Lithium ion battery, battery, and power consumption device

Abstract

To provide a lithium ion battery with improved cycle performance.SOLUTION: The battery comprises an electrolyte and a positive electrode plate, wherein the electrolyte comprises lithium hexafluorophosphate as a lithium salt, and a mass content of the lithium hexafluorophosphate is 15% to 20% of a total mass of the electrolyte, the positive electrode plate comprises a positive current collector and a positive electrode film disposed on at least one side of the positive current collector and comprising a positive active material, and the positive active material comprises a compound having a molecular formula of LidNiaCobMncM (1-a-b-c) Qz; 0 <d ≤ 2.1, 0.6 <a <1, 0 <b <1, 0 <c <1, and 0.6 <a + b + c <1, 1.8 ≤ z ≤ 3.5, the element M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and the element Q includes at least one of O and F.SELECTED DRAWING: None

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese Patent Application No. 202311422403.0, entitled "Lithium-ion Battery, Battery and Power Consumption Device," filed on October 30, 2023, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] This application relates to lithium-ion batteries, batteries and power consuming devices. [Background technology]

[0003] Due to their high capacity and long life, lithium ion batteries are widely used in electronic devices such as mobile phones, laptops, battery-powered vehicles, electric vehicles, electric airplanes, electric steamships, electric toy cars, electric toy steamships, electric toy airplanes, and power tools. As lithium ion batteries have made great progress, higher requirements are being placed on the performance of lithium ion batteries.

[0004] However, the cycling performance of current lithium-ion batteries remains low. Summary of the Invention

[0005] The present application provides a lithium-ion battery, a battery and a power consuming device, and the cycling performance of the lithium-ion battery described in the present application is relatively low.

[0006] According to a first aspect, an embodiment of the present application provides a lithium ion battery, the lithium ion battery comprising: an electrolyte; and a positive electrode plate; the electrolyte comprises a lithium salt; the lithium salt comprises lithium hexafluorophosphate; the mass content of the lithium hexafluorophosphate relative to the total mass of the electrolyte is 15% to 20%; the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and containing a positive electrode active material; the positive electrode active material has a molecular formula of Li d Ni a Co bMn c M (1-a-b-c) Q z and contains a compound where 0 < d ≦ 2.1, 0.6 < a < 1, 0 < b < 1, 0 < c < 1, and 0.6 < a + b + c < 1, 1.8 ≦ z ≦ 3.5. The M element contains at least one element among B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce. The Q element contains at least one element among O, F.

[0007] Thus, the nickel element content of the positive electrode active material in the embodiments of the present application is relatively high. To improve the stability of the positive electrode active material structure, the positive electrode active material of the embodiments of the present application further contains the M element. The introduction of the M element can improve the stability of the positive electrode active material crystal structure and the cycle performance of the lithium-ion battery. However, as the cycle progresses, both the metal elements and non-metal elements in the positive electrode active material have the risk of elution. The eluted metal elements and non-metal elements can move to the surface of the negative electrode plate through the electrolyte, destroy the solid electrolyte interphase (SEI) film on the surface of the negative electrode plate, and may precipitate as a metal single body on the surface of the negative electrode plate, thereby deteriorating the cycle performance. The embodiments of the present application further combine a high content of lithium hexafluorophosphate. The mass content of lithium hexafluorophosphate LiPF6 in the total mass of the electrolyte is 15% to 20%. The high content of lithium hexafluorophosphate can form a protective layer with lithium fluoride LiF as the main film component on the surface of the positive electrode active material, thereby alleviating the elution of metal elements and non-metal elements to a certain extent and further improving the cycle performance of the lithium-ion battery.

[0008] In some embodiments, the M element contains at least one element among Ti and Zr, the electrolyte contains a first additive, and the first additive contains at least one of lithium difluoro(oxalato)borate LiDFOB and lithium tetrafluoroborate LiBF4.

[0009] As a result, in the later cycle of the lithium-ion battery, there is a risk that metal ions, such as Ti and Zr ions, in the positive electrode active material will dissolve into the electrolyte and migrate to the surface of the negative electrode plate. The first additive contains fluorine ions and boron ions, which have a relatively strong bonding ability with the metal ions, reducing the risk of the metal ions migrating to the surface of the negative electrode plate, thereby improving the cycle performance of the lithium-ion battery. Although the Ti and Zr ions can improve the structural stability of the material, they may adversely affect the conduction of lithium ions within the crystal lattice, causing power degradation. The first additive can also compensate for the power degradation caused by the Ti and Zr ions.

[0010] In some embodiments, the M element includes Ti and Zr. When M includes both Ti and Zr, the two elements can be used together to further stabilize the material structure and improve the cycle performance.

[0011] In some embodiments, the mass content of the Ti element is 100 ppm to 600 ppm, based on the total mass of the positive electrode active material, and / or the mass content of the Zr element is 500 ppm to 2550 ppm, based on the total mass of the positive electrode active material; and the mass content of the first additive is 30 ppm to 1200 ppm, optionally 100 ppm to 400 ppm, based on the total mass of the electrolyte.

[0012] In some embodiments, the cathode active material comprises a single-crystal particle, the single-crystal particle comprising an inner region and an outer region, the outer region extending 500 nm from any point on the outer surface of the single-crystal particle directly toward the interior of the single-crystal particle, and the element M comprises Al, the Al being distributed in at least the outer region. The aluminum Al distributed in at least the outer region serves to form aluminum oxide (Al2O3) in the cathode active material, which passivates side reactions between the cathode active material and the electrolyte, further improving the stability of the cathode active material structure and improving the cycling performance of lithium-ion batteries.

[0013] In some embodiments, the electrolyte solution includes a second additive, and the second additive includes lithium difluorophosphate, LiPO2F2, which can be combined with Al in the positive electrode active material to improve the DCR of the positive electrode active material surface and increase the interfacial power.

[0014] In some embodiments, the mass content of the Al element is 500 ppm to 3000 ppm based on the total mass of the positive electrode active material, and the mass content of the second additive is 100 ppm to 3000 ppm based on the total mass of the electrolyte.

[0015] In some embodiments, the M element further comprises at least one of P, S, and B, where at least one of P, S, and B is distributed in the outer region, and the electrolyte solution comprises a third additive, where the third additive comprises lithium fluorosulfonate. The phosphorus (P), sulfur (S), and boron (B) elements act to absorb lithium into the oxygen layer and stabilize it, thereby improving the stability of the positive electrode active material structure and the cycle performance of the lithium-ion battery.

[0016] In some embodiments, the total mass content of the P, S, and B elements is 10 ppm to 800 ppm based on the total mass of the positive electrode active material, and the mass content of the third additive is 50 ppm to 200 ppm based on the total mass of the electrolyte. The third additive, in combination with the P, S, and B elements in the positive electrode active material, can reduce the DCR and improve the interfacial power of the positive electrode active material surface.

[0017] In some embodiments, the electrolyte solution contains a cyclic carbonate, and the ratio of the mass content of the cyclic carbonate to the mass content of lithium hexafluorophosphate, based on the total mass of the electrolyte solution, is (0.60 to 2.50): 1, and optionally (1.00 to 1.65): 1. When the ratio of the mass content of the cyclic carbonate to the mass content of lithium hexafluorophosphate is within the above range, it is advantageous to sufficiently dissociate more lithium ions from lithium hexafluorophosphate, thereby allowing the electrolyte system to contain more lithium ions even at the end of discharge at a low SOC, and allowing lithium ions to be continuously dissociated as the battery reaction progresses, improving the power performance of the battery.

[0018] In some embodiments, the cyclic carbonate has a mass content of 20% to 30% based on the total mass of the electrolyte solution, and / or includes at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Cyclic carbonates have high dielectric constants and ionic conductivity, and can form a stable SEI film on the surface of the negative electrode active material.

[0019] In some embodiments, the lithium-ion battery further includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and including a negative electrode active material, the negative electrode active material including elemental carbon and elemental silicon, and a ratio of the mass content of the silicon element to the mass content of the carbon element, based on the total mass of the negative electrode active material, is from (0.3:99.7) to (3:97).

[0020] The negative electrode active material thus contains both a carbon-based material and a silicon-based material, and the silicon-based material has a higher lithium release voltage plateau than the carbon-based material, allowing the silicon-based material to continue to participate in discharge even at low SOC (e.g., SOC≦10%), thereby compensating for the shortcomings of the carbon-based material, such as its difficulty in discharging / inability to continue discharging at low SOC, improving the direct current internal resistance (DCR) during the battery discharge process and further improving the battery's power performance during the discharge process. The electrolyte of this embodiment further uses 15% to 20% lithium hexafluorophosphate in combination, and the cooperation between the electrolyte and the negative electrode improves the battery's power performance at the end of discharge.

[0021] In some embodiments, the electrolyte solution comprises a fluorinated cyclic carbonate, and the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of elemental silicon relative to the total mass of the electrolyte solution is (0.5 to 9.5):1, optionally (1 to 2):1.

[0022] Therefore, the fluorinated cyclic carbonate can participate in the formation of an SEI film on the surface of the negative electrode active material, improving the film components and properties and effectively protecting the negative electrode active material. In particular, when the negative electrode contains silicon, the film composition for SEI film formation must be further optimized due to the expansion properties of silicon. The film composition can be optimized by adjusting the relative proportions of the film-forming additives in the electrolyte. The fluorinated cyclic carbonate can participate in the film formed to improve the flexibility of the SEI film and reduce the structural collapse caused by silicon releasing a large number of lithium ions in a short period of time at the end of discharge. In addition, the fluorinated cyclic carbonate has a certain desolvation ability, which is beneficial for lithium ion migration, improving DCR at low SOC and increasing discharge power.

[0023] In some embodiments, the mass content of the fluorinated cyclic carbonate is 0.95% to 5.8%, and optionally 1.5% to 3%, based on the total mass of the electrolyte, and / or the fluorinated cyclic carbonate comprises at least one of monofluoroethylene carbonate FEC, bisfluoroethylene carbonate DFEC, and trifluoropropylene carbonate TFPC, and optionally the fluorinated cyclic carbonate comprises monofluoroethylene carbonate FEC.

[0024] In some embodiments, the ratio of the compaction density of the positive electrode membrane layer to the compaction density of the negative electrode membrane layer is (2 to 2.5): 1. Optionally, the compaction density of the positive electrode membrane layer is 3.0 g / cm 3 to 3.5 g / cm 3 and the compaction density of the negative electrode film layer is 1.3 g / cm 3 to 1.7 g / cm 3 is.

[0025] In some embodiments, the electrolyte solution further includes a fourth additive, which includes at least one of 1,3-propane sultone PS, vinylene carbonate VC, and lithium fluorosulfonate LiSO3F. The above components can essentially participate in the formation of an SEI film on the surface of the negative electrode active material, and the SEI film can effectively mitigate the expansion of the silicon-based material.

[0026] In some embodiments, the mass content of 1,3-propane sultone PS is 0.1% to 1%, based on the total mass of the electrolyte solution; and / or the mass content of vinylene carbonate VC is 0.1% to 1%, based on the total mass of the electrolyte solution; and / or the mass content of lithium fluorosulfonate LiSOF is 0.1% to 1%, based on the total mass of the electrolyte solution.

[0027] According to a second aspect, the present application further provides a battery comprising the lithium ion battery according to any embodiment of the first aspect of the present application.

[0028] According to a third aspect, the present application further provides a power consuming device, the power consuming device comprising a battery according to any one of the embodiments of the second aspect of the present application. [Brief explanation of the drawings]

[0029] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application. It is obvious that the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without exerting any creative efforts. [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a lithium-ion battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of an embodiment of the lithium-ion battery of FIG. 1. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of one embodiment of the present application including a lithium-ion battery-powered power consuming device. The drawings are not necessarily drawn to scale. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the lithium-ion battery, battery, and power consumption device of the present application will be described in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of structures that are actually the same may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] The "ranges" disclosed in this application are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive, and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" represents a list of all real numbers between "0 and 5" and is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise stated, all embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0035] Charge-discharge batteries generally include ion batteries and metal batteries, and metal batteries, such as lithium metal batteries and sodium metal batteries, have relatively high negative electrode activity and a relatively high risk of dendrite formation, resulting in relatively low battery reliability, while ion batteries are widely used due to their relatively high reliability.

[0036] A lithium ion battery generally includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate to separate the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode membrane layer containing a positive electrode active material. The positive electrode active material is a donor that provides lithium ions to the lithium ion battery. The negative electrode plate includes a negative electrode membrane layer containing a negative electrode active material. The negative electrode active material can be a lithium ion acceptor. The electrolyte provides a migration path for lithium ions between the positive electrode plate and the negative electrode plate.

[0037] In order to improve the energy density of lithium-ion batteries, a positive electrode active material with a relatively high capacity is generally used, for example, by increasing the nickel content in the positive electrode active material. However, as the nickel content increases, the positive electrode active material is prone to generating microcracks in its structure during cycling, which causes damage and even collapse of the positive electrode active material structure. Particularly in the later stages of cycling, the cumulative damage to the positive electrode active material increases, resulting in poor cycling performance.

[0038] In view of the above problems, an embodiment of the present application provides a lithium ion battery, and the positive electrode active material of the lithium ion battery has a molecular formula of Li d Ni a Co b Mn c M (1-a-b-c) Y zA compound is included, where 0 < d ≤ 2.1, 0.6 < a < 1, 0 < b < 1, 0 < c < 1, and 0.6 < a + b + c ≤ 1, 1.8 ≤ z ≤ 3.5. The M element includes at least one element among B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce. The Y element includes at least one element among O, F. The nickel element content of this cathode active material is relatively high. To improve the stability of the cathode active material structure, the cathode active material of the embodiments of this application further includes the M element. The introduction of the M element can improve the stability of the cathode active material crystal structure and the cycle performance of the lithium-ion battery. However, as the cycle progresses, both the metal elements and non-metal elements in the cathode active material have a risk of elution. The eluted metal elements and non-metal elements can move to the surface of the anode plate through the electrolyte and deteriorate the cycle life. The embodiments of this application further combine a high content of lithium hexafluorophosphate. The mass content of lithium hexafluorophosphate LiPF6 in the total mass of the electrolyte is 15% to 20%. The high content of lithium hexafluorophosphate can form a protective layer with lithium fluoride LiF as the main film component on the surface of the cathode active material, thereby alleviating the elution of metal elements and non-metal elements to a certain extent and further improving the cycle performance of the lithium-ion battery. Next, the technical solution of this application will be described in detail.

[0039] Lithium-ion battery According to a first aspect, embodiments of this application provide a lithium-ion battery. The lithium-ion battery includes an electrolyte and a cathode plate. The electrolyte includes a lithium salt. The lithium salt includes lithium hexafluorophosphate. The mass content of lithium hexafluorophosphate in the total mass of the electrolyte is 15% to 20%. The cathode plate includes a cathode current collector and a cathode film layer provided on at least one side of the cathode current collector and containing a cathode active material. The cathode active material has a molecular formula of Li d Ni a Co b Mn c M(1-a-b-c) Q z A compound containing, where 0 < d ≤ 2.1, 0.6 < a < 1, 0 < b < 1, 0 < c < 1, and 0.6 < a + b + c < 1, 1.8 ≤ z ≤ 3.5, the M element contains at least one element among B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and the Q element contains at least one element among O, F.

[0040] Since the nickel element content of the positive electrode active material is relatively high, in order to improve the stability of the positive electrode active material structure or improve other properties advantageous to the electrical performance of the positive electrode active material, the positive electrode active material of the embodiment of the present application further contains the M element. The introduction of the M element can improve the stability of the positive electrode active material crystal structure and improve the cycle performance of the lithium-ion battery. However, with the progress of the cycle, both the metal elements and non-metal elements in the positive electrode active material have the risk of elution. The eluted metal elements and non-metal elements can move to the surface of the negative electrode plate through the electrolyte, destroy the solid electrolyte interphase (SEI) film on the surface of the negative electrode plate, and may precipitate as a single metal on the surface of the negative electrode plate, thereby deteriorating the cycle performance. The embodiment of the present application further combines a high content of lithium hexafluorophosphate. The mass content of lithium hexafluorophosphate LiPF6 with respect to the total mass of the electrolyte is 15% to 20%. The high content of lithium hexafluorophosphate can form a protective layer with lithium fluoride LiF as the main film component on the surface of the positive electrode active material, thereby alleviating the elution of metal elements and non-metal elements to a certain extent and further improving the cycle performance of the lithium-ion battery.

[0041] When the mass content of lithium hexafluorophosphate is less than 15%, the protection performance for the surface of the positive electrode active material weakens. Therefore, it is necessary to adjust the mass content of lithium hexafluorophosphate to 15% or more. When the mass content of lithium hexafluorophosphate is greater than 20%, it significantly improves the viscosity of the electrolyte, which is disadvantageous for the movement of lithium ions from the bulk inside of the negative electrode active material to the surface, slows down the movement rate of lithium ions from the negative electrode surface to the positive electrode surface, is disadvantageous for the movement of lithium ions from the surface of the negative electrode active material to the bulk of the negative electrode active material, and is disadvantageous for the improvement of cycle performance. Therefore, it is necessary to adjust the mass content of lithium hexafluorophosphate to 20% or less. Exemplarily, the mass content of lithium hexafluorophosphate with respect to the total mass of the electrolyte may be 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20% or a range consisting of any two of the above numerical values.

[0042] [Positive electrode plate] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0043] The positive electrode active material contains a compound with the molecular formula Li d Ni a Co b Mn c M (1-a-b-c) Q z where 0 < d ≦ 2.1, 0.6 < a < 1, 0 < b < 1, 0 < c < 1, and 0.6 < a + b + c < 1, 1.8 ≦ z ≦ 3.5. The M element contains at least one element among B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce, and the Q element contains at least one element among O, F.

[0044] The positive electrode active material contains, in addition to lithium, nickel, cobalt, manganese, and M. The nickel can improve the gram capacity of the positive electrode active material, the cobalt can stabilize the crystalline structure of the positive electrode active material, the manganese can improve the structural stability of the entire positive electrode active material, and the M can improve the stability of the crystalline structure of the positive electrode active material.

[0045] In some embodiments, d is 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 3, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, or a range consisting of any two of the above numerical values.

[0046] In some embodiments, a can be 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range consisting of any two of the foregoing values.

[0047] In some embodiments, b is 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range consisting of any two of the above values.

[0048] In some embodiments, c is 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range consisting of any two of the above values.

[0049] In some embodiments, a+b+c can be 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or a range consisting of any two of the foregoing values.

[0050] In some embodiments, z can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, or a range consisting of any two of the foregoing values.

[0051] Lithium-ion batteries release and consume active ions, such as Li, during charge and discharge, and the molar content of Li varies when the lithium-ion battery is discharged to different states. In the enumeration of the positive electrode active material in the embodiments of this application, the molar content of Li is the initial state of the material, i.e., the state before input. When the positive electrode active material is applied to a battery system and undergoes charge and discharge cycles, the molar content of Li may change.

[0052] In the enumeration of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value, and crystal lattice oxygen release causes a change in the molar content of oxygen O, and in reality, the molar content of oxygen O fluctuates.

[0053] In some embodiments, the element M includes at least one of titanium (Ti) and zirconium (Zr), and optionally M includes Ti and Zr. Both Ti and Zr can stabilize the structure of the positive electrode active material, thereby improving cycle performance. In particular, when M includes both Ti and Zr, the combined use of the two elements can further stabilize the material structure and improve cycle performance.

[0054] In some embodiments, the total mass content of Ti and Zr is 1600 ppm to 3150 ppm, based on the total mass of the positive electrode active material. When the amount of Ti and Zr added is within this range, the crystalline structure of the positive electrode active material can be further improved, and the cycle performance can be improved.

[0055] The total mass content of Ti and Zr elements is the ratio of the total mass of Ti and Zr elements to the total mass of the positive electrode active material.

[0056] For example, the total mass content of Ti and Zr elements may be 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3100 ppm, 3150 ppm, or a range consisting of any two of the above values.

[0057] In some embodiments, the mass content of Ti element, based on the total mass of the positive electrode active material, may be 100 ppm to 600 ppm, for example, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, or a range consisting of any two of the foregoing values.

[0058] In some embodiments, the mass content of Zr element, based on the total mass of the positive electrode active material, is 500 ppm to 2550 ppm, and optionally 1500 ppm to 2550 ppm, for example, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2550 ppm, or a range consisting of any two of the foregoing values.

[0059] In some embodiments, the electrolyte solution includes a first additive, the first additive including at least one of lithium difluoro(oxalato)borate (LiDFOB) and lithium tetrafluoroborate (LiBF). During the later cycle of a lithium-ion battery, metal ions, such as Ti and Zr ions, in the positive electrode active material may dissolve into the electrolyte and migrate to the surface of the negative electrode plate. The first additive includes fluorine ions and boron ions, which have a relatively strong bonding ability with the metal ions, reducing the risk of the metal ions migrating to the surface of the negative electrode plate, thereby improving the cycle performance of the lithium-ion battery. While the Ti and Zr ions can improve the stability of the material structure, they may adversely affect the conduction of lithium ions within the crystal lattice, resulting in power degradation. The first additive can also compensate for the power degradation caused by the Ti and Zr ions.

[0060] In some embodiments, the cathode active material comprises a single crystal particle, the single crystal particle comprising an inner region and an outer region, the outer region extending 500 nm from any point on the outer surface of the single crystal particle directly toward the interior of the single crystal particle, and the M element comprises aluminum Al, which is distributed in at least the outer region.

[0061] The inner region of the single crystal particle may be understood as the core of the single crystal particle, the outer region covers the outside of the inner region, and there may be no clear boundary between the outer region and the inner region, and the outer region and the inner region may be considered as two artificially defined regions, and the outer region is a region where any point on the outer surface of the single crystal particle extends 500 nm toward the inside of the single crystal particle, and the extension path is a straight path, and the outer region may be understood as a ring structure, and the radial spacing of the ring structure is 500 nm or less.

[0062] The aluminum (Al) element is distributed at least in the outer region, which serves to form aluminum oxide (Al2O3) in the positive electrode active material, passivating side reactions between the positive electrode active material and the electrolyte, further improving the stability of the positive electrode active material structure, and improving the cycle performance of the lithium-ion battery. Of course, in addition to being distributed in the outer region, the Al element may also be distributed in the inner region.

[0063] In some embodiments, the mass content of Al element is 500 ppm to 3000 ppm, and optionally 1000 ppm to 2000 ppm, based on the total mass of the positive electrode active material.

[0064] For example, the mass content of Al element may be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or a range consisting of any two of the above values.

[0065] In some embodiments, the electrolyte solution includes a second additive, and the second additive includes lithium difluorophosphate LiPO2F2. The lithium difluorophosphate LiPO2F2 can be combined with the Al element in the positive electrode active material to improve the DCR of the surface of the positive electrode active material and increase the interfacial power.

[0066] In some embodiments, the M element further comprises at least one of phosphorus P, sulfur S, and boron B, wherein at least one of the B, P, and S elements is distributed in the outer region.

[0067] Optionally, the M element includes phosphorus P, sulfur S, and boron B. The phosphorus P, sulfur S, and boron B elements act to absorb lithium into the oxygen layer and stabilize lithium, thereby improving the stability of the positive electrode active material structure and improving the cycle performance of the lithium-ion battery.

[0068] In some embodiments, the total mass content of P, S, and B elements, based on the total mass of the positive electrode active material, is 0 to 800 ppm, and optionally 10 ppm to 500 ppm, such as 0, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, or a range consisting of any two of the foregoing values. A total mass content of P, S, and B elements of 0 means that these elements are not added.

[0069] In some embodiments, the total mass content of the P element, based on the total mass of the positive electrode active material, may be 10 ppm to 500 ppm, for example, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, or a range consisting of any two of the foregoing values.

[0070] In some embodiments, the total mass content of the S element, based on the total mass of the positive electrode active material, may be 10 ppm to 500 ppm, for example, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, or a range consisting of any two of the foregoing values.

[0071] In some embodiments, the total mass content of the B element, based on the total mass of the positive electrode active material, may be 10 ppm to 500 ppm, for example, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, or a range consisting of any two of the foregoing values.

[0072] In some embodiments, the electrolyte solution includes a third additive, and the third additive includes lithium fluorosulfonate, which can form a low-resistance film component on the surface of the positive electrode active material. The third additive, in combination with the phosphorus (P), sulfur (S), and boron (B) elements in the positive electrode active material, can reduce the DCR and improve the interfacial power on the surface of the positive electrode active material.

[0073] In the present application, the element content of the positive electrode active material is defined as a value known in the art and can be detected using instruments and methods known in the art. For example, in accordance with EPA 6010D-2014, the element content is measured by inductively coupled plasma atomic emission spectroscopy (ICP-OES, instrument model: Thermo ICAP7400). First, 0.4 g of the positive electrode active material was weighed, and 10 ml of aqua regia (50% concentration) was added. The mixture was then placed on a plate at 180°C for 30 minutes. After decomposition on the plate, the volume was adjusted to 100 mL, and a quantitative test was performed using the standard curve method.

[0074] In some embodiments, the positive electrode film layer further optionally includes a positive electrode conductive agent. The embodiments of the present application are not particularly limited to the type of positive electrode conductive agent. For example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≦5% based on the total mass of the positive electrode film layer.

[0075] In some embodiments, the positive electrode membrane layer optionally further includes a positive electrode adhesive. The embodiments of the present application are not particularly limited to the type of positive electrode adhesive. For example, the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. In some embodiments, the mass content of the positive electrode adhesive is ≦5% based on the total mass of the positive electrode membrane layer.

[0076] In some embodiments, the ratio of the compaction density of the positive electrode membrane layer to the compaction density of the negative electrode membrane layer is (2 to 2.5):1, such as 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, or a range consisting of any two of the foregoing values.

[0077] In some embodiments, the packed density PD of the positive electrode membrane layer is 3.0 g / cm 3 to 3.5 g / cm 3 Optionally, 3.2 g / cm 3 to 3.5 g / cm 3 For example, 3 g / cm 3 , 3.1g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 , 3.35g / cm 3 , 3.4g / cm 3 , 3.5g / cm 3 Alternatively, it may be a range consisting of any two of the above values.

[0078] In the embodiments of the present application, the compaction density of the positive electrode active material layer has a meaning known in the art and can be tested using methods known in the art. For example, a positive electrode plate after one side has been coated and cold-pressed (if the positive electrode plate is coated on both sides, the positive electrode film on one side may be wiped off first) is taken and punched into a small disk with an area of ​​S1, which is weighed and recorded as M1. Next, the positive electrode film is wiped off from the weighed positive electrode plate, and the weight of the positive electrode current collector is weighed and recorded as M0. The areal density of the positive electrode active material layer = (weight of the positive electrode plate M1 - weight of the positive electrode current collector M0) / S1, and the compaction density of the positive electrode active material layer = areal density of the positive electrode active material layer / thickness of the positive electrode active material layer.

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

[0080] In some embodiments, the thickness of the positive electrode current collector is 10 μm or less, and optionally 8 μm to 10 μm.

[0081] The thickness of the positive electrode current collector is relatively thin, which can weaken the heat dissipation path of the lithium ion battery and allow some of the heat to be retained within the lithium ion battery during low SOC discharge, which is beneficial for improving the DCR at low SOC and thereby improving the discharge power at low SOC.

[0082] For example, the thickness of the positive electrode current collector may be 8 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9.0 μm, 9.2 μm, 9.5 μm, 9.6 μm, 9.8 μm, 10 μm, or a range consisting of any two of the above values.

[0083] In the embodiment of the present application, the thickness of the positive electrode current collector has a meaning known in the art and can be detected using an instrument and a method known in the art. For example, the positive electrode plate is used as a sample, and then the positive electrode film layer on the surface of the positive electrode plate is washed with an organic solvent such as alcohol, and the thickness of the positive electrode current collector is measured with a micrometer.

[0084] The positive electrode film layer is typically obtained by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other optional components in a solvent and stirring the resulting mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0085] [Electrolyte] organic solvents In some embodiments, the electrolyte further comprises an organic solvent.

[0086] In some embodiments, the organic solvent may include a cyclic carbonate, and the ratio of the mass content of the cyclic carbonate to the mass content of the lithium hexafluorophosphate, based on the total mass of the electrolyte, is (0.60 to 2.50):1, and optionally (1.00 to 1.65):1.

[0087] The expected beneficial effects are as follows: When the ratio of the mass content of the cyclic carbonate to the mass content of lithium hexafluorophosphate is within the above range, it is advantageous to sufficiently dissociate more lithium ions from the lithium hexafluorophosphate, so that even at the end of discharge with a low SOC, more lithium ions can be contained in the electrolyte system, and lithium ions can be continuously dissociated as the battery reaction progresses, improving the power performance of the battery.

[0088] For example, the ratio of the mass content of the cyclic carbonate to the mass content of the lithium hexafluorophosphate, based on the total mass of the electrolyte, may be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.37:1, 1.4:1, 1.5:1, 1.6:1, 1.65:1, 1.67:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, or a range consisting of any two of the above values.

[0089] In some embodiments, the mass content of the cyclic carbonate is 10% to 45%, and more preferably 20% to 30%, based on the total mass of the electrolyte solution. The cyclic carbonate has a high dielectric constant and high ionic conductivity, and can form a stable SEI film on the surface of the negative electrode active material.

[0090] For example, based on the total mass of the electrolyte, the mass content of the cyclic carbonate may be 10%, 10.92%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 20.93%, 21%, 22%, 23%, 23.66%, 24%, 25%, 26%, 27%, 28%, 29%, 29.12%, 30%, 30.03%, 31%, 32%, 33%, 34%, 35%, 36%, 36.4%, 37%, 38%, 39%, 40%, 40.4%, 41%, 42%, 43%, 44%, 45%, or a range consisting of any two of the above values.

[0091] In some embodiments, the cyclic carbonate may include at least one of ethylene carbonate EC, propylene carbonate PC, and butylene carbonate BC.

[0092] In some embodiments, the organic solvent may include a linear carbonate, and the ratio of the mass content of the linear carbonate to the mass content of the cyclic carbonate, based on the total mass of the electrolyte, is (0.9 to 6): 1, and optionally (1.5 to 2.65): 1. When the mass content ratio of the linear carbonate to the cyclic carbonate satisfies the above range, the viscosity and ionic conductivity of the electrolyte can be improved at the same time, and the kinetic performance of the lithium ion can be improved.

[0093] Exemplary ratios of the mass content of cyclic carbonate to the mass content of linear carbonate are 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.37:1, 1.4:1, 1.5:1, 1.6:1, 1.65:1, 1.67:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4.0:1, 4.10:1, 4.11:1, 4.12:1, 4.13:1, 4.14:1, 4.15:1, 4.16:1, 4.17:1, 4.18:1, 4.19:1, 4.20:1, 4.21:1, 4.22:1, 4.23:1, 4.24:1, 4.25:1, 4.26:1, 4.27:1, 4.28:1, 4.29:1, 4.30:1, 4.31:1, 4.32:1, 4.33:1, 4.34:1, 4.35:1, 4.36:1, 4.37:1, 4.38:1, 4.39:1, :1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4.0:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1, 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, 5.95:1, 6:1, or a range consisting of any two of the above values.

[0094] In some embodiments, the mass content of the linear carbonate is 35% to 75%, and more preferably 50% to 75%, based on the total mass of the electrolyte. The linear carbonate has a relatively low viscosity, which is favorable for rapid lithium ion migration, and can improve the electrochemical stability and low-temperature performance of the electrolyte.

[0095] For example, based on the total mass of the electrolyte, the mass content of the linear carbonate may be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 50.4%, 51%, 52%, 52.5%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 68%, 70%, 71%, 72%, 73%, 74%, 75%, or a range consisting of any two of the above values.

[0096] In some embodiments, the linear carbonate comprises at least one of ethyl methyl carbonate EMC, diethyl carbonate DEC, and dimethyl carbonate DMC.

[0097] additives In some embodiments, the electrolyte may further include an additive.

[0098] In some embodiments, the additive includes a first additive containing at least one of lithium difluoro(oxalato)borate LiDFOB and lithium tetrafluoroborate LiBF4. During the later cycle of a lithium-ion battery, metal ions, such as Ti and Zr ions, in the positive electrode active material may be eluted into the electrolyte and may migrate to the surface of the negative electrode plate. The first additive contains fluorine ions and boron ions, which have a relatively strong bonding ability with the metal ions, reducing the risk of the metal ions migrating to the surface of the negative electrode plate, improving the cycle performance of the lithium-ion battery, and compensating for the power degradation caused by Ti and Zr ions.

[0099] In some embodiments, based on the total mass of the electrolyte, the mass content of the first additive is 30 ppm to 1200 ppm, optionally 100 ppm to 400 ppm, and the mass content of Ti combined with the first additive is 100 ppm to 600 ppm, and the mass content of Zr element is 500 ppm to 2550 ppm. The first additive can improve the binding ability of Ti and Zr ions, and further improve the cycle performance of the lithium ion battery.

[0100] Exemplarily, the mass content of the first additive is 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, 210 ppm, 220 ppm, 230 ppm, 240 ppm, 250 ppm, 260 ppm, 270 ppm, 280 ppm, 290 ppm, 300 ppm , 310 ppm, 320 ppm, 330 ppm, 340 ppm, 350 ppm, 360 ppm, 370 ppm, 380 ppm, 390 ppm, 400 ppm, 410 ppm, 420 ppm, 430 ppm, 440 ppm, 450 ppm, 460 ppm, 470 ppm, 480 ppm, 490 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, or a range consisting of any two of the above numerical values.

[0101] In some embodiments, the additive includes a second additive containing lithium difluorophosphate LiPO2F2. Lithium difluorophosphate LiPO2F2 can form a film layer rich in inorganic components on the surface of the positive electrode active material, which is advantageous for improving the ionic and electronic conductivity performance of the film layer. The formed film layer has a relatively low interfacial ionic resistance, which is advantageous for lithium ion transport and can improve the DCR at low SOC. In particular, lithium difluorophosphate, when combined with Al element in the positive electrode active material, can improve the DCR on the surface of the positive electrode active material and increase interfacial power.

[0102] In some embodiments, the mass content of the second additive is 100 ppm to 3000 ppm, and optionally 1000 ppm to 2000 ppm, based on the total mass of the electrolyte solution. The second additive with the above mass content can be combined with 500 ppm to 3000 ppm of Al element to better improve the DCR and interfacial power on the surface of the positive electrode active material.

[0103] Exemplarily, the mass content of the second additive may be 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, or a range consisting of any two of the above values.

[0104] In some embodiments, the additive includes a third additive, and the third additive includes lithium fluorosulfonate. The third additive can form a film layer rich in inorganic components on the surface of the positive electrode active material, which is advantageous for improving the ionic and electronic conductivity performance of the film layer. The formed film layer also has a relatively low interfacial ionic resistance, which is advantageous for lithium ion transport and can improve the DCR at low SOC. In particular, lithium difluorophosphate, in combination with phosphorus (P), sulfur (S), and boron (B) elements in the positive electrode active material, can improve the DCR on the surface of the positive electrode active material and increase the interfacial power.

[0105] Illustratively, the lithium fluorosulfonate may include at least one of lithium trifluoromethanesulfonate and lithium perfluorohexanesulfonate.

[0106] In some embodiments, the mass content of the third additive is 50 ppm to 200 ppm based on the total mass of the electrolyte solution, and the third additive of this mass content can be combined with 10 ppm to 800 ppm of phosphorus (P), sulfur (S), and boron (B) elements to better improve the DCR and interfacial power on the surface of the positive electrode active material.

[0107] For example, the mass content of the third additive may be 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 200 ppm, or a range consisting of any two of the above values.

[0108] In some embodiments, the additive includes a fourth additive, and the fourth additive may further include at least one of 1,3-propane sultone PS, vinylene carbonate VC, and lithium fluorosulfonate LiSO3F.

[0109] In some embodiments, the ratio of the mass content of 1,3-propane sultone PS, the mass content of vinylene carbonate VC, and the mass content of lithium fluorosulfonate LiSO3F, based on the total mass of the electrolyte, is (0.050 to 0.300):(0.100 to 0.500):(0.001 to 0.300). The mass content of one of the additive components is 0, indicating that this component is not added to the electrolyte. When the ratio of the mass content of 1,3-propane sultone PS, the mass content of vinylene carbonate VC, and the mass content of lithium fluorosulfonate LiSO3F is within the above ranges, the components can essentially participate in forming an SEI film on the surface of the negative electrode active material, and the SEI film can effectively mitigate the expansion of the silicon-based material.

[0110] In some embodiments, the mass content of 1,3-propane sultone PS, based on the total mass of the electrolyte solution, may be 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range consisting of any two of the foregoing values.

[0111] In some embodiments, the mass content of vinylene carbonate (VC) based on the total mass of the electrolyte solution may be 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range consisting of any two of the foregoing values.

[0112] In some embodiments, the mass content of lithium fluorosulfonate LiSO3F, based on the total mass of the electrolyte solution, may be 0.1% to 1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range consisting of any two of the foregoing values.

[0113] In some embodiments, the additive may include a fluorinated cyclic carbonate, which can participate in the formation of an SEI film on the surface of the negative electrode active material, effectively protecting the negative electrode active material, and has a certain desolvation ability, which is favorable for lithium ion migration, improving DCR at low SOC, and increasing discharge power.

[0114] In some embodiments, the fluorinated cyclic carbonate includes at least one of monofluoroethylene carbonate (FEC), bisfluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC), and optionally the fluorinated cyclic carbonate includes monofluoroethylene carbonate (FEC). FEC contains a relatively small number of fluorine atoms, which makes it more polar and more likely to release fluorine atoms and participate in the film-forming reaction of the SEI film.

[0115] In some embodiments, the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of elemental silicon relative to the total mass of the electrolyte is (0.5 to 9.5):1, and optionally (1 to 2):1. Illustratively, the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of elemental silicon relative to the total mass of the electrolyte is 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.05:1, 1.1:1, 1.2:1, 1.3:1, 1.35:1, 1.4:1, 1.5:1, 1.57:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, The ratio may be 2.3:1, 2.36:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 4.7:1, 4.71:1, 4.8:1, 5:1, 5.5:1, 5.8:1, 6:1, 6.5:1, 7:1, 7.5:1, 7.8:1, 8:1, 8.5:1, 9:1, 9.1:1, 9.2:1, 9.3:1, 9.4:1, 9.43:1, 9.5:1, or a range consisting of any two of the above values.

[0116] Fluorinated cyclic carbonates can be used to form SEI films on the surface of negative electrode active materials, improving their composition and properties and effectively protecting the negative electrode active material. In particular, when the negative electrode contains silicon, the expansion of silicon necessitates optimizing the composition of the SEI film. This can be achieved by adjusting the relative proportions of the film-forming additives in the electrolyte. The fluorinated cyclic carbonates can contribute to the formation of SEI films, improving their flexibility and preventing structural collapse caused by silicon releasing a large number of lithium ions in a short period of time at the end of discharge. Furthermore, the fluorinated cyclic carbonates possess a certain desolvation ability, favoring lithium ion migration, improving DCR at low SOC and increasing discharge power. Research has shown that when the ratio of silicon content in the negative electrode active material to FEC content in the electrolyte is between 0.5 and 9.5:1, the rate performance of the battery at the end of discharge is significantly improved.

[0117] In some embodiments, the mass content of the fluorinated cyclic carbonate relative to the total mass of the electrolyte may be 0.95% to 5.8%, and optionally 1.5% to 3%, for example, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91%, 2.0%, 2.1%, 2.2%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9 ... %, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.82%, 3.9%, 4%, 4.1%, 4.5%, 5%, 5.2%, 5.5%, 5.7%, 5.73%, 5.8%, or a range consisting of any two of the above values.

[0118] lithium salts After being dissolved in an organic solvent, the lithium salt can release a large amount of active lithium ions to participate in charging and discharging.

[0119] In some embodiments, the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of the lithium salt, based on the total mass of the electrolyte, is (0.05 to 0.30):1, optionally (0.10 to 0.20):1. The fluorinated cyclic carbonate can form an organic substance on the surface of the silicon-based material, improving the flexibility of the SEI film. The lithium salt can participate in the formation of the SEI film, allowing the SEI film to contain an inorganic component, which is advantageous for improving the ionic and electronic conductivity of the SEI film and improving the ionic and electronic conductivity of the entire negative electrode plate. When the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of the lithium salt is within the above range, the flexibility of the SEI film and the improvement of the ionic and electronic conductivity can be achieved, while also reducing the DCR and improving the discharge power of the lithium-ion battery.

[0120] Illustratively, the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of the lithium salt may be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1, 0.20:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1, 0.30:1, or a range consisting of any two of the foregoing values.

[0121] In some embodiments, the lithium salt further comprises at least one of an inorganic phosphate and an inorganic borate, and optionally the lithium salt comprises a fluorine-containing inorganic borate. The inorganic phosphate and inorganic borate can participate in the formation of inorganic components in the SEI film, which is beneficial to improving the ion and electron conduction performance of the SEI film, and the formed SEI film has a low interfacial ionic resistance, which is beneficial to lithium ion transport, and can improve the DCR at low SOC.

[0122] In some embodiments, the inorganic phosphate comprises at least one of lithium monofluorophosphate Li2PO3F and lithium difluorophosphate LiPO2F2, and optionally, the inorganic phosphate comprises lithium difluorophosphate LiPO2F2.

[0123] In some embodiments, the borate salt comprises at least one of lithium tetrafluoroborate LiBF4, lithium difluoro(oxalato)borate LiDFOB, and lithium bis(oxalato)borate.

[0124] In some embodiments, based on the total mass of the electrolyte, the total mass content of inorganic phosphate and inorganic borate is 0.05% or more and 0.50% or less, and optionally 0.10% to 0.30%.

[0125] For example, the total mass content of inorganic phosphate and inorganic borate may be 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, or a range consisting of any two of the above values.

[0126] Exemplary lithium salts include lithium tetrafluoroborate LiBF4, lithium difluoro(oxalato)borate LiDFOB, and lithium bis(oxalato)borate.

[0127] Optionally, based on the total mass of the electrolyte, the mass content of lithium tetrafluoroborate LiBF4 may be 0.01% to 0.2%, for example, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, or a range consisting of any two of the above values.

[0128] Optionally, based on the total mass of the electrolyte, the mass content of lithium difluoro(oxalato)borate LiDFOB may be 0.01% to 0.1%, for example, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, or a range consisting of any two of the above values.

[0129] Optionally, based on the total mass of the electrolyte, the mass content of lithium bis(oxalato)borate may be 0.01% to 0.5%, for example, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or a range consisting of any two of the above values.

[0130] The qualitative and quantitative determination of each substance or element in this application can be performed using appropriate devices and methods known to those skilled in the art. For relevant detection methods, reference can be made to detection standards in China and abroad, and enterprise standards in China and abroad. Those skilled in the art can adaptively change some detection steps / instrument parameters, etc., from the perspective of detection accuracy, to obtain more accurate detection results. Qualitative or quantitative determination can be performed using a single detection method, or multiple detection methods can be combined to perform qualitative or quantitative measurement.

[0131] In the embodiments of the present application, the type and content of inorganic components / lithium salts in the electrolyte have the meanings known in the art and can be detected using instruments and methods known in the art. For example, the concentration of inorganic components / lithium salts in the electrolyte can be analyzed qualitatively or quantitatively by ion chromatography analysis with reference to standard JY / T020-1996 "General Principles for Ion Chromatography Analysis Methods." In the embodiments of the present application, a newly prepared electrolyte can be used as the sample, or a previously discharged battery (discharged to the lower cutoff voltage so that the battery's charge state is about 0% SOC) can be disassembled in the reverse direction and the free electrolyte obtained from the battery can be used as the sample for detection using ion chromatography analysis.

[0132] In the embodiments of the present application, the type and content of organic components in the electrolyte have the meaning known in the art and can be detected using instruments and methods known in the art, for example, qualitative and quantitative analysis of organic components in the electrolyte can be performed by gas chromatography with reference to GB / T9722-2006 "General Principles of Gas Chromatography for Chemical Reagents." In the embodiments of the present application, a newly prepared electrolyte can be used as the sample, or a previously discharged battery (discharged to the lower cutoff voltage so that the battery's charge state is about 0% SOC) can be reversely disassembled and the free electrolyte obtained from the battery can be used as the sample, and the detection can be performed using ion chromatography analysis.

[0133] Furthermore, for example, to test the presence of certain additives in an electrolyte by liquid-phase nuclear magnetic resonance (NMR) to detect lithium difluorophosphate and lithium hexafluorophosphate, a 7ml glass vial was prepared in a nitrogen gas glove box. 5ml of nuclear magnetic reagent premix was added to the vial and the vial was left to stand for 24 hours at room temperature (20-25°C) in the nitrogen gas glove box. This allowed the electrolyte in the electrode plate and separator to disperse into the nuclear magnetic reagent premix, thereby obtaining a nuclear magnetic test sample. The nuclear magnetic reagent premix consisted of 100ml of deuterated acetonitrile and 3ml of trifluoromethylbenzene (CF3ph). This nuclear magnetic reagent premix was pre-dried over 4A molecular sieves (100ml of nuclear magnetic reagent premix was added to 15g of freshly opened 4A molecular sieves and dried at room temperature (20-25°C) in a nitrogen gas glove box for at least 30 days). 19F NMR was measured (nuclear magnetic resonance (NMR): Bruker Avance 400HD).

[0134] To identify and quantify each species, the following settings were used in reversal angle and scan time:

[0135] Fluorine spectrum test pulse sequence: 2gfhigqn.2, Delay time: 1 second, Number of scans: 16, The relative content of trifluoromethylbenzene and LiPF6 is calculated based on the integrated intensity of the signal peaks of the two substances in F-NMR. The calculation method is as follows: PF6 - Relative content = (I PF6 - ×M PF6 - / 6) / (I CF3ph ×M CF3ph / 3), where I is the corresponding nuclear magnetic peak area, and M is the corresponding relative molecular mass. Then, calculate the content of lithium hexafluorophosphate in the electrolyte solution based on the molar composition ratio relationship between hexafluorophosphate and lithium ions.

[0136] The content of the deuteration reagent in the electrolyte is calculated based on the content of lithium hexafluorophosphate LiPF6.

[0137] Trifluoromethylbenzene and PO2F2 in F-NMR - Calculate the relative content of the two substances based on the integrated intensity of their signal peaks. The calculation method is as follows: PO2F2 - Relative content = (I PO2F2- ×M PO2F2- / 2) / (I CF3ph ×M CF3ph / 3), where I is the corresponding nuclear magnetic peak area, and M is the corresponding relative molecular mass. Then, calculate the content of lithium difluorophosphate in the electrolyte solution based on the molar composition ratio relationship between difluorophosphate and lithium ions.

[0138] In some embodiments, the lithium ion battery has a retention coefficient of 1.0 g / Ah to 2.5 g / Ah, optionally 1.8 g / Ah to 2.2 g / Ah.

[0139] The liquid retention coefficient of a lithium ion battery can reflect the liquid retention capacity of the electrolyte. When the liquid retention coefficient of a lithium ion battery is within the above range, the electrolyte can have good infiltration into the positive and negative electrode plates, and there is a certain gap between the negative electrode plate and the separator, which can provide an expansion space for the volume expansion of the silicon-based material, thereby reducing the risk of the entire battery swelling.

[0140] In some embodiments, the lithium ion battery has a retention coefficient of 1.0 g / Ah to 2.5 g / Ah, optionally 1.8 g / Ah to 2.2 g / Ah.

[0141] In some embodiments, the various solutes or solvents in the electrolyte solutions referred to in this application include not only substances that are actively added when the electrolyte solution is manufactured, but also substances that are derived from substances already present in some / some electrolyte solutions during the manufacturing of the electrolyte solution or during the manufacturing of a battery from said electrolyte solution or during the storage or use of a battery containing said electrolyte solution.

[0142] The liquid retention coefficient of a lithium ion battery can reflect the liquid retention capacity of the electrolyte. When the liquid retention coefficient of a lithium ion battery is within the above range, the electrolyte can have good infiltration into the positive electrode plate and the negative electrode plate, and there is a certain gap between the negative electrode plate and the separator, which can provide an expansion space for the volume expansion of the silicon-based material, thereby reducing the risk of the entire lithium ion battery expanding.

[0143] For example, the electrolyte retention coefficient of the lithium ion battery may be 1.0 g / Ah, 1.1 g / Ah, 1.2 g / Ah, 1.3 g / Ah, 1.4 g / Ah, 1.5 g / Ah, 1.6 g / Ah, 1.7 g / Ah, 1.8 g / Ah, 1.9 g / Ah, 2.0 g / Ah, 2.1 g / Ah, 2.2 g / Ah, 2.3 g / Ah, 2.4 g / Ah, 2.5 g / Ah, or a range consisting of any two of the above values.

[0144] In the embodiment of the present application, the liquid retention coefficient of a lithium ion battery has a meaning known in the art and can be determined using equipment and methods known in the art, for example, in accordance with GB / T 31486-2015 "Electrical Performance Requirements and Test Methods for Power Storage Batteries for Electric Vehicles," in which a lithium ion battery is charged at 1C to 4.35V and then discharged at 1C to 2.8V at 25°C to obtain the discharged capacity C, which is used as the denominator, and the lithium ion battery is weighed and designated as M0, and then the positive electrode plate, negative electrode plate, separator, and electrolyte are disassembled, where the free electrolyte is present in the housing / bag, and the entire solid assembly is placed in an oven at 60°C and baked for more than 4 hours (including, but not limited to, the positive electrode plate, negative electrode plate, separator, and other mechanical parts of the disassembled lithium ion battery that contribute to M0), and then the entire lithium ion battery assembly is weighed and designated as M1, where the weight difference between M0 and M1 is used as the numerator. The liquid retention coefficient is equal to the volume C divided by the weight difference between M0 and M1.

[0145] [Negative electrode plate] In some embodiments, the lithium ion battery further comprises a negative electrode plate.

[0146] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and containing a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on one or both of the two facing surfaces of the negative electrode current collector.

[0147] In some embodiments, the negative electrode film layer includes a negative electrode active material including elemental carbon and elemental silicon, and the ratio of the mass content of the elemental silicon to the mass content of the elemental carbon, based on the total mass of the negative electrode active material, is from (0.3:99.7) to (3:97).

[0148] The negative electrode active material of a lithium-ion battery includes a carbon-based material that provides carbon and a silicon-based material that provides silicon. The carbon-based material that provides carbon may contain carbon, silicon, or silicon alone. The silicon-based material that provides silicon may contain silicon, carbon, or silicon alone. The negative electrode active material also includes a carbon-based material and a silicon-based material. Compared with the carbon-based material, the silicon-based material has a higher lithium release voltage plateau, allowing the silicon-based material to continue discharging even at low SOC (e.g., SOC≦10%). This compensates for the shortcomings of the carbon-based material, which is that it is difficult to discharge / cannot continue discharging at low SOC. This improves the direct current internal resistance (DCR) during the battery discharge process and further improves the power performance during the battery discharge process.

[0149] The reasons for adjusting the mass content of silicon element to a lower content are as follows: Although silicon-based materials have a higher lithium release potential than carbon-based materials, they experience a relatively large degree of volume expansion or contraction during the charge / discharge process, which can lead to defects such as structural collapse and pulverization of the negative electrode active material, and can also cause undesirable side reactions within the battery. In addition, silicon-based materials themselves have relatively poor electrical conductivity, and a high content is unfavorable for improving DCR. Therefore, when other conditions are met, the power performance of batteries using negative electrode active materials with a high silicon content is conversely inferior to batteries with a lower silicon content.

[0150] The electrolyte of the embodiment of the present application further uses 15% to 20% lithium hexafluorophosphate in combination, and the cooperation between the electrolyte and the negative electrode improves the power performance of the battery at the end of discharge.

[0151] Lithium hexafluorophosphate can be involved in the formation of a solid electrolyte interphase (SEI) film component on the surface of the negative electrode active material. Lithium hexafluorophosphate with a high fluorine atomic ratio can optimize the SEI film component, and the improvement effect of lithium hexafluorophosphate with a high mass content on the SEI film component is more significant, increasing the proportion of lithium fluoride (e.g., lithium fluoride) in the SEI film. Such an SEI film with a relatively high lithium fluoride proportion can, on the one hand, mitigate the problem of silicon-based material pulverization and improve the overall structural stability of the negative electrode active material, and on the other hand, delay side reactions between the electrolyte and the surface of the negative electrode active material, thereby improving the discharge stability of the silicon-based material in the later stage of discharge and further improving the power performance of the battery.

[0152] Furthermore, during the final stage of discharge of a lithium-ion battery at a low SOC, the concentration of lithium ions in the negative electrode active material is relatively low, making it difficult for lithium ions to desorb from the negative electrode active material, reducing the concentration difference of lithium salts in the electrolyte system, improving the internal resistance of the lithium-ion battery, and further reducing the discharge power.The electrolyte in the embodiment of the present application contains a high content of lithium hexafluorophosphate, which can contribute more lithium ions to the battery system, improve the concentration of lithium ions in the electrolyte, effectively reduce the concentration polarization of lithium salts, and promote the migration of lithium ions from the negative electrode plate to the positive electrode plate, thereby further improving the power performance of the lithium-ion battery.

[0153] The mass content of carbon element relative to the total mass of the negative electrode active material is 97% or more and 99.7% or less, for example, 97%, 97.2%, 97.5%, 97.6%, 97.8%, 98%, 98.2%, 98.5%, 98.6%, 98.8%, 99%, 99.5%, 99.7%, or a range consisting of any two of the above values.

[0154] The mass content of silicon element relative to the total mass of the negative electrode active material is 0.3 to 3.0%, for example, 0.3%, 0.32%, 0.4%, 0.5%, 0.6%, 0.64%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.27%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91%, 2.0%, 2.1%, 2.2%, 2.23%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.86%, 2.9%, 3%, or a range consisting of any two of the above numerical values.

[0155] As described above, the silicon element may be derived from a silicon-based material, and the silicon-based material may be a raw material constituting the negative electrode film layer. In some embodiments, the silicon element contained in the negative electrode active material is present in the negative electrode film layer in at least one form of elemental silicon, a silicon-carbon composite, or silicon oxide SiOx (0 < x ≦ 2). The elemental silicon, silicon-carbon composite, and silicon oxide SiOx (0 < x ≦ 2) here may refer to a silicon-based material, or may refer to the form of the silicon element in the negative electrode plate in the battery after formation. For the silicon oxide SiOx here, 0 < x ≦ 2 because the bonding mode between silicon atoms and oxygen atoms in the negative electrode film layer is diverse, and it may be at least one of SiO, SiO 1.2 , or SiO2 and other possible silicon oxides. The silicon-carbon composite here may be a silicon-carbon composite formed by a specific chemical reaction of silicon and carbon elements in a lithium-ion battery. The voltage plateau of the silicon oxide itself is high, which is advantageous for releasing lithium ions at low SOC, contributes to the capacity and participates in discharging, and improves the power performance of the lithium-ion battery.

[0156] The carbon element is mainly a constituent element of a carbon-based material. In some embodiments, the carbon-based material may include at least one of artificial graphite and natural graphite. Optionally, the carbon-based material may include natural graphite. Natural graphite generally has a smaller particle size, faster lithium ion release, and its surface generally contains amorphous carbon. The presence of amorphous carbon can reduce DCR and improve power.

[0157] The qualitative and quantitative determination of each substance or element in this application can be detected using appropriate devices and methods known to those skilled in the art. The relevant detection methods can refer to detection standards at home and abroad in China, corporate standards at home and abroad in China, etc. Moreover, those skilled in the art can adaptively change several detection steps / instrument parameters from the perspective of detection accuracy to obtain more accurate detection results. It may be qualitatively or quantitatively analyzed using one detection method, or multiple detection methods may be combined for qualitative or quantitative measurement.

[0158] For example, taking the detection of silicon element in the negative electrode active material as an example, qualitative and quantitative analysis may be carried out by referring to JY / T015 - 1996 "General Rules for Inductively Coupled Plasma Atomic Emission Spectrometric Analysis Methods". Furthermore, referring to the GB - T17359 - 2012 standard, analysis may also be performed on the surface elements of the negative electrode plate or the cross - sectional elements after ion polishing.

[0159] For example, the graphite material in this application can be combined with JIS / K0131 - 1996 General Rules for X-ray Diffraction Analysis Method to perform X-ray powder diffraction test and qualitative analysis on the negative electrode plate or negative electrode active material. The single silicon, silicon - carbon composite, and silicon oxide SiOx(0 < x ≤ 2) in this application can also use the above X-ray powder diffraction test and qualitative analysis.

[0160] In some embodiments, based on the total mass of the negative electrode active material, the ratio of the mass content of silicon oxide SiOx(x = 1) to the mass content of artificial graphite is from (0.5:99.5 to (5:95). When the negative electrode active material satisfies the above content range, the discharge power at low SOC can be further improved.

[0161] Exemplarily, the ratio of the mass content of silicon oxide SiO to the mass content of artificial graphite may be 0.5:99.5, 1:99, 1.5:98.5, 2:98, 2.5:97.5, 3:97, 3.5:96.5, 4:96, 4.5:95.5, 5:95 or a range consisting of any two of the above numerical values.

[0162] In some embodiments, the mass content of silicon oxide SiO may be 0.5% to 5%, optionally 2% to 3.5%, e.g., 0.5%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%. , 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or a range consisting of any two of the above values. When the mass content of silicon oxide SiO satisfies the above content range, the discharge power at low SOC can be further improved.

[0163] In some embodiments, the mass content of the artificial graphite may be 95% to 99.5%, optionally 96.5% to 98%, e.g., 95%, 95.1%, 95.2%, 95.3%, 95.4%, 95.5%, 95.6%, 95.7%, 95.8%, 95.9%, 96%, 96.1%, 96.2%, 96.3%, 96.4%, 96.5%, 96.6%, 96.7%, %, 96.8%, 96.9%, 97%, 97.1%, 97.2%, 97.3%, 97.4%, 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, 98%, 98.1%, 98.2%, 98.3%, 98.4%, 98.5%, 98.6%, 98.7%, 98.8%, 98.9%, 99%, 99.5%, or a range consisting of any two of the above values. When the mass content of the artificial graphite satisfies the above content range, the cycle performance of the battery can be improved.

[0164] In some embodiments, the mass content of the negative electrode active material is 85% or more and less than 100% based on the total mass of the negative electrode film layer, such as 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range consisting of any two of the above values.

[0165] In some embodiments, the thickness of the single-sided negative electrode film layer is 65 μm to 90 μm. The thickness of the single-sided negative electrode film layer refers to the thickness of the single-sided negative electrode film layer. For example, when a negative electrode film layer is provided on both sides of the negative electrode current collector, the thickness of the negative electrode film layer on one side of the negative electrode current collector is the thickness of one side of the negative electrode film layer. Alternatively, when a negative electrode film layer is provided on one of the two sides of the negative electrode current collector, the thickness of the negative electrode film layer on that side is the thickness of the single-sided negative electrode film layer. When the thickness of the negative electrode film layer is in this range, the transport speed of lithium ions in the negative electrode plate and the transport speed in the separator can be approximately matched, reducing the risk of worsening concentration polarization and favoring improved discharge performance.

[0166] For example, the thickness of the negative electrode film layer may be 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, 71 μm, 72 μm, 73 μm, 74 μm, 75 μm, 76 μm, 77 μm, 78 μm, 79 μm, 80 μm, 81 μm, 82 μm, 83 μm, 84 μm, 85 μm, 86 μm, 87 μm, 88 μm, 89 μm, 90 μm, or a range consisting of any two of the above values.

[0167] In the embodiments of the present application, the thickness of the negative electrode film layer has a meaning known in the art and can be detected using instruments and methods known in the art. Relevant detection methods can be found in Chinese and foreign detection standards, Chinese and foreign enterprise standards, etc., and those skilled in the art can adaptively change some detection steps / instrument parameters to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative measurement, or multiple detection methods can be combined to achieve qualitative or quantitative measurement. For example, according to GB / T 17359-2012 "Quantitative Analysis by Microbeam Analysis Spectroscopy," a negative electrode plate containing no electrolyte can be used as a sample for ion-polished cross-sectional elemental analysis to determine the thickness of the negative electrode film layer. Furthermore, for example, multiple measurements are taken with a centimeter ruler and the average value is calculated. Take a negative electrode plate (a negative electrode plate coated with a negative electrode film layer on both sides) that does not contain an electrolyte, first measure the thickness of any five parts of the negative electrode plate using a centimeter ruler to obtain an average value H1, and after wiping off the negative electrode film layer, measure the thickness of any five parts of the remaining current collector to obtain an average value H2. The thickness of the single-layer negative electrode film layer is (H2-H1) / 2.

[0168] In some embodiments, the packed density PD of the negative electrode membrane layer is 1.3 g / cm 3 to 1.7 g / cm 3 When the compaction density of the negative electrode film layer is within this range, the negative electrode plate has good dynamic and cycling performance.

[0169] Exemplarily, the compaction density PD of the negative electrode film layer is 1.3 g / cm 3 , 1.35g / cm 3 , 1.4g / cm 3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 Alternatively, it may be a range consisting of any two of the above values.

[0170] Areal density = weight of negative electrode film layer on one side / area of ​​negative electrode film layer on one side, where since both sides of the negative electrode current collector have negative electrode film layers, the weight of negative electrode film layer on one side = (average weight of electrode plates - average weight of current collectors) / 2. Compaction density = areal density / average thickness of negative electrode film layer, where since both sides of the negative electrode current collector have negative electrode film layers, the average thickness of negative electrode film layer = (average thickness of electrode plates - average thickness of current collectors) / 2.

[0171] The "average" here may be the average value after five parallel tests.

[0172] In some embodiments, the negative electrode film layer further optionally includes a negative electrode conductive agent. The embodiments of the present application are not particularly limited to the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≦5% based on the total mass of the negative electrode film layer.

[0173] In some embodiments, the negative electrode film layer optionally further includes a negative electrode adhesive. The embodiments of the present application are not particularly limited to the type of negative electrode adhesive. For example, the negative electrode adhesive may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin (SR-1B), water-soluble acrylic acid-based resin (e.g., polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass content of the negative electrode adhesive is ≦5% based on the total mass of the negative electrode film layer.

[0174] In some embodiments, the negative electrode membrane layer further optionally contains other additives. For example, the other additives may include a thickener, such as carboxymethylcellulose sodium CMC-Na, a PTC thermistor material, etc. In some embodiments, the mass content of the other additives is ≦2% based on the total mass of the negative electrode membrane layer.

[0175] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet is copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymer base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0176] In some embodiments, the thickness of the negative electrode current collector is 6 μm or less, and optionally a thin current collector of 4.5 μm to 6 μm.

[0177] The negative electrode current collector of the lithium ion battery of the present application is optionally a thin current collector of 4.5 μm to 6 μm, which weakens the heat dissipation path of the lithium ion battery and can retain some of the heat within the battery under low SOC discharge conditions. The combination of a low-silicon negative electrode plate with a high-content lithium hexafluorophosphate electrolyte system further enhances the beneficial effect of reducing DCR growth at the end of discharge (under low SOC), thereby improving discharge power at low SOC.

[0178] For example, the thickness of the negative electrode current collector may be 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6 μm, or a range consisting of any two of the above numerical values.

[0179] In the embodiment of the present application, the thickness of the negative electrode current collector has a meaning known in the art and can be detected using an instrument and a method known in the art. For example, the negative electrode plate is used as a sample, and then the negative electrode film layer on the surface of the negative electrode plate is washed with an organic solvent such as alcohol, and the thickness of the negative electrode current collector is measured with a micrometer.

[0180] The negative electrode film layer is typically obtained by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional adhesive, and other optional auxiliary agents in a solvent and stirring the resulting mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0181] The negative electrode plate does not exclude additional functional layers other than the negative electrode film layer. For example, in some examples, the negative electrode plate of the present application further includes a conductive undercoating (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other examples, the negative electrode plate of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0182] [Separator] In some embodiments, the lithium ion battery further comprises a separator, wherein the porosity of the separator is between 30% and 45%.

[0183] Since the amount of lithium hexafluorophosphate added is relatively high, the viscosity of the entire electrolyte is relatively high, and the porosity of the separator is relatively high, which is advantageous for the electrolyte with a relatively high viscosity to permeate the separator, allowing lithium ions to move smoothly.

[0184] For example, the porosity of the separator may be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, or a range consisting of any two of the above values.

[0185] In the embodiment of the present application, the porosity refers to the percentage of the pore volume in the separator relative to the total volume of the separator. The porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries."

[0186] In some embodiments, the separator includes an organic substrate and a coating disposed on at least one side of the organic substrate, the coating including a ceramic layer and / or a polyacrylate layer. The coating may include only a ceramic layer, only a polyacrylate layer, or both a ceramic layer and a polyacrylate layer.

[0187] Alternatively, when the coating comprises a ceramic layer and a polypropylene layer, the polypropylene layer may be provided on at least one surface of the organic substrate and the ceramic layer may be provided on a surface of the polypropylene layer facing away from the organic substrate, or the ceramic layer may be provided on at least one surface of the organic substrate and the polypropylene layer may be provided on a surface of the ceramic layer facing away from the organic substrate.

[0188] The separator has a polyacrylate layer on its outer surface, which gives the outer surface of the separator a certain degree of flexibility, effectively mitigating the volume expansion or contraction of the silicon-based material, and improving the structural stability of the entire electrode assembly.

[0189] The material of the organic substrate is not particularly limited, and any known base film having good chemical and mechanical stability can be selected. For example, the organic substrate may include at least one of a porous polyolefin resin film (e.g., at least one of polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride), a porous glass fiber, and a porous nonwoven fabric. The organic substrate may be selected from a single-layer film or a multilayer composite film. When the organic substrate is a multilayer composite film, the materials of each layer may be the same or different.

[0190] In some embodiments, the thickness of the organic substrate is between 6.6 μm and 7.6 μm.

[0191] When the thickness of the organic substrate is within the above range, the transport speed of lithium ions in the negative electrode plate and the transport speed in the separator can be made to be approximately equal, which reduces the risk of worsening concentration polarization and is advantageous for improving discharge performance.

[0192] For example, the thickness of the organic substrate may be 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, or a range consisting of any two of the above values.

[0193] In some embodiments, the polyacrylate in the polyacrylate layer may be formed by polymerizing a polymer monomer, where the polymer monomer includes at least one of a first polymer monomer, a second polymer monomer, and a third polymer monomer. Optionally, the polymer monomer includes the first polymer monomer, the second polymer monomer, and the third polymer monomer. The polyacrylate is formed by polymerizing the three polymer monomers, which allows the separator to obtain suitable adhesion with the electrode plates and improves the dynamic performance of the lithium-ion battery.

[0194] The first polymer monomer has at least one ester linkage and is optionally one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, vinyl acetate, trifluoroethyl methacrylate, glycidyl methacrylate, or trimethylolpropane triacrylate, and further optionally one or more of methyl methacrylate, lauryl acrylate, lauryl methacrylate, or trimethylolpropane triacrylate.

[0195] The second polymer monomer has at least one cyano bond and is optionally one or more of acrylonitrile, methacrylonitrile, ethacrylonitrile, and further optionally one or more of acrylonitrile, methacrylonitrile.

[0196] The third polymer monomer has at least one amide bond and is optionally one or more of acrylamide, N-methylolacrylamide, N-butoxymethacrylamide, and further optionally one or more of acrylamide, N-methylolacrylamide.

[0197] In some embodiments, the weight ratio of the first polymer monomer, the second polymer monomer, and the third polymer monomer in the formed polyacrylate is (45 to 70):(10 to 25):(10 to 35), for example (50 to 70):(10 to 25):(10 to 35), (55 to 70):(10 to 25):(10 to 35), (60 to 70):(10 to 25):(10 to 35), (65 to 70):(10 to 25):(10 to 35), (45 to 70):(15 to 25):(10 to 35), (45 to 70):(20 to 25):(10 to 35), (45 to 70):(22 to 25):(10 to 35), (45 to 70):(10 to 25):(15 to 35), (45 to 70):(10 to 25):(20 to 35), (45 to 70):(10 to 25):(25 to 35), (45 to 70):(10 to 25):(30 to 35), (45 to 70):(10 to 25):(32 to 35), and so on.

[0198] In some embodiments, the ceramic layer contains inorganic particles having heat resistance, and the inorganic particles may include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having the ability to transport active ions, and inorganic particles in which electrochemical oxidation and reduction can occur.

[0199] In some embodiments, the inorganic particles having a dielectric constant of 5 or more are boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon oxide SiOx (0 < x ≦ 2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium dioxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti nO3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1) and at least one of Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT).

[0200] In some embodiments, the inorganic particles having the ability to transport active ions are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), at least one of them.

[0201] In some embodiments, the inorganic particles capable of electrochemical oxidation and reduction include at least one of lithium-containing transition metal oxides, olivine-structured lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium titanium compounds.

[0202] In some embodiments, the ceramic layer may further comprise an adhesive, optionally comprising one or more of polyacrylate, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, cyanoethyl pullulan.

[0203] In some embodiments, the coating thickness is between 1.5 μm and 2.5 μm.

[0204] The coating thickness is the thickness of the coating on one side, specifically including the total thickness of the ceramic layer and the polyacrylate layer. For example, when a coating is provided on both sides of the organic substrate, the thickness of the coating on one side of the organic substrate is the thickness of one side of the coating. Alternatively, when a coating is provided on one side of the organic substrate, the thickness of the coating on that side is the thickness of the one-side coating. When the coating thickness is within the above range, the transport speed of lithium ions in the negative electrode plate and the transport speed in the separator can be approximately equal, reducing the risk of worsening concentration polarization and favoring improved discharge performance.

[0205] Illustratively, the coating thickness may be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or a range consisting of any two of the foregoing values.

[0206] In some embodiments, the ratio of the thickness of the ceramic layer to the thickness of the polyacrylate layer is (0.5 to 2.0):1, such as 0.5:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or a range consisting of any two of the foregoing values.

[0207] In the embodiments of the present application, the meanings of the thickness of the organic substrate and coating are those known in the art and can be detected using equipment and methods known in the art, such as an ion cross-section polishing device in combination with a scanning electron microscope. For example, the following steps can be performed: First, cut the separator into a test sample of a certain size (e.g., 6 mm x 6 mm), sandwich the test sample between two electrically and thermally conductive sheets (e.g., copper foil), and use adhesive (e.g., double-sided adhesive) to secure the test sample and the foil together. Then, use a flat iron block with a certain mass (e.g., about 400 g) to press the test sample against the copper foil for a certain period of time (e.g., 1 hour) until the gap between the test sample and the copper foil is as small as possible. Then, cut the test sample with scissors so that the edges are even, and place the sample on a sample holder with conductive adhesive, ensuring that the sample protrudes slightly beyond the edge of the sample holder. The sample stage is then placed in a sample rack, locked and secured, and the argon ion cross-section polishing meter is turned on to draw a vacuum (e.g., from 10 Pa to 4 Pa). The argon gas flow rate (e.g., to 0.15 MPa), voltage (e.g., to 8 KV), and polishing time (e.g., to 2 hours) are set, and the sample stage is adjusted to oscillation mode to begin polishing. After polishing is completed, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to obtain an ion-polished cross-section morphology (CP) image of the test sample, and the thickness of the coating and the organic substrate are measured.

[0208] In some embodiments, the positive electrode plate, the separator, and the negative electrode plate can be manufactured into an electrode assembly by a winding process and / or a stacking process, and it may be understood that the electrode assembly may be a wound electrode assembly or a stacked electrode assembly. Optionally, the electrode assembly is a stacked electrode assembly, which can provide closer contact between the positive electrode plate and the negative electrode plate and further improve the DCR.

[0209] In some embodiments, the lithium-ion battery may include an outer casing, which may be used to package the electrode assembly and electrolyte.

[0210] In some embodiments, the lithium ion battery's exterior may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The lithium ion battery's exterior may be a pouch, such as a bag-like pouch. The pouch may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0211] The embodiments of the present application are not particularly limited to the shape of the lithium ion battery, which may be cylindrical, rectangular, or any other shape. For example, FIG. 1 shows an example of a lithium ion battery 5 having a rectangular structure.

[0212] In some embodiments, as shown in FIG. 2 , the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening and seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is packaged in the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the lithium-ion battery 5 may be one or more and can be adjusted as needed.

[0213] The manufacturing method of the lithium ion battery according to the embodiment of the present application is well known. In some embodiments, a lithium ion battery may be formed by assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. For example, the positive electrode plate, the separator, and the negative electrode plate may be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly may be placed in a housing, dried, and then injected with an electrolyte. The lithium ion battery may then be obtained through processes such as vacuum packaging, standing, chemical formation, and shaping.

[0214] In some examples of the embodiments of the present application, the lithium ion batteries according to the embodiments of the present application can be assembled into a battery module, and the number of lithium ion batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0215] 3 is a schematic diagram of an example battery module 4. As shown in FIG. 3, in the battery module 4, a plurality of lithium ion batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of lithium ion batteries 5 may be fixed in place by fasteners.

[0216] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of lithium ion batteries 5 are accommodated in the accommodating space.

[0217] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0218] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 covers the lower housing 3 and is used to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0219] power consumption equipment A third aspect of an embodiment of the present application provides a power consuming device, the power consuming device including at least one of the lithium ion battery, battery module, or battery pack of the embodiment of the present application. The lithium ion battery, battery module, or battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0220] The power consumption device can choose the lithium ion battery, the battery module or the battery pack according to its usage needs.

[0221] 6 is a schematic diagram of an example power consuming device 6, which may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density demands of the power consuming device 6, a battery pack or battery module may be employed.

[0222] Other examples of power consuming devices include mobile phones, tablet computers, laptops, etc. These power consuming devices generally require a thin design and may employ lithium ion batteries as their power source.

[0223] Example The following examples will more specifically describe the contents disclosed in the embodiments of the present application, and these examples are for illustrative purposes only, and various modifications and variations within the scope of the contents disclosed in the embodiments of the present application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples can be obtained commercially or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples can be obtained commercially.

[0224] Example 1 1. Manufacturing of positive electrode plates The positive electrode plate includes a positive electrode current collector and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 10 μm. The positive electrode film layer is a film layer formed by uniformly coating the surface of the aluminum foil of the positive electrode current collector with a positive electrode slurry (solvent: N-methylpyrrolidone (NMP)), drying, and cold pressing. The positive electrode film layer includes a positive electrode active material, a conductive agent: carbon black, and an adhesive: polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.4:1.1. The compaction density of the positive electrode film layer is 3.35 g / cm. 3 It was.

[0225] The positive electrode active material has a single crystal structure and its molecular formula is Lid Ni a Co b Mn c M (1-a-b-c) O z wherein the nickel cobalt manganese oxide substrate in the positive electrode active material comprises a compound having the molecular formula LiNi 0.70 Co 0.10 Mn 0.20 Contains compounds that are O2.

[0226] The M elements include 450 ppm of Ti element, 1700 ppm of Zr element, 1600 ppm of Al element, and 120 ppm of (B, S and P) elements.

[0227] 2. Manufacturing of negative electrode plates The negative electrode plate includes a negative electrode current collector and a negative electrode film layer. The negative electrode current collector is a copper foil with a thickness of 4.5 μm. The negative electrode film layer includes a film layer formed by uniformly applying a negative electrode slurry (the solvent is deionized water) to the surface of the negative electrode current collector copper foil, drying, and cold pressing. The negative electrode film layer includes a negative electrode active material in a weight ratio of 96.2:1.8:1.2:0.8, an adhesive styrene butadiene rubber (SBR), a thickener carboxymethyl cellulose sodium (CMC-Na), and a conductive agent carbon black (Super P).

[0228] The negative electrode active material contained 97% artificial graphite and 3% silicon oxide SiO. The mass content of silicon element relative to the total mass of the negative electrode active material was 1.91%. The compaction density of the negative electrode film layer was 1.4 g / cm. 3 It was.

[0229] 3. Separator The separator can be purchased directly from a separator supplier. The porosity of the separator is 30%. The separator includes an organic substrate (porous polypropylene PP (7 μm)) and a coating. The coating includes a ceramic layer (1 μm) and a polyacrylate layer (1 μm). The ceramic layer is provided on two surfaces of the organic substrate. The ceramic layer includes a film layer formed by dissolving an adhesive and inorganic aluminum oxide in N-methylpyrrolidone (NMP) and applying the solution to the organic substrate. The polyacrylate layer is provided on the surface of the ceramic layer away from the organic substrate. The polyacrylate layer is a film layer formed by applying a substance containing polyacrylates to the surface of the ceramic layer.

[0230] 4. Electrolyte production The electrolyte solution includes an organic solvent, a lithium salt, and an additive, and the organic solvent includes cyclic carbonates (EC, PC, and BC, the mass ratio of each component is 1:1:1) and linear carbonates (EMC, DMC, and DEC, the mass ratio of each component is 1:1:1).

[0231] 5. Battery manufacturing The positive electrode plate, separator, and negative electrode plate were stacked in this order, with the separator positioned between the positive electrode plate and the negative electrode plate to serve as an insulator, and then wound to obtain an electrode assembly. The electrode assembly was placed in an outer casing, dried, and then an electrolyte was injected. After vacuum packaging, standing, chemical formation, shaping, and other processes, a lithium ion battery was obtained. The lithium ion battery had a liquid retention coefficient of 2.0 g / Ah.

[0232] Comparative Example 1 A lithium ion battery was manufactured in a similar manner to Example 1, but differed from Example 1 in that the positive electrode active material of Comparative Example 1 was different and did not contain the M element.

[0233] Comparative Examples 2 and 3 Lithium ion batteries were manufactured in a manner similar to that of Example 1, except that in Comparative Examples 2 and 3, the components of the electrolyte, particularly the content of lithium hexafluorophosphate, were adjusted.

[0234] Example 2 A lithium ion battery was produced in a similar manner to Example 1, but differed from Example 1 in that the positive electrode active material in Example 2 was a different type, and polycrystalline particles were used as the positive electrode active material.

[0235] Example 3-1 and Example 3-2 A lithium ion battery was manufactured in a manner similar to that of Example 1, but differed from Example 1 in that the components of the electrolyte, particularly the content of lithium hexafluorophosphate, were adjusted in Examples 3-1 and 3-2.

[0236] Examples 4-1 to 4-4 Lithium ion batteries were manufactured in a manner similar to that of Example 1, except that the positive electrode active materials of Examples 4-1 to 4-4 were different, and the content of at least one of Ti and Zr in the M element of the positive electrode active material was adjusted.

[0237] Examples 4-5 to 4-7 The lithium ion batteries were manufactured in a similar manner to Example 1, but differed from Example 1 in that the electrolytes in Examples 4-5 to 4-7 were different, and the content of the first additive in the electrolytes was adjusted.

[0238] Example 5-1 and Example 5-2 A lithium ion battery was manufactured in a manner similar to that of Example 1, but differed from Example 1 in that the positive electrode active materials of Examples 5-1 and 5-2 were different, and the Al content in the M element of the positive electrode active material was adjusted.

[0239] Examples 5-3 to 5-4 The lithium ion battery was manufactured in a similar manner to Example 1, but the difference from Example 1 is that the electrolyte solution in Example 5-3 to Example 5-4 is different, and the content of the second additive in the electrolyte solution is adjusted.

[0240] Examples 6-1 to 6-3 Lithium ion batteries were manufactured in a manner similar to that of Example 1, except that the positive electrode active material and the electrolyte solution of Examples 6-1 to 6-3 were different from those of Example 1, and the positive electrode active material adjusted the total content of P, B, and S in the M element, and the electrolyte adjusted the content of the third additive.

[0241] Example 7-1 and Example 7-2 A lithium ion battery was manufactured in a manner similar to that of Example 1, except that the electrolyte solutions of Examples 7-1 and 7-2 were different, and a fluorinated cyclic carbonate was added to the electrolyte solution.

[0242] Example 8 A lithium ion battery was manufactured in a manner similar to that of Example 1, except that the electrolyte solution of Example 8 was different from that of Example 1, and a fourth additive was added to the electrolyte solution.

[0243] The parameters of the examples and comparative examples are as shown in Tables 1 to 3.

[0244] Performance Test 1. Lithium-ion cycle performance test At 25°C, the lithium ion batteries prepared in the examples and comparative examples were charged to 4.35 V at a rate of 1 C and discharged to 2.8 V at a rate of 1 C for 500 cycles, and the remaining capacity of the lithium ion batteries was recorded as a percentage of the initial capacity.

[0245] Test results The test results are shown in Tables 1 to 3.

[0246] [Table 1]

[0247] In Table 1, the positive electrode active material of Example 1 has a single crystal structure, which has the molecular formula LiNi a Co b Mn c M (1-a-b-c)O2, wherein the nickel cobalt manganese oxide substrate in the positive electrode active material has the molecular formula LiNi 0.70 Co 0.10 Mn 0.20 The M element contained 450 ppm of Ti, 1700 ppm of Zr, 1600 ppm of Al, and 120 ppm of (B, S, and P). The molecular formulas of the positive electrode active materials of Example 2, Example 3-1, and Example 3-2 were the same as those of Example 1, and Example 2 used a polycrystalline structure, while Examples 3-1 and 3-2 used single-crystal particles.

[0248] The positive electrode active material of Comparative Example 1 has the molecular formula LiNi 0.70 Co 0.10 Mn 0.20 The compound contained O2 and single crystal particles were used.

[0249] As can be seen from Table 1, The content of lithium hexafluorophosphate in Comparative Example 1 is relatively high, but the positive electrode active material in Comparative Example 1 is LiNi 0.70 Co 0.10 Mn 0.20 O2, and its structural stability is relatively low, so the cycle performance of lithium-ion batteries is still low.

[0250] Both Comparative Examples 2 and 3 used appropriate cathode active materials, including elements M, such as Ti, Zr, Al, B, S, and P, which improved the crystal lattice stability of the cathode active material system. However, Comparative Example 2 used a relatively low content of lithium hexafluorophosphate (12%), which produced relatively little lithium fluoride on the surface of the cathode active material, failing to adequately protect the cathode active material. There was still a risk of transition metal ions in the cathode active material dissolving into the electrolyte, resulting in poor battery cycling performance. Comparative Example 3 used a relatively high content of lithium hexafluorophosphate (23%), which resulted in a high viscosity of the electrolyte system, which was unfavorable to lithium ion migration, resulting in poor battery dynamics performance.

[0251] The positive electrode active material of Example 1 further contains an M element, and the introduction of the M element can improve the stability of the positive electrode active material's crystal structure. It also contains lithium hexafluorophosphate, with the mass content of lithium hexafluorophosphate LiPF6 relative to the total mass of the electrolyte being 15% to 20%. The lithium hexafluorophosphate forms a protective layer on the surface of the positive electrode active material, primarily composed of lithium fluoride LiF, which can reduce the leaching of metallic and non-metallic elements to some extent and improve the cycle performance of the lithium-ion battery. Compared to the positive electrode active material of Example 2, which uses polycrystalline particles, Example 1 uses single-crystalline particles, which reduces the contact interface between the single-crystalline particles and the electrolyte, reduces the risk of side reactions, and is more advantageous for improving cycle performance.

[0252] [Table 2]

[0253] As can be seen from Table 2, In Examples 4-1 to 4-7, the first additive is used in combination with Ti and Zr in the positive electrode active material. Ti and Zr can improve the stability of the positive electrode active material structure, and the first additive can compensate for the power degradation caused by Ti and Zr ions, thereby improving the cycle performance of the lithium-ion battery.

[0254] By using the second additive in Examples 5-1 to 5-4 in combination with Al in the positive electrode active material, and in particular by combining lithium difluorophosphate with the Al element in the positive electrode active material, the DCR of the surface of the positive electrode active material can be improved, and the interfacial power can be increased.

[0255] [Table 3]

[0256] As can be seen from Table 3, By combining the third additive in Examples 6-1 to 6-3 with at least one element selected from phosphorus (P), sulfur (S), and boron (B) in the positive electrode active material, the DCR of the surface of the positive electrode active material can be improved, and the interfacial power can be increased.

[0257] In Examples 7-1 and 7-2, a fluorinated cyclic carbonate was further added to the electrolyte solution. The fluorinated cyclic carbonate can participate in the formation of an SEI film on the surface of the negative electrode active material, effectively protecting the negative electrode active material and thereby improving the cycle performance of the lithium-ion battery.

[0258] In Example 8, a fourth additive was further added to the electrolyte solution. The fourth additive can participate in the formation of an SEI film on the surface of the negative electrode active material, effectively protecting the negative electrode active material and thereby improving the cycle performance of the lithium-ion battery.

[0259] Although exemplary embodiments have been shown and described, those skilled in the art should understand that the above-described embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications can be made to the embodiments without departing from the spirit, principles, and scope of the present application. [Explanation of symbols]

[0260] 1: Battery pack, 2: Upper housing, 3: Lower housing, 4: Battery module, 5: Lithium ion battery, 51: Case, 52: Electrode assembly, 53, cover plate, 6: Power consumption device.

Claims

1. A lithium-ion battery, an electrolyte solution comprising a lithium salt, the lithium salt comprising lithium hexafluorophosphate, the mass content of the lithium hexafluorophosphate being 15% to 20% relative to the total mass of the electrolyte solution; A positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and containing a positive electrode active material, the positive electrode active material having a molecular formula of Li ｄ Ni ａ Co ｂ Mn ｃ M （１－ａ－ｂ－ｃ） Q ｚ wherein 0<d≦2.1, 0.6<a<1, 0<b<1, 0<c<1, and 0.6<a+b+c<1, and 1.8≦z≦3.5, the M element includes at least one element selected from the group consisting of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce, and the Q element includes at least one element selected from the group consisting of O and F, and a positive electrode plate having a mass content of the first additive of 30 ppm to 1200 ppm based on the total mass of the electrolyte.

2. The M element includes at least one element of Ti and Zr, The electrolyte solution includes a first additive, and the first additive is lithium difluoro(oxalato)borate LiDFOB and lithium tetrafluoroborate LiBF ４ 10. The lithium ion battery of claim 1, comprising at least one of:

3. The lithium ion battery of claim 2 , wherein the M element includes Ti and Zr elements.

4. The mass content of the Ti element is 100 ppm to 600 ppm based on the total mass of the positive electrode active material, and / or The lithium ion battery according to claim 2 , wherein the mass content of the Zr element is 500 ppm to 2550 ppm based on the total mass of the positive electrode active material.

5. the positive electrode active material includes a single crystal particle, the single crystal particle including an inner region and an outer region, the outer region extending 500 nm from any point on an outer surface of the single crystal particle directly toward the interior of the single crystal particle, The lithium ion battery according to claim 1 , wherein the M element includes at least the Al element distributed in the outer region.

6. 6. The lithium-ion battery of claim 5, wherein the electrolyte solution includes a second additive, and the second additive includes lithium difluorophosphate.

7. The mass content of Al element is 500 ppm to 3000 ppm based on the total mass of the positive electrode active material, 7. The lithium ion battery according to claim 6, wherein the mass content of the second additive is 100 ppm to 3000 ppm based on the total mass of the electrolyte solution.

8. The M element further includes at least one element selected from P, S, and B, wherein at least one of P, S, and B is distributed in the outer region; 6. The lithium-ion battery of claim 5, wherein the electrolyte solution includes a third additive, and the third additive includes lithium fluorosulfonate.

9. The total mass content of P, S, and B elements is 10 ppm to 800 ppm based on the total mass of the positive electrode active material; 9. The lithium ion battery according to claim 8, wherein the mass content of the third additive is 50 ppm to 200 ppm based on the total mass of the electrolyte solution.

10. 2. The lithium ion battery according to claim 1, wherein the electrolyte solution contains a cyclic carbonate, and the ratio of the mass content of the cyclic carbonate to the mass content of the lithium hexafluorophosphate, based on the total mass of the electrolyte solution, is (0.60 to 2.50):

1.

11. 11. The lithium ion battery according to claim 10, wherein the ratio of the mass content of the cyclic carbonate to the mass content of the lithium hexafluorophosphate is (1.00 to 1.65):1, based on the total mass of the electrolyte solution.

12. The mass content of the cyclic carbonate is 20% to 30% based on the total mass of the electrolyte; and / or 11. The lithium ion battery of claim 10, wherein the cyclic carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

13. 2. The lithium ion battery according to claim 1, further comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and containing a negative electrode active material, the negative electrode active material containing carbon and silicon, and a ratio of the mass content of the silicon element to the mass content of the carbon element based on the total mass of the negative electrode active material is from (0.3:99.7) to (3:97).

14. 14. The lithium ion battery according to claim 13, wherein the electrolyte solution contains a fluorinated cyclic carbonate, and the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of the silicon element relative to the total mass of the electrolyte solution is (0.5 to 9.5):

1.

15. 15. The lithium ion battery according to claim 14, wherein the ratio of the mass content of the fluorinated cyclic carbonate to the mass content of the silicon element relative to the total mass of the electrolyte is (1 to 2):

1.

16. the mass content of the fluorinated cyclic carbonate is 0.95% to 5.8%, based on the total mass of the electrolyte; and / or 15. The lithium ion battery of claim 14, wherein the fluorinated cyclic carbonate comprises at least one of monofluoroethylene carbonate FEC, bisfluoroethylene carbonate DFEC, and trifluoropropylene carbonate TFPC.

17. the mass content of the fluorinated cyclic carbonate is 1.5% to 3% based on the total mass of the electrolyte; and / or 17. The lithium ion battery of claim 16, wherein the fluorinated cyclic carbonate comprises monofluoroethylene carbonate FEC.

18. 14. The lithium ion battery of claim 13, wherein the ratio of the compaction density of the positive electrode film layer to the compaction density of the negative electrode film layer is (2 to 2.5):

1.

19. The electrolyte solution further includes a fourth additive, and the fourth additive is a mixture of 1,3-propane sultone PS, vinylene carbonate VC, and lithium fluorosulfonate LiSO ３ 10. The lithium ion battery of claim 1, further comprising at least one of:

20. Based on the total mass of the electrolyte, the mass content of the 1,3-propane sultone PS is 0.1% to 1%; and / or 20. The lithium ion battery of claim 19, wherein the mass content of the vinylene carbonate VC is 0.1% to 1% based on the total mass of the electrolyte.

21. A battery comprising the lithium ion battery of any one of claims 1 to 20.

22. 22. A power consuming device comprising the battery of claim 21.

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