Positive electrode active materials, secondary batteries and electrical devices

Abstract

This invention relates to a positive electrode active material, a secondary battery, and an electrical device. The positive electrode active material comprises positive electrode active particles and a fluoride coating material covering at least a portion of the surface of the positive electrode active particles. The fluoride coating material comprises a compound of formula I: A 7‑(2n+3m) M n M' m F 7‑x R x / y Formula I; where 0 < n ≤ 2, 0 < m ≤ 2, 0 ≤ x ≤ 2, y is the absolute value of the valence state of R; A includes Na and / or Li; M includes at least one of Ca, Zn, Mg, Sr, Ba; M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, Sb; R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, BH4.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a fluoride coating material, a positive electrode active material comprising positive electrode active particles coated with the fluoride coating material, and a secondary battery. BACKGROUND

[0002] During the cycle process of the battery, electrochemical degradation phenomena such as voltage drop and capacity attenuation often occur. In addition, in the high charged state, the oxygen ions in the oxide positive electrode participate in the redox reaction, and the reaction between the generated oxygen and the organic electrolyte will release a large amount of heat, leading to thermal runaway of the battery, which has great safety hazards. SUMMARY

[0003] The present application provides a positive electrode active material, a secondary battery comprising the same, and an electric device, the positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, wherein the fluoride coating material has good corrosion resistance and air stability, and at the same time has high thermodynamic stability, a wide electrochemical window, high ionic conductivity and excellent mechanical properties, which can be adapted to common high-voltage positive electrode materials, so that the positive electrode active particles coated with it can bring improvement in battery cycle stability and thermal runaway.

[0004] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material. The positive electrode active material comprises positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, the fluoride coating material comprising a compound represented by Formula I:

[0005] Formula I;

[0006] wherein 0

[0007] A comprises Na and / or Li;

[0008] M comprises at least one of Ca, Zn, Mg, Sr, Ba;

[0009] M' comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi, Sb;

[0010] R comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, BH4.

[0011] The fluoride-coated material of this invention possesses high thermodynamic stability, a wide electrochemical window, high ionic conductivity, and excellent mechanical properties. When used to coat positive electrode active particles, it can alleviate the side reactions between the positive electrode active particles and the electrolyte, allowing the positive electrode active particles to operate at higher voltages. This can improve the battery's capacity and energy density, as well as its first-cycle coulombic efficiency, cycle stability, safety, and rate performance, and in particular, it can improve battery thermal runaway.

[0012] Regarding thermodynamic stability, the anionic framework of the fluoride-coated material is mainly composed of fluoride ions. Fluorine has high electronegativity (stronger than oxygen and chlorine), resulting in stronger interactions with the cations in the structure, thus leading to better structural stability. The fluoride-coated material, coating at least a portion of the surface of the positive electrode active particles, enhances the structural stability of the positive electrode active particles, thereby improving the cycle stability of the battery. In terms of electrochemical window, the fluoride-coated material can cover the operating voltage range of the high-voltage positive electrode and electrolyte, exhibiting significantly stronger high-voltage resistance than oxides. Due to the excellent electrochemical stability of the coating material, electrochemical side reactions between the high-voltage positive electrode and the electrolyte can be avoided. Regarding ionic conductivity, the fluoride-coated material possesses a Weberite configuration (also known as a magnesium cryolite structure or magnesium cryolite-like structure), which provides three-dimensional ion transport channels, and the alkali metal in this structure is in a higher octet coordination environment. On the one hand, the high coordination environment forms a "cage of alkali metals" with a larger space, reducing the migration barrier of alkali metal ions; on the other hand, the alkali metal -F bonds in the structure are longer, and their binding ability to alkali metal ions is weaker, resulting in a higher diffusion coefficient of alkali metal ions; therefore, fluoride-coated materials have excellent ionic conductivity. Furthermore, the M and M' in the fluoride-coated material are octahedrally coordinated at their vertices in the Weberite configuration, playing a supporting role in the structural framework. The vertices-connected framework has a larger creep space, which can improve mechanical properties. This application further selects M (at least one of Ca, Zn, Mg, Sr, Ba) and M' (at least one of Ga, Al, La, Y, B, In, Sc, Bi, Sb) with suitable ionic radii to increase the crystal axis length and lattice volume, thereby widening the lattice structure, increasing ion transport channels, and further improving ionic conductivity. The ionic conductivity of the fluoride-coated material in this application is 3-7 orders of magnitude higher than that of coating materials such as Li₂ZrF₆ and LiF. This indicates that it has potential fast-charging capability without affecting the battery's rate performance. Furthermore, in terms of mechanical properties, the fluoride-coated material can have a lower mechanical modulus than LiF, Li2ZrF6, LiNbO3, and Li3PO4. This suggests that the fluoride-coated material is softer and easier to process than other fluorides and oxides, and is less prone to breakage during rolling and cycling, thus not adversely affecting the efficiency and capacity of the cathode material.

[0013] In any embodiment, based on the total moles of M, M further includes no more than 10 mol% of a first transition metal element, wherein the first transition metal element includes at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

[0014] In any embodiment, based on the total moles of M', M' further includes no more than 10 mol% of a second transition metal element, wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

[0015] When fluoride-coated materials include the above-mentioned variable-valence transition metals in appropriate amounts, the electronic conductivity of the fluoride-coated materials can be improved.

[0016] In any implementation, based on the total moles of A, A further includes no more than 20 mol% of K and / or Ag.

[0017] In any implementation, based on the total moles of M, M further includes at least one element of A and at least one element of M' totaling no more than 10 mol%.

[0018] In the crystal lattice of fluoride-coated materials, M sites can be occupied by monovalent ions of at least one element of A (i.e., one or more of Li, Na, K, and Ag) and trivalent ions of at least one element of M' (i.e., one or more of Ga, Al, La, Y, B, In, Sc, Bi, and Sb). Monovalent ions occupy M sites because mixing occurs during the synthesis of fluoride-coated materials, with some ions from A sites occupying M sites. Furthermore, allowing trivalent ions to occupy M sites creates alkali metal ion vacancies, thereby improving the conductivity of alkali metal ions.

[0019] In any embodiment, M includes at least one of Ca, Zn, and Mg.

[0020] In any embodiment, M' includes at least one of Ga and Al.

[0021] When fluoride coating materials include one or more elements selected from Ca, Zn, and Mg, and one or more elements selected from Ga and Al, they exhibit further improved ion conductivity and high voltage stability, thereby improving the battery's capacity, energy density, cycle stability, safety, and rate performance.

[0022] In any embodiment, the positive electrode active material comprises 0.01 to 10% by weight of fluoride-coated material based on the total weight of the positive electrode active particles.

[0023] If the weight percentage of the coating material in the positive electrode active material is less than 0.01%, the coating area on the surface of the positive electrode active particles will be too small and the coating will be uneven. Most of the positive electrode active particles will still be in direct contact with the electrolyte, thus failing to achieve the desired coating effect. Under high voltage, the positive electrode active particles will still react violently with the electrolyte, affecting the battery's cycle performance and thermal stability. If the weight percentage of the coating material in the positive electrode active material is greater than 10%, the coating layer on the surface of the positive electrode active particles will be too thick, increasing the battery's impedance and thus affecting the battery's performance.

[0024] In any embodiment, the coating thickness of the fluoride coating material is 5 to 20 nm.

[0025] The oxide (e.g., Al2O3, MgO) and fluoride (e.g., AlF3, Li2ZrF6) coatings commonly found on the surface of positive electrode active particles are typically thin, for example, 2 to 10 nm, due to their low ionic conductivity, in order to ensure high rate performance. However, thin coatings may degrade or fail during high temperatures or long-term cycling, leading to partial exposure of the positive electrode and thermal runaway. The fluoride coating material of this invention possesses high thermodynamic stability, a wide electrochemical window, and high ionic conductivity, thus eliminating the need for precise control of the coating thickness. The coating can be prepared on the surface of corresponding high-voltage positive electrode active particles through a simple coating process, such as wet coating.

[0026] In any embodiment, the positive electrode active particles include at least one of layered oxide materials, spinel oxide materials, and fluoride materials, wherein:

[0027] The layered oxide material includes the compound shown in Formula II:

[0028] Formula II

[0029] In equation II, 0 ≤ e ≤ 0.2, and f is R. 1 The absolute value of the price state,

[0030] A 1 Including Li or Na, M a Including transition metal elements, R 1 Includes at least one of F and Cl;

[0031] The spinel oxide material includes the compound shown in Formula III:

[0032] Formula III

[0033] In Equation III, 0 ≤ g ≤ 0.4, and h is R. 2 The absolute value of the price state,

[0034] A 2 Including Li or Na, M b Including transition metal elements, R 2 Includes at least one of F and Cl;

[0035] The fluoride material includes compounds of formula IV:

[0036] Formula IV

[0037] In equation IV, 0 < k ≤ 2, 0 < p ≤ 2, 0 ≤ i ≤ 2, and j is R. 3 The absolute value of the price state,

[0038] A 3 Including Li or Na, M c Including transition metal elements with a divalent valence state, M d Including transition metals with trivalent oxidation states, R 3 Including at least one of F and Cl.

[0039] The electrochemical window of the fluoride-coated material of this invention can cover the operating voltage range of common high-voltage cathode active materials. Coating the aforementioned high-voltage cathode active materials with fluoride-coated materials can improve battery capacity, energy density, cycle stability, safety, and rate performance.

[0040] In any embodiment, the positive electrode active material has one or more of the following characteristics:

[0041] (1) The Dv50 particle size of the positive electrode active material is in the range of 5 to 30 μm;

[0042] (2) The BET specific surface area of ​​the positive electrode active material is between 0.1 and 14 m². 2 Within the range of / g;

[0043] (3) The tap density of the positive electrode active material is between 1.1 and 2.3 g / cm³. 3 ;

[0044] (4) The hardness of the positive electrode active material is in the range of 6 to 12 GPa.

[0045] Controlling the Dv50 particle size, BET specific surface area, tap density, and hardness of the positive electrode active particles within a suitable range can improve the processing performance of the positive electrode sheet, improve electrochemical reaction kinetics, and enhance cycle stability.

[0046] In any embodiment, the positive electrode includes a current collector and a positive electrode film layer disposed on at least one surface of the current collector, wherein the positive electrode film layer comprises 70% to 98% by weight of positive electrode active material based on the total weight of the positive electrode film layer.

[0047] Controlling the proportion of positive electrode active material in the positive electrode film layer within an appropriate range can effectively improve the energy density of the battery.

[0048] In any embodiment, the positive electrode film layer further comprises 2% to 30% by weight of binder based on the total weight of the positive electrode film layer.

[0049] In any embodiment, the positive electrode has a strength of 2.3 to 3.7 g / cm³. 3 The compaction density within the range.

[0050] A second aspect of the present invention provides a positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least a portion of the surface of the positive electrode active particles. The fluoride coating material comprises a compound of formula I:

[0051] Formula I;

[0052] Where 0 < n ≤ 2, 0 < m ≤ 2, 0 ≤ x ≤ 2, and y is the absolute value of the valence state of R;

[0053] A includes Na and / or Li;

[0054] M includes at least one of Ca, Zn, Mg, Sr, and Ba;

[0055] M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb;

[0056] R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

[0057] A third aspect of the present invention provides an electrical device comprising a secondary battery according to the first aspect or a positive electrode active material according to the second aspect. Attached Figure Description

[0058] Figure 1 The X-ray diffraction (XRD) patterns of the fluoride-coated materials of Examples 1 and 3 are shown, in which... Figure 1 (a) is the fluoride coating material of Example 1. The X-ray diffraction (XRD) pattern, Figure 1 (b) is the fluoride coating material of Example 3. The X-ray diffraction (XRD) pattern.

[0059] Figure 2 A schematic diagram of a secondary battery according to one embodiment of the present invention is shown.

[0060] Figure 3 It shows Figure 2 An exploded view of a secondary battery according to one embodiment of the present invention is shown.

[0061] Figure 4 A schematic diagram of a battery module according to one embodiment of the present invention is shown.

[0062] Figure 5 A schematic diagram of a battery pack according to one embodiment of the present invention is shown.

[0063] Figure 6 It shows Figure 5 An exploded view of a battery pack according to one embodiment of the present invention is shown.

[0064] Figure 7 A schematic diagram of an electrical device using a secondary battery as a power source according to one embodiment of the present invention is shown.

[0065] Explanation of reference numerals in the attached figures:

[0066] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0067] Hereinafter, embodiments of the fluoride-coated material, positive electrode, and secondary battery of the present invention are disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present invention and are not intended to limit the subject matter of the claims.

[0068] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0071] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0073] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0074] One reason for the electrochemical degradation phenomena such as voltage drop and capacity decay in batteries during cycling is that the cycle stability of the positive electrode cannot meet the requirements. After cycling, cracks form on the surface and inside the particles of the positive electrode, leading to continuous side reactions and increased lithium consumption. Transition metal ions dissolved from the positive electrode (such as...) The electrolyte migrates to the negative electrode, catalyzes the decomposition of the electrolyte, thickens the SEI (solid electrolyte interface) layer, and consumes reversible lithium. When metal ions are reduced and deposited on the negative electrode surface, they disrupt the uniform nucleation of lithium, leading to an increase in lithium dendrites and "dead lithium" (i.e., lithium metal that has lost its electrochemical activity), further reducing coulombic efficiency. Moreover, the oxygen released from the oxide positive electrode promotes further side reactions between the positive electrode and the electrolyte.

[0075] A common way to improve the cycle stability of the cathode is through doping modification / elemental concentration control of the cathode active material. Doping with cations such as Mg, Cu, and Al can suppress phase transitions to some extent and improve the structural stability of the cathode active material. Furthermore, designing cathode active particle structures with gradient elemental concentration distributions, such as a nickel-rich center and a manganese-rich outer shell, can improve the capacity and surface stability of the cathode material. However, the aforementioned elemental doping strategies have limited effect on improving cathode cycle stability and cannot completely solve the problem of side reactions between the cathode and electrolyte. Moreover, the fabrication process for special cathode active particle structures is complex and difficult to scale up.

[0076] Another way to improve the cycle stability of the cathode is through coating / interface modification. Coating the cathode active particles with oxides (Al₂O₃, MgO, etc.), phosphates and silicates (AlPO₄, MnSiO₄, etc.), and fluorides (AlF₃, Li₂ZrF₆, etc.) can form a stable surface layer, reducing direct contact between the cathode active particles and the electrolyte and suppressing cathode phase transition. However, most fluoride and oxide coating materials have low ionic conductivity. To ensure high rate performance, the coating thickness needs to be precisely controlled, resulting in complex processes. The uniformity of thin coatings is difficult to control, and they cannot completely prevent contact between the cathode and the electrolyte. Furthermore, uniform coating techniques such as atomic layer deposition are costly.

[0077] To address battery thermal runaway and improve battery safety, solid-state electrolytes can be used instead of organic electrolytes. While solid-state electrolytes can improve battery safety to some extent, they do not fundamentally solve the thermal runaway problem. At around 200°C, oxide solid-state electrolytes react with the electrode interface, releasing oxygen and leading to thermal runaway. At around 300°C, sulfur ions in sulfide solid-state electrolytes are reduced to sulfur vapor, which reacts with oxygen released from the oxide cathode, causing thermal runaway.

[0078] Common methods for addressing battery thermal runaway include using flame-retardant electrolyte additives. However, flame-retardant additives have low solubility, making it difficult to achieve high concentrations and limiting their flame-retardant effect. Some flame retardants also have poor compatibility with the electrodes, leading to side reactions that affect battery cycle life.

[0079] Another solution is to use a coating layer to coat the positive electrode active particles. Using a coating layer reduces side reactions between the positive electrode active material and the electrolyte, and suppresses structural changes and oxygen evolution at high temperatures. However, as already mentioned, most coating layers have low ionic conductivity, necessitating a reduction in coating thickness. Thin coating layers may degrade or fail during high temperatures or long-term cycling, losing their flame-retardant properties. Ensuring the uniformity of thin coating layers is difficult, and partial exposure of the positive electrode can lead to thermal runaway.

[0080] Furthermore, regarding improving battery cycle stability, fluorides possess strong corrosion resistance, maintain structural stability over a long voltage range, and do not release flammable gases. Therefore, fluorinated solvents, fluorinated lithium / sodium salts, and fluorinated additives are often used in high-voltage electrolyte formulations. During the formation stage or the first charging cycle, a lithium / sodium fluoride (LiF / NaF)-rich inorganic layer is formed at the electrode / electrolyte interface, inhibiting further electrolyte decomposition and improving battery cycle stability. However, fluorides typically have very low ionic conductivity (<10). -6 The low efficiency (S / cm) makes it difficult for fluoride battery materials to be practically applied.

[0081] Regarding improving cathode stability, cathode doping modification or element concentration control can enhance cycle stability but cannot completely solve the problem of side reactions between the cathode and electrolyte. Coating cathode active particles with oxides, phosphates, silicates, and fluorides can form a stable surface layer, reducing direct contact between the cathode and electrolyte. However, most fluoride and oxide coating materials have low ionic conductivity, requiring precise control of the coating thickness to ensure high rate performance. In terms of improving battery thermal runaway, while flame-retardant electrolyte additives can suppress thermal runaway, their low solubility makes high-concentration addition difficult, limiting their flame-retardant effect. Furthermore, using coatings to reduce side reactions between the cathode and electrolyte and suppress structural changes and oxygen evolution at high temperatures is also beneficial. However, most coatings have low ionic conductivity, necessitating reduced coating thickness. Thin coatings may degrade or fail during high temperatures or long-term cycling, losing their flame-retardant effect. In terms of improving the cycle stability of batteries, fluorinated solvents, fluorinated lithium / sodium salts, and fluorinated additives are often used in the formulation of high-voltage electrolytes. They can inhibit further decomposition of the electrolyte and improve the cycle stability of the battery. However, common fluorides have low ionic conductivity, making them difficult to apply in practice.

[0082] [Positive electrode active material]

[0083] Based on this, the present invention proposes a positive electrode active material, comprising positive electrode active particles and a fluoride coating material coating at least a portion of the surface of the positive electrode active particles, wherein the fluoride coating material comprises a compound of formula I:

[0084] Formula I;

[0085] Where 0 < n ≤ 2, 0 < m ≤ 2, 0 ≤ x ≤ 2, and y is the absolute value of the valence state of R;

[0086] A includes Na and / or Li;

[0087] M includes at least one of Ca, Zn, Mg, Sr, and Ba;

[0088] M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb;

[0089] R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

[0090] The fluoride-coated material of the present invention possesses high thermodynamic stability, a wide electrochemical window, high ionic conductivity, and excellent mechanical properties. When used to coat positive electrode active particles, it can alleviate the side reactions between the positive electrode active particles and the electrolyte, allowing the positive electrode active particles to operate at higher voltages. This improves the battery's capacity, energy density, cycle stability, safety, and rate performance, and in particular, it can improve battery thermal runaway.

[0091] In this invention, thermodynamic stability is characterized by the reaction energy between the coating material and the electrolyte. The reaction energy can be calculated as follows:

[0092] ,in It is the ground state energy of the coating material. It is the ground-state energy of the electrolyte. It is the ground-state energy of the reaction products of the coating material and the electrolyte, where the ground-state energy of each material can be calculated according to density functional theory.

[0093] In this invention, the term "electrochemical window" refers to the voltage range within which the fluoride-coated material can stably exist on a specific electrode material, i.e., within this voltage range, the fluoride-coated material does not undergo significant oxidation or reduction decomposition reactions. The electrochemical window of the fluoride-coated material can be calculated, for example, using the giant potential phase diagram method, as follows:

[0094] Electrode potential Under the influence of [the specific conditions], the expression for the chemical potential of the migrating ion A (Li or Na) is: ,in It is the chemical potential of metal A. e It is the absolute value of the electron charge. The phase decomposition energy of a material is used to determine whether it will undergo redox reactions; the expression for the phase decomposition energy is... ,in E It is the energy of the material itself. It is the energy in equilibrium. This refers to the change in the amount of migrating ions. The electrochemical window is defined as the point at which the material is neither oxidized nor reduced. Time corresponding scope.

[0095] In this invention, the term "ionic conductivity" refers to the ratio of the current density contributed solely by the migration of alkali metal ions to the applied electric field strength in a fluoride-coated material per unit cross-sectional area and unit length under a given temperature and electric field, characterizing the ability of the fluoride-coated material to conduct alkali metal ions. As an example, the ionic conductivity of the coating material can be determined using the AC impedance method. For example, the following steps can be performed:

[0096] 1: Sample preparation

[0097] A dense, flat sheet with a certain thickness (usually 0.5-2 mm) is produced by pressing the coating material powder into sheets (cold pressing or hot pressing and sintering).

[0098] 2. Electrode fabrication (blocking electrode):

[0099] Commonly used electrode materials: precious metals, such as gold (Au), platinum (Pt) or stainless steel;

[0100] A dense and uniform electrode layer is formed on both sides of the electrolyte sheet by magnetron sputtering, vapor deposition, or coating with conductive paste followed by sintering.

[0101] 3. Battery clamp:

[0102] Place the prepared electrolyte sheet into a dedicated test fixture, ensuring good contact between the electrode and the metal probe of the fixture, and that the pressure is uniform and constant (commonly used fixtures include spring clamps or screw-fastened fixtures);

[0103] 4. EIS Testing

[0104] 4.1. Equipment: Electrochemical workstation

[0105] 4.2. Parameter Settings:

[0106] Frequency range: Typically, a wide range is set, for example, from 1 MHz to 0.1 Hz;

[0107] AC disturbance voltage: a small amplitude, typically 10-100 mV;

[0108] Test environment: Depending on the electrolyte's sensitivity to air / moisture, testing can be conducted in a glove box (for air-sensitive materials such as sulfides and metal-organic frameworks) or in an atmospheric environment (for stable materials such as oxides).

[0109] 5. Data Processing and Computation

[0110] 5.1. Obtaining the impedance spectrum:

[0111] The Nyquist plot was obtained after the test, which is the curve showing how the imaginary part (-Z'') of the impedance changes with the real part (Z').

[0112] 5.2. Fitting the equivalent circuit:

[0113] Use ZView or similar software to fit the spectrum to obtain the accurate value of Rb (electrolyte bulk resistance).

[0114] 6. Calculate ionic conductivity :

[0115]

[0116] Ionic conductivity (unit: S / cm)

[0117] L: Thickness of the electrolyte sheet (unit: cm). Measured precisely with a micrometer.

[0118] R: Bulk resistance obtained from the EIS spectrum b (Unit: Ω)

[0119] A: Electrode contact area (unit: cm²) 2 ).

[0120] Furthermore, the ion diffusion coefficient of the coating material can be calculated using the obtained ion conductivity using the following formula:

[0121] formula: Where D is the ion diffusion coefficient, σ is the ion conductivity, N is the number of diffusing ions (= the number of alkali metal ions per mole of coating material × the molar amount of coating material), q is the charge of the ions (for alkali metal ions, q=1), V is the volume of the coating material, k is the Boltzmann yield, and T is the temperature. In this invention, the mechanical properties of the fluoride-coated material can be characterized by the bulk modulus B, shear modulus G, and Young's modulus E. The term "bulk modulus" is a physical quantity describing the ability of a material to resist volume compression under uniform pressure, defined as the ratio of pressure change to relative volume change. The term "shear modulus" is a physical quantity describing the ability of a material to resist shear deformation, equal to the ratio of shear stress to shear strain. The term "Young's modulus" is a physical quantity describing the ability of a solid material to resist deformation in the elastic deformation stage, defined as the ratio of stress to strain experienced by the material, reflecting the stiffness characteristics of the material itself. The bulk modulus B, shear modulus G, and Young's modulus E of the fluoride-coated material can be calculated as follows:

[0122] First, calculate the elasticity matrix of the material, and then calculate the upper limits of the bulk modulus and shear modulus using the Voigt approximation and the Reuss approximation, respectively. and lower limit Bulk modulus formula Shear modulus formula Young's modulus formula .

[0123] In some embodiments, in the compound shown in Formula I, M comprises, based on the total moles of M, not less than 90 mol% of elements selected from Ca, Zn, Mg, Sr, and Ba, which are referred to as the host elements of M.

[0124] In some embodiments, in the compound shown in Formula I, M' comprises, based on the total moles of M', an element selected from Ga, Al, La, Y, B, In, Sc, Bi, and Sb, which are referred to as the host element of M'.

[0125] In some embodiments, A in the compound shown in Formula I may optionally be Na. In this case, for lithium battery applications, such a coating material can be directly used to coat the positive electrode active particles of the lithium battery. During the charging and discharging process of the lithium battery, the Na ions in the coating material will be at least partially exchanged for Li ions.

[0126] In some embodiments, A in the compound shown in Formula I may optionally be Na and Li. In this case, for lithium battery applications, the Na ions in the coating material can be at least partially exchanged for Li ions before the ion-exchanged coating material is used to coat the positive electrode active particles of the lithium battery.

[0127] In some embodiments, the compound represented by Formula I may optionally not include anions other than fluorine, i.e., has the general formula .

[0128] In the structure of fluoride-coated materials, the anionic framework can optionally be composed entirely of fluoride ions. Fluorine has high electronegativity (stronger than oxygen and chlorine), resulting in stronger interactions with cations in the structure and thus better structural stability. Such fluoride-coated materials exhibit low absolute reaction energies with lithium / sodium salts and solvents, demonstrating excellent compatibility with electrolytes and significantly improving battery cycle stability. The fluoride-coated materials have a wide electrochemical window, allowing for good matching with high-voltage cathode materials, reducing electrochemical side reactions, and suppressing cathode oxygen loss. Furthermore, the coating material possesses a unique Weberite configuration, promoting ion transport. Compared to fluoride-coated systems such as Li₂ZrF₆ and LiF, its ionic conductivity is 3-7 orders of magnitude higher, comparable to the ion conduction capacity of layered oxide cathodes. Moreover, the coating material exhibits good mechanical properties, is easier to machine than most fluorides and oxides, and is less prone to breakage.

[0129] In this invention, instruments and methods known in the art can be used to characterize the fluoride-coated material represented by Formula I, such as X-ray diffraction (XRD). For characterizing the coating material in the coating layer of the positive electrode active material in a secondary battery, the secondary battery can be disassembled to obtain the positive electrode sheet. The electrode sheet is washed with electrolyte in a glove box, dried, and the powder is scraped off and collected to obtain the positive electrode active material. The positive electrode active material is then cut open, and XRD analysis is performed on selected areas (depending on the coating layer thickness) to determine the phase composition of the coating material.

[0130] In some embodiments, based on the total molar amount of M, M may further include a first transition metal element of no more than 10 mol%, wherein the first transition metal element includes at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

[0131] In some embodiments, based on the total moles of M, M may also include selected first transition metal elements of 0 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, or values ​​within a range of any two of these values.

[0132] In some embodiments, based on the total moles of M', M' may further include a second transition metal element of no more than 10 mol%, wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

[0133] In some embodiments, based on the total moles of M', M' may also include a second transition metal element with a value within the range of 0 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, or any two of these values.

[0134] When fluoride-coated materials include the above-mentioned variable-valence transition metal ions in appropriate amounts, they can improve electronic conductivity and systematically improve the overall performance of the cathode.

[0135] In some implementations, based on the total moles of A, A also includes no more than 20 mol%, for example no more than 15 mol%, no more than 10 mol%, no more than 5 mol%, no more than 2.5 mol%, no more than 1 mol%, and no more than 0.5 mol% of K and / or Ag.

[0136] In some implementations, based on the total moles of M, M further includes at least one element of A and at least one element of M', representing no more than 10 mol%, for example, no more than 9 mol%, no more than 8 mol%, no more than 7 mol%, no more than 6 mol%, no more than 5 mol%, no more than 4 mol%, no more than 3 mol%, no more than 2 mol%, no more than 1 mol%, and no more than 0.5 mol%.

[0137] In the crystal lattice of fluoride-coated materials, M sites can also be occupied by monovalent ions of at least one element of A (i.e., one or more of Li, Na, K, and Ag) and trivalent ions of at least one element of M', particularly the host element of M' (i.e., one or more of Ga, Al, La, Y, B, In, Sc, Bi, and Sb). Monovalent ions occupy M sites because mixing occurs during the synthesis of fluoride-coated materials, with some ions from A sites occupying M sites. Furthermore, the occupation of M sites by trivalent ions creates alkali metal ion vacancies, thereby improving the conductivity of alkali metal ions.

[0138] When the M site is occupied by monovalent metal ions, trivalent metal ions, or other variable-valence transition metal ions, its overall valence state is +2; when the M' site is occupied by monovalent metal ions, trivalent metal ions, or other variable-valence transition metal ions, its overall valence state is +3.

[0139] In this invention, instruments and methods known in the art can be used to determine the elements at each lattice point of the fluoride-coated material and the proportion of each element at the corresponding site. For example, a Rietveld refinement can be performed using a spectrum obtained from neutron diffraction to determine the types and proportions of elements at sites M and M'. Specifically, as an example, the following operations can be performed:

[0140] 1. Sample preparation: 2g powder sample, vacuum dried, and sealed in a V-shaped sample box.

[0141] 2. Experiment Application: Submit an experiment application through the China Spallation Neutron Source (CSNS) website and communicate the feasibility of the experiment with scientists at the experimental station.

[0142] 3. Experiment:

[0143] 3.1 Sample loading and changing: Load the sample into the sample box and seal it, then install it in the sample position of the spectrometer.

[0144] 3.2 Parameter settings: Neutron source type: spallation source; Wavelength: 1 Å; Angle range: 10-80°; Temperature: 300 K

[0145] 3.3 Acquiring Diffraction Data

[0146] 4. Data Processing

[0147] 4.1 Background subtraction, normalization, absorption correction, and angle correction

[0148] 4.2 Preliminary processing using Mantid software

[0149] 4.3 Use TOPAS software to refine Rietveld and determine the cell parameters, atomic positions, and the types and proportions of elements at each point.

[0150] For the coating material in the coating layer of the positive electrode active material in a secondary battery, the secondary battery can be disassembled to obtain the positive electrode sheet. After washing the electrode sheet with electrolyte in a glove box and drying it, the powder is scraped off and collected to obtain the positive electrode active material. Then, the positive electrode active material is cut open, and the selected area (depending on the coating layer thickness) is subjected to the spectral analysis as described above to determine the elements at each lattice point of the fluoride coating material and the proportion of the element at the corresponding site.

[0151] In some embodiments, the fluoride-coated material has a general formula M is optionally composed of one or more elements selected from Ca, Zn, and Mg; M' is optionally composed of one or more elements selected from Ga and Al. Such a fluoride-coated material exhibits further improved stability with the electrolyte and cathode, significantly enhancing battery cycle stability; and the fluoride-coated material possesses a wide electrochemical window, for example, 2.33-6.23 V, exhibiting significantly stronger high-voltage stability than oxides. Furthermore, the room-temperature alkali metal ion conductivity of the fluoride-coated material is within 10... -5 The diffusion capacity is on the order of S / cm, significantly stronger than that of LiF(10). -13 S / cm) and Li2ZrF6(10 -9 S / cm), comparable to layered oxide cathodes (10 -5 S / cm).

[0152] In this invention, the term "room temperature" refers to 25 ± 5°C.

[0153] In some embodiments, the positive electrode active material may include 0.01 to 10% by weight of fluoride-coated material, based on the total weight of the positive electrode active material.

[0154] If the weight percentage of the coating material in the positive electrode active material is less than 0.01%, the coating area on the surface of the positive electrode active particles will be too small and the coating will be uneven. Most of the positive electrode active particles will still be in direct contact with the electrolyte, thus failing to achieve the desired coating effect. Under high voltage, the positive electrode active particles will still react violently with the electrolyte, affecting the battery's cycle performance and thermal stability. If the weight percentage of the coating material in the positive electrode active material is greater than 10%, the coating layer on the surface of the positive electrode active particles will be too thick, increasing the battery's impedance and thus affecting the battery's performance.

[0155] In some embodiments, the fluoride coating material completely coats the positive electrode active particles, and the coating layer formed by the fluoride coating material may have a thickness of 5-20 nm.

[0156] The oxide (e.g., Al2O3, MgO) and fluoride (e.g., AlF3, Li2ZrF6) coatings commonly found on the surface of positive electrode active particles are typically thin, for example, 2 to 10 nm, due to their low ionic conductivity, in order to ensure high rate performance. However, thin coatings may degrade or fail during high temperatures or long-term cycling, leading to partial exposure of the positive electrode and thermal runaway. The fluoride coating material of this invention possesses high thermodynamic stability, a wide electrochemical window, and high ionic conductivity, thus eliminating the need for precise control of the coating thickness. The coating can be prepared on the surface of corresponding high-voltage positive electrode active particles through a simple coating process, such as wet coating.

[0157] In this invention, instruments and methods known in the art can be used to characterize the fluoride coating layer. For example, scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (STEM-EDS mapping) can be used to characterize the fluoride coating layer on the surface of the positive electrode active particles. Furthermore, the thickness of the coating layer formed by the fluoride coating material can be measured using instruments and methods known in the art. For example, the composite material particles can be sliced, and the thickness of the coating layer can be measured through the cross-section of the particles under a high-power electron microscope (TEM).

[0158] In some embodiments, the positive electrode active particles may include at least one of layered oxide materials, spinel oxide materials, and fluoride materials, wherein:

[0159] The layered oxide material includes the compound shown in Formula II:

[0160] Formula II

[0161] In equation II, 0 ≤ e ≤ 0.2, and f is R. 1 The absolute value of the price state,

[0162] A 1 Including Li or Na, M a Including transition metal elements, R 1 Includes at least one of F and Cl;

[0163] The spinel oxide material includes the compound shown in Formula III:

[0164] Formula III

[0165] In Equation III, 0 ≤ g ≤ 0.4, and h is R. 2 The absolute value of the price state,

[0166] A 2 Including Li or Na, M b Including transition metal elements, R 2Includes at least one of F and Cl;

[0167] The fluoride material includes compounds of formula IV:

[0168] Formula IV

[0169] In equation IV, 0 < k ≤ 2, 0 < p ≤ 2, 0 ≤ i ≤ 2, and j is R. 3 The absolute value of the price state,

[0170] A 3 Including Li or Na, M c Including transition metal elements with a divalent valence state, M d Including transition metals with trivalent oxidation states, R 3 Including at least one of F and Cl.

[0171] In some embodiments, the positive electrode active particles may optionally be high-voltage positive electrode active particles, which may include at least one of the following: , .

[0172] The electrochemical window of the fluoride-coated material of the present invention can very well cover the operating voltage range of the above-mentioned high-voltage cathode active material. Using the fluoride-coated material to coat the above-mentioned high-voltage cathode active material can effectively improve the battery's capacity, energy density, cycle stability, safety, and rate performance.

[0173] Furthermore, in principle, this invention is not limited by the size of the positive electrode active material. Positive electrode active materials of any common size are suitable for this invention. In some embodiments, the positive electrode active material may have a Dv50 particle size of 5 to 30 μm.

[0174] Dv50 particle size is a well-known concept in the art and can be determined using instruments and methods known in the art. As an example, a laser particle size analyzer can be used by following these steps: Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant and then a dispersant, and sonicate at 120W for 5 minutes to ensure that the sample is completely dispersed in the dispersant; after the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics (opause: 8-12%) can be obtained by receiving and measuring the energy distribution of the scattered light. Based on the particle size distribution curve, the Dv50 particle size can be obtained.

[0175] In some embodiments, the positive electrode active material optionally has a particle size of 0.1 to 14 μm. 2 BET specific surface area in the range of / g.

[0176] BET specific surface area is a well-known concept in the art and can be measured using methods and equipment known in the art. As an example, referring to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis method is used. A sample tube containing a porous carbon sample is immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the surface of the solid sample at different pressures (0.05~0.30 MPa) is measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount of the sample is obtained, and thus the BET specific surface area is calculated. This test can be performed, for example, using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0177] In some embodiments, the positive electrode active material optionally has a content of 1.1 to 2.3 g / cm³. 3 The tap density within the range.

[0178] In this invention, "tap density" refers to the mass per unit volume of powder or granular material when it reaches its most compacted state under specific vibration or tapping conditions. Tap density can be measured using methods and equipment known in the art. As an example, the following procedure can be performed: a measured quantity of powder (typically ≥50 g) is placed into a graduated cylinder, gently tapped to remove air bubbles, and then mechanically compacted at a frequency of 300 times / minute and a height of 3 mm until the volume remains constant. The final volume is recorded, and the tap density is obtained by dividing the weight by the volume. The commonly used unit is g / cm³. 3 .

[0179] In some embodiments, the positive electrode active material may optionally have a hardness in the range of 6 to 12 GPa.

[0180] In this invention, "hardness" specifically refers to nanoindentation hardness, that is, the ability of a material to resist localized plastic deformation at the nanoscale. Hardness can be measured using methods and equipment known in the art. As an example, the following operation can be performed: using the single-particle compression method. A single particle of the positive electrode active material is placed under the indenter of a micro / nano mechanical testing machine and loaded at a constant rate (e.g., 0.1 μm / s) until it breaks. The maximum load F and the particle diameter d are recorded. Calculate compressive strength This refers to the hardness of the particles.

[0181] [Positive electrode plate]

[0182] The positive electrode includes a current collector and a positive electrode film layer disposed on at least one surface of the current collector, the positive electrode film layer including positive electrode active particles coated with a fluoride coating material as described in some embodiments.

[0183] As an example, the current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the current collector.

[0184] In some embodiments, the current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0185] In some embodiments, the positive electrode active particles may include high-voltage layered oxide materials, spinel oxide materials, and fluoride materials known in the art for use in batteries. As an example, the positive electrode active particles may include at least one of the following materials: , .

[0186] In some embodiments, based on the total weight of the positive electrode film, the positive electrode film may include 70% to 98% by weight of positive electrode active particles coated with the fluoride coating material.

[0187] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0188] In some embodiments, the positive electrode film may further include 2% to 30% by weight of binder, based on the total weight of the positive electrode film.

[0189] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0190] In some embodiments, the positive electrode film layer may also include additional additives, such as dispersants, thickeners, stabilizers, and flame retardants.

[0191] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0192] In some embodiments, the positive electrode may have a density of 2.3 to 3.7 g / cm³. 3 The compaction density within the range.

[0193] In this invention, the term "compacted density" refers to the mass of the electrode sheet per unit volume after compaction, usually expressed in grams per cubic centimeter (g / cm³). 3 The formula for its calculation is:

[0194] Compacted density = Mass per unit area of ​​electrode (g / cm³) 2 Electrode thickness (cm).

[0195] The compaction density of the electrode can be determined using instruments and methods known in the art. As an example, the following operations can be specifically performed:

[0196] 1. Sampling and Preprocessing

[0197] 1.1 The total electrode mass m1 (including the current collector) is determined.

[0198] 1.2 Wipe off the coating with an electrolyte-soaked cotton swab, rinse with deionized water, dry, and weigh the current collector (m2).

[0199] 1.3 Coating Quality

[0200] 2. Thickness test

[0201] 2.2 Select three points on the electrode and measure the thickness H at each point using a micrometer.

[0202] 2.3 Measure the thickness h of the current collector at the same location

[0203] 3. Data Analysis

[0204] 3.1 Coating Thickness

[0205] 3.2 Coating volume

[0206] 3.3 Compacted density .

[0207] [Negative electrode plate]

[0208] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0209] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0210] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0211] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present invention is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0212] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0213] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes (e.g., single-arm carbon nanotubes (SWCNTs)), graphene, and carbon nanofibers.

[0214] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0215] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0216] [Electrolytes]

[0217] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This invention does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0218] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0219] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium difluorosulfonylimide, sodium difluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate; or selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorosulfonylimide, lithium difluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0220] In some embodiments, the solvent may be selected from solvents with good high-pressure stability. Examples include sulfolane, dimethyl sulfoxide, dimethyl sulfone, acetonitrile, propionitrile, butyronitrile, glutaronitrile, adiponitrile, phenylacetonitrile, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, 2,2,2-trifluoroethyl carbonate, fluorodimethoxyethane, fluorobenzene, o-difluorobenzene, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, N,N-difluoromethanesulfonamide with fluorinated terminal groups, and ionic liquids.

[0221] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0222] [Isolation membrane]

[0223] In some embodiments, the secondary battery also includes a separator. The present invention does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0224] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0225] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0226] In some embodiments, a secondary battery includes a positive electrode, an electrolyte, a separator, and a negative electrode as described in some examples.

[0227] In some embodiments, the secondary battery includes a sodium-ion battery, a lithium-ion battery, or a lithium polymer battery; optionally, the secondary battery is a lithium-ion battery.

[0228] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0229] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0230] This invention does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0231] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0232] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0233] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0234] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0235] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0236] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0237] In addition, the present invention also provides an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack provided by the present invention. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, aerospace vehicles, energy storage systems, etc.

[0238] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements. Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0239] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0240] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0241] Example

[0242] The following describes embodiments. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0243] I. Preparation Method

[0244] Example 1:

[0245] (I) Preparation of coated positive electrode active particles

[0246] 1) Dissolve 10 mg of sodium fluoride, ammonium fluoride, calcium nitrite, and gallium nitrate in 30 mL of deionized water at a molar ratio of 3:11:1:3. Stir at room temperature for 1 hour to generate Na. 3 / 2 Ca 1 / 2 Ga 3 / 2 Solution of F7 coating material;

[0247] 2) Add 1g of positive electrode active particles (Na2(Fe) 1 / 3 Co 1 / 3 Ni 1 / 3 ) 2+ (Mn 1 / 3 Fe 1 / 3 Co 1 / 3 ) 3+ F7, Dv50 (particle size 15 μm) is dispersed in the solution obtained in step 1), wherein the positive electrode active particles and Na 3 / 2 Ca 1 / 2 Ga 3 / 2 The mass ratio of F7 is 99:1. Stir for 1 hour, then put into a stainless steel autoclave with a polytetrafluoroethylene liner. Heat at 160°C in air for 5 hours, and then cool naturally to room temperature to obtain the coated positive electrode active material. The coating layer formed at this time is amorphous.

[0248] 3) The coated positive electrode active material was washed three times with deionized water and dried at 80°C for 6 hours. The resulting powder was calcined at 500°C in argon for 6 hours to improve the crystallization of the coating layer and promote the exchange of matter between the coating layer and the positive electrode active particles, thereby increasing the compactness. After naturally cooling to room temperature, a dense and uniform nanocrystalline coating layer with a thickness of 5-8 nm was obtained (measured by TEM of the cross-section of the particles). Based on the total weight of the obtained positive electrode active material, the positive electrode active material includes 1% by weight of fluoride coating material.

[0249] After drying the solution of the coating material obtained in step 1) above, the fluoride coating material Na can be obtained. 3 / 2 Ca 1 / 2 Ga 3 / 2 F7. Figure 1 (a) shows the X-ray diffraction (XRD) pattern of the fluoride-coated material.

[0250] (II) Preparation of positive electrode sheet

[0251] A slurry is prepared by mixing coated positive electrode active particles, conductive carbon (Super P) particles, carbon nanotubes (TUBALL™ BATT), polyvinylidene fluoride (PVDF) binder and N-methylpyrrolidone (NMP) solvent (based on the dry weight of the slurry, the slurry comprises 70 wt% coated positive electrode active particles, 19 wt% Super P, 1 wt% carbon nanotubes, and 10 wt% PVDF);

[0252] The obtained slurry was coated onto a 12 μm thick Al foil using a doctor blade and dried in a vacuum at 80 °C for 12 hours to evaporate the NMP.

[0253] The dried electrode sheets are rolled and cut into suitable sizes (600mm in length and 70mm in width).

[0254] (III) Negative electrode plate

[0255] A sodium metal anode with a thickness of 30 μm is used.

[0256] (IV) Preparation of electrolytes:

[0257] N,N-dimethyltrifluoromethanesulfonamide (PreTFSI) with fluorinated terminal groups was used as the solvent, and sodium difluorosulfonamide (NaFSI) was used as the sodium salt.

[0258] 0.05 mol NaFSI was mixed with 100 mL PreTFSI at 60 °C, cooled to 25 °C, and filtered through a 0.5 μm PTFE filter in an argon atmosphere to obtain the electrolyte.

[0259] (V) Battery fabrication

[0260] Stack the positive electrode, separator (polyolefin microporous membrane), and negative electrode in sequence, ensuring alignment.

[0261] Use an ultrasonic spot welder to weld the electrode tab to the current collector;

[0262] The battery cells are placed in a vacuum drying oven for further drying;

[0263] The battery cell is placed in the molded aluminum-plastic film, and the top and sides of the aluminum-plastic film are heat-sealed.

[0264] Inject an appropriate amount of electrolyte into the battery cell, allow it to stand under vacuum, and then seal it.

[0265] Example 2

[0266] The battery was prepared in the same manner as in Example 1, except that NaNi with a Dv50 particle size of 15 μm was used in the preparation of the coated positive electrode active particles. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0267] Example 3

[0268] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, magnesium oxalate, gallium nitrate, boron oxide, and aluminum nitrate were dissolved in deionized water in a molar ratio of 9:33:1:1:1:5:2:2 in step 1) to generate Na 3 / 2 (Ca 1 / 6 Zn 1 / 6 Mg 1 / 6 (Ga) 5 / 6 B 1 / 3Al 1 / 3 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle. In this example, the fluoride-coated material Na... 3 / 2 (Ca 1 / 6 Zn 1 / 6 Mg 1 / 6 (Ga) 5 / 6 B 1 / 3 Al 1 / 3 The XRD pattern of F7 is shown in Figure 1 (b) in.

[0269] Example 4:

[0270] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, strontium acetate, barium oxalate, gallium nitrate, lanthanum nitrate, and yttrium nitrate were dissolved in deionized water in a molar ratio of 9:33:1:1:1:5:2:2 in step 1) to generate Na 3 / 2 (Ca 1 / 6 Sr 1 / 6 Ba 1 / 6 (Ga) 5 / 6 La 1 / 3Y 1 / 3 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0271] Example 5:

[0272] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, indium nitrate, and scandium nitrate were dissolved in deionized water in a molar ratio of 10:32:3:1:4:2:2 in step 1) to generate Na 5 / 3 (Ca 1 / 2 Zn 1 / 6 (Ga) 2 / 3 In 1 / 3 Sc 1 / 3 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0273] Example 6:

[0274] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, bismuth acetate, and antimony acetate were dissolved in deionized water in a molar ratio of 9:33:1:2:5:2:2 in step 1) to generate Na 3 / 2 (Ca 1 / 6 Zn 1 / 3 (Ga) 5 / 6 Bi 1 / 3 Sb 1 / 3 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0275] Example 7:

[0276] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, cobalt oxalate, gallium nitrate, aluminum nitrate, and ammonium fluorotitanate were dissolved in deionized water in a molar ratio of 9:27:10:7:1:30:23:1 in step 1) to generate Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Co 1 / 36 (Ga) 5 / 6Al 23 / 36 Ti 1 / 36 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0277] Example 8:

[0278] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium oxide, and sodium chloride were dissolved in deionized water in a molar ratio of 5:33:3:9:1:2 in step 1) to generate Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 Cl 1 / 3 O 1 / 6 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0279] Example 9:

[0280] The battery was prepared in the same manner as in Example 1, except that LiNi with a Dv50 particle size of 10 μm was used. 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode active particle, and a lithium metal negative electrode sheet with a thickness of 30 μm is used. The electrolyte is obtained by mixing 0.05 mol lithium bisfluorosulfonylimide (LiFSI) with 100 mL PreTFSI at 60 °C, cooling to 25 °C, and filtering with a 0.5 m PTFE filter in an argon atmosphere to obtain the electrolyte.

[0281] Example 10

[0282] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, cobalt oxalate, gallium nitrate, aluminum nitrate, and manganese acetate were dissolved in deionized water in a molar ratio of 54:198:10:7:1:30:23:1 in step 1) to generate Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Co 1 / 36 (Ga) 5 / 6Al 23 / 36 Mn 1 / 36 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0283] Example 11

[0284] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, copper oxalate, gallium nitrate, aluminum nitrate, and manganese acetate were dissolved in deionized water in a molar ratio of 54:198:10:7:1:30:23:1 in step 1) to generate Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Cu 1 / 36 (Ga) 5 / 6Al 23 / 36 Mn 1 / 36 The solution of F7 coating material; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0285] Example 12

[0286] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, aluminum nitrate, chromium nitrate, and titanium chloride were dissolved in deionized water in a molar ratio of 54:192:11:7:30:20:2:2 in step 1) to generate Na 3 / 2 (Ca 11 / 36 Zn 7 / 36 (Ga) 5 / 6 Al 5 / 9Cr 1 / 18 Ti 1 / 18 )F41 / 6 Cl 1 / 6 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0287] Example 13

[0288] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, aluminum nitrate, and vanadium bromide were dissolved in deionized water in step 1) at a molar ratio of 54:192:10:8:30:22:2 to generate Na 3 / 2 (Ca 5 / 18 Zn 2 / 9 (Ga) 5 / 6 Al 11 / 18 V 1 / 18 )F 41 / 6Br 1 / 6 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0289] Example 14

[0290] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, and sodium sulfide were dissolved in deionized water in a molar ratio of 5:33:3:9:2 in step 1) to generate Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 S 1 / 3 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0291] Example 15

[0292] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, and sodium cyanide were dissolved in deionized water in a ratio of 5:33:3:9:4 in step 1) to generate Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F19 / 3 (CN) 2 / 3 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0293] Example 16

[0294] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, and sodium fluoroborate were dissolved in deionized water in a molar ratio of 5:33:3:9:4 in step 1) to generate Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 (BF4) 2 / 3 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0295] Example 17

[0296] The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, and sodium borohydride were dissolved in deionized water in a molar ratio of 5:33:3:9:4 in step 1) to generate Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 (BH4) 2 / 3 The coating material solution; in step 2), NaNi with a Dv50 particle size of 15 μm is used. 0.4 Fe 0.2 Mn 0.4 O2 is used as the positive electrode active particle.

[0297] Examples 18 to 20

[0298] Batteries of Examples 18, 19, and 20 were prepared in the same manner as in Examples 1, 2, and 9, and the batteries of Examples 18, 19, and 20 were tested at a higher charging cutoff voltage than those of Examples 1, 2, and 19 (see Test Method 4 for charge and discharge test for details). The results are shown in Table 5 below.

[0299] In Examples 2-20 above, the proportion of the coating material in the positive electrode active material is the same as in Example 1.

[0300] Comparative Example 1

[0301] The battery was prepared in the same manner as in Example 1, except that uncoated Na2(Fe) was used. 1 / 3 Co 1 / 3Ni 1 / 3 ) 2+ (Mn 1 / 3 Fe 1 / 3 Co 1 / 3 ) 3+ F7 positive electrode active particles.

[0302] Comparative Example 2

[0303] The battery was prepared in the same manner as in Example 1, except that uncoated NaNi was used. 0.4 Fe 0.2 Mn 0.4 O2 positive electrode active particles.

[0304] Comparative Example 3

[0305] The battery was prepared in the same manner as in Example 1, except that uncoated LiNi was used. 0.8 Co 0.1 Mn 0.1 The positive electrode uses O2 active particles and a lithium metal negative electrode with a thickness of 30 μm. The electrolyte is obtained by mixing 0.05 mol lithium bisfluorosulfonylimide (LiFSI) with 100 mL PreTFSI at 60 °C, cooling to 25 °C, and filtering with a 0.5 m PTFE filter in an argon atmosphere.

[0306] II. Testing Methods

[0307] 1. Characterize the structure of the coated material using XRD:

[0308] 1) Equipment and Instruments

[0309] X-ray source: Cu-Kα (wavelength 1.54178 nm) is commonly used. ).

[0310] Sample stage: Select different types of sample stages according to the sample form (powder, film, bulk).

[0311] 2) Sample preparation

[0312] 2.1) Grinding: Grind the sample into fine powder (particle size <10 µm) in a glove box using a mortar and pestle or a ball mill to improve the quality of the diffraction signal.

[0313] 2.2.) Tableting: Coat the powder evenly on the sample stage, ensuring a smooth surface.

[0314] 3) Test parameter settings

[0315] 3.1) Scan range: 10°–80°.

[0316] 3.2) Step interval: It is recommended to choose 0.1°–0.15° to balance resolution and test time.

[0317] 3.3) Scanning speed: 1°–5° / minute (slower scanning speeds can improve signal quality).

[0318] 3.4) Operating voltage and current: usually set to 40 kV and 40 mA.

[0319] 4) Test Procedure

[0320] 4.1) Equipment calibration: Check whether the XRD instrument is working properly and calibrate the peak position using standard materials (such as Si powder).

[0321] 4.2) Sample installation: Fix the sample on the sample stage to ensure it is stable and does not wobble.

[0322] 4.3) Test condition settings: Input parameters such as scan range, step interval, and scan speed.

[0323] 4.4) Start the test: Start the XRD test and collect diffraction data.

[0324] 5) Data Analysis

[0325] The diffraction data were processed using analysis software such as Jade and HighScore Plus.

[0326] Background subtraction: Removes noise and background signals.

[0327] Peak fitting: Fitting the shape and intensity of diffraction peaks.

[0328] Peak Index: Match diffraction peak positions based on known crystal databases (such as PDF-4+).

[0329] 2. The ionic conductivity and ion diffusion coefficient of the coated positive electrode active material during charge and discharge processes were evaluated using galvanostatic intermittent titration (GITT).

[0330] 1) Material preparation

[0331] Refer to the battery preparation method described above.

[0332] 2) Initial charging

[0333] The battery was charged at a current density of 0.05C until it reached 5V to eliminate the effects of side reactions.

[0334] After pre-charging is complete, let it stand for 30 minutes to allow the battery to stabilize.

[0335] 3) GITT test loop

[0336] Pulse charging: Charge at a current density of 0.05 C for 5 minutes and record the voltage;

[0337] Relaxation phase: Disconnect the current, let stand for 30 minutes, and record the voltage relaxation process;

[0338] Pulse discharge: Discharge at a current density of 0.05 C for 5 minutes and record the voltage;

[0339] Relaxation phase: Disconnect the current, let stand for 30 minutes, and record the voltage relaxation process;

[0340] Repeat the above charge-discharge cycle until the battery reaches the required depth of charge / discharge.

[0341] 4) Data Recording

[0342] Voltage, current, and time data are recorded during each pulse and relaxation phase.

[0343] 5) Data Analysis

[0344] 5.1) Voltage relaxation curve analysis:

[0345] Analyze the battery relaxation curve to determine the voltage change trend over time;

[0346] The chemical diffusion coefficient D of alkali metal ions was calculated by linearly fitting the voltage relaxation curve.

[0347] 5.2) Calculation of ion diffusion coefficient:

[0348] formula: , where L is the electrode thickness and t is the relaxation time;

[0349] The ion diffusion coefficients under different amounts of alkali metal were calculated using voltage relaxation curves under different conditions.

[0350] 5.3) Calculation of ionic conductivity:

[0351] formula: , where N is the number of diffused ions (= the number of alkali metal ions per mole of coating material × the molar amount of coating material), q is the charge of the ions (for alkali metal ions, q=1), V is the total volume of the positive electrode active material, k is the Boltzmann yield, and T is the temperature.

[0352] 3. Measurement of the electrochemical window of the coated material using cyclic voltammetry (CV).

[0353] 1) Instruments and equipment:

[0354] Electrochemical workstations (such as Gamry, Solartron, etc.);

[0355] Three-electrode system: working electrode (such as glassy carbon electrode, platinum electrode, etc.), counter electrode (such as platinum wire), reference electrode (such as saturated calomel electrode or silver / silver chloride electrode);

[0356] Electrolytic cells (such as three-electrode electrolytic cells);

[0357] A constant temperature water bath or constant temperature chamber (optional, used to control the experimental temperature);

[0358] Gas purification devices (such as argon or nitrogen, used to remove oxygen from the solution).

[0359] 2) Reagents and solutions:

[0360] Electrolyte solution: 0.5 mol / L NaFSI dissolved in PreTFSI;

[0361] Test material: The coating material and PVDF binder are mixed at a weight ratio of 9:1. N-methylpyrrolidone is used as a solvent to adjust the solid content to 15-25% to obtain a slurry. The slurry is dropped onto the center of the working electrode (Pt disk) to spread into a uniform film and then vacuum dried.

[0362] 3) Experimental Procedure

[0363] 3.1) Electrode preparation:

[0364] Clean the working electrode to ensure the surface is clean and free of impurities. For glassy carbon electrodes, polishing with alumina slurry is usually required, followed by cleaning with ultrapure water and ethanol.

[0365] The material to be tested is prepared into a thin film and attached to the working electrode.

[0366] 3.2) Solution preparation:

[0367] Prepare the electrolyte solution, ensuring it is free of impurities and oxygen. Argon or nitrogen gas can be used to degas the solution.

[0368] 3.3) Electrode mounting:

[0369] Install the working electrode, counter electrode, and reference electrode into the electrolytic cell, and ensure that the electrodes are properly connected to the electrolytic cell.

[0370] 3.4) Parameter Settings:

[0371] Set the parameters for cyclic voltammetry in the electrochemical workstation software:

[0372] Initial potential: 1 V;

[0373] Upper limit potential: 7 V;

[0374] Lower limit potential: 1 V;

[0375] Scan rate: 10 mV / s;

[0376] Number of iterations: 5 times, to ensure data repeatability and reliability.

[0377] 3.5) Experiment begins:

[0378] Start the electrochemical workstation and begin cyclic voltammetry. The electrode potential increases linearly from the initial potential, then reverses to the lower limit potential after reaching the upper limit potential, completing one cycle.

[0379] 3.6) Data Recording:

[0380] An electrochemical workstation records the curve of electrode current changing with potential, i.e., a cyclic voltammetry diagram.

[0381] 4) Data Analysis

[0382] In a cyclic voltammetry diagram, the oxidation peak is the peak with positive current, and the reduction peak is the peak with negative current.

[0383] Oxidation potential is defined as the peak potential of the oxidation peak, and the oxidation potential is recorded.

[0384] The reduction potential is defined as the peak potential of the reduction peak, and the reduction potential is recorded.

[0385] The difference between the oxidation potential and the reduction potential is the electrochemical window.

[0386] 4. Charge and discharge test

[0387] 1) Samples and equipment

[0388] 1.1) The battery to be tested (see the battery preparation method above);

[0389] 1.2) Battery testing system (Arbin or Marccor);

[0390] 1.3) Temperature control chamber (used to control the temperature of the test environment);

[0391] 1.4) A computer or data logger used to record test data.

[0392] 2) Parameter settings

[0393] 2.1) Voltage range: 1.5-5 V (vs.) );

[0394] 2.2) Multiplier range: C / 20, C / 10, C / 5, C / 2, 1C, 2C, 5C.

[0395] 3) Testing Process

[0396] 3.1) Charge and discharge tests were performed using a battery testing system in a 25°C constant temperature chamber;

[0397] 3.2) Charge at a constant current rate of 1C to the cutoff voltage, then charge at a constant voltage to the C / 20 cutoff. After standing for 0.5 hours, discharge at a 1C rate to the termination voltage (wherein, in Example 1 and Comparative Example 1 below, the cutoff voltage is 5V; in Examples 2-17 and Comparative Examples 2-3, the cutoff voltage is 4.3V; in Example 18, the cutoff voltage is 5.5V; in Examples 19-20, the cutoff voltage is 4.7V; in Examples 1-20 and Comparative Examples 1-3, the termination voltage is 1.5V).

[0398] 3.3) The battery was charged and discharged at C / 20, C / 10, C / 5, C / 2, 1C, 2C and 5C rates respectively, with 5 cycles at each rate;

[0399] 3.4) Record voltage, current and time data.

[0400] 4) Data Analysis

[0401] Specific capacity (mAh / g) = Discharge capacity (mAh) / Mass of active material (g)

[0402] Wherein, discharge capacity (mAh) = current intensity (mA) × discharge time (h),

[0403] For example, 0.1C specific capacity (mAh / g) = [current intensity at 0.1C rate (mA) × discharge time at 0.1C rate (h)] / mass of active material (g).

[0404] 2C specific capacity (mAh / g) = [current intensity at 2C rate (mA) × discharge time at 2C rate (h)] / mass of active material (g);

[0405] First-week coulomb efficiency = (First-week discharge capacity / Charge capacity) × 100%

[0406] Average operating voltage: obtained from the voltage curve (voltage-capacity curve) measured at a C / 20 ratio.

[0407] Average operating voltage = Where V is voltage and Q is capacitance. That is the maximum capacity.

[0408] 5. Gas release test

[0409] In a glove box filled with argon gas, individual battery cells are charged to a cutoff voltage of 5V at a current density of 0.1C, and the release of oxygen and carbon dioxide is monitored in real time using a gas detection device.

[0410] III. Results Analysis of Examples and Comparative Examples

[0411] Table 1: Reaction energies (eV / atom) of coating materials and commonly used coating materials with electrolyte in the embodiments, calculated according to the calculation method described in the "Detailed Embodiments" section.

[0412]

[0413] As can be seen from the results in Table 1, compared with LiNbO3, Li3PO4, and LATP, the absolute value of the reaction energy between the fluoride coating material of the present invention and the electrolyte is lower (the more negative the reaction energy, the more vigorous the reaction). This indicates that the coating material of the present invention has better compatibility with the electrolyte than LiNbO3, Li3PO4, and LATP. Furthermore, the absolute value of the reaction energy between the fluoride coating material of the present invention and some electrolytes is even comparable to that of LiF and Li2ZrF6. This shows that the fluoride coating material of the present invention can replace commonly used LiF and Li2ZrF6 coating materials to achieve good battery cycle stability without the disadvantages of LiF and Li2ZrF6.

[0414] Table 2: Electrochemical windows of coating materials and commonly used coating materials in the examples, calculated using the giant potential phase diagram method described in the "Detailed Embodiments" section.

[0415]

[0416] As can be seen from the results in Table 2, compared with commonly used coating materials, the coating material of the perfluorinated anion framework of the present invention has a considerable, or even wider, electrochemical window, which can cover the working range of high-voltage cathode (working voltage, for example, higher than 5 V) and electrolyte. This indicates that the coating material of the present invention has good electrochemical stability and can avoid electrochemical side reactions between high-voltage cathode and electrolyte.

[0417] Table 3: Room temperature ionic conductivity and room temperature alkali metal ion diffusion coefficient of the coating materials and commonly used coating materials in the embodiments obtained by the AC impedance method described in the "Detailed Embodiments" section.

[0418]

[0419] As can be seen from the results in Table 3, the room temperature ionic conductivity of the coating material of the present invention is within 10. -5The S / cm magnitude indicates that the alkali metal ion diffusion capacity is significantly stronger than that of LiF and Li₂ZrF₆, and comparable to that of layered oxide cathodes (10). -5 The S / cm indicates that the coating material of this invention has potential fast-charging capability and will not adversely affect the rate performance of the battery. The loose structure of LATP material is conducive to the transport of alkali metal ions, so it has a high ionic conductivity. However, LATP has poor stability, a narrow electrochemical window, and cannot suppress side reactions at the interface between the high-voltage cathode and the electrolyte.

[0420] Table 4: Mechanical modulus of the coating material and commonly used coating materials in the embodiments, calculated according to the relevant calculation methods described in the "Detailed Implementation" section.

[0421]

[0422] As can be seen from the results in Table 4, the mechanical modulus of the coating material of the present invention is lower than that of LiF, Li2ZrF6, LiNbO3, and Li3PO4. This indicates that the fluoride coating material of the present invention is softer and easier to process than commonly used fluorides and oxides. It is not easily broken during rolling and cycling, and will not have an adverse effect on the efficiency and capacity of the cathode material.

[0423] Table 5: Performance test results of the examples and comparative examples

[0424]

[0425] The results in the table above show that, compared to uncoated positive electrode active particles, the positive electrode active particles coated with the coating material of this invention can improve the first-cycle coulombic efficiency, rate performance, cycle stability, and safety of the battery. In particular, the results of O2 and CO2 release show that, for high-voltage oxide positive electrodes (NaNi... 0.4 Fe 0.2 Mn 0.4 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2), the coating material of the present invention can effectively improve battery thermal runaway under high charge state and improve battery safety. In addition, as can be seen from the comparison of Examples 18, 19 and 20 with Comparative Examples 1, 2 and 3, after coating the positive electrode active particles with the coating material of the present invention, the coated positive electrode active particles can operate at a higher voltage and achieve an improvement in battery capacity.

[0426] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A secondary battery comprising a positive electrode sheet comprising a positive electrode active material, characterized by, The positive electrode active material includes positive electrode active particles and a fluoride coating material coating at least part of surfaces of the positive electrode active particles, the fluoride coating material including a compound represented by Formula I: A 7-(2n+3m) M n M' m F 7-x R x / y Formula I wherein 0 < n < 2, 0 < m < 2, 0 < x < 2, y is an absolute value of a valence of R; A includes Na and / or Li; M includes at least one of Ca, Zn, Mg, Sr, and Ba; M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4; and M further includes, based on total moles of M, not more than 10 mol% of at least one of elements of A and at least one of elements of M'.

2. The secondary battery according to claim 1, characterized by M further includes, based on total moles of M, not more than 10 mol% of a first transition metal element, wherein the first transition metal element includes at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

3. The secondary battery according to claim 1 or 2, characterized by M' further includes, based on total moles of M', not more than 10 mol% of a second transition metal element, wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

4. The secondary battery according to claim 1 or 2, characterized by A further includes, based on total moles of A, not more than 20 mol% of K and / or Ag.

5. The secondary battery according to claim 1 or 2, characterized by M includes at least one of Ca, Zn, and Mg.

6. The secondary battery according to claim 1 or 2, characterized by M' includes at least one of Ga and Al.

7. The secondary battery according to claim 1 or 2, characterized by The positive electrode active material includes 0.01 to 10 wt% of the fluoride coating material, based on total weight of the positive electrode active material.

8. The secondary battery according to claim 1 or 2, characterized by The fluoride coating material has a coating thickness of 5 to 20 nm.

9. The secondary battery according to claim 1 or 2, characterized by The positive electrode active particles include at least one of a layered oxide material, a spinel oxide material, and a fluoride material, wherein: The layered oxide material includes a compound represented by Formula II: A 1 M a O 2-e / 2 R 1 e / f Formula II In formula II, 0 < e < 0.2, f is the absolute value of the valence state of R 1 , A 1 comprising Li or Na, M a comprising a transition metal element, R 1 comprising at least one of F, Cl; The spinel oxide material includes a compound represented by Formula III: A 2 M b 2O 4-g / 2 R 2 g / h Formula III In formula III, 0 < g < 0.4, h is the absolute value of the valence state of R 2 , and i is the absolute value of the valence state of R A 2 comprising Li or Na, M b comprising a transition metal element, R 2 comprising at least one of F, Cl; The fluoride material includes a compound represented by Formula IV: A 3 7-2k-3p M c k M d p F 7-i R 3 (i / j) Formula IV In formula IV, 0 < k < 2, 0 < p < 2, 0 < i < 2, j is the absolute value of the valence of R 3 , A 3 comprising Li or Na, M c comprising a transition metal element having a divalent valence, M d comprising a transition metal element having a trivalent valence, R 3 comprising at least one of F, Cl.

10. The secondary battery according to claim 1 or 2, characterized by The positive electrode active material has one or more of the following characteristics: (1) the positive electrode active material has a Dv50 particle size in a range of 5 to 30 pm; (2) the BET specific surface area of the positive electrode active material is in the range of 0.1 to 14 m 2 / g. (3) the tap density of the positive electrode active material is 1.1 to 2.3 g / cm 3 ; (4) the positive electrode active material has a hardness in a range of 6 to 12 GPa.

11. The secondary battery according to claim 1 or 2, characterized by The positive electrode tab includes a current collector and a positive electrode film layer disposed on at least one surface of the current collector, the positive electrode film layer including 70 wt% to 98 wt% of the positive electrode active material, based on total weight of the positive electrode film layer.

12. The secondary battery according to claim 11, characterized by The positive electrode film layer further includes, based on total weight of the positive electrode film layer, a total of 2 wt% to 30 wt% of a binder.

13. The secondary battery according to claim 1 or 2, characterized by The compacted density of the positive electrode plate is 2.3 g / cm 3 to 3.7 g / cm 3 .

14. A positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, characterized in that, The fluoride coating material includes a compound represented by Formula I: A 7-(2n+3m) M n M' m F 7-x R x / y Formula I; wherein 0 < n < 2, 0 < m < 2, 0 < x < 2, y is an absolute value of a valence of R; A includes Na and / or Li; M includes at least one of Ca, Zn, Mg, Sr, and Ba; M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4; and M further comprises, based on total moles of M, not more than 10 mol% of elements of at least one A and elements of at least one M'.

15. The positive electrode active material according to claim 14, characterized by M further comprises, based on total moles of M, not more than 10 mol% of a first transition metal element, wherein the first transition metal element comprises at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, V.

16. The positive electrode active material according to claim 14 or 15, characterized by M' further comprises, based on total moles of M', not more than 10 mol% of a second transition metal element, wherein the second transition metal element comprises at least one of Fe, Co, Ni, Mn, V, Ti, Cr.

17. The positive electrode active material according to claim 14 or 15, characterized by The positive electrode active material comprises 0.01 to 10 wt% of a fluoride coating material, based on the total weight of the positive electrode active material.

18. The positive electrode active material according to claim 14 or 15, characterized by The fluoride coating material has a coating thickness of 5 to 20 nm.

19. An electrical device, comprising: A secondary battery comprising the secondary battery according to any one of claims 1 to 13 or the positive electrode active material according to any one of claims 14 to 18.

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