Lithium secondary battery and electrical device

Abstract

A lithium secondary battery and an electrical device. The lithium secondary battery comprises a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material comprises at least one doping element selected from aluminum, zirconium, boron, magnesium, zinc, calcium, and titanium; the electrolyte contains a silane-based first additive containing C2-C8 alkenyl and a second additive, and the second additive is selected from at least one of lithium fluorosulfonate, lithium bis (fluorosulfonyl) imide, and lithium tetrafluoroborate; the ratio of the weight percentage content W1 of the first additive in the electrolyte to the weight percentage content W2 of the second additive in the electrolyte to the weight percentage content W3 of the doping element in the positive electrode active material is 1:(0.2-2):(0.1-0.5). The lithium secondary battery has good cycle performance, dynamic performance, and storage life.

Description

Lithium secondary batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310613348.7, filed on May 29, 2023, entitled “Lithium Secondary Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of energy storage devices, and specifically relates to a lithium secondary battery and an electrical device. Background Art

[0004] Lithium secondary batteries, which use lithium ions as active ions, offer advantages such as high energy density and high operating voltage, and are widely used in various electronic products and electric devices. With the increasing emphasis on environmental protection and the growing popularity of new energy vehicles, the demand for lithium secondary batteries has seen explosive growth.

[0005] As lithium-ion batteries become increasingly widely used, users are placing higher demands on their performance. Improving the cycle performance, kinetics, and storage life of lithium-ion batteries is a key area of ​​current research.

[0006] Summary of the Invention

[0007] The purpose of the present application is to provide a lithium secondary battery that has good cycle performance, dynamic performance and storage life while maintaining high energy density; the present application also provides an electrical device comprising the above-mentioned lithium secondary battery.

[0008] In a first aspect, an embodiment of the present application provides a lithium secondary battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material comprises at least one doping element selected from the group consisting of aluminum, zirconium, boron, magnesium, zinc, calcium, and titanium;

[0009] The electrolyte comprises a first additive and a second additive of a silane containing a C2-C8 alkenyl group, wherein the second additive is selected from at least one of lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate;

[0010] The ratio of the mass percentage W1 of the first additive in the electrolyte, the mass percentage W2 of the second additive in the electrolyte and the mass percentage W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5).

[0011] According to the technical solution of the embodiment of the present application, the positive electrode active material contains at least one doping element including aluminum, zirconium, boron, magnesium, zinc, calcium and titanium, which can enable the positive electrode active material to have a high energy density while maintaining better structural stability during the charge and discharge process, thereby improving the cycle performance and kinetic performance of the lithium secondary battery.

[0012] In the lithium secondary battery according to the embodiment of the present application, the electrolyte contains a certain amount of a first C2-C8 alkenylsilane additive; when the lithium secondary battery is formed, such a first additive participates in the film-forming reaction of the SEI film (Solid Electrolyte Interface Membrane) on one side of the negative electrode plate and can enhance the strength and toughness of the resulting SEI film, avoid repeated destruction and formation of the SEI film, and can effectively reduce or avoid, for example, side reactions between the electrolyte and the negative electrode active material, thereby improving the cycle performance and kinetic performance of the lithium secondary battery.

[0013] The electrolyte also contains a certain amount of a second additive; this second additive can participate in and promote the formation of the CEI film on one side of the positive electrode plate, inhibiting the dissolution of doping elements in the positive electrode active material, thereby improving the structural stability of the positive electrode active material. Furthermore, by promoting the formation of the CEI film, the second additive can effectively inhibit the redox reaction of the first additive on the positive electrode plate, thereby avoiding or reducing the gassing effect of such redox reactions and advantageously extending the storage life of the lithium secondary battery.

[0014] When the ratio of the mass percentage W1 of the first additive in the electrolyte, the mass percentage W2 of the second additive in the electrolyte and the mass percentage W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5), the first additive and the second additive can cooperate with each other to form an SEI film and a CEI film with good stability and toughness, inhibiting the dissolution of the doping elements in the positive electrode active material and the gas production side reaction of the first additive, which can effectively improve the cycle performance and kinetic performance of the lithium secondary battery, and also extend the storage life of the lithium secondary battery.

[0015] In any embodiment of the present application, the ratio of W1, W2, and W3 can further satisfy 1: (0.5-1.5): (0.2-0.4); optionally, 1: (0.8-1.2): (0.2-0.4). The ratio of W1, W2, and W3 within the above range can further enhance the synergistic effect between the first additive and the second additive, thereby further improving the cycle performance, kinetic performance, and storage life of the lithium secondary battery.

[0016] In any embodiment of the present application, the mass percentage W1 of the first additive in the electrolyte is 0.05% to 1%, and optionally, 0.1% to 1%. When the mass percentage W1 of the first additive in the electrolyte is within the above range, the first additive can effectively participate in the SEI film formation reaction on one side of the negative electrode during the formation of the lithium secondary battery, significantly improving the composition of the SEI film, so that the formed SEI film has improved strength and toughness.

[0017] In any embodiment of the present application, the first additive includes at least one of tetravinylsilane, ethyltrivinylsilane, diethyldivinylsilane, triethylvinylsilane, and trivinylalkynylsilane. The aforementioned first additive is a type of silane compound containing C2-C8 alkenyl groups. During formation, the C2-C8 alkenyl groups can undergo a polyaddition reaction on one side of the negative electrode to produce a product with a higher molecular weight, thereby participating in the formation of the SEI film. When the C2-C8 alkenyl silane compound participates in the formation of the SEI film, it can introduce a carbon chain compound with a larger molecular weight and chemically stable silicon atoms into the SEI film, thereby enhancing the strength, toughness, and stability of the SEI film.

[0018] In any embodiment of the present application, the mass percentage W2 of the second additive in the electrolyte is 0.01% to 2%, optionally 0.02% to 2%. The mass percentage W2 of the second additive in the electrolyte within the above range can, on the one hand, synergize with the first additive to form a high-performance SEI film; on the other hand, it can effectively promote the formation of a CEI film on one side of the positive electrode plate. The formed CEI film can inhibit the dissolution of doping elements in the positive electrode active material and inhibit the decomposition and gas production reaction of the first additive on the positive electrode plate side.

[0019] In any embodiment of the present application, the electrolyte includes an organic solvent, and the organic solvent includes one or more of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate. When the organic solvent in the electrolyte is of the above type, it can be combined to have a suitable viscosity, can effectively disperse the first additive and the second additive therein, and is beneficial to the storage performance of the electrolyte in the lithium secondary battery.

[0020] In any embodiment of the present application, the mass percentage content W3 of the doping element in the positive electrode active material is 0.005% to 0.5%, optionally, 0.005% to 0.45%. Controlling the mass percentage content W3 of the doping element in the positive electrode active material within the above range can effectively reduce or avoid the occurrence of Li / Ni mixing and H2-H3 phase transition in the positive electrode active material during the charge and discharge process of the lithium secondary battery, thereby improving the cycle life and storage life of the lithium secondary battery.

[0021] In any embodiment of the present application, the positive electrode active material includes a structural formula of Li a Ni b Co c Mn f M d O e One or more lithium transition metal oxides or modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, and M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B.

[0022] In any embodiment of the present application, the ratio of b to (b+c+f) is 0.8-0.98:1; optionally, 0.82-0.96:1. It can be understood that when the ratio of the molar amount of nickel to the sum of the molar amounts of nickel, cobalt, and manganese is within the above range, the positive electrode material can have good cycle performance, high specific capacity, high safety, and low cost, and can also increase the specific capacity of the positive electrode active material.

[0023] In any embodiment of the present application, the ratio of c to (b+c+f) is 0.01-0.2:1; optionally, 0.015-0.15:1. It can be understood that when the ratio of the molar amount of cobalt to the sum of the molar amounts of nickel, cobalt, and manganese is within the above range, the positive electrode material can have good cycle performance, high specific capacity, high safety, and low cost, and can also improve the cycle performance of the positive electrode active material.

[0024] In any embodiment of the present application, the ratio of f to (b+c+f) is 0.1-0.2:1; it can be optionally 0.15-0.2:1, wherein (b+c+f) represents the sum of b, c and f. The ratio of the molar amount of manganese element to the sum of the molar amounts of nickel element, cobalt element and manganese element is within the above range, which can make the positive electrode material have good cycle performance, high specific capacity, high safety and low cost, and can also improve the cycle performance of the positive electrode active material. In any embodiment of the present application, the surface density of the positive electrode active material layer is 3.0g / cm 3 The surface density of the positive electrode active material layer is within the above range. According to conventional positive electrode active material, the content of the positive electrode active material in the positive electrode active material layer is generally 92% to 98.5%, indicating that there is more positive electrode active material, which can improve the cycle performance of the lithium secondary battery.

[0025] In any embodiment of the present application, the negative electrode active material layer further includes silicon. Silicon, as a negative electrode active material, has advantages such as high capacity (4200 mA·h / g) and low delithiation voltage. Adding silicon to the negative electrode active material layer helps improve the storage performance of the negative electrode sheet for active lithium and reduce the delithiation voltage of the negative electrode.

[0026] In any embodiment of the present application, the negative electrode active material layer contains less than or equal to 8% silicon based on the total mass of the negative electrode active material layer. The mass content of silicon in the negative electrode active material layer within the above range is beneficial for controlling the volume expansion rate of the negative electrode active material layer and improving the performance of the lithium secondary battery, while increasing the capacity of the negative electrode sheet and reducing the delithiation voltage.

[0027] In any embodiment of the present application, the compacted density of the negative electrode active material layer is 1.3-1.7 g / cm³. A compacted density of the negative electrode active material layer within this range helps control the risk of current collector extension due to volume changes of the active material during charge and discharge of the lithium secondary battery, as well as the risk of positive electrode sheet fracture caused by negative electrode sheet extension, thereby improving the problem of negative electrode sheet wrinkling and battery deformation.

[0028] In a second aspect, an embodiment of the present application provides an electrical device comprising the lithium secondary battery of the first aspect.

[0029] The electric device of the present application includes the lithium secondary battery provided by the present application, and thus has at least the same advantages as the lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0031] FIG1 is a schematic diagram of one embodiment of a lithium secondary battery.

[0032] FIG2 is an exploded view of FIG1 .

[0033] FIG. 3 is a schematic diagram of an embodiment of a battery module.

[0034] FIG. 4 is a schematic diagram of a battery pack according to an embodiment.

[0035] FIG. 5 is an exploded view of FIG. 4 .

[0036] FIG. 6 is a schematic diagram of an embodiment of a device using a lithium secondary battery as a power source. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and beneficial technical effects of this application clearer, the following describes this application in detail with reference to specific embodiments. It should be understood that the embodiments described in this specification are only for the purpose of explaining this application and are not intended to limit this application.

[0038] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, although not explicitly stated, each point or individual value between the endpoints of a range is included in the range. Thus, each point or individual value can serve as its own lower limit or upper limit and be combined with any other point or individual value, or with other lower limits or upper limits, to form an unspecified range.

[0039] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number themselves, and “several” in “one or several” means two or more.

[0040] The foregoing of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided at many places through a series of examples, which can be used in various combinations. In each example, enumeration is provided only as a representative group and should not be construed as exhaustive.

[0041] Lithium secondary batteries have attracted much attention due to their high energy, long cycle life, and good safety performance. Currently, lithium-ion batteries have been used in all aspects of daily life, such as cameras, laptops, and electric vehicles.

[0042] Lithium secondary batteries include an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive and negative electrode sheets. Improving the cycle performance and energy density of lithium secondary batteries has always been a pursuit within the industry.

[0043] To increase the energy density of battery cells, the nickel content in the positive electrode is generally high. However, as the nickel content increases, the Li / Ni mixing and H2-H3 phase transformation in the positive electrode active material during the charge and discharge process of lithium secondary batteries become more serious, affecting the battery's cycle life and storage life.

[0044] Research has found that changes in the valence state of transition metal ions in nickel-cobalt-manganese ternary materials can reduce the cycling performance of lithium secondary batteries. Therefore, doping the positive electrode active material with specific elements can change the energy band structure of the positive electrode active material and address the above-mentioned problem. However, the doping elements in the positive electrode active material are gradually released during long-term charge and discharge processes and deposited on the negative electrode. The release of the doping elements will reduce the cycling performance of the positive electrode active material during charge and discharge, and the deposition of the doping elements will damage the SEI film on the negative electrode surface, further affecting the cycling stability of the lithium secondary battery.

[0045] During the charge and discharge process of lithium secondary batteries, side reactions often occur in the electrolyte at the interface between the positive electrode and the negative electrode, which affects the overall performance of the lithium secondary battery.

[0046] Research has found that in order to inhibit the deposition of doping elements in the negative electrode, additives including tetravinylsilane can be added. Such additives are easily oxidized in the positive electrode and produce gas, which is not conducive to the performance of lithium secondary batteries.

[0047] In view of this, the technical solution of the embodiment of the present application provides a lithium secondary battery, which can at least reduce the deposition of doping elements on the negative electrode during the battery charging and discharging process, thereby reducing or avoiding the adverse effects of the doping elements on the cycle performance of the battery; reduce the oxidation of the additive that inhibits the release of the doping elements on the positive electrode, so that it participates in the formation of the CEI film on one side of the positive electrode, thereby protecting the positive electrode active material, thereby improving the comprehensive performance of the lithium secondary battery containing it, such as cycle life and storage life.

[0048] lithium secondary batteries

[0049] In a first aspect, an embodiment of the present application provides a lithium secondary battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material comprises at least one doping element selected from the group consisting of aluminum, zirconium, boron, magnesium, zinc, calcium, and titanium;

[0050] The electrolyte comprises a first additive and a second additive of a silane containing a C2-C8 alkenyl group, wherein the second additive is selected from at least one of lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate;

[0051] The ratio of the mass percentage W1 of the first additive in the electrolyte, the mass percentage W2 of the second additive in the electrolyte and the mass percentage W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5).

[0052] According to the technical solution of the embodiment of the present application, the positive electrode active material contains at least one doping element including aluminum, zirconium, boron, magnesium, zinc, calcium and titanium, which can enable the positive electrode active material to have a high energy density while maintaining better structural stability during the charge and discharge process, thereby improving the cycle performance and kinetic performance of the lithium secondary battery.

[0053] In the lithium secondary battery according to the embodiment of the present application, the electrolyte contains a certain amount of a first C2-C8 alkenylsilane additive; when the lithium secondary battery is formed, such a first additive and the second additive participate in the film-forming reaction of the SEI film (Solid Electrolyte Interface Membrane) on one side of the negative electrode plate and can enhance the strength and toughness of the resulting SEI film, avoid repeated destruction and formation of the SEI film, and can effectively reduce or avoid, for example, side reactions between the electrolyte and the negative electrode active material, thereby improving the cycle performance and kinetic performance of the lithium secondary battery.

[0054] The electrolyte also contains a certain amount of a second additive; this second additive can participate in and promote the formation of the CEI film on one side of the positive electrode plate, inhibiting the dissolution of doping elements in the positive electrode active material, thereby improving the structural stability of the positive electrode active material. Furthermore, by promoting the formation of the CEI film, the second additive can effectively inhibit the redox reaction of the first additive on the positive electrode plate, thereby avoiding or reducing the gassing effect of such redox reactions and advantageously extending the storage life of the lithium secondary battery.

[0055] When the ratio of the mass percentage W1 of the first additive in the electrolyte, the mass percentage W2 of the second additive in the electrolyte and the mass percentage W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5), optionally, the ratio of W1, W2 and W3 is any one of 1:0.3:0.1, 1:1:0.3:0.1, 1:0.4:0.1, 1:1.6:0.5, 1:1.7:0.5, 1:1.8:0.5, 1:1.9:0.5, 1:2.0:0.5 or a range of their compositions.

[0056] The first additive and the second additive can cooperate with each other to form an SEI film and a CEI film with good stability and toughness, inhibiting the dissolution of the doping elements of the positive electrode active material and the gas production side reaction of the first additive, which can effectively improve the cycle performance and kinetic performance of the lithium secondary battery, and also extend the storage life of the lithium secondary battery.

[0057] In some optional embodiments, the ratio of W1, W2 and W3 satisfies 1: (0.5-1.5): (0.2-0.4); optionally, 1: (0.8-1.2): (0.2-0.4). The ratio of W1, W2 and W3 can be

[0058] 1:0.5:0.2, 1:0.6:0.2, 1:0.7:0.2, 1:0.85:0.2, 1:0.9:0.2, 1:1.0:0.2, 1:1.1:0.2, 1:1.2:0.2, 1:1.3:0.2, 1:0.4:0.2, 1:0.5:0.3, 1:0.6:0.3, 1:0.7:0.3, 1:0.85:0.3, 1:0.9:0.3, 1:1.0. The ratio of W1, W2 and W3 is within the above range, which can further enhance the synergistic effect between the first additive and the second additive, thereby further improving the cycle performance, kinetic performance and storage life of the lithium secondary battery.

[0059] [Electrolyte]

[0060] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0061] In some optional embodiments, the electrolyte includes an electrolyte salt. In some optional embodiments, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate), and LiTFOP (lithium tetrafluorooxalatophosphate).

[0062] In some optional embodiments, the electrolyte includes an organic solvent, and the organic solvent includes one or more of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate. When the organic solvent in the electrolyte is of the above type, it can be combined to have a suitable viscosity, can effectively disperse the first additive and the second additive therein, and is beneficial to the storage performance of the electrolyte in the lithium secondary battery.

[0063] In some optional embodiments, the viscosity of the electrolyte is 2.0 mPas to 5.0 mPas at a temperature of 25° C. The electrolyte within the above viscosity range is beneficial to the transport of active ions and the kinetic performance of the lithium secondary battery.

[0064] In some optional embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0065] In some optional embodiments, the additive includes a first additive and a second additive.

[0066] In some optional embodiments, the mass percentage content W1 of the first additive in the electrolyte is 0.05% to 1%, optionally, W2 is 0.01% to 2%, optionally, 0.05% to 1%. The mass percentage content W1 of the first additive in the electrolyte is any value or a range consisting of any values ​​selected from 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, or 1.0%. When the mass percentage W1 of the first additive in the electrolyte is within the above range, the first additive can effectively participate in the SEI film formation reaction on one side of the negative electrode during the formation of the lithium secondary battery, significantly improve the composition of the SEI film, and make the formed SEI film have improved toughness.

[0067] When the content of the first additive is less than 0.05%, the SEI film cannot be significantly improved. When the content of the first additive is greater than 1%, the SEI film is too thick and the SEI film strength is reduced, which adversely affects the cycle performance and kinetic performance of the lithium secondary battery.

[0068] In some optional embodiments, the first additive includes at least one of tetravinylsilane, ethyltrivinylsilane, diethyldivinylsilane, triethylvinylsilane, and trivinylalkynylsilane. The first additive of the aforementioned type is a silane compound containing a C2-C8 alkenyl group. During formation, the C2-C8 alkenyl group can undergo an addition polymerization reaction on one side of the negative electrode to produce a product with a higher molecular weight, thereby participating in the formation of the SEI film. When the C2-C8 alkenyl silane compound participates in the formation of the SEI film, it can introduce a carbon chain compound with a larger molecular weight and chemically stable silicon atoms into the SEI film, thereby enhancing the strength, toughness, and stability of the SEI film.

[0069] In some optional embodiments, the mass percentage content W2 of the second additive in the electrolyte is 0.01% to 2%, optionally, (0.02%) to (2%). The mass percentage content W1 of the second additive in the electrolyte is 0.01%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1. Any value among 0%, 1.01%, 1.05% / 1.1%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, 1.60%, 1.65%, 1.70%, 1.75%, 1.80%, 1.85%, 1.90%, 1.95%, 2%, or a range consisting of any values.

[0070] The mass percentage W2 of the second additive in the electrolyte is within the above range. On the one hand, it can cooperate with the first additive to form an SEI film with good performance; on the other hand, it can effectively promote the formation of a CEI film on one side of the positive electrode plate. The formed CEI film can inhibit the dissolution of the doping elements of the positive electrode active material, and inhibit the decomposition and gas production reaction of the first additive on the positive electrode plate side.

[0071] When the content of the second additive is lower than 0.01%, it is not conducive to the formation of CEI film and SEI film; when the content of the second additive is higher than 2%, it may affect the solvation of lithium ions in the electrolyte, reduce the ionic conductivity of the electrolyte, and affect the kinetic performance of the lithium secondary battery.

[0072] [Positive electrode]

[0073] In some optional embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two surfaces opposing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0074] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may be a positive electrode active material commonly known in the art and used in battery cells.

[0075] In some optional embodiments, the positive electrode active material includes a positive electrode active material doped with a doping element.

[0076] In some optional embodiments, the mass percentage W3 of the doping element in the positive electrode active material is 0.005% to 0.5%, optionally, 0.005% to 0.45%. The mass percentage content W3 of the doping element in the positive electrode active material is any value or any value composed of 0.005%, 0.01%, 0.015%, 0.020%, 0.025%, 0.030%, 0.035%, 0.040%, 0.045%, 0.050%, 0.055%, 0.060%, 0.065%, 0.070%, 0.075%, 0.080%, 0.085%, 0.090%, 0.095%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%

[0077] By controlling the mass percentage content W3 of the doping element in the positive electrode active material within the above range, the Li / Ni mixing and H2-H3 phase transition phenomena in the positive electrode active material can be effectively reduced or avoided during the charge and discharge process of the lithium secondary battery, thereby improving the cycle life and storage life of the lithium secondary battery. In some optional embodiments, the positive electrode active material includes a structural formula of Li a Ni b Co c Mn f M d O e One or more lithium transition metal oxides or modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, and M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B.

[0078] In some optional embodiments, the positive electrode active material may be a layered transition metal oxide. In some optional embodiments, the positive electrode active material may be a doped ternary positive electrode nickel-cobalt-manganese material. When the positive electrode active material is of the above type, the use of a positive electrode active material doped with a doping element can effectively improve the energy band structure of the positive electrode active material, thereby improving the cycle stability of the lithium secondary battery including the positive electrode active material. As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0079] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0080] In some optional embodiments, the mass percentage content W3 of the doping element in the positive electrode active material is 0.005% to 0.5%, optionally, 0.005% to 0.45%. By controlling the mass percentage content W4 of the doping element in the positive electrode active material within the above range, during the charge and discharge process of the lithium secondary battery, the phenomenon of Li / Ni mixing and H2-H3 phase transition in the positive electrode active material can be effectively reduced or avoided, thereby improving the cycle life, storage life, and power performance of the lithium secondary battery. When the mass percentage content W4 of the doping element in the positive electrode active material is lower than 0.005%, the structure of the positive electrode active material cannot be improved, or the improvement effect is small; when the mass percentage content W4 of the doping element in the positive electrode active material is higher than 0.5%, the energy density of the lithium secondary battery may be reduced.

[0081] In some optional embodiments, the ratio of b to (b+c+f) is 0.8-0.98:1; optionally, 0.82-0.96:1. The ratio of the molar amount of nickel to the sum of the molar amounts of nickel, cobalt, and manganese within the above range can enable the positive electrode material to have good cycle performance, high specific capacity, high safety, and low cost, and can also increase the specific capacity of the positive electrode active material.

[0082] In some optional embodiments, the ratio of c to (b+c+f) is 0.01-0.2:1, or optionally 0.015-0.15:1. The ratio of the molar amount of cobalt to the sum of the molar amounts of nickel, cobalt, and manganese within the above range can enable the positive electrode material to have good cycle performance, high specific capacity, high safety, and low cost, and can also improve the cycle performance of the positive electrode active material.

[0083] In some optional embodiments, the ratio of f to (b+c+f) is 0.1-0.2:1; optionally 0.15-0.2:1. Wherein, (b+c+f) represents the sum of b, c and f. The ratio of the molar amount of manganese element to the sum of the molar amounts of nickel element, cobalt element and manganese element is within the above range, which can make the positive electrode material have good cycle performance, high specific capacity, high safety and low cost, and can also improve the cycle performance of the positive electrode active material. In some optional embodiments, the surface density of the positive electrode active material layer is 3.0g / cm 3 Above. The surface density of the positive electrode active material layer is within the above range. According to conventional positive electrode active material, the content of the positive electrode active material in the positive electrode active material layer is generally 92% to 98.5%, indicating that it contains more positive electrode active material, which can improve the cycle performance of the lithium secondary battery. The surface density of the positive electrode active material layer is a well-known meaning in the art and can be measured using instruments and methods well-known in the art. For example, take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode active material layer on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, and record it as M1. Then wipe off the positive electrode active material layer of the weighed positive electrode sheet, weigh the weight of the positive electrode current collector, and record it as M0. Surface density of the positive electrode active material layer = (weight of the positive electrode sheet M1 - weight of the positive electrode current collector M0) / S1.

[0084] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0085] In some optional embodiments, the positive electrode active material layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some optional embodiments, the positive electrode active material layer may further optionally include a positive electrode binder. The present application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0087] In some optional embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0088] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0089] [Negative electrode]

[0090] In some optional embodiments, the lithium secondary battery further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the negative electrode active material layer comprises graphite. The negative electrode active material layer of the lithium secondary battery comprises a battery, which can effectively store active lithium and is beneficial to the cycle performance of the lithium secondary battery.

[0091] The specific composition and structure of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0092] For example, when the battery cell is a lithium-ion battery cell, 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 and including a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0093] The negative electrode active material is a material that can extract and embed active ions (such as lithium ions, etc.), and the negative electrode active material can adopt materials well known in the art. As an example, the negative electrode active material includes but is not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0094] In some optional embodiments, the negative electrode active material layer further includes silicon. Silicon, as a negative electrode active material, has advantages such as high capacity (4200 mA·h / g) and low delithiation voltage. Adding silicon to the negative electrode active material layer helps improve the storage performance of the negative electrode sheet for active lithium and reduce the delithiation voltage of the negative electrode.

[0095] In some optional embodiments, the negative electrode active material layer contains less than or equal to 8% silicon based on the total mass of the negative electrode active material layer. The mass content of silicon in the negative electrode active material layer is within the above range. On the basis of increasing the capacity of the negative electrode plate and reducing the delithiation voltage, it is beneficial to control the volume expansion rate of the negative electrode active material layer and improve the performance of the lithium secondary battery. In some optional embodiments, the compaction density of the negative electrode active material layer is 1.3-1.7g / cm 3The compaction density of the negative electrode active material layer within the above range is beneficial for controlling the risk of current collector extension due to volume changes of the active material during the charge and discharge process of the lithium secondary battery; as well as the risk of positive electrode sheet fracture caused by the extension of the negative electrode sheet, thereby improving the problems of wrinkling of the negative electrode sheet and battery deformation.

[0096] In addition, when the negative electrode active material layer contains a certain amount of silicon element, it is particularly important to control the compaction density of the negative electrode active material layer, which is beneficial to improve or avoid the problems of wrinkling of the negative electrode sheet and deformation of the battery.

[0097] The compacted density of the negative electrode active material layer is well known in the art and can be measured using instruments and methods known in the art. For example, the thickness of the negative electrode active material layer can be measured on a single-sided coated and cold-pressed negative electrode sheet. The areal density of the negative electrode active material layer can then be determined using the same method as for measuring the areal density of the positive electrode active material layer. The compacted density of the negative electrode active material layer = the areal density of the negative electrode film / the thickness of the negative electrode film.

[0098] In some optional embodiments, when the positive electrode active material is a doped ternary positive electrode nickel-cobalt-manganese material and the negative electrode active material includes graphite, the electromotive force difference of the lithium secondary battery is ≥4.2 V. An electromotive force difference of ≥4.2 V in a lithium secondary battery is beneficial for improving the battery's energy density.

[0099] In some optional embodiments, the negative electrode active material layer may further include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As examples, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some optional embodiments, the negative electrode active material layer may further include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0101] In some optional embodiments, the negative electrode active material layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, and the like.

[0102] In some optional embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0103] The negative electrode active material layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0104] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some optional embodiments, the negative electrode sheet of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector; in some optional embodiments, the negative electrode sheet of the present application may further include a protective layer covering the surface of the negative electrode active material layer.

[0105] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some optional embodiments, the negative electrode plate may include a lithium plate or a lithium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam-like three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0106] [Isolation film]

[0107] Lithium secondary batteries using electrolytes and some lithium secondary batteries using solid electrolytes also include a separator. The separator is arranged between the positive electrode and the negative electrode to serve as an isolation. The present application does not particularly limit the type of separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected. In some optional embodiments, the separator can be selected from one or more of a glass fiber film, a non-woven film, a polyethylene (PE) film, a polypropylene (PP) film, a polyvinylidene fluoride film, and their multilayer composite films.

[0108] The present application has no particular limitation on the type of lithium secondary battery. For example, the lithium secondary battery may be a lithium ion battery.

[0109] In some optional embodiments, the lithium secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0110] In some optional embodiments, the outer packaging of the lithium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0111] The present application has no particular limitation on the shape of the lithium secondary battery, which can be cylindrical, flat, rectangular or any other shape. FIG1 shows a lithium secondary battery 5 with a square structure as an example.

[0112] In some optional embodiments, the lithium secondary battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0113] In some optional embodiments, referring to FIG2 , the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected thereto, the bottom plate and side plates together forming a receiving cavity. The housing 51 may have an opening communicating with the receiving cavity, and the cover 53 may be positioned over the opening to seal the receiving cavity.

[0114] The positive electrode sheet, the negative electrode sheet, and the separator can be laminated or wound to form an electrode assembly 52. ​​The electrode assembly 52 is enclosed in the housing cavity. The electrolyte can be an electrolyte solution, which is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the lithium secondary battery 5 can be one or more, and can be adjusted according to needs.

[0115] In some optional embodiments, the outer packaging of the lithium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0116] In some optional embodiments, lithium secondary batteries can be assembled into a battery module. The battery module can contain multiple lithium secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0117] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple lithium secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple lithium secondary batteries 5 may be secured using fasteners.

[0118] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of lithium secondary batteries 5 are received in the receiving space.

[0119] In some optional embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0120] Figure 4 shows an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0121] [Preparation method]

[0122] The preparation method of a lithium secondary battery may include the steps of assembling a negative electrode sheet, a positive electrode sheet, and an electrolyte to form a lithium secondary battery. In some optional embodiments, the positive electrode sheet, separator, and negative electrode sheet may be wound or stacked in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation, thereby obtaining an electrode assembly (i.e., a battery cell). The electrode assembly is then placed in an outer packaging, injected with electrolyte, and sealed to obtain a lithium secondary battery. In some optional embodiments, the lithium secondary battery is obtained through vacuum packaging, standing, formation, and shaping.

[0123] In some optional embodiments, the preparation of a lithium secondary battery may further include the step of preparing a positive electrode sheet. For example, the positive electrode active material, conductive agent, and binder may be dispersed in a solvent (e.g., N-methylpyrrolidone, NMP) to form a uniform positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector, and the positive electrode sheet is obtained after drying, cold pressing, and other processes.

[0124] In some optional embodiments, the preparation of a lithium secondary battery may further include the step of preparing a negative electrode sheet. For example, the negative electrode active material, a binder, and optionally a thickener and a conductive agent are dispersed in a solvent, which may be deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on a negative electrode current collector, and the negative electrode sheet is obtained after drying, cold pressing, and other processes.

[0125] In some embodiments of the present application, the lithium secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple lithium secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0126] Optionally, the battery module may further include a housing having a receiving space, wherein the plurality of lithium secondary batteries are received in the receiving space.

[0127] In some optional embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0128] Electrical devices

[0129] In a second aspect, an embodiment of the present application provides an electrical device comprising the lithium secondary battery of the first aspect.

[0130] The electric device of the present application includes the lithium secondary battery of the first aspect of the present application, and thus has at least the advantages of using lithium secondary batteries.

[0131] Lithium secondary batteries can be used as power sources or energy storage units for electrical devices. These devices include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0132] Figure 6 is a schematic diagram of an exemplary electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high energy density requirements of the electric device, a battery pack or battery module may be used.

[0133] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a lithium secondary battery as a power source.

[0134] Example

[0135] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0136] Example 1

[0137] (1) Preparation of positive electrode sheet:

[0138] Preparation of positive electrode active material: The precursor powder of the nickel-cobalt-manganese ternary positive electrode active material is mixed with a salt solution containing a doping element and subjected to a liquid phase diffusion reaction, and then dried to obtain a doped precursor powder. The salt solution of the doping element is a soluble metal solution containing the doping element, and its solute is one of zinc sulfate, magnesium sulfate, aluminum chloride or zirconium nitrate, and its solvent is ethanol. The above solute and solvent are mixed to prepare a doping element salt solution, and then the ternary precursor powder is mixed with the doping element salt solution and subjected to a liquid phase diffusion reaction. The solid content percentage is 30% to 50% by weight, and the doping element is uniformly infiltrated into the voids of the nickel-cobalt-manganese ternary positive electrode active material through the solution in a liquid phase diffusion manner.

[0139] The specific liquid phase diffusion reaction process conditions are: reaction temperature of 25-40 ° C, reaction time of 30-90 min, stirring speed of 15-45 Hz, and the positive electrode active material is prepared. The positive electrode active material is Li a Ni b Co c Mn f M d O e In Example 1, a is 1, e is 2, and the ratio of b:c:f is 8:1:1. M is Al. The prepared positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry.

[0140] The solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.5 Co 0.2 Mn 0.3 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the current collector aluminum foil and dried at 85°C and then cold pressed. Then, after trimming, cutting, and slitting, it is dried under vacuum conditions at 85°C for 4 hours to make the positive electrode sheet. (2) Preparation of electrolyte:

[0141] In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate and ethyl methyl carbonate were added to a beaker in a mass ratio of 1:1 and stirred and mixed. Subsequently, an appropriate amount of LiPF6 and LiFSI were slowly added to a non-aqueous organic solvent. After the lithium salt was completely dissolved, an appropriate amount of the first additive: tetrafluorovinylsilane and the second additive were added to the above electrolyte and mixed evenly to obtain the target electrolyte. The ratio of the additives in Table 1 is the mass percentage calculated based on the total mass of the electrolyte.

[0142] (3) Preparation of negative electrode sheet:

[0143] Graphite, the negative electrode active material, a certain amount of silicon, a conductive agent (Super P), a thickener (CMC), and a binder (SBR) are mixed evenly in deionized water to create a negative electrode slurry. The solids content in the negative electrode slurry is 30% by weight, and the mass ratio of graphite, Super P, CMC, and SBR is 80:15:3:2. The negative electrode slurry is coated onto a current collector copper foil and dried at 85°C. The negative electrode sheet is then cold-pressed, trimmed, cut, and slit, and then dried at 120°C under vacuum for 12 hours.

[0144] (4) Isolation film

[0145] A 16 μm polyethylene film (PE) was used as the separator.

[0146] (5) Preparation of lithium-ion batteries:

[0147] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed in the middle of the positive and negative electrode sheets to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in an outer package, and the above-prepared electrolyte is injected into the dried battery cell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery (the thickness of the soft-pack lithium-ion battery is 4.0 mm, the width is 60 mm, and the length is 140 mm).

[0148] Examples 2 to 21 and Comparative Examples 1 to 4

[0149] The preparation method is similar to that of Example 1, except that different positive electrode active materials are used and relevant parameters in the positive electrode sheet preparation steps are regulated; see Table 1 for details.

[0150] Test section

[0151] In the following tests, when the positive electrode active material is lithium nickel cobalt manganese oxide, the discharge cut-off voltage is 2.8V and the charge cut-off voltage is 4.25 or 4.3V; when the positive electrode active material is lithium iron phosphate, the discharge cut-off voltage is 2.5V and the charge cut-off voltage is 3.65V.

[0152] The method for determining the mass percentage of doping elements in the positive electrode active material is: Inductively coupled plasma (ICP) test

[0153] (1) Cycling performance test of lithium-ion batteries.

[0154] The ambient temperature is adjusted to 25°C, and the first charge and discharge are carried out. The battery cell is charged to 4.25V at a charging current of 1C, and then charged to 0.05C at a constant voltage. After standing for 10 minutes, 1C constant current discharge is performed until the discharge cut-off voltage is 2.8V. This is one charge and discharge cycle, and the discharge capacity is recorded as C0. According to the above charge and discharge process, 300 cycles are carried out. The discharge capacity at the 300th cls is C1. The cycle capacity retention rate of the battery cell = C1 / C0*100%

[0155] (2) Storage life test of lithium-ion batteries

[0156] At 25°C, charge the battery at 1C constant current to 4.25V, then charge it at constant voltage to a current of 0.05C, let it stand for 10 minutes, discharge it at 1C to 2.8V, and record the discharge capacity D0. Then place the battery in a 60°C constant temperature box and keep it warm for 60 days. Take out the battery cell and wait until the surface temperature of the battery cell returns to room temperature. Discharge it at 1C to 2.8V, then charge it at 1C to 4.25V, charge it at constant voltage to 0.05C, let it stand for 10 minutes, discharge it at 1C to 2.8V, and record the discharge capacity D1. The high temperature storage capacity retention rate of the battery = D1 / D0*100%

[0157] (3) DC internal resistance DCR performance test of lithium-ion batteries

[0158] The battery is charged to 4.25V at 1C, then charged to 0.05C at constant voltage, left to stand for 30min, discharged at 1C for 0.5h, left to stand for 30min, and the voltage V1 after standing is recorded. Then it is discharged at 4C for 30s with a sampling interval of 0.1s, and the voltage V2 at the end of discharge is recorded. Battery DCR = (V1-V2) / I, I = 4C.

[0159] From the comparison results of Examples 1-7 and Comparative Examples 1-3, it can be seen that when the content of the second additive in Comparative Examples 1-3 is not within an appropriate range, the cycle performance, high-temperature storage performance and resistance performance of the lithium secondary batteries of Comparative Examples 1-3 are relatively poor compared to the embodiments, which shows that when the mass ratio of the content of the second additive to the content of the first additive and the doping element is within an appropriate range, the cycle performance, high-temperature storage performance and resistance performance of the lithium secondary battery can be improved.

[0160] From the comparison results of Examples 8-14 and Comparative Examples 4-6, it can be seen that when the content of the doping element in Comparative Examples 4-6 is too much, the cycle performance, high-temperature storage performance and resistance performance of the lithium secondary batteries of Comparative Examples 4-6 are relatively poorer than those of the embodiments; it shows that when the ratio of the mass percentage W1 of the first additive in the electrolyte, the mass percentage W2 of the second additive in the electrolyte and the mass percentage W3 of the doping element in the positive electrode active material satisfies 1: (0.2-2): (0.1-0.5), the cycle performance, high-temperature storage performance and resistance performance of the lithium secondary battery can be improved.

[0161] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A lithium secondary battery, wherein: Including positive electrode and electrolyte, Wherein, the positive electrode plate comprises a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material comprises at least one doping element selected from the group consisting of aluminum, zirconium, boron, magnesium, zinc, calcium and titanium; The electrolyte includes a first additive and a second additive of a silane containing a C2-C8 alkenyl group, wherein the second additive is selected from at least one of lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate; The ratio of the mass percentage content W1 of the first additive in the electrolyte, the mass percentage content W2 of the second additive in the electrolyte and the mass percentage content W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5).

2. The lithium secondary battery according to claim 1, wherein The ratio of W1, W2 and W3 satisfies 1:(0.5-1.5):(0.2-0.4).

3. The lithium secondary battery according to claim 1 or 2, wherein: The mass percentage W1 of the first additive in the electrolyte is 0.05% to 1%; and / or, The first additive includes at least one of tetravinylsilane, ethyltrivinylsilane, diethyldivinylsilane, triethylvinylsilane, and trivinylalkynylsilane.

4. The lithium secondary battery according to any one of claims 1 to 3, wherein: The mass percentage W2 of the second additive in the electrolyte is 0.01% to 2%.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein: The electrolyte contains an organic solvent, and the organic solvent includes one or more of ethylene carbonate, propylene carbonate, fluorobenzene, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, and methyl formate.

6. The lithium secondary battery according to any one of claims 1 to 5, wherein: The mass percentage W3 of the doping element in the positive electrode active material is 0.005% to 0.5%.

7. The lithium secondary battery according to any one of claims 1 to 6, wherein: The positive electrode active material includes a structural formula of Li a Ni b Co c Mn f M d O e One or more of lithium transition metal oxides or modified compounds thereof; wherein 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, and M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B.

8. The lithium secondary battery according to claim 7, wherein: The ratio of b to (b+c+f) is (0.8-0.98):1; and / or, The ratio of c to (b+c+f) is (0.01-0.2):1; and / or, The ratio of f to (b+c+f) is (0.1-0.2):1; Among them, (b+c+f) represents the sum of b, c and f.

9. The lithium secondary battery according to any one of claims 1 to 8, wherein: The surface density of the positive electrode active material layer is greater than or equal to 3.0 g / cm 3 .

10. The lithium secondary battery according to any one of claims 1 to 9, wherein: The lithium secondary battery further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material layer; and the negative electrode active material layer comprises graphite.

11. The lithium secondary battery according to claim 10, wherein: The negative electrode active material layer further includes silicon element.

12. The lithium secondary battery according to claim 10 or 11, wherein: The negative electrode active material layer contains silicon element in an amount less than or equal to 8% by mass based on the total mass of the negative electrode active material layer.

13. The lithium secondary battery according to any one of claims 10 to 12, wherein: The compaction density of the negative electrode active material layer is 1.3-1.7 g / cm 3 .

14. An electrical device, wherein: A lithium secondary battery comprising the lithium secondary battery according to any one of claims 1 to 13.

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