cycle volume expansion rate = D2 / D1×100%, normal temperature impedance growth rate = I2 / I1×100%.

[0075] 3. High temperature storage test

[0076] Place the lithium-ion battery in a 25℃ constant temperature environment and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature of 25℃. Charge it to 4.5V at a constant current of 0.5C, and charge it to a current of 0.025C at a constant voltage of 4.5V. Record the thickness of the lithium-ion battery at this time as the initial thickness H0. Transfer the lithium-ion battery to a 60℃ constant temperature box and store it for 30 days. During this period, test and record the thickness of the lithium-ion battery every 6 days. The test thickness recorded after 30 days is the storage thickness H1.

[0077] High temperature storage volume expansion rate = (H1-H0) / H0×100%.

[0078] Table 1

[0079]

[0080]

[0081]

[0082] Note: “ / ” in the table means there is no related parameter.

[0083] Combined with Table 1, compared with Example 1-1, the mass ratio (a / b) of the compound of formula I and substance A in the electrolyte of Comparative Examples 1 to 2 is not within the appropriate range, the content a of the compound of formula I in the electrolyte of Comparative Example 3 is not within the appropriate range, the content of silicon in the negative electrode sheet of Comparative Examples 4 to 5 is not within the appropriate range, the electrolyte of Comparative Example 6 does not contain substance A, and the electrolyte of Comparative Example 7 does not contain the compound of formula I. It can be seen from Table 1 that the room temperature performance of the lithium ion batteries corresponding to Comparative Examples 1 to 7 is not as good as the room temperature performance of the lithium ion battery of Example 1-1, especially, the volume expansion rate of the lithium ion batteries of Comparative Examples 1 to 7 at room temperature is above 17.9%, and can be as high as 23.3%, and its impedance growth rate at room temperature is also as high as 76.4% or more, and can be as high as 85.3%. The lithium ion battery of Example 1-1 has an appropriate silicon content, and the electrolyte contains compounds of formula I and substance A in appropriate types and mass proportions. Its volume expansion rate at room temperature is only 14.3%, and the impedance growth rate is reduced to 74.8%.

[0084] In particular, further regulating the content of silicon in the silicon-based material and the content of the compound of formula I and substance A in the electrolyte within a preferred range is conducive to the synergistic effect among the three, and can further inhibit the volume expansion and impedance growth of the electrochemical device at room temperature.

[0085] Table 2

[0086]

[0087]

[0088] It can be seen from Table 2 that by further adding fluoroethylene carbonate and / or vinylene carbonate to the electrolyte containing the compound of formula I and substance A, and regulating the content of fluoroethylene carbonate and / or vinylene carbonate within the above range, it is possible to further improve the high temperature performance of the lithium ion battery while taking into account the room temperature cycle performance, especially inhibiting the storage volume expansion at high temperature.

[0089] In particular, when the electrolyte further contains dinitrile compounds and trinitrile compounds, and the types and contents of dinitrile compounds and trinitrile compounds are also appropriate, the effects of improving the room temperature performance and high temperature performance of the lithium-ion battery are better, especially being able to further suppress its volume expansion rate under room temperature cycle and improve its storage volume expansion rate at high temperature.

[0090] Table 3

[0091]

[0092] Combined with Table 3, when an appropriate amount of substance B is further added to the electrolyte and an appropriate amount of ethylene carbonate is added in combination, the comprehensive performance of the electrochemical device is better, and the improvements in the room temperature cycle capacity rate, high temperature cycle capacity rate and high temperature storage volume expansion rate are all obvious.

[0093] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An electrochemical device, It is characterized in that The electrochemical device comprises a negative electrode sheet and an electrolyte; The negative electrode plate includes a negative electrode active material, the negative electrode active material contains a silicon-based material, and based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, 0.1<Z1<15; The electrolyte comprises a compound of formula I; wherein R is selected from fluorine-substituted or unsubstituted C 2 ~C 6 Alkyl, fluorine-substituted or unsubstituted C 6 ~C 12 Nitrogen-containing heterocyclic group, fluorine-substituted or unsubstituted C 6 ~C 12 Aryl; The electrolyte further includes a substance A, wherein the substance A is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethylphenyl sulfide or methylene methanedisulfonate; Based on the mass of the electrolyte, the mass percentage of the compound of formula I is a%, the mass percentage of the substance A is b%, 0.5≤a / b≤20, 0.5≤a≤20.

2. The electrochemical device according to claim 1, It is characterized in that The compound of formula I includes at least one of the following compounds:

3. The electrochemical device according to claim 1, It is characterized in that At least one of the following conditions is met: (1) 0.1≤a / Z1≤6; (2)0.3≤b≤8。 4. The electrochemical device according to any one of claims 1 to 3, It is characterized in that The electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate; Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is c1%, and the mass percentage of the vinylene carbonate is c2%, satisfying: 12≤(c1+c2×60)≤25.

5. The electrochemical device according to claim 4, It is characterized in that 0.5≤(c1+c2×60) / Z1≤10.

6. The electrochemical device according to claim 4, It is characterized in that The electrolyte includes a dinitrile compound; The dinitrile compound is selected from at least one of succinonitrile, adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether or 1,4-dicyano-2-butene; Based on the mass of the electrolyte, the mass percentage of the dinitrile compound is d%, and 0.1≤d≤5.

7. The electrochemical device according to claim 6, It is characterized in that The electrolyte includes a trinitrile compound; The trinitrile compound is selected from at least one of 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, 1,3,5-pentanetricarbonitrile or tricyanobenzene; Based on the mass of the electrolyte, the mass percentage of the trinitrile compound is e%, and 1≤d / e≤2.

8. The electrochemical device according to any one of claims 1 to 3, It is characterized in that The electrolyte further comprises substance B and ethylene carbonate; The substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate or ethyl propionate; Based on the mass of the electrolyte, the mass percentage of the substance B is f%, 10≤f≤50, and the mass percentage of the ethylene carbonate is g%, 10≤g≤20.

9. The electrochemical device according to claim 8, It is characterized in that 0.5≤f / g≤3.

10. An electronic device, It is characterized in that The electronic device comprises the electrochemical device according to any one of claims 1 to 9.

Images