Electrochemical device and electronic device

Abstract

The invention belongs to the technical field of energy storage, and particularly relates to an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least part of the surface of the positive electrode current collector; the compaction density of the positive electrode active material layer is pd mg / cm < 3 >, and pd is more than or equal to 2.6 and less than or equal to 2.86; based on the mass of the electrolyte, the electrolyte comprises ethylene carbonate with the mass content of A%, propylene carbonate with the mass content of B%, diethyl carbonate with the mass content of C%, ethyl propionate with the mass content of D% and propyl propionate with the mass content of E%; 1 < = B / A < = 8, and 5 < = (E + D) / C < = 14. Through cooperation of the carboxylic ester and the linear ester in the electrolyte, transmission of lithium ions in the electrochemical device can be accelerated, so that the dynamic performance is improved, and the impedance increase problem is solved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and specifically relates to an electrochemical device and an electronic device. Background Art

[0002] Various electrochemical devices, mainly secondary batteries, convert electrical energy into chemical energy through chemical reactions and release energy when needed, which has become an important pillar of modern energy storage and sustainable development. At present, electrochemical devices are widely used in electronic equipment, automobiles, aerospace and other fields due to their high energy density, long life and environmental protection.

[0003] However, with the continuous development of battery technology and the expansion of its application fields, the performance requirements for electrochemical devices are also increasing. In particular, it is necessary to increase the energy density of electrochemical devices to meet the requirements of electronic devices in terms of battery life. Increasing the compaction density of the electrode of the electrochemical device can increase its energy density to a certain extent, but too high a compaction density will deteriorate the kinetic performance of the electrochemical device, and it is also easy to cause the problem of rapid impedance growth during the cycle, affecting the performance of the electronic device under high-rate conditions or long-term application. Therefore, how to improve the kinetic performance of electrochemical devices and the problem of impedance growth during the cycle has become a problem that needs to be solved in the practical application of electrochemical devices. Summary of the invention

[0004] In view of this, the present application provides an electrochemical device and an electronic device, which can accelerate the transmission of lithium ions inside the electrochemical device through the combination of carboxylic acid esters and linear esters in the electrolyte, thereby improving the kinetic performance and impedance growth problem.

[0005] In a first aspect, the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least a portion of the surface of the positive electrode current collector; the compaction density of the positive electrode active material layer is pd g / cm 3 , 2.6×10 -3 ≤pd≤2.86×10 -3; Based on the mass of the electrolyte, the electrolyte includes: ethylene carbonate with a mass content of A%, propylene carbonate with a mass content of B%, diethyl carbonate with a mass content of C%, ethyl propionate with a mass content of D% and propyl propionate with a mass content of E%; 1≤B / A≤8, and 5≤(E+D) / C≤14. The present application adopts ethyl propionate, propyl propionate and diethyl carbonate to reduce the viscosity of the electrolyte, accelerate the transmission of lithium ions in the liquid phase, improve the kinetic performance of the electrochemical device and the ability to inhibit the impedance growth during the cycle; adding propylene carbonate and ethylene carbonate to closely cooperate with the above-mentioned electrolyte components can optimize the film formation quality of the negative electrode solid electrolyte interface film (SEI film), and under the condition of high positive electrode compaction density, it can further improve the rate performance of the electrochemical device and reduce the impedance growth during the cycle.

[0006] In some more preferred embodiments, in order to further improve the kinetic performance of the electrochemical device and the ability to inhibit the growth of cyclic impedance, the electrolyte satisfies at least one of the following conditions: (1) 3≤A≤6; (2) 12≤B≤20; (3) 5≤C≤8; (4) 20≤D≤30; (5) 20≤E≤40; (6) 2≤B / A≤6; (7) 6.6≤(E+D) / C≤9.2.

[0007] In some embodiments, the electrolyte includes fluoroethylene carbonate; based on the mass of the electrolyte, the mass content of fluoroethylene carbonate is P%, 5≤P≤20. Adding fluoroethylene carbonate (FEC) to the above electrolyte system can reduce interfacial side reactions and improve the high-temperature intermittent cycle performance of the electrochemical device. When the mass content of FEC is adjusted to meet the above range, the high-temperature intermittent cycle performance of the electrochemical device and the ability to inhibit the growth of cycle impedance can be further improved.

[0008] In some embodiments, the electrolyte includes 1,3,6-hexane trinitrile; based on the mass of the electrolyte, the mass content of 1,3,6-hexane trinitrile is Q%, 1≤Q≤6. The present application adds 1,3,6-hexane trinitrile to the electrolyte, which can complex with the transition metal sites exposed on the surface of the positive electrode material, strengthen the protection of the positive electrode, reduce the oxidation and decomposition ability of the positive electrode material to the electrolyte and other irreversible reactions on the positive electrode interface, and improve the storage gas generation and cycle attenuation rate in the high temperature intermittent cycle test.

[0009] In some embodiments, the electrolyte includes 1,3-propane sultone; based on the mass of the electrolyte, the mass content of 1,3-propane sultone is U%, 1≤U≤4. The present application adds 1,3-propane sultone to the electrolyte, which can decompose into a film on the surface of the negative electrode, reduce the reduction and decomposition of other components on the negative electrode interface, and improve the storage gas production performance in the high temperature intermittent cycle test.

[0010] In some embodiments, the electrolyte satisfies at least one of the following conditions: (1) 8≤P≤15; (2) 2≤Q≤4; (3) 2≤U≤3.

[0011] When the electrolyte meets the above conditions, it can promote better coordination among the components, which is beneficial to further improve the high-temperature intermittent cycle performance, kinetics and cycle impedance of the electrochemical device.

[0012] In some embodiments, the electrolyte includes lithium hexafluorophosphate and a second lithium salt, the second lithium salt includes lithium tetrafluoroborate or lithium difluorophosphate; based on the mass of the electrolyte, the mass content of the second lithium salt is V%, 0.1≤V≤0.8, preferably, 0.2≤V≤0.4. Adding the second lithium salt to the electrolyte in combination with lithium hexafluorophosphate can enhance the protection of the interface in the positive electrode and / or the negative electrode, reduce the side reaction at the interface, and thus further improve the high temperature intermittent cycle performance and impedance growth in the cycle of the electrochemical device.

[0013] In some embodiments, the electrolyte satisfies at least one of the following conditions: (1) the electrolyte includes dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione; based on the mass of the electrolyte, the mass content of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione is X%, 1≤X≤2; (2) the electrolyte includes lithium tetraborate; based on the mass of the electrolyte, the mass content of lithium tetraborate is Y%, 0.3≤Y≤0.6; (3) the electrolyte includes bis(neopentylethylene glycol)dibor; based on the mass of the electrolyte, the mass content of bis(neopentylethylene glycol)dibor is Z%, 0.3≤Z≤0.6.

[0014] Based on the above electrolyte solution, through the coordinated action of each component, it is possible to further improve the high-temperature intermittent cycle, kinetics and cycle impedance growth of the electrochemical device.

[0015] In some embodiments, the positive electrode active material layer includes lithium cobalt oxide, carbon black, and polyvinylidene fluoride (PVDF).

[0016] In a second aspect, the present application provides an electronic device comprising any one of the above-mentioned electrochemical devices. DETAILED DESCRIPTION

[0017] 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.

[0018] In a first aspect, the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least a portion of the surface of the positive electrode current collector; the compaction density of the positive electrode active material layer is pd g / cm 3 , 2.60×10 -3 ≤pd≤2.86×10 -3 ; Based on the mass of the electrolyte, the electrolyte includes: ethylene carbonate with a mass content of A%, propylene carbonate with a mass content of B%, diethyl carbonate with a mass content of C%, ethyl propionate with a mass content of D% and propyl propionate with a mass content of E%; 1≤B / A≤8, and 5≤(E+D) / C≤14.

[0019] The inventors found that in the high-density positive electrode, the small porosity of the electrode makes it difficult for the electrolyte to penetrate, which will affect the conduction of lithium ions in the electrochemical device system. In addition, the high-density electrode requires a higher pressure during preparation, which easily causes the positive electrode active particles to break, and the side reactions between the finer particles and the electrolyte increase, resulting in a higher impedance increase of the electrochemical device during the cycle. The present application adds carboxylic acid esters (ethyl propionate and propyl propionate) and linear esters (diethyl carbonate) to the electrolyte, and controls the mass contents of carboxylic acid esters and linear esters to satisfy the above relationship, which can significantly reduce the viscosity of the electrolyte, accelerate the transmission of lithium ions in the liquid phase, and at the same time enhance the wetting ability of the electrolyte in the electrochemical device, optimize the conductivity of the electrochemical device for lithium ions, thereby improving the conductivity of the electrochemical device, reducing the internal resistance, and improving the impedance growth problem during the cycle; in addition, controlling the electrolyte to include the above-mentioned cyclic esters, and regulating the mass contents of propylene carbonate and ethylene carbonate to satisfy the above-mentioned relationship, can change the solvation structure of lithium ions and the composition of the negative electrode solid electrolyte interface film, and cooperate with the above-mentioned carboxylic acid esters and linear esters to further improve the kinetics of the electrochemical device and improve the rate performance; by regulating the composition of the SEI film, it is also possible to inhibit side reactions at the positive and negative electrode interfaces during the cycle, reduce the thickness growth of the interface layer SEI film, and thus help reduce the impedance growth during the cycle.

[0020] In some embodiments, 1≤B / A≤8, preferably 2≤B / A≤6. Exemplarily, the value of B / A can be 1, 1.6, 2, 2.7, 3.6, 4.6, 5.6, 6, 7.1, 7.4, 8 or a value in the range of any two thereof. By regulating the mass content of ethylene carbonate and propylene carbonate to conform to the above relationship, the two can be better coordinated to achieve both improvement of the kinetics and cycle impedance growth of the electrochemical device.

[0021] In some embodiments, 5≤(E+D) / C≤14, preferably 8≤(E+D) / C≤10, and more preferably 7≤(E+D) / C≤9.6. Exemplarily, the value of (E+D) / C can be 5, 5.8, 6.6, 7, 8.2, 9.6, 10.7, 11.1, 12.3, 13.5, 14, or a value within the range of any two thereof. Regulating the mass content of carboxylic acid esters and linear esters in the electrolyte of the present application to satisfy the above relationship is conducive to further improving the kinetics and cyclic impedance growth problems of the electrochemical device.

[0022] In some embodiments, based on the mass of the electrolyte, the mass content of ethylene carbonate is A%, 3≤A≤6, for example, A can be 3, 3.3, 3.5, 3.8, 4.1, 4.6, 4.8, 5.1, 5.4, 6 or a value in the range of any two thereof. By regulating the mass content of ethylene carbonate in the electrolyte within the above range and cooperating with other components, the kinetic performance of the electrochemical device can be further improved, and the impedance growth during the cycle can be reduced.

[0023] In some embodiments, based on the mass of the electrolyte, the mass content of propylene carbonate is B%, 12≤B≤20, for example, B can be 12, 12.5, 13.2, 14.0, 14.8, 15.9, 17.1, 18, 18.7, 19.5, 20 or a value in the range of any two thereof. By regulating the mass content of propylene carbonate to meet the above range and cooperating with other components, the kinetic performance and impedance growth problem of the electrochemical device can be further improved.

[0024] In some embodiments, based on the mass of the electrolyte, the mass content of diethyl carbonate is C%, 5≤C≤8, for example, C can be 5, 5.2, 5.5, 5.8, 6.1, 6.6, 7, 7.3, 7.4, 7.7, 8 or a value in the range of any two thereof. By adjusting the mass content of diethyl carbonate to meet the above range and cooperating with other components, the kinetic performance and impedance growth problem of the electrochemical device can be further improved.

[0025] In some embodiments, based on the mass of the electrolyte, the mass content of ethyl propionate is D%, 20≤D≤30. For example, D can be a value in the range of 20, 20.3, 22, 22.3, 23.9, 24.9, 26.3, 26.9, 28.4, 29.1, 30 or any two thereof. By adjusting the mass content of ethyl propionate to meet the above range and cooperating with other components, the kinetic performance and impedance growth problem of the electrochemical device can be further improved.

[0026] In some embodiments, based on the mass of the electrolyte, the mass content of propyl propionate is E%, 20≤E≤40. Exemplarily, E can be a value within the range of 20, 20.4, 24.3, 25.5, 28.6, 29.4, 32.4, 34.6, 36.2, 39.4, 40 or any two thereof. By adjusting the mass content of propyl propionate to meet the above range and cooperating with other components, the kinetic performance and impedance growth problem of the electrochemical device can be further improved.

[0027] In some embodiments, the electrolyte includes fluoroethylene carbonate; based on the mass of the electrolyte, the mass content of fluoroethylene carbonate is P%, 5≤P≤20, preferably 8≤P≤15. For example, P can be 5, 5.8, 8.3, 9.7, 11.6, 12.4, 14.8, 16.3, 16.9, 19.5, 20 or a value within the range of any two thereof. The inventors have found that adding fluoroethylene carbonate (FEC) to the electrolyte system of the present application can reduce and decompose on the negative electrode interface before ethylene carbonate to form lithium fluoride (LiF), and cooperate with the above-mentioned ethylene carbonate and propylene carbonate to optimize the film quality and stability of the SEI film, reduce side reactions at the interface, and help reduce the impedance growth during the cycle. On the other hand, fluoroethylene carbonate cooperates with the electrolyte system of the present application to reduce irreversible reactions on the positive electrode interface and improve gas production during high-temperature storage, which is beneficial to improving the high-temperature intermittent cycle performance of the electrochemical device. During the high-temperature intermittent cycle, the electrochemical device undergoes periodic charging, high-temperature storage and discharging processes. This working mode easily leads to the attenuation of the capacity of the electrochemical device. The electrolyte containing the above-mentioned mass content of FEC in the present application can optimize the stability of the positive and negative electrode interfaces, thereby reducing cycle attenuation and improving the high-temperature intermittent cycle performance of the electrochemical device.

[0028] In some embodiments, the electrolyte includes 1,3,6-hexane trinitrile; based on the mass of the electrolyte, the mass content of 1,3,6-hexane trinitrile is Q%, 1≤Q≤6, preferably 2≤Q≤4. Exemplarily, Q can be a value within the range of 1, 1.4, 1.6, 2.5, 2.8, 3.5, 4.1, 4.4, 5.2, 5.8, 6 or any two thereof. The present application adds 1,3,6-hexane trinitrile to the electrolyte. When its mass content is adjusted to meet the above range, it can complex with the transition metal sites exposed on the surface of the positive electrode material, thereby enhancing the protection of the positive electrode, reducing the ability of the positive electrode material to oxidize and decompose the electrolyte under full charge conditions and other irreversible reactions on the positive electrode interface, improving the storage gas production and cycle attenuation rate in the high temperature intermittent cycle test, thereby improving the high temperature intermittent cycle performance of the electrochemical device.

[0029] In some embodiments, the electrolyte includes 1,3-propane sultone; based on the mass of the electrolyte, the mass content of 1,3-propane sultone is U%, 1≤U≤4, preferably 2≤U≤3. Exemplarily, U can be a value within the range of 1, 1.3, 1.4, 1.9, 2.3, 2.6, 2.7, 3.1, 3.5, 4 or any two thereof. When the present application adds 1,3-propane sultone to the electrolyte and regulates its mass content in the electrolyte within the above range, it can promote the decomposition of 1,3-propane sultone into a film on the surface of the negative electrode, reduce the reductive decomposition of other components of the electrolyte at the negative electrode interface, and is beneficial to improve the storage gas production performance in the high-temperature intermittent cycle test and optimize the high-temperature intermittent cycle performance of the electrochemical device.

[0030] In some embodiments, the electrolyte includes lithium hexafluorophosphate and a second lithium salt, and the second lithium salt includes lithium tetrafluoroborate or lithium difluorophosphate; based on the mass of the electrolyte, the mass content of the second lithium salt is V%, 0.1≤V≤0.8, preferably, 0.2≤V≤0.4. Exemplarily, the value of V can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or a value in the range of any two thereof. The second lithium salt with the above mass content is added to the electrolyte, wherein lithium tetrafluoroborate can absorb residual hydrogen fluoride (HF) in the electrolyte, reduce the corrosion of the positive electrode material by the acidic substance, and participate in the interfacial film formation on the positive electrode side, reducing the oxidative decomposition of the electrolyte at high temperature; lithium difluorophosphate can be oxidatively decomposed to form a film on the positive and negative electrodes at the same time, and the generated film-forming substance can inhibit the irreversible side reaction of the electrolyte at the interface and protect the stability of the electrode structure. After the two are closely combined with lithium hexafluorophosphate (LiPF6), they can be oxidized and decomposed to form films on the positive and / or negative electrode sides, optimize the film formation quality of the positive and negative electrode interface films, reduce side reactions at the interface between the electrolyte and the positive and negative electrodes, and improve the high-temperature intermittent cycle capacity attenuation rate and impedance growth during the cycle.

[0031] In some embodiments, the electrolyte includes dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione; based on the mass of the electrolyte, the mass content of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione is X%, 1≤X≤2; for example, X can be selected from 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a value within the range of any two thereof. The present application adds dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione to the electrolyte, which can inhibit the side reaction of the positive electrode interface at high temperature, especially when its mass content is adjusted to meet the above range, which is conducive to further improving the storage and gas production performance of high temperature intermittent cycles.

[0032] In some embodiments, the electrolyte includes lithium tetraborate; based on the mass of the electrolyte, the mass content of lithium tetraborate is Y%, 0.3≤Y≤0.6; for example, Y can be 0.3, 0.4, 0.5, 0.6 or a value within the range of any two thereof. The present application adds lithium tetraborate to the electrolyte, which can participate in film formation at both the positive and negative electrodes, inhibit side reactions at the positive electrode interface at high temperatures, and improve the high-temperature intermittent cycle performance of the electrochemical device. When the mass content of lithium tetraborate in the electrolyte is adjusted to meet the above range, the kinetics can also be improved, and the capacity retention rate under high-temperature intermittent cycles can be further improved.

[0033] In some embodiments, the electrolyte includes bis(neopentyl glycol) dibor; based on the mass of the electrolyte, the mass content of bis(neopentyl glycol) dibor is Z%, 0.3≤Z≤0.6; for example, Z can be 0.3, 0.4, 0.5, 0.6 or a value within the range of any two thereof. The present application adds bis(neopentyl glycol) dibor to the electrolyte, which can form a film at the negative electrode interface, reduce side reactions of the electrolyte, and improve the high-temperature intermittent cycle performance of the electrochemical device. When its mass content in the electrolyte is adjusted to meet the above range, it can also cooperate with the electrolyte system to improve the kinetics and enhance the rate performance of the electrochemical device.

[0034] According to some embodiments of the present application, the electrolyte further includes a lithium salt and a non-aqueous solvent. The lithium salt may include, but is not limited to, at least one of: lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2(LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2)(LiFSI), lithium bis(oxalate borate) LiB(C2O4)2(LiBOB), lithium difluorooxalate borate LiBF2(C2O4)(LiDFOB), LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, and Li2SiF6. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of an ether compound or other organic solvent. The above-mentioned ether compound may include, but is not limited to, at least one of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0035] The present application has no special restrictions on the positive electrode, as long as the purpose of the present application can be achieved. For example, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode active material layer located on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0036] 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, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0037] The positive electrode active material layer of the present application includes a positive electrode active material. The present application has no particular limitation on the type of 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 lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In the present application, the positive active material may also contain non-metallic elements, for example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive current collector and the positive active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5μm to 20μm, and the thickness of the single-sided positive active material layer is 30μm to 120μm.

[0038] In some embodiments, the compaction density of the positive electrode active material layer is pd g / cm 3 , 2.60×10 -3 ≤pd≤2.86×10 -3 For example, pd can be 2.6×10 -3 , 2.63×10 -3 , 2.64×10 -3 , 2.67×10-3 , 2.69×10 -3 , 2.72×10 -3 , 2.75×10 -3 , 2.81×10 -3 , 2.83×10 -3 , 2.86×10 -3 When the compaction density of the positive electrode active material layer is within the above range, it can better cooperate with the electrolyte system, improve the rate performance of the electrochemical device, inhibit the growth of cycle impedance and high temperature intermittent cycle performance.

[0039] In the present application, the positive electrode active material layer may further include a positive electrode binder and a positive electrode conductor. The present application does not particularly limit the type of positive electrode binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode binder may include but is not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene butadiene rubber (SBR) or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.

[0040] The present application has no particular restrictions on the type of positive electrode conductive agent in the positive electrode active material layer, as long as the purpose of the present application can be achieved. In some embodiments, the positive electrode conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof. The present application has no particular restrictions on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the loading amount of the positive electrode active material in the positive electrode sheet is 4.0 mg / cm 2 Up to 10.0mg / cm 2 .

[0041] In some more preferred embodiments, the positive electrode active material layer includes lithium cobalt oxide, carbon black and polyvinylidene fluoride.

[0042] In the present application, there is no particular restriction on the negative electrode plate, as long as the purpose of the present application can be achieved. For example, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In the present application, the negative electrode active material layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector, or it can be a partial area of ​​the negative electrode current collector. There is no particular restriction in the present application, as long as the purpose of the present application can be achieved.

[0043] 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 may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved.

[0044] The negative electrode active material layer of the present application includes a negative electrode active material, and the negative electrode active material may include but is not limited to graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x (0.5<x<1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate TiO2-Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0045] The negative electrode active material layer in the present application may also include a negative electrode binder and a negative electrode conductor, or the negative electrode active material layer may also include a negative electrode binder, a negative electrode conductor and a thickener. The present application has no particular restrictions on the types of negative electrode binders and negative electrode conductors, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include but is not limited to at least one of the above-mentioned positive electrode binders, and the negative electrode conductor may include but is not limited to at least one of the above-mentioned positive electrode conductors. The present application has no particular restrictions on the types of thickeners, as long as the purpose of the present application can be achieved. For example, the thickener may include but is not limited to at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. The present application has no particular restrictions on the mass ratio of the negative electrode active material, the negative electrode conductor, the negative electrode binder, and the thickener in the negative electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0046] The electrochemical device of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction, such as a secondary battery. The present application is described below using a secondary battery as an example in combination with the embodiments of the present application. The secondary battery of the present application is not particularly limited, and may include, but is not limited to, a lithium-ion secondary battery (also known as a lithium-ion battery) or a sodium-ion secondary battery.

[0047] The secondary battery of the present application also includes a separator. The material and shape of the separator used in the secondary battery of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0048] For example, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, 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 selected.

[0049] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from 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 and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).

[0050] The secondary battery of the present application also includes a packaging bag for containing a positive electrode, a negative electrode, a separator and an electrolyte, as well as other components known in the art in the secondary battery, 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.

[0051] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no special limitation in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0052] In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect.

[0053] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. For example, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0054] The following is an example of a lithium-ion battery and the scheme of the present application is described in conjunction with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from ordinary commercial products, and the devices or equipment used are all purchased from conventional market sales channels. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0055] High temperature intermittent cycle performance test:

[0056] The lithium-ion batteries of the embodiment and the comparative example were left to stand for 2 hours at a test temperature of 45°C to reach thermal equilibrium, and then the initial thickness d0 of the lithium-ion battery was tested. After that, the thermally balanced lithium-ion battery was subjected to the following test process: 1C rate constant current charging to a cut-off voltage of 4.52V, followed by constant voltage charging to a current less than or equal to 0.05C, and then stored at 45°C for 24 hours; the lithium-ion battery after storage was discharged to 3V at a constant current of 0.5C rate, and then left to stand at 45°C for 5 minutes. One test process is a cycle, and the above test process is repeated. The thickness d1 of the lithium-ion battery is tested once each cycle, and the number of cycles when the thickness d1 of the lithium-ion battery is greater than or equal to 120% d0 is recorded, which is recorded as the number of high-temperature intermittent cycle gas production cycles. Under high-temperature intermittent cycle conditions, gas production will occur when the internal side reactions of the lithium-ion battery are difficult to suppress. After gas production, the lithium-ion battery will expand rapidly, resulting in a thickness d1 exceeding 120% of the initial thickness d0. Therefore, the greater the number of high-temperature intermittent cycle gas production cycles of the lithium-ion battery, the stronger its ability to suppress internal gas production under high-temperature intermittent cycle conditions, that is, the better the high-temperature intermittent cycle performance of the lithium-ion battery.

[0057] Alternatively, the lithium ion battery of the embodiment and the comparative example is charged at 1C constant current at 25°C to a cut-off voltage of 4.52V, then charged at constant voltage to a current less than or equal to 0.05C, and discharged at 1C constant current to a cut-off voltage of 3V after charging, and the initial discharge capacity is recorded. Then the lithium ion battery of the embodiment and the comparative example is left to stand for 2 hours at a test temperature of 45°C to achieve thermal equilibrium, and the thermally balanced lithium ion battery is subjected to the following test process: 1C rate constant current charging to a cut-off voltage of 4.52V, followed by constant voltage charging to a current less than or equal to 0.05C, and then stored at 45°C for 24 hours; the lithium ion battery after storage is discharged at a 0.5C rate constant current to 3V, and then left to stand at 45°C for 5 minutes. Performing one test process is a cycle, repeating the above test process, and recording the discharge capacity when the number of high-temperature intermittent cycles of the lithium ion battery is 120. High-temperature intermittent cycle capacity retention rate (%) = 120 cycles of discharge capacity / initial discharge capacity × 100%.

[0058] Dynamic (rate) performance test:

[0059] The lithium-ion batteries of the embodiment and comparative example are charged at 1C constant current to a cut-off voltage of 4.52V, and then charged at constant voltage until the current is less than or equal to 0.05C. After charging, they are discharged at 1C constant current to a cut-off voltage of 3V, and the discharge capacity at 1C rate is recorded. Then, they are charged at 1C constant current to a cut-off voltage of 4.52V, and then charged at constant voltage until the current is less than or equal to 0.05C. After charging, they are discharged at 2C constant current to a cut-off voltage of 3V, and the discharge capacity at 2C rate is recorded. 2C discharge capacity percentage R1 (%) = [(discharge capacity at 1C rate - discharge capacity at 2C rate) / discharge capacity at 1C rate] × 100.

[0060] Loop Impedance Test:

[0061] The lithium ion batteries of the embodiment and the comparative example were charged and discharged at 25°C under the following conditions: charged at a constant current of 1C to a cut-off voltage of 4.52V, then charged at a constant voltage to a current less than or equal to 0.05C, and then discharged at a constant current of 0.5C to a cut-off voltage of 3V. After charging and discharging three times according to the above charging and discharging process, the battery was set to SOC 50% based on the last discharge capacity. The DC internal resistance was then measured by the voltage drop displayed when a discharge pulse was applied at 2.5C for 10 seconds (PNE-0506 charging and discharging device), and the resistance at this time was defined as the initial resistance.

[0062] After the above charge and discharge process was cycled 100 times, the lithium-ion battery was moved to 25°C and the SOC was set to 50%. Then, the resistance after 100 cycles was measured by the voltage drop displayed when a discharge pulse was applied at 2.5C for 10 seconds using a PNE-0506 charge and discharge device. Cycle resistance increase rate R2 (%) = [(resistance after 100 cycles - initial resistance) / initial resistance] × 100.

[0063] Example 1-1

[0064] <Preparation of Electrolyte>

[0065] In a dry argon atmosphere glove box, lithium hexafluorophosphate (LiPF6) as a supporting electrolyte was dissolved in a solution containing dimethyl carbonate (DMC), ethyl acetate (EA), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP). Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 12%, the mass content of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate is shown in Table 1 below, and the remainder is dimethyl carbonate and ethyl acetate, and the mass ratio of dimethyl carbonate to ethyl acetate is 1:3.

[0066] <Preparation of negative electrode sheet>

[0067] The negative electrode active material artificial graphite, the negative electrode conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC), and the negative electrode binder styrene butadiene rubber (SBR) are mixed in a mass ratio of 96.4:1.5:0.5:1.6, and then deionized water is added as a solvent to prepare a negative electrode slurry with a solid content of 30wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side, and then the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. After coating, the negative electrode sheet is cold pressed and cut into negative electrode sheets with a specification of 76.6mm×875mm for standby use.

[0068] <Preparation of positive electrode sheet>

[0069] The positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode binder polyvinylidene fluoride (PVDF), and the positive electrode conductive agent Super P are mixed in a mass ratio of 97:1.6:1.4, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. 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 110°C to obtain a positive electrode sheet coated with a single-sided positive electrode active material. After that, the above steps are repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with a double-sided positive electrode active material. After the coating is completed, the positive electrode sheet is cold pressed, wherein the pressure is adjusted to make the compaction density of the positive electrode active material layer pd g / cm 3 Satisfy the requirements in Table 1 and cut into positive electrode sheets with specifications of 74mm×867mm for standby use.

[0070] <Diaphragm>

[0071] A polyethylene-polypropylene film with a thickness of 7 μm was used.

[0072] <Preparation of lithium-ion batteries>

[0073] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play a barrier role, and then wound to obtain an electrode assembly. After welding the pole ears, the electrode assembly is placed in an aluminum-plastic film packaging shell, 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 and other processes, a lithium-ion battery is obtained.

[0074] Examples 1-2 to 1-22, Comparative Examples 1-1 to 1-6

[0075] The only difference compared with Example 1-1 is that the parameters shown in Table 1 are adjusted. The performance test results of each embodiment and comparative example are shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] As can be seen from Table 1, the electrolyte regulated by the present application includes ethylene carbonate with a mass content of A%, propylene carbonate with a mass content of B%, diethyl carbonate with a mass content of C%, ethyl propionate with a mass content of D%, and propyl propionate with a mass content of E%. When the mass content of each component is controlled to satisfy 1≤B / A≤8, and 5≤(E+D) / C≤14, the kinetic performance and impedance growth problems of lithium-ion batteries with high positive electrode compaction density can be improved. Among them, although the 2C discharge capacity retention rate of comparative example 1-1 is relatively high, its positive electrode compaction density is relatively low, which will affect the overall energy density and result in a lower total discharge capacity. The scheme of the present application can balance the kinetic performance and impedance growth problems under high positive electrode compaction density, and achieve an overall higher yield.

[0080] In particular, when the mass content of each component satisfies 3≤A≤6, 12≤B≤20, 5≤C≤8, 20≤D≤30 and / or 20≤E≤40, the kinetic performance and impedance growth problem of the lithium ion battery can be further improved. In particular, when the mass content of ethylene carbonate and propylene carbonate satisfies 2≤B / A≤6, the kinetic performance and impedance growth problem of the lithium ion battery can be more significantly improved. More preferably, when the mass content of diethyl carbonate, ethyl propionate and propyl propionate satisfies 6.6≤(E+D) / C≤9.2, the kinetic performance and impedance growth problem of the lithium ion battery can be further improved.

[0081] Examples 2-1 to 2-20

[0082] The only difference compared with Example 1-21 is that the parameters of the electrolyte are adjusted according to Table 2. In the preparation process of the electrolytes of Example 2-1 to Example 2-20, the corresponding mass content of the substance is dissolved in a solution containing dimethyl carbonate (DMC), ethyl acetate (EA), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP). The performance test results of each embodiment are shown in Table 2.

[0083] Table 2

[0084]

[0085]

[0086] As can be seen from Table 2, adding fluoroethylene carbonate to the electrolyte system of the present application and adjusting its mass content P% to meet 5≤P≤20 can further improve the high temperature intermittent cycle performance and the ability to inhibit the growth of cycle impedance of the lithium ion battery. In particular, when 8≤P≤15 is met, the high temperature intermittent cycle performance and the ability to inhibit the growth of cycle impedance of the lithium ion battery can be more significantly improved.

[0087] In particular, adding 1,3,6-hexanetrinitrile to the electrolyte and adjusting its mass content Q% to meet: 1≤Q≤6 can further improve the high temperature intermittent cycle performance and the ability to inhibit the growth of cycle impedance of the lithium ion battery. In particular, when 2≤Q≤4 is met, the high temperature intermittent cycle performance and the ability to inhibit the growth of cycle impedance of the lithium ion battery can be further improved.

[0088] In particular, when the electrolyte includes 1,3-propane sultone and its mass content U% satisfies: 1≤U≤4, the high temperature intermittent cycle performance and the ability to inhibit the growth of cycle impedance of the lithium ion battery can be significantly improved. In particular, when the electrolyte satisfies 2≤U≤3, the problem of cycle impedance growth of the lithium ion battery is further improved.

[0089] In particular, the electrolyte includes a second lithium salt, and the second lithium salt includes lithium tetrafluoroborate or lithium difluorophosphate. When the mass content V% of the second lithium salt is regulated to meet 0.1≤V≤0.8, the high temperature intermittent cycle performance and the impedance growth problem during the cycle of the lithium ion battery can be further improved. In particular, when 0.2≤V≤0.4 is met, the high temperature intermittent cycle performance and the impedance growth problem during the cycle of the lithium ion battery can be more significantly improved.

[0090] Example 3-1 to Example 3-10

[0091] The only difference compared with Example 2-18 is that the parameters of the electrolyte are adjusted according to Table 3. In the preparation process of the electrolytes of Example 3-1 to Example 3-10, the corresponding mass content of the substance is dissolved in a solution containing dimethyl carbonate (DMC), ethyl acetate (EA), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP) and propyl propionate (PP). The performance test results of each embodiment are shown in Table 3.

[0092] Table 3

[0093]

[0094] As shown in Table 3, further adding at least one of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione, lithium tetraborate and bis(neopentylethylene glycol)diboron to the electrolyte, and regulating the respective mass contents to satisfy 1≤X≤2, 0.3≤Y≤0.6, and 0.3≤Z≤0.6, can further improve high temperature intermittent cycling and cycle impedance growth. In particular, when the above three substances are included in the electrolyte at the same time, the components interact with each other, which can more significantly improve the high temperature intermittent cycling, kinetics and cycle impedance growth of lithium ion batteries.

[0095] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least a part of the surface of the positive electrode current collector; the compaction density of the positive electrode active material layer is pd mg / cm 3 , 2.60≤pd≤2.86; Based on the mass of the electrolyte, the electrolyte comprises: ethylene carbonate with a mass content of A%, propylene carbonate with a mass content of B%, diethyl carbonate with a mass content of C%, ethyl propionate with a mass content of D%, and propyl propionate with a mass content of E%; 1≤B / A≤8, and 5≤(E+D) / C≤14.

2. The electrochemical device according to claim 1, characterized in that The electrolyte satisfies at least one of the following conditions: (1)3≤A≤6； (2)12≤B≤20； (3)5≤C≤8； (4)20≤D≤30； (5)20≤E≤40； (6)2≤B / A≤6; (7)8≤(E+D) / C≤10.

3. The electrochemical device according to claim 1 or 2, characterized in that: The electrolyte includes fluoroethylene carbonate; based on the mass of the electrolyte, the mass content of the fluoroethylene carbonate is P%, 5≤P≤20.

4. The electrochemical device according to claim 3, characterized in that The electrolyte includes 1,3,6-hexane trinitrile; based on the mass of the electrolyte, the mass content of the 1,3,6-hexane trinitrile is Q%, 1≤Q≤6.

5. The electrochemical device according to claim 4, characterized in that The electrolyte includes 1,3-propane sultone; based on the mass of the electrolyte, the mass content of the 1,3-propane sultone is U%, 1≤U≤4.

6. The electrochemical device according to claim 5, characterized in that The electrolyte satisfies at least one of the following conditions: (1)8≤P≤15； (2)2≤Q≤4； (3)2≤U≤3。 7. The electrochemical device according to any one of claims 4 to 6, characterized in that: The electrolyte includes lithium hexafluorophosphate and a second lithium salt, and the second lithium salt includes lithium tetrafluoroborate or lithium difluorophosphate; Based on the mass of the electrolyte, the mass content of the second lithium salt is V%, 0.1≤V≤0.8, preferably, 0.2≤V≤0.

4.

8. The electrochemical device according to any one of claims 4 to 6, characterized in that: The electrolyte satisfies at least one of the following conditions: (1) The electrolyte includes dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione; based on the mass of the electrolyte, the mass content of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione is X%, 1≤X≤2; (2) The electrolyte includes lithium tetraborate; based on the mass of the electrolyte, the mass content of the lithium tetraborate is Y%, 0.3≤Y≤0.6; (3) The electrolyte includes bis(neopentyl glycol)dibor; based on the mass of the electrolyte, the mass content of bis(neopentyl glycol)dibor is Z%, and 0.3≤Z≤0.

6.

9. The electrochemical device according to claim 1, characterized in that The positive electrode active material layer includes lithium cobalt oxide, carbon black and polyvinylidene fluoride.

10. An electronic device, characterized in that: An electrochemical device comprising any one of claims 1 to 9.

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