Lithium secondary battery and electric device comprising same

Abstract

A lithium secondary battery and an electric device comprising same. The lithium secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, and at least one side of the positive electrode current collector is provided with a positive electrode film layer. The positive electrode film layer comprises a positive electrode active material and a lithium-supplementing material, and the lithium-supplementing material comprises a compound as represented by formula Π: Lix2Ni(1-y2-z2)Coy2Mz2O2±α <sb / > formula Π, wherein M comprises one or more elements of Mn, Al, Fe, Zr, Mg, Ti, Cr, Ga, Cu, Zn and Nb, 0<x2≤1.2, 0.001≤y2≤0.05, 0.001≤z2≤0.05, 0≤α≤0.2, and 0.9≤1-y2-z2<1.

Description

Lithium secondary batteries and electrical equipment containing them

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202411745955.X, filed on November 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a lithium secondary battery and an electrical device containing the same. Background Technology

[0004] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Lithium-ion rechargeable batteries consume active lithium during the initial charge and during cycling, causing capacity decay and reducing cycle performance. Summary of the Invention

[0005] This application aims to at least partially address one of the technical problems in the related art.

[0006] Therefore, one object of this application is to provide a lithium secondary battery, the lithium secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector, the positive current collector having a positive electrode film layer on at least one side, the positive electrode film layer comprising a positive electrode active material and a lithium supplementation material, the positive electrode active material comprising a compound represented by Formula I: Li m A x1 Fe 1-y1 D y1 P 1-z1 E z1 O 4-n G n Formula I, wherein A includes one or more elements selected from Zn, Al, Na, K, and Mg; D includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; E includes one or more elements selected from B, S, Si, and N; G includes one or more elements selected from S, F, Cl, and Br; 0.5 ≤ m ≤ 1.15, 0 ≤ x1 ≤ 0.1, 0 ≤ y1 ≤ 0.5, 0 ≤ z1 ≤ 0.5, and 0 ≤ n ≤ 0.5; the lithium replenishing material includes the compound shown in Formula II: Li x2 Ni (1-y2-z2) Co y2 M z2 O 2±αFormula Π, where M includes one or more elements selected from Mn, Al, Fe, Zr, Mg, Ti, Cr, Ga, Cu, Zn, and Nb, 0 < x² ≤ 1.2, 0.001 ≤ y² ≤ 0.05, 0.001 ≤ z² ≤ 0.05, 0 ≤ α ≤ 0.2, and 0.9 ≤ 1 - y² - z² < 1. The lithium secondary battery proposed in this application has a high-nickel material structure on the positive electrode with poor stability. Structural cracking occurs within the conventional operating voltage range of lithium iron phosphate, releasing active lithium ions. This allows for lithium replenishment of lithium iron phosphate materials during the initial charging process and battery cycling, reducing capacity decay and improving cycle life.

[0007] According to some embodiments of this application, 0.95 ≤ 1 - y² - z² ≤ 0.99. Therefore, the lithium replenishment material has poor structural stability, which improves the lithium replenishment effect. Simultaneously, it increases the specific capacity of the lithium replenishment material and improves the energy density of the battery.

[0008] According to some embodiments of this application, 0.97 ≤ 1 - y² - z² ≤ 0.99. Therefore, the lithium replenishment material has poor structural stability, which improves the lithium replenishment effect. Simultaneously, it increases the specific capacity of the lithium replenishment material and improves the energy density of the battery.

[0009] According to some embodiments of this application, the mass ratio of the positive electrode active material to the lithium replenishment material is 9-97. This increases the capacity of the positive electrode, thereby improving both the cycle life and energy density of the lithium secondary battery.

[0010] According to some embodiments of this application, the sum of the mass of the positive electrode active material and the lithium replenishment material is 91%-98%, and satisfies one or two of the following conditions: based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material is 90%-97%; based on the total mass of the positive electrode film, the mass percentage of the lithium replenishment material is 1%-10%. This increases the capacity of the positive electrode, thereby improving both the cycle life and energy density of the lithium secondary battery.

[0011] According to some embodiments of this application, the sum of the mass of the positive electrode active material and the lithium replenishment material is 96%-98%, and satisfies one or two of the following conditions: based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material is 95%-97%; based on the total mass of the positive electrode film, the mass percentage of the lithium replenishment material is 1%-3%. This increases the capacity of the positive electrode, thereby improving both the cycle life and energy density of the lithium secondary battery.

[0012] According to some embodiments of this application, the positive electrode active material and the lithium replenishment material are located in the same layer. This shortens the solid-phase diffusion path of lithium ions and improves the lithium replenishment effect of the high-nickel material.

[0013] According to some embodiments of this application, at least a portion of the surface of the lithium replenishment material does not have a coating layer. This reduces the structural stability of the lithium replenishment material and improves the lithium replenishment effect.

[0014] According to some embodiments of this application, the lithium replenishment material is a polycrystalline particle. Therefore, compared to monocrystalline materials, polycrystalline materials have a less stable structure, allowing the released lithium ions to be primarily used for lithium replenishment in lithium iron phosphate materials, thus improving the lithium replenishment effect.

[0015] According to some embodiments of this application, the ratio of the reversible capacity of the negative electrode to the reversible capacity of the positive electrode in the lithium secondary battery is 1.05-1.1. This improves the energy density of the lithium secondary battery.

[0016] According to some embodiments of this application, the volume average particle size Dv50 of the lithium replenishment material satisfies: 1.2 μm ≤ Dv50 ≤ 5 μm. This shortens the solid-phase transport path of lithium ions, reduces polarization, and improves capacity utilization.

[0017] According to some embodiments of this application, the BET specific surface area of ​​the lithium replenishment material satisfies: 0.8 m² / m³. 2 / g≤BET≤3.5m 2 / g. Therefore, by ensuring that the BET specific surface area of ​​the lithium replenishment material is within the above range, the kinetic performance of the lithium replenishment material is improved, while the side reactions of the electrolyte on the positive electrode surface are reduced, thereby increasing the cycle life of the lithium secondary battery.

[0018] According to some embodiments of this application, the lithium secondary battery satisfies one or two of the following conditions: the positive electrode active material includes Li m Fe 1-y1 Mn y1 In formula PO4, M includes one or more elements selected from Mn, Zr, Mg, and Ti, where 0.005 ≤ y² ≤ 0.03, 0.005 ≤ z² ≤ 0.03, and 0.94 ≤ 1 - y² - z² ≤ 0.99. Therefore, doping lithium-filling materials with the aforementioned M elements can reduce the first-cycle coulombic efficiency of the lithium-filling material, further improving the lithium-filling effect.

[0019] According to some embodiments of this application, an electrolyte is also included, said electrolyte comprising a cyclic sulfate compound of formula III:

[0020] Among them, R 1 R 2 R 3 R4 Each of the following groups independently comprises the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R 5 and R 6 Each group independently comprises one of the following: a group having the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, wherein 0≤n1≤2, 0≤n2≤2, 0≤n3≤2, and n1, n2, and n3 are integers;

[0021] Therefore, cyclic sulfate compounds can form a more stable electrolyte interface film (SEI film) on the negative electrode surface. This SEI film can effectively block electrons, reduce the deposition of transition metals and the excessive decomposition of electrolyte, and improve the cycle life of lithium secondary batteries.

[0022] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the cyclic sulfate compound is W, and satisfies: 0.001% ≤ W ≤ 20%. Thus, while forming a stable SEI film, the viscosity of the electrolyte is reduced, and the ionic conductivity of the electrolyte is increased.

[0023] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the cyclic sulfate compound is W, and satisfies: 0.1% ≤ W ≤ 5%. Thus, while forming a stable SEI film, the viscosity of the electrolyte is reduced, and the ionic conductivity of the electrolyte is increased.

[0024] According to some embodiments of this application, R 1 and R 2 Not simultaneously hydrogen atoms and R 3 and R 4 Instead of being hydrogen atoms, substituents can be introduced to form an elastic SEI film at the negative electrode. This improves the SEI film's tolerance to negative electrode volume changes during cycling, reduces the risk of SEI film rupture, and increases the cycle life of lithium secondary batteries.

[0025] According to some embodiments of this application, R 1 and R 2 Both are hydrogen atoms and R 3 and R 4One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R in the group having the structure shown in formula (Ⅳ) 5 and R 6 They are not both hydrogen atoms. Therefore, the mechanical strength and stability of the SEI film are improved, further enhancing the cycle performance of the lithium-ion secondary battery.

[0026] According to some embodiments of this application, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom and the other is any one of the following: a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R in the group having the structure shown in formula (Ⅳ) 5 and R 6 They are not both hydrogen atoms. Therefore, the mechanical strength and stability of the SEI film are improved, further enhancing the cycle performance of the lithium-ion secondary battery.

[0027] According to some embodiments of this application, the cyclic sulfate compound includes the compound represented by Formula III-1:

[0028] Among them, R 1 R 2 R 3 R 4 Each of the following groups independently comprises the structure shown in formula (Ⅳ-1): a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R. 5 and R 6 Each of the following groups independently includes the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group.

[0029] This improves the compactness of the SEI film and increases the SEI film formation rate.

[0030] According to some embodiments of this application, R 1R 2 R 3 R 4 R 5 and R 6 Each group independently comprises one of the following: a group with the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, a C2-C3 alkenyl group, a C1-C3 ester group, a cyano group, or a sulfonic acid group. This improves the density of the SEI film and increases the SEI film formation rate.

[0031] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following: a group with the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group. This improves the density of the SEI film and increases the SEI film formation rate.

[0032] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the groups, hydrogen atoms, F atoms, Cl atoms, Br atoms, methyl, ethyl, propyl, or isopropyl groups representing the structure shown in formula (Ⅳ-1). This improves the density of the SEI film and increases its formation rate.

[0033] According to some embodiments of this application, the groups in the structure shown in formula (Ⅳ-1) include one of the following groups:

[0034] X includes one of F, Cl, or Br atoms. This improves the compactness of the SEI film and increases its formation rate.

[0035] According to some embodiments of this application, R 1 R 2 R 3 and R 4 Each independently includes The atom X is selected from one of the following: hydrogen atom, F atom, Cl atom, Br atom, methyl, ethyl, propyl, and isopropyl, where X includes an F atom. This improves the stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle performance of the lithium secondary battery.

[0036] According to some embodiments of this application, R 1 R 2 R 3 and R 4 Each independently includes The element X is one of hydrogen, methyl, or ethyl, and includes an F atom. This improves the stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle performance of lithium-ion batteries.

[0037] According to some embodiments of this application, the cyclic sulfate compound includes one or more of the following compounds:

[0038] This improves the stability of the SEI film, reduces the deposition of transition metals and the excessive decomposition of the electrolyte, and enhances the cycle performance of lithium secondary batteries.

[0039] Another object of this application is to provide an electrical device including the lithium secondary battery provided in the first aspect of this application.

[0040] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0041] Figure 1 is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0042] Figure 2 is a SEM image of the lithium replenishment material according to one embodiment of this application.

[0043] Figure 3 is a schematic diagram of a lithium secondary battery according to an embodiment of this application.

[0044] Figure 4 is an exploded view of a lithium secondary battery according to an embodiment of this application, as shown in Figure 3.

[0045] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0048] Figure 8 is a schematic diagram of an electrical device using a lithium secondary battery as a power source according to an embodiment of this application.

[0049] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Lithium secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 521 Positive electrode sheet; 5211 Positive current collector; 5212 Positive film layer. Detailed Implementation

[0050] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0051] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing. During the cycling process, the active lithium in lithium-ion batteries is gradually consumed, leading to a gradual decrease in capacity and a reduction in cycle life.

[0056] To compensate for the active lithium ions consumed during the formation stage, a lithium replenishing agent is typically placed on the positive electrode. This agent decomposes and releases active lithium ions during formation, thereby improving the battery's initial efficiency and cycle performance. Related technologies involve simultaneously placing lithium iron phosphate (LFP) materials and ternary materials on the positive electrode. Under high charging voltage conditions, the ternary material can replenish the lithium iron phosphate material; however, high charging voltage can exacerbate side reactions in the electrolyte and on the positive electrode surface, degrading battery performance.

[0057] The lithium-ion secondary battery proposed in this application incorporates a high-nickel material as a lithium replenishment material on the positive electrode. This high-nickel material exhibits poor structural stability, and during the initial charge and cycling processes, it undergoes structural cracking, resulting in the loss of active sites and the release of active lithium ions. After structural collapse, the released active lithium ions cannot be reinserted into the high-nickel material, thus enabling lithium replenishment for lithium iron phosphate batteries. During cycling within the conventional operating voltage range of lithium iron phosphate (e.g., 2.0V-3.8V), the high-nickel material gradually undergoes structural cracking with each charge and discharge cycle, replenishing lithium gradually and reducing the capacity decay of the lithium-ion secondary battery, thereby improving its capacity and cycle performance. Compared to high-voltage designs, the high-nickel material's gradual lithium replenishment within the conventional operating voltage range of lithium iron phosphate reduces side reactions between the electrolyte and the positive electrode, further enhancing the cycle performance of the lithium-ion secondary battery. Because lithium ions in high-nickel materials are always partially released during cycling (i.e., a large amount of active lithium is not released at once), compared to designs that require replenishing lithium after a one-time release of active lithium, there is no need to set additional capacity at the negative electrode to avoid lithium plating, thus improving the energy density of lithium-ion batteries. Furthermore, high-nickel materials have high capacity and, compared to materials with conventional nickel content (medium to low nickel content), can release more lithium ions, further increasing the capacity of lithium-ion batteries.

[0058] The lithium secondary battery proposed in this application can be used in electrical devices that use lithium secondary batteries as a power source or in various energy storage systems that use lithium secondary batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0059] This application provides a lithium secondary battery, the lithium secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector, the positive current collector having a positive electrode film layer on at least one side, the positive electrode film layer comprising a positive electrode active material and a lithium supplementation material, the positive electrode active material comprising a compound represented by Formula I:

[0060] Lim A x1 Fe 1-y1 D y1 P 1-z1 E z1 O 4-n G n Formula I,

[0061] Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; D includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; E includes one or more elements selected from B, S, Si, and N; G includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x1≤0.1, 0≤y1≤0.5, 0≤z1≤0.5, and 0≤n≤0.5;

[0062] The lithium supplement material includes compounds represented by formula Π:

[0063] Li x2 Ni (1-y2-z2) Co y2 M z2 O 2±α Π,

[0064] Wherein, M includes one or more elements selected from Mn, Al, Fe, Zr, Mg, Ti, Cr, Ga, Cu, Zn, and Nb, 0 < x² ≤ 1.2, 0.001 ≤ y² ≤ 0.05, 0.001 ≤ z² ≤ 0.05, 0 ≤ α ≤ 0.2, and 0.9 ≤ 1 - y² - z² < 1.

[0065] The lithium-ion secondary battery proposed in this application utilizes a high-nickel material that, within the conventional operating voltage range of lithium iron phosphate materials, replenishes lithium ions to the lithium iron phosphate materials during the initial charge and cycling processes, reducing capacity decay and improving cycle performance. Compared to high-voltage or conventional lithium replenishment designs, this reduces side reactions between the electrolyte and the positive electrode, eliminating the need for additional capacity at the negative electrode to prevent lithium plating, thereby increasing the energy density of the lithium-ion secondary battery. Furthermore, the high-nickel material releases more lithium ions than medium- or low-nickel materials, further enhancing the battery's capacity.

[0066] In this application, after scraping off the powder of the positive electrode film, the contents of Fe, Ni, Co and Mn in the powder can be determined by inductively coupled plasma atomic emission spectrometry (ICP), thereby determining the composition of the positive electrode active material and the lithium replenishment material.

[0067] In this application, high-nickel material refers to material with 1-y²-z² ≥ 0.9 and satisfying Li x2 Ni (1-y2-z2) Coy2 M z2 O 2±α M includes one or more elements selected from Mn, Al, Fe, Zr, Mg, Ti, Cr, Ga, Cu, Zn, and Nb, where 0 < x² ≤ 1.2, 0.001 ≤ y² ≤ 0.05, 0.001 ≤ z² ≤ 0.05, and 0 ≤ α ≤ 0.2.

[0068] As an example, 1-y2-z2 can be 0.9, 0.92, 0.94, 0.96, 0.98, 0.99, 0.995, or any range of the above values. Therefore, a higher nickel content results in poor structural stability and high specific capacity in the lithium replenishment material, which can improve both the lithium replenishment effect and the battery's energy density.

[0069] According to some specific embodiments of this application, 0.95 ≤ 1-y2-z2 ≤ 0.99.

[0070] According to some specific embodiments of this application, 0.97 ≤ 1-y2-z2 ≤ 0.99.

[0071] According to some embodiments of this application, in formula Π, M includes one or more elements selected from Mn, Zr, Mg, and Ti, where 0.005≤y²≤0.03, 0.005≤z²≤0.03, and 0.94≤1-y²-z²≤0.99. Therefore, by doping the lithium replenishment material with the aforementioned types of M elements, the first-cycle coulombic efficiency of the lithium replenishment material can be reduced, further improving the lithium replenishment effect and enhancing the cycle performance of the lithium secondary battery.

[0072] As an example, x2 can be 0.2, 0.4, 0.6, 0.8, 1, 1.2, etc., or it can be a range of any of the above values.

[0073] As an example, y2 can be 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, etc., or it can be a range of any of the above values.

[0074] As an example, z2 can be 0.001, 0.01, 0.02, 0.03, 0.04, 0.05, etc., or it can be a range of any of the above values.

[0075] As an example, α can be 0, 0.05, 0.1, 0.15, 0.2, etc., or a range of any of the above values.

[0076] As an example, m can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.05, 1.15, etc., or a range of any of the above values.

[0077] Because lithium-ion batteries undergo formation and cycling processes, lithium ions are consumed, resulting in a lithium content (m) in the measured positive electrode active material being less than 1. Conversely, if lithium replenishment agents are used on both the positive and negative electrode plates, the lithium content (m) in the measured positive electrode active material may be greater than 1 after formation and cycling.

[0078] As an example, x1 can be 0, 0.02, 0.04, 0.06, 0.08, 0.1, etc., or a range of any of the above values.

[0079] As an example, y1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or it can be a range of any of the above values.

[0080] As an example, z1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or it can be a range of any of the above values.

[0081] As an example, n can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range of any of the above values.

[0082] According to some embodiments of this application, the positive electrode active material includes Li m Fe 1-y1 Mn y1 PO4. This improves the cycle performance and safety performance of lithium secondary batteries.

[0083] According to some embodiments of this application, the mass ratio of the positive electrode active material to the lithium replenishment material is 9-97. For example, it can be 9, 15, 30, 45, 60, 75, 90, 97, or any range of the above values. Within the operating voltage range of lithium iron phosphate materials, the specific capacity of high-nickel materials is lower than that of lithium iron phosphate materials. By maintaining the mass ratio of the positive electrode active material to the lithium replenishment material within the above range, the cycle life of the lithium secondary battery can be improved while simultaneously increasing its energy density. Furthermore, it can reduce the risk of thermal runaway during overcharging of the lithium secondary battery.

[0084] According to some embodiments of this application, based on the total mass of the positive electrode film layer, the sum of the mass of the positive electrode active material and the lithium replenishment material is 91%-98%, for example, it can be 91%, 92%, 94%, 96%, 98%, etc., or it can be any range of the above values. According to some specific embodiments of this application, the sum of the mass of the positive electrode active material and the lithium replenishment material is 96%-98%.

[0085] According to some embodiments of this application, based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material can be 90%-97%, for example, 90%, 92%, 94%, 96%, 97%, etc., or a range of any of the above values. According to some specific embodiments of this application, the mass percentage of the positive electrode active material is 95%-97%.

[0086] According to some embodiments of this application, based on the total mass of the positive electrode film, the mass percentage of the lithium replenishing material can be 1%-10%, for example, it can be 1%, 3%, 5%, 7%, 9%, 10%, etc., or it can be any range of the above values. According to some specific embodiments of this application, the mass percentage of the lithium replenishing material is 1%-3%.

[0087] Therefore, the cycle life of lithium secondary batteries is improved while the energy density of lithium secondary batteries is also increased.

[0088] In this application, after scraping off the powder of the positive electrode film, the content of Fe, Ni, Co and Mn in the powder is determined by ICP, thereby determining the composition and content of the positive electrode active material and the lithium replenishment material.

[0089] According to some embodiments of this application, the positive electrode active material and the lithium replenishment material are located in the same layer. For example, referring to FIG1, the positive electrode sheet 521 includes a positive electrode current collector 5211, and a positive electrode film layer 5212 is disposed on at least one side of the positive electrode current collector 5211. The positive electrode active material and the lithium replenishment material are both located in the positive electrode film layer 5212. Thus, the lithium replenishment material is uniformly dispersed in the positive electrode active material, shortening the solid-phase diffusion path of lithium ions, improving the lithium replenishment effect of the high-nickel material, and increasing the cycle life of the lithium secondary battery.

[0090] According to some embodiments of this application, referring to FIG2, at least a portion of the surface of the lithium replenishment material does not have a coating layer. This reduces the structural stability of the lithium replenishment material and improves the lithium replenishment effect.

[0091] According to some embodiments of this application, referring to Figure 2, the lithium replenishment material is a polycrystalline particle. Therefore, compared to monocrystalline materials, polycrystalline materials have a less stable structure, allowing the released lithium ions to be primarily used for lithium replenishment in lithium iron phosphate materials, thus improving the lithium replenishment effect.

[0092] According to some embodiments of this application, the ratio of the reversible capacity of the negative electrode to the reversible capacity of the positive electrode in the lithium secondary battery is 1.05-1.1, for example, it can be 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, etc., or it can be any range of the above values. This improves the energy density of the lithium secondary battery.

[0093] According to some embodiments of this application, the volume average particle size Dv50 of the lithium replenishment material satisfies: 1.2 μm ≤ Dv50 ≤ 5 μm. For example, it can be 1.2 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., or a range of any of the above values. This shortens the solid-phase transport path of lithium ions, reduces polarization, and improves capacity utilization.

[0094] In this application, Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, for example, measured using a laser particle size analyzer (Malvern Master Size 2000) according to standard GB / T19077-2016 / ISO 13320:2009. The specific testing procedure is as follows: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20 ml of deionized water, and sonicate for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to the standard GB / T19077-2016 / ISO 13320:2009.

[0095] According to some embodiments of this application, the BET specific surface area of ​​the lithium replenishment material satisfies: 0.8 m² / m³. 2 / g≤BET≤3.5m 2 / g, for example, can be 0.8m 2 / g, 1.2m 2 / g, 1.6m 2 / g、2m 2 / g, 2.4m 2 / g, 2.8m 2 / g, 3.2m 2 / g, 3.5m 2 / g, etc., or can be any of the above-mentioned values ​​within a range. Therefore, by ensuring the BET specific surface area of ​​the lithium replenishment material is within the above-mentioned range, the kinetic performance of the lithium replenishment material is improved, while side reactions of the electrolyte on the positive electrode surface are reduced, thereby increasing the cycle life of the lithium secondary battery.

[0096] In this application, the specific surface area of ​​the positive electrode active material can be obtained by the following method: using a US-made Gemini VII2390 multi-station fully automated specific surface area and porosity analyzer, about 7g of sample is placed in a 9cc long tube with a bulb, degassed at 200℃ for 2h, and then placed in the main unit to test and obtain the BET (specific surface area) data of the positive electrode active material.

[0097] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0098] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0100] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0102] The lithium secondary battery also includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0103] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0104] 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. When the battery is a lithium-ion battery, lithium titanate is used; when the battery is a sodium-ion battery, sodium titanate is used. However, this application is not limited to these materials, and other conventional 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.

[0106] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from one or more 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).

[0107] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0109] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0110] According to some embodiments of this application, the lithium secondary battery further includes an electrolyte comprising a cyclic sulfate compound represented by Formula III:

[0111] Among them, R 1 R 2 R 3 R 4 Each of the following groups independently comprises the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R 5 and R 6 Each group independently comprises one of the following: a group having the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, wherein 0≤n1≤2, 0≤n2≤2, 0≤n3≤2, and n1, n2, and n3 are integers;

[0112] Therefore, the cyclic sulfate compound with the above composition exhibits high film-forming efficiency at the negative electrode, rapidly forming a uniform, dense, and stable SEI film on the negative electrode surface. The SEI film effectively reduces direct contact between the electrolyte and the negative electrode active material, preventing continuous side reactions on the negative electrode surface that consume lithium ions and lead to lithium loss. This, in turn, reduces lithium ion loss on the negative electrode surface, improving the charging capacity of the lithium secondary battery. Furthermore, the stable SEI film formed by the cyclic sulfate compound effectively blocks electrons, reducing the deposition of transition metal ions dissolved from high-nickel materials on the negative electrode surface and the excessive decomposition of the electrolyte, thus improving the cycle life of the lithium secondary battery.

[0113] It should be noted that the curved line segment in Formula IV represents the chemical bond connected to Formula III.

[0114] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the cyclic sulfate compound is W, and satisfies: 0.001% ≤ W ≤ 20%, for example, it can be 0.001%, 0.1%, 1%, 5%, 10%, 15%, 20%, etc., or a range of any of the above values. Thus, while forming a stable SEI film, the viscosity of the electrolyte is reduced, and the ionic conductivity of the electrolyte is increased. According to some specific embodiments of this application, 0.1% ≤ W ≤ 5%. Thus, while forming a stable SEI film, the viscosity of the electrolyte is reduced, and the ionic conductivity of the electrolyte is increased.

[0115] In this application, the content of cyclic sulfate compounds can be calculated using nuclear magnetic resonance (NMR) spectroscopy.

[0116] According to some embodiments of this application, R 1 and R 2 Not simultaneously hydrogen atoms and R 3 and R 4 Instead of being hydrogen atoms simultaneously, at least two of them contain substituents. Thus, by introducing substituents, an elastic SEI film can be formed at the negative electrode. During cycling, the SEI film's tolerance to negative electrode volume changes can be improved, the risk of SEI film rupture can be reduced, and the cycle life of lithium secondary batteries can be increased.

[0117] According to some embodiments of this application, R 1 and R 2 Both are hydrogen atoms and R 3 and R 4 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R in the group having the structure shown in formula (Ⅳ) 5 and R 6 They are not both hydrogen atoms.

[0118] According to some embodiments of this application, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom and the other is any one of the following: a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R in the group having the structure shown in formula (Ⅳ) 5 and R 6 They are not both hydrogen atoms.

[0119] By making R 1 R 2 R 3 R 4The presence of substituents, such as alkyl substituents, in the group can form a flexible, long-chain elastic SEI film on the negative electrode surface. During battery cycling, when the negative electrode active material undergoes volume expansion and contraction, this improves the SEI film's resilience and reduces the risk of SEI film rupture. When cyclic sulfate compounds contain substituents such as F and N, an SEI film rich in inorganic components such as LiF and Li3N can be formed on the negative electrode surface, improving the mechanical strength of the SEI film, thereby enhancing its stability and further improving the cycle performance of the lithium secondary battery.

[0120] According to some embodiments of this application, the cyclic sulfate compound includes the compound represented by Formula III-1:

[0121] Among them, R 1 R 2 R 3 R 4 Each of the following groups independently comprises the structure shown in formula (Ⅳ-1): a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R. 5 and R 6 Each of the following groups independently includes the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group.

[0122] Therefore, the above-mentioned cyclic sulfates are all five-membered rings, which have greater ring strain than six-membered rings. They are easier to form films on the negative electrode surface, which can improve film formation efficiency, form a dense SEI film on the negative electrode, improve the blocking effect on electrons, reduce transition metal deposition and electrolyte decomposition, and improve the cycle life of lithium secondary batteries.

[0123] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6Each component independently comprises one of the following groups: a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, a C2-C3 alkenyl group, a C1-C3 ester group, a cyano group, or a sulfonic acid group. This improves the density and stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle life of the lithium-ion secondary battery.

[0124] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following: a group with the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 haloalkyl group. This improves the density and stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle life of the lithium secondary battery.

[0125] According to some embodiments of this application, R 1 R 2 R 3 R 4 R 5 and R 6 Each component independently comprises one of the following groups: a hydrogen atom, a F atom, a Cl atom, a Br atom, a methyl group, an ethyl group, a propyl group, or an isopropyl group, as shown in formula (Ⅳ-1). This improves the density and stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle life of the lithium secondary battery.

[0126] According to some embodiments of this application, the groups in the structure shown in formula (Ⅳ-1) include one of the following groups:

[0127] X includes one of F, Cl, or Br atoms. This improves the density and stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle life of lithium-ion batteries.

[0128] According to some embodiments of this application, R 1 R 2 R 3 and R 4 Each independently includes The atom X is selected from one of the following: hydrogen atom, F atom, Cl atom, Br atom, methyl, ethyl, propyl, and isopropyl, where X includes an F atom. This improves the stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle performance of the lithium secondary battery.

[0129] According to some embodiments of this application, R 1 R 2 R 3 and R 4 Each independently includes The element X is one of hydrogen, methyl, or ethyl, and includes an F atom. This improves the stability of the SEI film, reduces transition metal deposition and electrolyte decomposition, and enhances the cycle performance of lithium-ion batteries.

[0130] According to some embodiments of this application, the cyclic sulfate compound includes one or more of the following compounds:

[0131] This improves the stability of the SEI film, reduces the deposition of transition metals and the excessive decomposition of the electrolyte, and enhances the cycle performance of lithium secondary batteries.

[0132] According to some embodiments of this application, the cyclic sulfate compound includes

[0133] In some embodiments, the electrolyte further includes an electrolyte salt, which may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0134] In some embodiments, the electrolyte further includes a solvent, which may be selected from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0135] In some embodiments, the electrolyte may also optionally include other types of negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0136] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven 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.

[0138] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0139] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0140] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square-structured lithium secondary battery 5 as an example.

[0142] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0143] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0144] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple lithium secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple lithium secondary batteries 5 can be fixed in place using fasteners.

[0145] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of lithium secondary batteries 5 are received.

[0146] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0147] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0148] The second aspect of this application provides an electrical device, including the lithium secondary battery provided in the first aspect of this application.

[0149] The electrical equipment includes one or more of the lithium secondary batteries, battery modules, or battery packs provided in this application. The lithium secondary batteries, battery modules, or battery packs can be used as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. The electrical equipment may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0150] As for the aforementioned electrical equipment, lithium secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0151] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0152] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0153] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0154] Example 1

[0155] 1. Preparation of positive electrode sheet

[0156] Positive electrode active material: lithium iron phosphate (LiFePO4); Lithium supplementation material: LiNi 0.9 Co 0.06 Mn 0.04 O2), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) in a weight ratio of 96:2:1:1. After thorough stirring and mixing, a positive electrode slurry is obtained. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0157] 2. Preparation of negative electrode sheet

[0158] The negative electrode active material graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a weight ratio of 90:4:4:2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil once or multiple times, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0159] 3. Preparation of electrolyte

[0160] An electrolyte was prepared using a mixture of EC and EMC (ethylene carbonate and methyl ethyl carbonate) in a volume ratio of 3:7 as the solvent, and lithium hexafluorophosphate (LiPF6) was used as the electrolyte, with a mass content of 10% in the electrolyte.

[0161] 4. Separating membrane

[0162] Conventional polypropylene film is used as the separator.

[0163] 5. Assemble the battery

[0164] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain the electrode assembly. The electrode assembly is placed in the battery casing, dried, and then injected with electrolyte. After formation and settling processes, a lithium-ion battery is obtained.

[0165] The preparation methods of lithium secondary batteries in Examples 2-29, Comparative Examples 1 and 2 are the same as those in Example 1, with the differences detailed in Table 1.

[0166] Table 1

[0167] Performance testing

[0168] 1. Cyclic performance testing method

[0169] At 25°C, the prepared battery was left to stand for 30 minutes before the following test was performed. The battery was charged to 3.65V at a constant power of 0.5P; after standing for 10 minutes, the battery was discharged to 2.5V at a constant power of 0.5P. The above steps were repeated until the battery's discharge capacity decreased to 90% of the initial discharge capacity, and the number of battery cycles was recorded.

[0170] 2. Energy density testing method

[0171] At 25℃, the lithium-ion battery is charged to 3.65V at a constant power of 0.5P; after standing for 10 minutes, the battery is discharged to 2.5V at a constant power of 0.5P. This is one charge-discharge cycle. After three charge-discharge cycles, the discharge energy E0 is recorded. The lithium-ion battery is weighed using an electronic balance, and its mass M0 is recorded. The ratio of the actual 0.5P discharge energy E0 of the lithium-ion battery to the mass M0 of the lithium-ion battery is the mass energy density of the lithium-ion battery.

[0172] 3. Volume average particle size of lithium replenishment material

[0173] The particle size distribution was determined using a laser particle size analyzer (Malvern Master Size 2000). The specific testing procedure was as follows: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% with sufficient light-blocking properties), add 20 ml of deionized water, and sonicate for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, the sample was measured according to the standard GB / T19077-2016 / ISO 13320:2009.

[0174] 4. BET specific surface area of ​​lithium replenishment materials

[0175] Using a US-made Gemini VII2390 multi-station fully automated surface area and porosity analyzer, approximately 7g of sample was placed in a 9cc long tube with a bulb, degassed at 200℃ for 2 hours, and then placed in the main unit for testing to obtain the BET (specific surface area) data of the positive electrode active material.

[0176] The test methods for lithium secondary batteries in Examples 1-29, Comparative Examples 1 and 2 are shown in Table 2.

[0177] Table 2

[0178] As can be seen from Examples 1-29 and Comparative Examples 1 and 2, this application can improve the cycle life and energy density of the battery within the working voltage range of lithium iron phosphate by adding high-nickel material as a lithium replenisher to the positive electrode sheet. This shows that the high-nickel material can replenish lithium iron phosphate during the first charge and cycle of the battery, while reducing the side reactions between the positive electrodes of the electrolyte.

[0179] As can be seen from Examples 1-6 and Comparative Examples 1 and 2, by selecting lithium replenishment materials with different nickel contents, the cycle life and energy density of the battery can be improved. As the nickel content in the lithium replenishment material increases, the lithium replenishment effect gradually improves, and the cycle life of the battery gradually improves.

[0180] As can be seen from Examples 7-11, by selecting high-nickel materials as lithium replenishment materials and adjusting the mass ratio of positive electrode active materials and lithium replenishment materials in the positive electrode film layer, the cycle life and energy density of the battery can be adjusted to obtain a lithium secondary battery with both excellent cycle life and high energy density.

[0181] As can be seen from Examples 12 and 13, high-nickel materials can replenish lithium in different lithium iron phosphate materials.

[0182] As can be seen from Examples 14-17, lithium secondary batteries with both excellent cycle life and high energy density can be obtained by selecting lithium replenishment materials with different Dv50.

[0183] As can be seen from Examples 18-23 and Example 10, adding cyclic sulfate compounds to the electrolyte can further improve the cycle life of the battery, indicating that sulfate compounds can further reduce lithium-ion consumption and reduce excessive electrolyte decomposition. By adjusting the content of cyclic sulfate compounds, lithium secondary batteries with better cycle life can be obtained.

[0184] As can be seen from Examples 24-27, different types of cyclic sulfate compounds can all improve the cycle life of batteries.

[0185] As can be seen from Examples 28 and 29, different types of lithium replenishing materials can all replenish lithium in lithium iron phosphate materials and improve the cycle life of batteries.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium secondary battery, wherein, include: A positive electrode sheet, comprising a positive current collector, wherein at least one side of the positive current collector has a positive electrode film layer, the positive electrode film layer comprising a positive electrode active material and a lithium supplementation material, the positive electrode active material comprising a compound represented by Formula I: Li m A x1 Fe 1-y1 D y1 P 1-z1 E z1 O 4-n G n Formula Ι Wherein, A includes one or more elements selected from Zn, Al, Na, K, and Mg; D includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; E includes one or more elements selected from B, S, Si, and N; G includes one or more elements selected from S, F, Cl, and Br; 0.5≤m≤1.15, 0≤x1≤0.1, 0≤y1≤0.5, 0≤z1≤0.5, and 0≤n≤0.5; The lithium supplement material includes compounds represented by formula Π: Li x2 Ni (1-y2-z2) Co y2 M z2 O 2±α Formula Π Wherein, M includes one or more elements selected from Mn, Al, Fe, Zr, Mg, Ti, Cr, Ga, Cu, Zn, and Nb, 0 < x² ≤ 1.2, 0.001 ≤ y² ≤ 0.05, 0.001 ≤ z² ≤ 0.05, 0 ≤ α ≤ 0.2, and 0.9 ≤ 1 - y² - z² < 1.

2. The lithium secondary battery according to claim 1, wherein, 0.95≤1-y2-z2≤0.

99.

3. The lithium secondary battery according to claim 1 or 2, wherein, 0.97≤1-y2-z2≤0.

99.

4. The lithium secondary battery according to any one of claims 1-3, wherein, The mass ratio of the positive electrode active material to the lithium replenishment material is 9-97.

5. The lithium secondary battery according to any one of claims 1-4, wherein, The sum of the mass of the positive electrode active material and the lithium replenishment material is 91%-98%, and satisfies one or two of the following conditions: Based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material is 90%-97%. Based on the total mass of the positive electrode film, the mass percentage of the lithium replenishment material is 1%-10%.

6. The lithium secondary battery according to any one of claims 1-4, wherein, The sum of the mass of the positive electrode active material and the lithium replenishment material is 96%-98%, and satisfies one or two of the following conditions: Based on the total mass of the positive electrode film, the mass percentage of the positive electrode active material is 95%-97%. Based on the total mass of the positive electrode film, the mass percentage of the lithium replenishment material is 1%-3%.

7. The lithium secondary battery according to any one of claims 1-6, wherein, The positive electrode active material and the lithium replenishment material are located in the same layer.

8. The lithium secondary battery according to any one of claims 1-7, wherein, At least a portion of the surface of the lithium replenishment material does not have a coating layer.

9. The lithium secondary battery according to any one of claims 1-8, wherein, The lithium replenishing material is a polycrystalline particle.

10. The lithium secondary battery according to any one of claims 1-9, wherein, The ratio of the reversible capacity of the negative electrode to the reversible capacity of the positive electrode in the lithium secondary battery is 1.05-1.

1.

11. The lithium secondary battery according to any one of claims 1-10, wherein, The volume average particle size Dv50 of the lithium replenishment material satisfies: 1.2μm≤Dv50≤5μm.

12. The lithium secondary battery according to any one of claims 1-11, wherein, The BET specific surface area of ​​the lithium replenishment material satisfies: 0.8 m² 2 / g≤BET≤3.5m 2 / g.

13. The lithium secondary battery according to claim 1 or 2, wherein, One or two of the following conditions must be met: The positive electrode active material includes Li m Fe 1-y1 Mn y1 PO4; In formula Π, M includes one or more elements selected from Mn, Zr, Mg, and Ti, with 0.005≤y2≤0.03, 0.005≤z2≤0.03, and 0.94≤1-y2-z2≤0.

99.

14. The lithium secondary battery according to any one of claims 1-13, wherein, It also includes an electrolyte comprising a cyclic sulfate compound of Formula III: Among them, R 1 R 2 R 3 R 4 Each of the following groups independently comprises the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R 5 and R 6 Each group independently comprises one of the following: a group having the structure shown in formula (Ⅳ), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, wherein 0≤n1≤2, 0≤n2≤2, 0≤n3≤2, and n1, n2, and n3 are integers; 15. The lithium secondary battery according to claim 14, wherein, Based on the total mass of the electrolyte, the mass percentage of the cyclic sulfate compound is W, and satisfies: 0.001% ≤ W ≤ 20%.

16. The lithium secondary battery according to claim 14 or 15, wherein, Based on the total mass of the electrolyte, the mass percentage of the cyclic sulfate compound is W, and satisfies: 0.1% ≤ W ≤ 5%.

17. The lithium secondary battery according to any one of claims 14-16, wherein, R 1 and R 2 Not simultaneously hydrogen atoms and R 3 and R 4 They are not both hydrogen atoms.

18. The lithium secondary battery according to any one of claims 14-16, wherein, R 1 and R 2 Both are hydrogen atoms and R 3 and R 4 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, or a sulfonic acid group, and R in the group having the structure shown in formula (Ⅳ) 5 and R 6 They are not both hydrogen atoms.

19. The lithium secondary battery according to any one of claims 14-16, wherein, R 3 and R 4 Both are hydrogen atoms and R 1 and R 2 One is a hydrogen atom, and the other is a group having the structure shown in formula (Ⅳ), a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, and R is present in the group having the structure shown in formula (Ⅳ). 5 and R 6 They are not both hydrogen atoms.

20. The lithium secondary battery according to any one of claims 14-19, wherein, The cyclic sulfate compounds include those represented by Formula III-1: Among them, R 1 R 2 R 3 R 4 Each of the following groups independently comprises the structure shown in formula (Ⅳ-1): a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group, R. 5 and R 6 Each of the following groups independently includes the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C1-C6 haloalkyl group, a C1-C6 alkoxy group, a C1-C6 haloalkoxy group, a C2-C6 alkenyl group, a C2-C6 ester group, a cyano group, and a sulfonic acid group.

21. The lithium secondary battery according to any one of claims 14-20, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each of the following groups independently includes the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, a C2-C3 alkenyl group, a C1-C3 ester group, a cyano group, and a sulfonic acid group.

22. The lithium secondary battery according to any one of claims 14-21, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each of the following independently includes a group with the structure shown in formula (Ⅳ-1), a hydrogen atom, a halogen atom, a C1-C3 alkyl group, and a C1-C3 haloalkyl group.

23. The lithium secondary battery according to any one of claims 14-22, wherein, R 1 R 2 R 3 R 4 R 5 and R 6 Each of the following groups, including the group with the structure shown in formula (Ⅳ-1), a hydrogen atom, an F atom, a Cl atom, a Br atom, a methyl group, an ethyl group, a propyl group, and an isopropyl group, is independently included.

24. The lithium secondary battery according to any one of claims 14-23, wherein, The groups in the structure shown in formula (Ⅳ-1) include one of the following groups: X includes one of F, Cl, or Br atoms.

25. The lithium secondary battery according to any one of claims 14-24, wherein, R 1 R 2 R 3 and R 4 Each independently includes One of hydrogen atom, F atom, Cl atom, Br atom, methyl, ethyl, propyl, and isopropyl, where X includes F atom.

26. The lithium secondary battery according to any one of claims 14-25, wherein, R 1 R 2 R 3 and R 4 Each independently includes One of hydrogen atom, methyl, or ethyl, where X includes F atom.

27. The lithium secondary battery according to claim 14, wherein, The cyclic sulfate compound includes one or more of the following compounds:

28. An electrical appliance, wherein, Includes the lithium secondary battery as described in any one of claims 1-27.

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