Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, the positive pole piece comprises a positive current collector and a positive film layer located on at least one surface of the positive current collector and containing a positive active material; the positive electrode active material includes a first active material, wherein the first active material includes a manganese element; the electrolyte comprises an additive, and 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 is more than or equal to 0.01% and less than or equal to 3%; the ratio r of the first active material in the positive electrode active material is greater than or equal to 0.1 and less than or equal to 0.95; the specific surface area n of the first active material is more than or equal to 10 m < 2 > / g and less than or equal to 20 m < 2 > / Wherein the values of m, r and n meet the following relation: 0.001 < = m / (n * r) < = 3.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a secondary battery and an electrical device using the same. Background Art

[0002] As a green energy system, batteries have attracted much attention due to their high specific energy, long cycle life, low self-discharge, good safety performance, etc., and are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of batteries, higher requirements are also put forward for their performance.

[0003] The interface between the electrode and the electrolyte plays an important role in the cycle, 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 cathode / electrolyte interface phase (Composite Electrolyte Interface membrane, CEI). The CEI film is formed on the surface of the positive electrode and is a solid electrolyte interface film through which ions can pass but electrons cannot, playing an important role in lithium-ion batteries. Therefore, it is necessary to form a stable CEI film, thereby stabilizing the positive electrode structure, reducing side reactions, and optimizing the storage and cycle performance of the battery. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a secondary battery with improved stability of the CEI film on the surface of the positive electrode, and thus improved storage performance and cycle performance, and an electrical device using the secondary battery.

[0005] To achieve the above object, a first aspect of the present application 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 element. The electrolyte includes an additive, and the additive includes 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: 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 of the present application 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 in the positive electrode interface reaction is denser and more 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 cycling performance of the battery. Moreover, 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 cycling performance and storage performance of the secondary battery. When the first active material has a large specific surface area and a high content in the positive electrode, the first active material causes an increase in the overall specific surface area of the positive electrode. Although the cost can be reduced and the power performance can be improved, 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 product is deposited at the interface, which can effectively inhibit the occurrence of side reactions. Specifically, the additive in the electrolyte of the present application 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 in 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 cycling performance and storage performance of the battery.

[0006] In addition, when the specific surface area of the first active material is within the above range, lithium ions can be quickly inserted and extracted, improving the power performance of the battery.

[0007] In some embodiments, the values of m, r, and n satisfy: 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, the dissolution of Mn in the positive electrode active material and the side reactions of the positive electrode can be further inhibited, which is more conducive to improving the structural stability of the positive electrode material.

[0008] In some embodiments, 0.01% ≤ m% ≤ 2%. When the content of the additive is within the above range, on the one hand, it can prevent the electrolyte from easily undergoing side reactions at the positive electrode interface, thereby effectively protecting the positive electrode interface; on the other hand, it can make the electrolyte have a suitable degree of dissociation and a suitable conductivity, thereby improving the kinetic performance of the battery and the high-temperature storage performance and cycling performance of the battery.

[0009] 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.

[0010] In some embodiments, the additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxaloborate, fluorosulfonate, bis(fluorosulfonyl)imide salt, and aminosulfonate. Optionally, the additive is at least one of difluorophosphate, tetrafluoroborate, and fluorosulfonate; optionally, the salt is an alkali metal salt. Thus, a CEI film can be effectively formed on the surface of the positive electrode, thereby suppressing the side reaction of the electrolyte at the positive electrode through the CEI film, reducing the consumption of active lithium in the electrolyte, and improving the service life of the battery.

[0011] 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 O 4 ; where x is from -0.1 to 0.1, y is from 0.001 to 0.5, z is from 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, Br; optionally, E is selected from one of B, Si, N, S. When the first active material is selected from the above types, the specific surface area of the first active material is relatively large, which can provide more active sites and is beneficial to improving the power performance of the battery. In addition, when the first active material is selected from the above types, the safety performance of the battery can also be improved, and the cost of the battery can be reduced.

[0012] In some embodiments, the surface of the first active material has a coating layer.

[0013] In some embodiments, the positive electrode active material further includes a second active material, and the chemical formula of the second active material is Li a Ni b Co c Mn f M d O e ; where 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 nickel-cobalt-manganese ternary material selected from the above types, it can have a high specific capacity. Thus, it is beneficial to further improve the energy density of the battery.

[0014] In some embodiments, the surface of the second active material has a coating layer.

[0015] In some embodiments, the coating layer is selected from one or more of a pyrophosphate coating layer, a phosphate coating layer, and a carbon coating layer. By providing the coating layer, on the one hand, the electronic conductivity of the cathode material can be improved, which is beneficial to the rate performance of the battery; on the other hand, the possibility of contact between the cathode active material and the electrolyte can be reduced, thereby improving the stability of the cathode material.

[0016] In some embodiments, the electrolyte includes at least one lithium salt selected from lithium hexafluorophosphate, lithium fluorosulfonyl (perfluorobutanesulfonyl) imide, and lithium bis(trifluoromethylsulfonyl) imide. The lithium salt has properties such as good solubility, high ion conduction ability, and high ion dissociation degree. When applied to the electrolyte, it can improve the transport rate of lithium ions, thereby being beneficial to improving the cycle performance of the battery.

[0017] 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, not only can the conductivity of the electrolyte be effectively improved, but also the electrolyte can have a lower viscosity and better fluidity. With good fluidity of the electrolyte, it can more easily infiltrate the positive electrode plate and the negative electrode plate, thereby reducing the internal resistance of the battery. Thus, the energy density and cycle performance of the battery can be balanced.

[0018] The second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

[0019] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0021] Figure 2 is Figure 1 the exploded view of the battery cell according to an embodiment of the present application shown in

[0022] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0023] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0024] Figure 5 is Figure 4 the exploded view of the battery pack according to an embodiment of the present application shown in

[0025] Figure 6It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0026] Explanation of reference numerals:

[0027] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Specific embodiments

[0028] Hereinafter, embodiments of the secondary battery and the electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent 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 application and are not intended to limit the subject matter recited in the claims.

[0029] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or not include the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0031] If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all steps of this application can be carried out 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) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0034] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be determined by various commonly used testing methods in the art. For example, they can be determined according to the testing methods given in this application.

[0035] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0036] In order to improve the battery safety performance and at the same time reduce the battery cost, it has become a consensus to mix a certain proportion of lithium iron manganese phosphate into the ternary cathode material. However, the specific surface area of the ternary mixed lithium iron manganese phosphate system is large, which easily induces the oxidation reaction of the electrolyte on its surface, resulting in the collapse of the positive electrode and the dissolution of manganese. The dissolved manganese ions migrate to the negative electrode, damaging the solid electrolyte interface (SEI), causing the continuous reduction reaction of the electrolyte at the negative electrode interface, consuming active lithium, and deteriorating the cycle performance and storage life of the battery.

[0037] Based on this, the technical solution of the embodiment of this application provides a lithium secondary battery. The CEI film in this secondary battery is stable and dense, which can effectively inhibit the Mn dissolution of the positive electrode active material and the side reaction 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.

[0038] Secondary battery

[0039] The term "secondary battery" mentioned in this article refers to a battery cell, a battery module, or a battery pack.

[0040] Under normal circumstances, a secondary battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte solution, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0041] In a first aspect of the present application, a secondary battery is provided, including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution. The positive electrode plate 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 element; the electrolyte solution includes an additive, and 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 solution 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; wherein, m represents the mass percentage content of the additive in the electrolyte solution; r represents the proportion of the first active material in the positive electrode active material; n represents the value of the specific surface area of the first active material.

[0042] Aiming at the problem that side reactions are likely to occur on the surface of the positive electrode plate, in the present application, by controlling 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 solution, the solid electrolyte interface (CEI) film formed by the additive in the positive electrode interface reaction is made denser and more stable. The stable and dense CEI film can effectively inhibit the dissolution of Mn in the first active material. In this way, the damage of Mn ions to the negative electrode SEI film can be inhibited, and the cycle stability of the battery can be improved. In addition, there is a good synergistic effect between the mass percentage content of the first active material in the positive electrode active material and the content of the additive in the electrolyte solution, which can improve the stability of the interface between the positive electrode plate and the electrolyte solution, reduce the occurrence of side reactions, alleviate the attenuation of the battery capacity, and thus significantly improve the cycle performance and storage performance of the secondary battery.

[0043] 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 reaction active sites are provided, which will exacerbate the side reactions of the electrolyte. At this time, a film-forming additive is needed to strengthen the film formation and inhibit the interfacial side reactions. In the present application, when the values of 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 formed CEI film 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.

[0044] In some embodiments, the values of m, r, and n satisfy: 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 composed of any two of the above numerical values.

[0045] When the values of 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 inhibited, which is more conducive to improving the structural stability of the positive electrode material.

[0046] In some embodiments, 10m 2 / g ≤ n ≤ 20m 2 / g. For example, n can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20. When the specific surface area of the first active material is within the above range, lithium ions can be quickly inserted and extracted, improving the power performance of the battery.

[0047] 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%, 3%.

[0048] When the content of the additive is within the above range, on the one hand, it can make the electrolyte not easily undergo side reactions at the positive electrode interface, thereby effectively protecting the positive electrode interface; on the other hand, it can make the electrolyte have a suitable degree of dissociation and a suitable conductivity, thereby improving the kinetic performance of the battery and improving the high-temperature storage performance and cycle performance of the battery. Thus, the formation of the CEI film and the conductivity of the electrolyte can be balanced.

[0049] In some embodiments, 0.1 ≤ r ≤ 0.95. Optionally, 0.15 ≤ r ≤ 0.9. More optionally, r can 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.

[0050] In some embodiments, the additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxaloborate, fluorosulfonate, bis(fluorosulfonyl)imide salt, and aminosulfonate. Optionally, the additive is at least one of difluorophosphate, tetrafluoroborate, and fluorosulfonate; optionally, the salt is an alkali metal salt. Thus, a CEI film can be effectively formed on the surface of the positive electrode, thereby suppressing the side reaction of the electrolyte on the positive electrode through the CEI film, reducing the consumption of active lithium in the electrolyte, and improving the service life of the battery.

[0051] In some embodiments, the electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements.

[0052] In some embodiments, the above additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxaloborate, fluorosulfonate, bis(fluorosulfonyl)imide salt, and aminosulfonate. In some embodiments, the above salt is an alkali metal salt.

[0053] In some embodiments, the anion of the additive in the above electrolyte is selected from at least one of difluorophosphate, tetrafluoroborate, difluorooxaloborate, fluorosulfonate, bis(fluorosulfonyl)imide, and aminosulfonate; the cation of the additive is selected from at least one of lithium ion, sodium ion, and potassium ion.

[0054] When the anion and cation of the additive are selected from the above types, a CEI film can be effectively formed on the surface of the positive electrode, and the CEI film can inhibit the oxidation reaction of the electrolyte on the positive electrode, reducing the consumption of active lithium in the electrolyte. Thus, the service life of the battery can be improved.

[0055] In some embodiments, the above electrolyte includes a lithium salt; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium (perfluorobutanesulfonyl)fluorosulfonimide, and lithium bis(trifluoromethylsulfonyl)imide.

[0056] The lithium salt has properties such as good solubility, high ionic conductivity, and high ionic dissociation degree. When applied to the electrolyte, it can improve the transmission rate of lithium ions, thereby facilitating the improvement of the power performance of the battery.

[0057] In some embodiments, the concentration of the above lithium salt in the above electrolyte is 0.8 mol / L to 1.3 mol / L. For example, it can be 1 mol / L.

[0058] 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 enable the electrolyte to have a lower viscosity and better fluidity. With good fluidity of the electrolyte, it can more easily infiltrate the positive electrode sheet and the negative electrode sheet, thereby reducing the internal resistance of the battery. Thus, both the energy density and the cycle performance can be taken into account.

[0059] In some embodiments, the above-mentioned electrolyte includes an organic solvent; the above-mentioned 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, propyl propionate.

[0060] When the organic solvent in the electrolyte is of the above types, it can make the mixture 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.

[0061] In some embodiments, the composition of the electrolyte can be determined by equipment and methods known in the art. As an example, quantitative analysis of the organic components (such as additives) in the electrolyte can be carried out by gas chromatography with reference to standard GB / T9722-2006. As an example, quantitative analysis of the inorganic components and lithium salt concentration in the electrolyte can be carried out by ion chromatography analysis method with reference to standard JY / T020-1996.

[0062] In some embodiments, the electrolyte provided by the embodiments of the present application can be prepared by the following steps: In a glove box filled with argon (water content < 10 ppm, oxygen content < 1 ppm), mix solvent 1 (for example, it can be ethylene carbonate) and solvent 2 (for example, it can be ethyl methyl carbonate) evenly according to a volume ratio of 3:7 to form an organic solvent, slowly add an appropriate amount of lithium salt (for example, it can be LiPF 6 ) to the organic solvent. After the lithium salt is completely dissolved, a 1 mol / L electrolyte is obtained. Finally, a certain amount of additive (for example, it can be lithium difluorophosphate) is added to the electrolyte.

[0063] In some embodiments, the chemical formula of the first active material in the above-mentioned positive electrode active material is Li 1+x Mn 1- y A y P 1-z E z O 4; wherein, x ranges from -0.1 to 0.1, y ranges from 0.001 to 0.5, and z ranges from 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, Br; optionally, E is selected from one of B, Si, N, S.

[0064] When the first active material is selected from the above types, the specific surface area of the first active material is relatively large, which can provide more active sites and is beneficial to improving the power performance of the battery. In addition, when the first active material is selected from the above types, the safety performance of the battery can also be improved, and the cost of the battery can be reduced.

[0065] In addition, adding elements B, Si, N, S, F, Cl, Br to the first active material can improve the stability of the cathode structure and inhibit the phase transition during cycling.

[0066] In this application, on the one hand, the first active material (such as lithium iron manganese phosphate) can improve the safety performance of the battery, and on the other hand, it can reduce the cost of the battery. However, the specific surface area of the first active material is relatively large, which easily induces the oxidation reaction of the electrolyte on its surface, resulting in the dissolution of Mn in the cathode and collapse. Therefore, when the values of 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 satisfy the above relationship, the dissolution of Mn in the cathode and the oxidation reaction of the electrolyte at the cathode can be effectively inhibited, and the cycle life and storage life of the battery can be improved.

[0067] In some embodiments, the surface of the above-mentioned first active material has a coating layer.

[0068] In some embodiments, the above-mentioned cathode active material further includes a second active material, and 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.

[0069] When the second active material is a nickel-cobalt-manganese ternary material selected from the above types, it can have a high specific capacity. Therefore, it is beneficial to further improve the energy density of the battery.

[0070] In addition, adding elements such as Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, or B to the second active material can improve the stability of the cathode structure and inhibit phase transformation during cycling.

[0071] In some embodiments, the second active material is Li a Ni b Co c Mn f M d O e one or more of lithium transition metal oxides and their modified compounds, wherein the modified compound can be a compound obtained by doping modification and / or surface coating modification of the second active material.

[0072] In some embodiments, the surface of the above-mentioned second active material has a coating layer.

[0073] In some embodiments, the above-mentioned coating layer is selected from one or more of a pyrophosphate coating layer, a phosphate coating layer, and a carbon coating layer.

[0074] In the present application, the cathode active material can have a core-shell structure, that is, a coating layer is provided on the surface of the above-mentioned cathode active material. On the one hand, this coating layer can improve the electronic conductivity of the cathode material, which is beneficial to the rate performance of the battery; on the other hand, it can reduce the possibility of contact between the cathode active material and the electrolyte, thereby improving the stability of the cathode material.

[0075] In some embodiments, the cathode current collector has two surfaces opposite to each other in its own thickness direction, and the cathode film layer is provided on either or both of the two opposite surfaces of the cathode current collector.

[0076] In some embodiments, the cathode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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.).

[0077] In some embodiments, the cathode film layer may optionally further include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0078] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an 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.

[0079] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0080] In the present application, the BET specific surface area of a material (such as the first active material, etc.) has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, it can be measured by the nitrogen adsorption specific surface area analysis test method with reference to GB / T19587-2017 and calculated by the BET (Brunauer Emmett Teller) method. The test instrument can be the Tri-Star3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0081] In the present application, the mass percentage content of the first active material can be obtained by detection with reference to the inductively coupled plasma atomic emission spectrometry method of EPA 6010D-2014. Specifically, the content of phosphorus element in the positive electrode material is detected, and then the mass of lithium iron phosphate manganese is deduced.

[0082] In the present application, whether there is a coating layer on the surface of the positive electrode active material can be judged by a transmission electron microscope.

[0083] In the present application, both the above-mentioned first active material and the second active material can be obtained commercially, and the manufacturer is DFD Nanotech. Exemplarily, the second active material can be Li[N 0.5 Co 0.2 Mn 0.3 O 2 , and the first active material can be LiMn 0.3 Fe 0.7 PO 4 .

[0084] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0085] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0086] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0087] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries 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, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0088] In some embodiments, the negative electrode film layer may also optionally 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).

[0089] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0091] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the above components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0092] In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous separator with good chemical stability and mechanical stability can be selected.

[0093] 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.

[0094] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0095] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0096] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and examples of the plastic can include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0097] The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0098] In some embodiments, referring to Figure 2 , the outer package can include a housing 51 and a top cover assembly 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with 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 separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates into the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0099] In some embodiments, the battery cells can be assembled into a battery module, and the number of the battery cells included in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0100] Figure 3 is a battery module 4 as an example. Referring to Figure 3, in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other arbitrary manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0101] 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.

[0102] In some embodiments, the above battery module may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0103] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0104] In addition, a second aspect of the present application further provides an electrical device. The electrical device includes the secondary battery provided in each of the above embodiments. The secondary battery may be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, 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, satellites, energy storage systems, etc., but is not limited thereto.

[0105] As the electrical device, battery cells, battery modules or battery packs may be selected according to its usage requirements.

[0106] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module may be adopted.

[0107] Another example of the device may be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinning and can use battery cells as the power source.

[0108] Embodiment

[0109] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technical or conditions noted in the embodiments, the technologies or conditions described in the literature in the field or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0110] Example 1

[0111] Preparation of electrolyte: In a glove box filled with argon (water content < 10 ppm, oxygen content < 1 ppm), ethylene carbonate and ethyl methyl carbonate were mixed evenly at a volume ratio of 3:7 to obtain an organic solvent. An appropriate amount of LiPF 6 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 as an additive to the electrolyte.

[0112] Preparation of the positive electrode sheet: 1) Preparation of the positive electrode active material: The chemical formula of the first active material in the positive electrode active material prepared by DFD Nanotech is LiMn 0.3 Fe 0.7 PO 4 , and the chemical formula of the second active material is Li[Ni 0.3 Co 0.3 Mn 0.4 O 2 ; 2) The prepared positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were made into a positive electrode slurry in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The solid content in the positive electrode slurry was 50 wt%. The positive electrode slurry was coated on the current collector aluminum foil, dried at 85°C, and then cold-pressed. After trimming, slicing, and slitting, it was dried in a vacuum at 85°C for 4 h to make the positive electrode sheet.

[0113] Preparation of the negative electrode sheet: The negative electrode active material graphite, conductive agent Super P, thickening agent CMC, and binder styrene-butadiene rubber (SBR) were mixed evenly in deionized water at a ratio of 80:15:3:2 to make a negative electrode slurry. The solid content in the negative electrode slurry was 30 wt%. The negative electrode slurry was coated on the current collector copper foil and dried at 85°C, and then cold-pressed, trimmed, sliced, and slit. After that, it was dried in a vacuum at 120°C for 12 h to make the negative electrode sheet.

[0114] Separator: A 16-μm polyethylene film (PE) was used as the separator.

[0115] Preparation of Secondary Battery

[0116] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet, and then wound to obtain a bare battery cell. The electrode tabs are welded, and the bare battery cell is placed in an outer package. The prepared electrolyte is injected into the dried battery cell, followed by encapsulation, standing, formation, shaping, capacity testing, etc., 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.

[0117] Examples 2 to 6

[0118] The positive electrode sheet was prepared in a method similar to that of Example 1 and assembled into a soft-pack battery, except that the content of the electrolyte, the surface area of the first active material, and the content of the first active material in the soft-pack battery were different. For details, please refer to Table 1.

[0119] Comparative Examples 1 to 5

[0120] The positive electrode sheet was prepared in a method similar to that of Example 1 and assembled into a soft-pack battery, except that the content of the electrolyte, the surface area of the first active material, and the content of the first active material in the soft-pack battery were different. For details, please refer to Table 1.

[0121] Performance Test of Secondary Battery

[0122] 1. Cycle performance test

[0123] 1) At an ambient temperature of 25 °C, the secondary battery was charged at a constant current of 1C to 4.4 V and then charged at a constant voltage to 0.05C;

[0124] 2) Stand for 10 min;

[0125] 3) Discharge at 1C to 2.5 V and record the first discharge capacity C 0 ,

[0126] 4) Perform 300 charge-discharge cycles according to the charge-discharge process of steps 1 to 3 above, and record the discharge capacity C 1 .

[0127] The cycle capacity retention rate of the battery = C 1 / C 0 * 100%.

[0128] 2. Storage performance test

[0129] 1) Charge the secondary battery at 1C to 4.4 V and then charge at a constant voltage to 0.05C;

[0130] 2) Stand for 5 min;

[0131] 3) Discharge at a constant current of 1C to 2.5 V and record the discharge capacity D 0 ;

[0132] 4) Place the secondary battery in storage at 60 °C for 30 days, and after taking it out, restore it to 25 °C;

[0133] 5) Discharge at a constant current of 1C until 2.5V;

[0134] 6) Stand still for 2 hours;

[0135] 7) Charge at a constant current of 1C to 4.4V and then charge at a constant voltage to 0.05C;

[0136] 8) Stand still for 2h;

[0137] 9) Discharge at 1C to 2.5V, and record the discharge capacity as D 1 。

[0138] Discharge capacity retention rate = D 1 / D 0 *100%.

[0139] 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:

[0140] Table 1:

[0141]

[0142]

[0143] From the above results, it can be seen that when the value of any one of 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 0.001 ≤ m / (n*r) ≤ 3 is outside the protection scope of this application, the cycle performance and storage performance of the battery will deteriorate 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 inhibited, which is more conducive to improving the structural stability of the positive electrode material.

[0144] Examples 7 to 24

[0145] Prepare the positive electrode sheet according to a method similar to that of Example 1, and assemble it into a soft-pack battery, the difference being that the content of the electrolyte, the surface area of the first active material, and the content of the first active material in the soft-pack battery are different. For details, please refer to Table 2.

[0146] Table 2:

[0147] Item Second Active Material First Active Material r <![CDATA[n(m 2 / g)]]> Additive m％ Example 7 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.8 14 Lithium Difluorophosphate 0.01 Example 8 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.6 14.5 Lithium Difluorophosphate 0.09 Example 9 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.95 15 Lithium Difluorophosphate 0.2 Example 10 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.3 14 Lithium Difluorophosphate 0.1 Example 11 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.6 15 Lithium Difluorophosphate 0.3 Example 12 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.5 15 Lithium Difluorophosphate 1 Example 13 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.5 15 Lithium Difluorophosphate 1.5 Example 14 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.2 10 Lithium Difluorophosphate 0.5 Example 15 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.2 10 Lithium Tetrafluoroborate 0.5 Example 16 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.2 10 Lithium Bis(fluorosulfonyl)imide 0.5 Example 17 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.2 10 Lithium Trifluoromethanesulfonate 0.5 Example 18 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 15 Lithium Difluorophosphate 0.5 Example 19 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 10 Lithium Difluorophosphate 0.5 Example 20 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.3 15 Lithium Difluorophosphate 2.5 Example 21 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.13 10 Lithium Difluorophosphate 2 Example 22 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 23 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 10 Lithium Difluorophosphate 2.5 Example 24 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 10 Lithium Difluorophosphate 3

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

[0149] Table 3:

[0150]

[0151]

[0152] As can be seen from Table 3 above, when the mass percentage content 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 respectively meet the requirements of their respective ranges, and the values of m, r, and n satisfy: 0.01 ≤ m / (n*r) ≤ 2, the inhibition effect on the Mn dissolution of the positive electrode active material and the side reactions of the positive electrode is better, which is more beneficial to the cycle performance and storage performance of the battery. In addition, when selecting the specific type of additive in this application, an effective solid electrolyte interface film can be formed at the positive electrode interface reaction, which is beneficial to the cycle performance and storage performance of the battery.

[0153] In addition, compared with Example 17, the specific type of additive is used in Examples 14 - 16, which is beneficial to improving the cycle performance and storage performance of the battery. This may be because the specific type of additive can form a more effective CEI film in the positive electrode interface reaction.

[0154] Examples 25 to 33

[0155] The positive electrode sheet was prepared by a method similar to that of Example 1 and assembled into a soft-pack battery, except that the first active material and the second active material in the soft-pack battery were different. For details, please refer to Table 4.

[0156] Table 4:

[0157] Item Second Active Material First Active Material r <![CDATA[n(m 2 / g)]]> Additive m％ Example 25 <![CDATA[Li[Ni 0.3 Co 0.3 Mn 0.4 O 2 > <![CDATA[LiMn 0.5 Fe 0.5 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 26 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.5 Fe 0.5 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 27 <![CDATA[Li[Ni 0.6 Co 0.2 Mn 0.2 O 2 > <![CDATA[LiMn 0.5 Fe 0.5 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 28 <![CDATA[Li[Ni 0.8 Co 0.1 Mn 0.1 O 2 > <![CDATA[LiMn 0.5 Fe 0.5 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 29 <![CDATA[Li[Ni 0.9 Co 0.05 Mn 0.05 O 2 > <![CDATA[LiMn 0.5 Fe 0.5 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 30 <![CDATA[Li[Ni 0. 5Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.3 Fe 0.7 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 31 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.4 Fe 0.6 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 32 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.6 Fe 0.4 PO 4 > 0.1 10 Lithium Difluorophosphate 2 Example 33 <![CDATA[Li[Ni 0.5 Co 0.2 Mn 0.3 O 2 > <![CDATA[LiMn 0.8 Fe 0.2 PO 4 > 0.1 10 Lithium Difluorophosphate 2

[0158] The relevant data of Examples 25 to 33 are shown in Table 5 below.

[0159] Table 5:

[0160]

[0161]

[0162] As can be seen from Table 5 above, Examples 25 to 33 have all improved the cycle performance and storage performance of the battery, indicating that the solution of this application is not limited by the types of the first active material and the second active material.

[0163] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments with the same structure and the same effect within the scope of the technical solution of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A secondary battery, comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The positive electrode plate includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector and containing a positive active material. Characterized in that, The positive active material includes a first active material, wherein the first active material contains manganese element; The electrolyte includes an additive, and the additive includes 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: 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.

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

3. The secondary battery according to claim 1 or 2, Characterized in that, 0.01％≤m％≤2％。 4. The secondary battery according to any one of claims 1 to 3, Characterized in that, 0.15≤r≤0.9。 5. The secondary battery according to any one of claims 1 to 4, Characterized in that, The additive includes at least one of difluorophosphate, tetrafluoroborate, difluorooxalate borate, fluorosulfonate, bis(fluorosulfonyl)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, Characterized in that, The chemical formula of the first active material is Li 1+x Mn 1-y A y P 1-z E z O 4 ; In the formula, 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, Br; Optionally, E is selected from one of B, Si, N, S, Optionally, the surface of the first active material has a coating layer.

7. The secondary battery according to any one of claims 1 to 6, Characterized in that, The positive electrode active material further includes a second active material, and the chemical formula of the second active material is Li a Ni b Co c Mn f M d O e ; In the formula, 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 surface of the second active material has a coating layer.

8. The secondary battery according to claim 6 or 7, Characterized in that, The coating layer includes one or more layers of pyrophosphate coating layer, phosphate coating layer, and carbon coating layer.

9. The secondary battery according to any one of claims 1 to 8, Characterized in that, The electrolyte includes at least one lithium salt of lithium hexafluorophosphate, lithium fluorosulfonyl(perfluorobutanesulfonyl)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, Characterized in that, It includes the secondary battery according to any one of claims 1 to 9.

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