Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer which is located on at least one surface of the positive electrode current collector and comprises a positive electrode active material. The positive electrode active material comprises a first active material, wherein the first active material comprises a manganese element. The electrolyte comprises an additive. The additive comprises at least one of a phosphorus-containing additive, a boron-containing additive, and a sulfur-containing additive, and the mass percentage content m of the additive in the electrolyte satisfies: 0.01%≤m%≤3%. The proportion r of the first active material in the positive electrode active material satisfies: 0.1≤r≤0.95. The specific surface area n of the first active material satisfies: 10 m2 / g≤n≤ 20 m2 / g, wherein the values of m, r, and n satisfy the following relationship: 0.001≤m / (n*r)≤3.

Description

Secondary batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311641648.2, application date November 30, 2023, and invention name “Secondary Battery and Electrical Device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device. Background Art

[0004] As a green energy system, batteries have attracted considerable attention for their high specific energy, long cycle life, low self-discharge, and excellent safety performance. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. As batteries have made great progress, higher requirements have been placed on their performance.

[0005] The interface between the electrode and the electrolyte plays an important role in the cycling, rate, and safety performance of lithium-ion batteries. Under high voltage conditions, the oxidized positive electrode will further react with the electrolyte, easily triggering interfacial redox reactions and the formation of the positive electrode / electrolyte interface (Composite Electrolyte Interface membrane, CEI). The CEI membrane is generated on the surface of the positive electrode and is a solid electrolyte interface membrane that allows ions to pass but not electrons. It plays an important role in lithium-ion batteries. Therefore, it is necessary to form a stable CEI membrane, thereby stabilizing the positive electrode structure, reducing side reactions, and optimizing the storage and cycling performance of the battery.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery with improved CEI film stability on the positive electrode surface, thereby having improved storage performance and cycle performance, and an electric device using the secondary battery.

[0008] In order to achieve the above-mentioned object, the first aspect of the present disclosure provides a secondary battery. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector and containing a positive electrode active material; the positive electrode active material includes a first active material, wherein the first active material contains manganese; the electrolyte includes an additive, wherein the additive includes at least one of a phosphorus-containing additive, a boron-containing additive and a sulfur-containing additive; the mass percentage content m of the additive in the electrolyte satisfies: 0.01% ≤ m% ≤ 3%; the proportion r of the first active material in the positive electrode active material satisfies: 0.1 ≤ r ≤ 0.95; the specific surface area n of the first active material satisfies: 10m 2 / g≤n≤20m 2 / g; wherein, the values ​​of m, r, and n satisfy the following relationship: 0.001≤m / (n*r)≤3. The secondary battery disclosed herein controls the proportion and specific surface area of ​​the first active material in the positive electrode active material and the content of the special additive in the electrolyte, so that the solid electrolyte interface (CEI) film formed by the additive reaction at the positive electrode interface is more compact and stable, which can effectively inhibit the dissolution of transition metal ions such as manganese (Mn) in the first active material and improve the storage and cycle performance of the battery. In addition, there is a good synergistic effect between the proportion of the first active material in the positive electrode active material and the content of the additive in the electrolyte, which can improve the stability of the interface between the positive electrode sheet and the electrolyte, reduce side reactions, alleviate the attenuation of the battery capacity, and thus significantly improve the cycle performance and storage performance of the secondary battery. The first active material has a large specific surface area, and when the content of the first active material in the positive electrode is high, the first active material causes the specific surface area of ​​the positive electrode as a whole to increase. Although it can reduce costs and improve power performance, the side reactions are aggravated. The additive in the electrolyte undergoes an oxidation reaction on the surface of the first active material, and the reaction products are deposited at the interface, which can effectively inhibit the occurrence of side reactions. Specifically, the additive in the electrolyte of the present disclosure can effectively participate in the formation of the CEI film. When the mass percentage content m of the additive, the proportion r of the first active material, and the specific surface area value n satisfy 0.001≤m / (n*r)≤3, the formed CEI film is dense and stable, which can effectively inhibit the dissolution of Mn from the positive electrode active material and side reactions of the positive electrode, thereby improving the structural stability of the positive electrode material and further improving the cycle performance and storage performance of the battery.

[0009] In addition, when the specific surface area of ​​the first active material is within the above range, lithium ions can be quickly inserted into and extracted from the battery, thereby improving the power performance of the battery.

[0010] In some embodiments, the values ​​of m, r, and n satisfy the following: 0.01≤m / (n*r)≤2. When the content m of the additive, the proportion r of the first active material, and the specific surface area n satisfy 0.01≤m / (n*r)≤2, Mn dissolution from the positive electrode active material and side reactions at the positive electrode can be further suppressed, which is more conducive to improving the structural stability of the positive electrode material.

[0011] In some embodiments, 0.01% ≤ m% ≤ 2%. When the content of the additive is within the above range, on the one hand, the electrolyte is less likely to undergo side reactions at the positive electrode interface, thereby effectively protecting the positive electrode interface; on the other hand, the electrolyte can have an appropriate degree of dissociation and appropriate conductivity, thereby improving the battery's kinetic performance, high-temperature storage performance, and cycle performance.

[0012] In some embodiments, 0.15≤r≤0.9. When the content r of the first active material is within the above range, the power performance of the battery can be effectively improved.

[0013] In some embodiments, the additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxalatoborate, fluorosulfonate, bisfluorosulfonimide salt, and aminosulfonate. Alternatively, the additive is at least one of difluorophosphate, tetrafluoroborate, and fluorosulfonate; and optionally, the salt is an alkali metal salt. This effectively forms a CEI film on the positive electrode surface, thereby suppressing side reactions of the electrolyte at the positive electrode through the CEI film, reducing the consumption of active lithium in the electrolyte, and extending the battery life.

[0014] In some embodiments, the chemical formula of the first active material is Li 1+x Mn 1-y A y P 1-z E z O4; wherein x is -0.1 to 0.1, y is 0.001 to 0.5, and z is 0.001 to 0.1; A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; optionally, A is selected from one of Fe, Ti, V, Ni, Co, and Mg; E is selected from one or more of B, Si, N, S, F, Cl, and Br; optionally, E is selected from one of B, Si, N, and S. When the first active material is selected from the above types, the first active material has a larger specific surface area, can provide more active sites, and is conducive to improving the power performance of the battery. In addition, when the first active material is selected from the above types, it can also improve the safety performance of the battery and reduce the cost of the battery.

[0015] In some embodiments, the first active material has a coating layer on its surface.

[0016] In some embodiments, the positive electrode active material further includes a second active material, the chemical formula of the second active material is Li a Ni b Co c Mn f M d O e Wherein, 0.8≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1; M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B. When the second active material is a ternary material containing nickel, cobalt, and manganese selected from the above types, it can have a high specific capacity, thereby further improving the energy density of the battery.

[0017] In some embodiments, the second active material has a coating layer on its surface.

[0018] In some embodiments, the coating layer is selected from one or more layers of a pyrophosphate coating layer, a phosphate coating layer, and a carbon coating layer. The coating layer can improve the electronic conductivity of the positive electrode material, thereby improving the rate performance of the battery; it can also reduce the likelihood of contact between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode material.

[0019] In some embodiments, the electrolyte includes at least one lithium salt selected from lithium hexafluorophosphate, lithium fluorosulfonyl (perfluorobutylsulfonyl) imide, and lithium bis(trifluoromethylsulfonyl) imide. Lithium salts have properties such as good solubility, high ion conductivity, and high ion dissociation. Their use in the electrolyte can increase the lithium ion transport rate, thereby improving the battery's cycling performance.

[0020] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L. When the concentration of the lithium salt in the electrolyte is within the above range, it can not only effectively improve the conductivity of the electrolyte, but also make the electrolyte have lower viscosity and better fluidity. The good fluidity of the electrolyte can more easily infiltrate the positive and negative electrode sheets, thereby reducing the internal resistance of the battery. In this way, the energy density and cycle performance of the battery can be taken into account.

[0021] A second aspect of the present disclosure provides an electric device including the secondary battery according to the first aspect of the present disclosure.

[0022] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0024] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 1 .

[0025] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0026] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0027] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0028] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0029] Explanation of reference numerals: 1 battery pack; 2 upper housing; 3 lower housing; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0030] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0031] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0033] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0036] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0037] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0038] Currently, new energy batteries are increasingly being used in everyday life and industry. They are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in a variety of fields such as aerospace. As the application of power batteries continues to expand, market demand is also growing.

[0039] In order to improve battery safety and reduce battery costs, it has become a consensus to mix a certain proportion of lithium manganese iron phosphate into the ternary positive electrode material. However, the ternary mixed lithium manganese iron phosphate system has a large specific surface area, which easily induces electrolyte oxidation reactions on its surface, causing positive electrode collapse and manganese dissolution. The dissolved manganese ions migrate to the negative electrode, destroying the solid electrolyte interface (SEI), causing the electrolyte to continuously undergo reduction reactions at the negative electrode interface, consuming active lithium and deteriorating the battery's cycle performance and storage life.

[0040] Based on this, the technical solution of the embodiment of the present disclosure provides a lithium secondary battery in which the CEI film is stable and dense, which can effectively inhibit the Mn dissolution of the positive electrode active material and the side reactions of the positive electrode, thereby improving the structural stability of the positive electrode material and further improving the cycle life and storage life of the battery.

[0041] secondary batteries

[0042] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0043] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0044] According to a first aspect of the present disclosure, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector and comprising a positive electrode active material; the positive electrode active material comprises a first active material, wherein the first active material comprises a manganese element; the electrolyte comprises an additive, wherein the additive comprises at least one of a phosphorus-containing additive, a boron-containing additive, and a sulfur-containing additive; the mass percentage m of the additive in the electrolyte satisfies the following: 0.01%≤m%≤3%; the proportion r of the first active material in the positive electrode active material satisfies the following: 0.1≤r≤0.95; the specific surface area n of the first active material satisfies the following: 10m 2 / g≤n≤20m 2 / g; wherein the values ​​of m, r, and n satisfy the following relationship: 0.001≤m / (n*r)≤3; wherein m represents the mass percentage of the additive in the electrolyte; r represents the proportion of the first active material in the positive electrode active material; and n represents the specific surface area of ​​the first active material.

[0045] To address the problem of side reactions easily occurring on the surface of the positive electrode, the present disclosure controls the proportion and specific surface area of ​​the first active material in the positive electrode active material and the content of special additives in the electrolyte, making the solid electrolyte interface (CEI) film formed by the additive reaction at the positive electrode interface more dense and stable. The stable and dense CEI film can effectively inhibit the dissolution of Mn in the first active material, thereby inhibiting the damage of Mn ions to the negative electrode SEI film and improving the cycle stability of the battery. In addition, there is a good synergistic effect between the mass percentage of the first active material in the positive electrode active material and the content of the additive in the electrolyte, which can improve the stability of the interface between the positive electrode and the electrolyte, reduce the occurrence of side reactions, alleviate the attenuation of battery capacity, and thus significantly improve the cycle performance and storage performance of the secondary battery.

[0046] The product of the specific surface area of ​​the first active material and its content ratio in the positive electrode reflects the active surface area of ​​the first active material in the entire positive electrode active layer. The higher the active surface area, the more reactive sites are provided, which will aggravate the side reactions of the electrolyte. At this time, a film-forming additive is needed to enhance film formation and inhibit interfacial side reactions. In the present disclosure, when the mass percentage content m of the additive, the proportion r of the first active material, and the specific surface area n of the first active material satisfy 0.001≤m / (n*r)≤3, the CEI film formed can effectively inhibit the dissolution of Mn from the positive electrode active material and the side reactions of the positive electrode, thereby improving the structural stability of the positive electrode material and further improving the cycle life and storage life of the battery.

[0047] In some embodiments, the values ​​of m, r, and n satisfy the following: 0.01 ≤ m / (n*r) ≤ 2. For example, m / (n*r) can be 0.01, 0.02, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.7, 1.9, or 2, or a range consisting of any two of the above values.

[0048] When the content m of the additive, the proportion r of the first active material and the specific surface area n satisfy 0.01≤m / (n*r)≤2, the Mn dissolution of the positive electrode active material and the side reactions of the positive electrode can be further suppressed, which is more conducive to improving the structural stability of the positive electrode material.

[0049] In some embodiments, 10 m 2 / g≤n≤20m 2 / g, for example, n can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. When the specific surface area of ​​the first active material is within the above range, lithium ions can be quickly inserted into and removed from the battery, thereby improving the power performance of the battery.

[0050] In some embodiments, 0.01%≤m%≤3%, optionally, 0.01%≤m%≤2%. For example, m% can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, or 3%.

[0051] When the additive content is within the above range, on the one hand, the electrolyte is less likely to undergo side reactions at the positive electrode interface, thereby effectively protecting the positive electrode interface; on the other hand, the electrolyte can have an appropriate degree of dissociation and appropriate conductivity, thereby improving the battery's dynamic performance, high-temperature storage performance, and cycle performance. In this way, both the formation of the CEI film and the conductivity of the electrolyte can be taken into account.

[0052] In some embodiments, 0.1≤r≤0.95, alternatively, 0.15≤r≤0.9, and more alternatively, r may be 0.2. When the content r of the first active material is within the above range, the power performance of the battery can be effectively improved.

[0053] In some embodiments, the additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxalatoborate, fluorosulfonate, bisfluorosulfonimide salt, and aminosulfonate. Optionally, the additive is at least one of difluorophosphate, tetrafluoroborate, and fluorosulfonate; and optionally, the salt is an alkali metal salt. This effectively forms a CEI film on the positive electrode surface, thereby inhibiting side reactions of the electrolyte at the positive electrode through the CEI film, reducing the consumption of active lithium in the electrolyte, and extending the battery life.

[0054] In some embodiments, the electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present disclosure has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0055] In some embodiments, the additive comprises at least one of difluorophosphate, tetrafluoroborate, difluorooxalatoborate, fluorosulfonate, bisfluorosulfonimide salt and aminosulfonate. In some embodiments, the salt is an alkali metal salt.

[0056] In some embodiments, the anion of the additive in the above-mentioned electrolyte is selected from at least one of difluorophosphate, tetrafluoroborate, difluorooxalatoborate, fluorosulfonate, bisfluorosulfonimide, and aminosulfonate; the cation of the above-mentioned additive is selected from at least one of lithium ion, sodium ion, and potassium ion.

[0057] When the anions and cations of the additives are selected from the above types, a CEI film can be effectively formed on the positive electrode surface. The CEI film can inhibit the oxidation reaction of the electrolyte at the positive electrode and reduce the consumption of active lithium in the electrolyte, thereby increasing the service life of the battery.

[0058] In some embodiments, the electrolyte includes a lithium salt; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium fluorosulfonyl (perfluorobutylsulfonyl) imide, and lithium bis(trifluoromethylsulfonyl) imide.

[0059] Lithium salts have properties such as good solubility, high ion conductivity, and high ion dissociation. When used in electrolytes, they can increase the transmission rate of lithium ions, thereby helping to improve the power performance of the battery.

[0060] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L, for example, 1 mol / L.

[0061] When the lithium salt concentration in the electrolyte is within the above range, it not only effectively improves the electrolyte's conductivity but also provides lower viscosity and better fluidity. This fluidity allows the electrolyte to more easily wet the positive and negative electrodes, thereby reducing the battery's internal resistance. This balances energy density and cycle performance.

[0062] In some embodiments, the electrolyte includes an organic solvent; the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, fluoroethylene carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0063] When the organic solvent in the electrolyte is of the above type, it can be matched to have a suitable viscosity, which is beneficial to the dispersion of additives and lithium salts, thereby improving the storage performance of the electrolyte in the secondary battery.

[0064] In some embodiments, the composition of the electrolyte can be determined by equipment and methods known in the art. As an example, the organic components (e.g., additives) in the electrolyte can be quantitatively analyzed by gas chromatography in accordance with the standard GB / T9722-2006. As an example, the inorganic components and lithium salt concentration in the electrolyte can be quantitatively analyzed by ion chromatography in accordance with the standard JY / T020-1996.

[0065] In some embodiments, the electrolyte provided by the embodiments of the present disclosure can be prepared by the following steps: in a glove box filled with argon (water content <10ppm, oxygen content <1ppm), solvent 1 (for example, ethylene carbonate) and solvent 2 (for example, ethyl methyl carbonate) are mixed evenly in a volume ratio of 3:7 to form an organic solvent, and an appropriate amount of lithium salt (for example, LiPF6) is slowly added to the organic solvent. After the lithium salt is completely dissolved, a 1 mol / L electrolyte is obtained, and finally a certain amount of additive (for example, lithium difluorophosphate) is added to the electrolyte.

[0066] In some embodiments, the chemical formula of the first active material in the positive electrode active material is Li 1+x Mn 1-y A y P 1-z E z O4; wherein, x is -0.1 to 0.1, y is 0.001 to 0.5, and z is 0.001 to 0.1; A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; optionally, A is selected from one of Fe, Ti, V, Ni, Co, and Mg; E is selected from one or more of B, Si, N, S, F, Cl, and Br; optionally, E is selected from one of B, Si, N, and S.

[0067] When the first active material is selected from the above categories, the first active material has a larger specific surface area, can provide more active sites, and is conducive to improving the power performance of the battery. In addition, when the first active material is selected from the above categories, it can also improve the safety performance of the battery and reduce the cost of the battery.

[0068] In addition, adding B, Si, N, S, F, Cl, and Br elements to the first active material can improve the stability of the positive electrode structure and inhibit phase transition during the cycle.

[0069] In the present disclosure, the first active material (for example, lithium manganese iron phosphate) can improve the safety performance of the battery on the one hand, and reduce the cost of the battery on the other hand. However, the specific surface area of ​​the first active material is large, which can easily induce an oxidation reaction of the electrolyte on its surface, resulting in the dissolution of the positive electrode Mn and collapse. Therefore, by setting the content m of the additive, the proportion r of the first active material, and the specific surface area n of the first active material to meet the above relationship, the dissolution of the positive electrode Mn and the oxidation reaction of the electrolyte at the positive electrode can be effectively inhibited, thereby improving the cycle life and storage life of the battery.

[0070] In some embodiments, the first active material has a coating layer on its surface.

[0071] In some embodiments, the positive electrode active material further includes a second active material, the chemical formula of which is Li a Ni b Co c Mn f M d O e ; Wherein, 0.8≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1; M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B.

[0072] When the second active material is a ternary material containing nickel, cobalt and manganese selected from the above types, it can have a high specific capacity, thereby further improving the energy density of the battery.

[0073] In addition, adding Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti or B elements to the second active material can improve the stability of the positive electrode structure and inhibit phase transformation during the cycle.

[0074] In some embodiments, the second active material is Li a Ni b Co c Mn f M d O eOne or more of lithium transition metal oxides and modified compounds thereof, wherein the modified compound can be a compound obtained by doping and / or surface coating the second active material.

[0075] In some embodiments, the second active material has a coating layer on its surface.

[0076] In some embodiments, the coating layer is selected from one or more layers of a pyrophosphate coating layer, a phosphate coating layer, and a carbon coating layer.

[0077] In the present disclosure, the positive electrode active material can be a core-shell structure, that is, a coating layer is provided on the surface of the above-mentioned positive electrode active material. On the one hand, the coating layer can improve the electronic conductivity of the positive electrode material, which is beneficial to the rate performance of the battery; on the other hand, it can reduce the possibility of contact between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode material.

[0078] In some embodiments, the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0079] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0081] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0083] In the present disclosure, the specific surface area (BET) of a material (e.g., the first active material, etc.) is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0084] In the present disclosure, the mass percentage of the first active material can be determined by inductively coupled plasma atomic emission spectrometry according to EPA 6010D-2014. Specifically, the phosphorus content in the positive electrode material is determined, and the mass of the lithium manganese iron phosphate is then inferred.

[0085] In the present disclosure, whether a coating layer exists on the surface of the positive electrode active material can be determined by transmission electron microscopy.

[0086] In the present disclosure, the first active material and the second active material mentioned above can be obtained commercially, and the manufacturer thereof is Defang Nano. For example, the second active material can be Li[N 0.5 Co 0.2 Mn 0.3 ]O2, the first active material can be LiMn 0.3 Fe 0.7 PO4.

[0087] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0088] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0089] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0091] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0092] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0094] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0095] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0096] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0097] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0098] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0099] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0100] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0101] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0102] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0103] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0104] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0105] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0106] Figures 4 and 5 illustrate 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.

[0107] In addition, the second aspect of the present disclosure further provides an electric device, which includes the secondary battery provided by each of the above embodiments. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0108] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0109] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0110] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0111] Example

[0112] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0113] Example 1

[0114] Preparation of electrolyte: In an argon-filled glove box (water content <10ppm, oxygen content <1ppm), ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7 to prepare an organic solvent. An appropriate amount of LiPF6 was slowly added to the organic solvent. After the lithium salt was completely dissolved, a 1 mol / L electrolyte was obtained. Finally, 0.3% lithium bis(fluorosulfonyl)imide was added to the electrolyte as an additive.

[0115] Preparation of positive electrode sheet: 1) Preparation of positive electrode active material: The chemical formula of the first active material in the positive electrode active material prepared by Defang Nano is LiMn 0.3 Fe 0.7 PO4, the chemical formula of the second active material is Li[Ni 0.3 Co 0.3 Mn 0.4 ]O2; 2) The prepared positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to form a positive electrode slurry with a solid content of 50 wt%. The positive electrode slurry was coated on a current collector aluminum foil, dried at 85°C, and then cold-pressed. The positive electrode sheet was then trimmed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to form a positive electrode sheet.

[0116] Preparation of the negative electrode sheet: Graphite, the negative electrode active material, Super P, a conductive agent, CMC, a thickener, and styrene-butadiene rubber (SBR) binder were mixed in deionized water at a ratio of 80:15:3:2 to prepare a negative electrode slurry with a solids content of 30 wt%. The slurry was coated onto a current collector copper foil and dried at 85°C. The sheet was then cold-pressed, trimmed, cut, and slit, and then dried at 120°C under vacuum for 12 hours to produce the negative electrode sheet.

[0117] Diaphragm: 16 μm polyethylene film (PE) was used as the diaphragm.

[0118] Preparation of secondary batteries

[0119] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets. The cells are wound to obtain bare cells, the tabs are welded, and the bare cells are placed in outer packaging. The prepared electrolyte is injected into the dried cells. The cells are then packaged, left to rest, formed, shaped, and capacity tested to complete the preparation of the secondary battery. The prepared soft-pack lithium-ion battery has a thickness of 40 mm, a width of 60 mm, and a length of 140 mm.

[0120] Examples 2 to 6

[0121] A positive electrode sheet was prepared in a manner similar to that of Example 1 and assembled into a soft-pack battery. The only differences were the electrolyte content, the surface area of ​​the first active material, and the content of the first active material in the soft-pack battery. Please see Table 1 for details.

[0122] Comparative Examples 1 to 5

[0123] A positive electrode sheet was prepared in a manner similar to that of Example 1 and assembled into a soft-pack battery. The only differences were the electrolyte content, the surface area of ​​the first active material, and the content of the first active material in the soft-pack battery. Please see Table 1 for details.

[0124] Secondary battery performance test

[0125] 1. Cycle performance test

[0126] 1) At an ambient temperature of 25°C, charge the secondary battery to 4.4V at a constant current of 1C and to 0.05V at a constant voltage;

[0127] 2) Let it stand for 10 minutes;

[0128] 3) 1C discharge to 2.5V, record the first discharge capacity C0,

[0129] 4) Perform 300 cycles of charge and discharge according to the above steps 1 to 3, and record the discharge capacity C1 at the 300th cycle.

[0130] The battery's cycle capacity retention rate = C1 / C0*100%.

[0131] 2. Storage performance test

[0132] 1) Charge the secondary battery to 4.4V at 1C and constant voltage charge to 0.05C;

[0133] 2) Let it stand for 5 minutes;

[0134] 3) Discharge at 1C constant current to 2.5V and record the discharge capacity D0;

[0135] 4) Store the secondary battery at 60°C for 30 days and then return it to 25°C.

[0136] 5) 1C constant current discharge to 2.5V;

[0137] 6) Let stand for 2 hours;

[0138] 7) 1C constant current charging to 4.4V, constant voltage charging to 0.05C;

[0139] 8) Let stand for 2 hours;

[0140] 9) Discharge at 1C to 2.5V and record the discharge capacity as D1.

[0141] Discharge capacity retention rate = D1 / D0*100%.

[0142] The coating layer elements and test results of the soft-pack batteries prepared in the above examples and comparative examples are shown in Table 1 below:

[0143] Table 1:

[0144] The above results show that when the mass percentage content m of the additive in the electrolyte, the specific surface area n of the first active material, the proportion r of the first active material in the positive electrode active material, and the value of any of the variables 0.001≤m / (n*r)≤3 are outside the protection scope of the present disclosure, the cycling performance and storage performance of the battery will be deteriorated to a certain extent. Without wishing to be bound by theory, this may be because only when m, n, r, and m / (n*r) simultaneously meet their respective range requirements can the Mn dissolution of the positive electrode active material and the side reactions of the positive electrode be effectively suppressed, which is more conducive to improving the structural stability of the positive electrode material.

[0145] Examples 7 to 24

[0146] A positive electrode sheet was prepared in a manner similar to that of Example 1 and assembled into a soft-pack battery. The difference lies in the content of the electrolyte in the soft-pack battery, the surface area of ​​the first active material, and the content of the first active material. Please see Table 2 for details.

[0147] Table 2:

[0148] The relevant data of Examples 7 to 24 are shown in Table 3 below.

[0149] Table 3:

[0150] As can be seen from Table 3 above, when the mass percentage m of the additive in the electrolyte, the specific surface area n of the first active material, and the proportion r of the first active material in the positive electrode active material meet their respective range requirements, and the values ​​of m, r, and n meet: 0.01≤m / (n*r)≤2, the Mn dissolution of the positive electrode active material and the side reaction of the positive electrode are better inhibited, which is more conducive to the cycle performance and storage performance of the battery. In addition, when a specific type of additive is selected in the present disclosure, it can react at the positive electrode interface to form an effective solid electrolyte interface film, which is beneficial to the cycle performance and storage performance of the battery.

[0151] In addition, the use of specific types of additives in Examples 14-16 is beneficial for improving the cycle performance and storage performance of the battery compared to Example 17. This may be because the specific types of additives can form a more effective CEI film at the positive electrode interface reaction.

[0152] Examples 25 to 33

[0153] A positive electrode sheet was prepared in a similar manner to Example 1 and assembled into a soft-pack battery. The difference is that the first active material and the second active material in the soft-pack battery are different. For details, please see Table 4.

[0154] Table 4:

[0155] The relevant data of Examples 25 to 33 are shown in Table 5 below.

[0156] Table 5:

[0157] As can be seen from Table 5 above, Examples 25 to 33 all improve the cycle performance and storage performance of the battery, indicating that the solution of the present disclosure is not limited by the types of the first active material and the second active material.

[0158] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector and comprising a positive electrode active material, The positive electrode active material includes a first active material, wherein the first active material contains manganese; The electrolyte includes an additive, wherein the additive includes at least one of a phosphorus-containing additive, a boron-containing additive, and a sulfur-containing additive; The mass percentage content m of the additive in the electrolyte satisfies: 0.01%≤m%≤3%; the proportion r of the first active material in the positive electrode active material satisfies: 0.1≤r≤0.95; the specific surface area n of the first active material satisfies: 10m 2 / g≤n≤20m 2 / g; in, The values ​​of m, r, and n satisfy the following relationship: 0.001≤m / (n*r)≤3.

2. The secondary battery according to claim 1, wherein The values ​​of m, r, and n satisfy: 0.01≤m / (n*r)≤2.

3. The secondary battery according to claim 1 or 2, wherein: 0.01％≤m％≤2％。 4. The secondary battery according to any one of claims 1 to 3, wherein 0.15≤r≤0.9。 5. The secondary battery according to any one of claims 1 to 4, wherein The additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxalatoborate, fluorosulfonate, bisfluorosulfonyl imide salt and aminosulfonate. Optionally, the additive is at least one of difluorophosphate, tetrafluoroborate and fluorosulfonate; optionally, the salt is an alkali metal salt.

6. The secondary battery according to any one of claims 1 to 5, wherein The chemical formula of the first active material is Li 1+x Mn 1-y A y P 1-z E z O4; Wherein, x is -0.1 to 0.1, y is 0.001 to 0.5, and z is 0.001 to 0.1; A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, Ge; optionally, A is selected from one of Fe, Ti, V, Ni, Co, Mg; E is selected from one or more of B, Si, N, S, F, Cl, and Br; alternatively, E is selected from one of B, Si, N, and S, Optionally, the first active material has a coating layer on its surface.

7. The secondary battery according to any one of claims 1 to 6, wherein The positive electrode active material further includes a second active material, the chemical formula of which is Li a Ni b Co c Mn f M d O e ; Wherein, 0.8≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1; M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, Optionally, the second active material has a coating layer on its surface.

8. The secondary battery according to claim 6 or 7, wherein: The coating layer includes one of a pyrophosphate coating layer, a phosphate coating layer, and a carbon coating layer. or multiple layers.

9. The secondary battery according to any one of claims 1 to 8, wherein The electrolyte includes at least one lithium salt selected from lithium hexafluorophosphate, lithium fluorosulfonyl (perfluorobutylsulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide; optionally, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L.

10. An electrical device comprising the secondary battery according to any one of claims 1 to 9.

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