Positive electrode active materials and their preparation, positive electrode sheets and secondary batteries

Abstract

This application provides a positive electrode active material comprising a positive electrode bulk material and a coating layer covering its surface, wherein the coating layer is composed of a material with the molecular formula Li. a MF x Cl (a+n‑x) The compound composition, M, a, n, and x, are as defined in the specification. Starting from the surface of the positive electrode material and extending towards the outermost edge of the coating layer, the proportion of F in the compound gradually decreases, while the proportion of Cl in the compound gradually increases. This application also provides a method for preparing the aforementioned positive electrode active material, as well as a positive electrode sheet and a lithium secondary battery including the same. Using the positive electrode active material provided in this application can reduce battery resistance and improve battery capacity retention.

Description

Technical Field

[0001] This application relates to a positive electrode active material. Furthermore, this application also relates to a method for preparing the said positive electrode active material, a positive electrode sheet prepared therefrom, and a secondary battery. Background Technology

[0002] In recent years, with the increasingly widespread application of secondary ion batteries, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of secondary ion batteries, higher requirements have been placed on their positive electrode active materials.

[0003] Coating positive electrode active materials is a common method to improve battery performance and has been a research topic for a long time. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material with good stability and a secondary battery with low impedance and high capacity retention.

[0005] To achieve the above objectives, a first aspect of this application provides a positive electrode active material, comprising a positive electrode bulk material and a coating layer covering the surface of the positive electrode bulk material, wherein the coating layer is composed of a material with the molecular formula Li. a MF x Cl (a+n-x) The composition of the compounds, in which

[0006] 1≤a≤3, 0≤x≤a+n; n is the valence state of the M ion, and n is in the range of 2-4.

[0007] M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb.

[0008] Specifically, starting from the surface of the positive electrode body material, and extending outwards to the outermost part of the coating layer, the F element in the molecular formula Li a MF x Cl (a+n-x) The proportion of Cl in the compound gradually decreases, and the element in the molecular formula Li a MF x Cl (a+n-x) The proportion of these compounds gradually increases.

[0009] The coating layer described in this application serves as a "blocking" and "barrier," combining the advantages of fluoride and chloride coating layers while mitigating their disadvantages to a certain extent. Furthermore, this application employs a fluorine-rich compound in areas with higher levels of transition metal ions within the coating layer, and a less fluorine-rich compound in areas with lower levels of transition metal ions on the outer surface. This allows for more targeted and effective complexation of fluorine and transition metal ions, thereby more effectively preventing the leakage of transition metal ions. Additionally, the application uses a method where the fluorine content gradually decreases from the inside out, while the chloride content gradually increases from the inside out, which is more conducive to the smooth migration and deintercalation of lithium ions, thus improving lithium-ion conductivity.

[0010] Since the modified positive electrode active material of this application has the above-mentioned beneficial effects, it can improve the capacity retention of the battery and reduce the impedance of the positive electrode active material and the corresponding impedance of the battery.

[0011] In any embodiment, the gradient of the F element content from large to small along the direction extending outward to the outermost edge of the coating layer, i.e., the gradient of x from a+n→0, is (a+n) / (h / b), where h is the coating layer thickness and b is the minimum thickness at which the gradient change occurs; wherein h is in the range of 0-5 nm; b is in the range of 0-0.5 nm, and optionally in the range of 0.1-0.5 nm. Correspondingly, the gradient of the C1 element content from small to large along the direction extending outward to the outermost edge of the coating layer, i.e., the gradient of a+nx from 0→a+n, is (a+n) / (h / b).

[0012] The fluorine and chlorine content in the coating layer changes uniformly through a gradient, resulting in a more uniform variation in fluorine and chlorine content. This is more conducive to the precise capture of transition metal ions generated by the cathode material and to the smooth intercalation and deintercalation of lithium.

[0013] In any embodiment, the material of the coating layer is selected from Li3InF. x Cl (6-x) 、Li3YF x Cl (6-x) Li3ScF x Cl (6-x) Li3MnF x Cl (6-x) Li3ZrF x Cl (6-x) At least one of the following, where 0 ≤ x ≤ 6.

[0014] In any embodiment, the electrochemical window of the positive electrode active material is 5.0V or higher, and / or the lithium-ion conductivity of the positive electrode active material is 10.-8 -10 -3 S / cm.

[0015] In any embodiment, the positive electrode body material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.

[0016] A second aspect of this application provides a method for preparing a positive electrode active material, the method comprising a coating step, the coating step including:

[0017] (1) Prepare or prepare the positive electrode material;

[0018] (2) Li under an inert atmosphere a MF x Cl (a+n-x) The source is vaporized, optionally at a vaporization temperature of 200-300°C; the vaporized source is adsorbed and deposited on the surface of the positive electrode body material to coat the positive electrode body material, thereby obtaining the positive electrode active material.

[0019] Among them, the molecular formula Li a MF x Cl (a+n-x) middle,

[0020] 1≤a≤3, 0≤x≤a+n; n is the valence state of the M ion, and n is in the range of 2-4.

[0021] M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb.

[0022] Specifically, starting from the surface of the positive electrode body material, and extending outwards to the outermost part of the coating layer, the F element in the molecular formula Li a MF x Cl (a+n-x) The proportion of Cl in the compound gradually decreases, and the element in the molecular formula Li a MF x Cl (a+n-x) The proportion of these compounds gradually increases.

[0023] In any embodiment, the method for adsorbing and depositing the vaporized source onto the surface of the positive electrode material is atomic deposition. Optionally, the number of depositions is m, where m ranges from 1 to 100.

[0024] In any implementation, the Li a MF x Cl (a+n-x) The sources include lithium sources, M sources, fluorine sources, and chlorine sources, wherein the boiling points of each source are between 70 and 300°C.

[0025] Optionally, the lithium source includes one or more of lithium halides, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester.

[0026] Optionally, the source of M includes one or more of the following: alkyl metals, carboxylic acid metals, alcohol metals, and ester metals of element M;

[0027] Optionally, the fluorine source includes one or more of fluoroalkanes, fluorocarboxylic acids, fluoroalcohols, and fluoroesters;

[0028] Optionally, the chlorine source includes one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols, and chlorinated esters.

[0029] The coating described in this application can be achieved using atomic layer deposition (ALD), a method based on ordered surface self-saturation chemical vapor deposition of thin films. It can form a deposition layer several atoms thick on the surface of the cathode material to achieve uniform coating, and can achieve precise control over the gradient of fluorine and chlorine elements and the coating thickness.

[0030] In any embodiment, after the coating step, the resulting coated positive electrode material is calcined. Optionally, the calcination temperature is 150-300℃ and the calcination time is 4-20h.

[0031] Calcination after coating can reduce the impedance of the positive electrode active material, improve the stability of the material, and improve the rate performance, capacity retention and cycle stability of the resulting battery cell.

[0032] A third aspect of this application provides a secondary battery comprising the positive electrode active material described in the first aspect of this application or the positive electrode active material prepared according to the method described in the second aspect of this application.

[0033] In any embodiment, the secondary battery includes an electrolyte comprising lithium hexafluorophosphate and / or lithium perchlorate. Attached Figure Description

[0034] Figure 1 This is a scanning electron microscope (SEM) image of the positive electrode active material particles prepared in Example 1 after surface coating.

[0035] Figure 2 The image shows a SEM image of the positive electrode active material particles prepared in Example 1 after surface coating. Figure 1 A magnified view of a portion of the image. Detailed Implementation

[0036] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, the positive electrode sheet, and the secondary battery of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0037] The "range" disclosed in this application 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 a 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 also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-6. In this application, 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 article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated 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.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating 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.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application 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.

[0042] Unless otherwise specified, the term "or" is inclusive in this application. 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).

[0043] During battery use, under high voltage or high temperature conditions, the positive electrode active material is susceptible to corrosion by H2O and HF in the electrolyte, and irreversible changes in the crystal lattice may occur during lithium insertion / extraction, causing the generated transition metal ions to dissolve. These dissolved transition metal ions easily migrate to the negative electrode surface and are reduced back to metal. Such metals readily catalyze and decompose the SEI film, and consume active lithium, leading to a continuous deterioration in electrical performance. To address these issues, halides of transition metals or other metals can currently be used to coat the positive electrode active material. However, when using fluorides to coat the positive electrode active material, the fluoride coating is air-sensitive and easily absorbs water, thus easily undergoing irreversible hydrolysis and subsequent failure. When using chlorides to coat the positive electrode active material, the chloride coating has a low electrochemical window and poor stability under high voltage. Furthermore, when using halides for coating, the cathode material particles are typically first mechanically crushed before coating. However, the particle size of the cathode active material is approximately 2 μm, resulting in a coating thickness generally exceeding 2 μm. Such a thickness significantly increases the electron transport resistance between the positive and negative electrode materials, increasing ohmic impedance and leading to poor conductivity of the cathode material. To address these issues, the inventors of this application, after extensive research, proposed a scheme using substances containing both fluorine and chlorine to coat the cathode material. This scheme combines the advantages of fluorides and chlorides while avoiding their disadvantages. Moreover, by gradually decreasing or increasing the amount of fluorine and chlorine elements in the coating layer, the migration and deintercalation of lithium ions within the coating layer are facilitated, reducing the impedance of the cathode material. Additionally, the proposed scheme achieves an ultra-thin thickness, further reducing the impedance of the cathode material.

[0044] To address the aforementioned problems, a first aspect of this application provides a positive electrode active material, comprising a positive electrode bulk material and a coating layer covering the surface of the positive electrode bulk material, wherein the coating layer is composed of a material with the molecular formula Li. a MF x Cl (a+n-x) The composition of the compounds, in which

[0045] 1≤a≤3, 0≤x≤a+n; n is the valence state of the M ion, and n is in the range of 2-4.

[0046] M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb.

[0047] Specifically, starting from the surface of the positive electrode body material, and extending outwards to the outermost part of the coating layer, the F element in the molecular formula Li a MF x Cl (a+n-x)The proportion of Cl in the compound gradually decreases, and the element in the molecular formula Li a MF x Cl (a+n-x) The proportion of these compounds gradually increases.

[0048] In this application, the material that plays a major role in the positive electrode is referred to as the "positive electrode body material" or "positive electrode body active material".

[0049] The coating layer described in this application serves to "block" and "isolate." Specifically, during several charge-discharge cycles of a lithium-ion battery, the positive electrode active material inevitably generates transition metal ions. Furthermore, after several charge-discharge cycles, the electrolyte in the electrolyte solution decomposes, potentially producing water and highly corrosive substances (such as hydrofluoric acid). If the positive electrode material comes into direct contact with the corrosive electrolyte, it will be directly corroded, decomposing and generating even more transition metal ions. The coating layer described in this application effectively prevents transition metal ions generated by the positive electrode active material during battery charge-discharge from directly entering the electrolyte, thus acting as a "block." It also prevents the positive electrode material from directly contacting the electrolyte and being corroded, thereby generating even more transition metal ions, thus acting as a "isolate." This reduces the number of transition metal ions in the battery system and significantly slows down the corrosive decomposition of the positive electrode material by corrosive substances, thereby improving battery performance.

[0050] According to this application, a halide containing both fluorine and chlorine is used to coat the positive electrode bulk material, forming a material with the molecular formula Li. a MF x Cl (a+n-x) The coating layer is composed of substances. Furthermore, according to this application, the amount of fluorine in the coating layer gradually decreases (x gradually decreases) from the inside out, while the amount of chlorine gradually increases from the inside out. Thus, the advantages of both fluoride and chloride coating layers are combined while their disadvantages are avoided to a certain extent.

[0051] Specifically, in this application, when a fluoride coating is used, during battery use, the fluorine in the coating of the positive electrode active material migrates into the interior of the positive electrode body material to form a transition layer. This reduces the migration energy of Li ions and stabilizes lattice oxygen, thereby improving the lithium-ion conductivity and structural stability of the positive electrode active material, and also improving the capacity retention of the lithium-ion battery. Furthermore, fluoride ions can complex with transition metal ions, thus reducing the number of transition metal ions already generated inside the battery through chemical reactions or adsorption effects, thereby preventing transition metal ion overflow. Additionally, fluorides have a high electrochemical window (>6.0V), and their coating of the positive electrode body material can improve the lithium-ion stability of the positive electrode active material and protect it from structural instability even at a high voltage of 4.6V. However, fluorides are air-sensitive and easily absorb water, leading to irreversible hydrolysis and failure. When using a chloride coating, the chloride solid electrolyte has an extremely high lithium-ion conductivity (>10). -3 The chloride coating has a conductivity of S / cm, allowing lithium ions to rapidly penetrate the chloride layer during charging and discharging, thus increasing the rate of lithium ion extraction and insertion and reducing the impedance of the positive electrode active material. Furthermore, chloride exhibits good air stability, recovering from water absorption by reheating and drying. It also protects the internal fluoride from contact with external air and prevents it from failing. Therefore, in the coating layer, using a coating material with less chloride and more fluoride closer to the positive electrode material effectively utilizes the aforementioned effects of fluoride, improving the stability of the positive electrode active material and increasing the battery's capacity retention. Conversely, using a coating material with more chloride and less fluoride further away from the positive electrode material and closer to the outer edge of the coating layer utilizes the air stability of chloride to protect the internal fluoride from contact with external air and prevent failure, thereby stabilizing the internal fluorine-containing coating material and achieving coating layer stability. The ultra-high conductivity of chloride also reduces the impedance of the positive electrode active material.

[0052] Further analysis revealed that when transition metal ions generated by the positive electrode active material leak out, they first enter the coating layer. Therefore, the innermost layer of the coating layer on the surface of the positive electrode material contains a higher concentration of transition metal ions, which gradually decreases outwards from the coating layer. Based on this principle, this application designs a coating layer with a higher fluorine content in areas with a higher concentration of transition metal ions inside the coating layer, and a coating layer with a lower concentration of transition metal ions in areas with a lower concentration of transition metal ions on the outer side of the coating layer. That is, the fluorine content is highest at the innermost part of the coating layer, and gradually decreases outwards from the coating layer. This allows for more targeted and effective complexation between fluorine and transition metal ions, thus more effectively preventing the leakage of transition metal ions. Furthermore, the application of a gradual decrease in fluorine content and a gradual increase in chlorine content from the inside out is more conducive to the smooth migration and deintercalation of lithium ions, and improves lithium-ion conductivity.

[0053] Optionally, the part of the coating closest to the positive electrode material contains only fluorine and no chlorine, while the outermost part of the coating contains only chlorine and no fluorine.

[0054] Because the modified positive electrode active material of this application has the above-mentioned beneficial effects, it can slow down the generation of transition metals and their catalytic decomposition on the negative electrode SEI film (if any) during battery storage or use, thereby improving the battery capacity retention rate and reducing battery impedance.

[0055] It should be understood that in this application, the changes in fluorine and chlorine elements in the coating layer can be achieved by any means, as long as the trend of fluorine content gradually decreasing from the inside to the outside and chlorine content gradually increasing from the inside to the outside is satisfied.

[0056] like Figure 1 As shown, the large particles are the cathode material NCM811, with an outer coating layer. A large field of view shows the cathode particles are completely coated. The coating layer is magnified (…). Figure 2 It can be observed that the coating layer is uniform and dense, with no missing areas. This proves that the coating layer in the positive electrode active material of this application is uniform, dense, and relatively complete.

[0057] In some embodiments, the gradient of the F element content from large to small along the direction extending outward to the outermost edge of the coating layer, i.e., the gradient of x from a+n→0, is (a+n) / (h / b), where h is the coating layer thickness and b is the minimum thickness at which the gradient change occurs; wherein h is in the range of 0-5 nm, optionally in the range of 0.5-5 nm; and b is in the range of 0-0.5 nm, optionally in the range of 0.1-0.5 nm. Correspondingly, the gradient of the Cl element content from small to large along the direction extending outward to the outermost edge of the coating layer, i.e., the gradient of a+nx from 0→a+n, is (a+n) / (h / b).

[0058] The fluorine and chlorine content in the coating layer changes uniformly through a gradient, resulting in a more uniform variation in fluorine and chlorine content. This is more conducive to the precise capture of transition metal ions generated by the cathode material and to the smooth intercalation and deintercalation of lithium.

[0059] In some optional embodiments, the content of element F decreases from large to small along the direction extending outward to the outermost part of the coating layer, that is, the gradient of x from a+n→0, is in the range of (a+n) / (h / 0.1) to (a+n) / (h / 0.5), where h is the thickness of the coating layer, and h is in the range of 0-5nm, optionally in the range of 0.5-5nm.

[0060] Optionally, when preparing the gradient coating layer, the F element content variation gradient is changed every 0.1nm-0.5nm of thickness, and the gradient change amount is (a+n) / (h / 0.1) to (a+n) / (h / 0.5) each time.

[0061] Correspondingly, as the concentration of Cl increases in the direction extending outward to the outermost part of the coating layer, i.e., the gradient of a+nx from 0 to a+n, is also within the range of (a+n) / (h / 0.1) to (a+n) / (h / 0.5).

[0062] The gradual gradient of fluorine and chlorine elements reduces the grain boundary resistance inside the coating layer, thereby reducing the impedance of the positive electrode active material and the corresponding battery impedance, further improving the cycle stability of the battery.

[0063] In some alternative implementations, the coating thickness is in the range of 0.5-5 nm.

[0064] The thickness of the coating layer significantly affects the overall battery performance, such as impedance, cycle stability, and rate performance. Commonly used solid-state coating methods achieve coating thicknesses in the micrometer range, leading to a significant decrease in both lithium-ion and electronic conductivity, resulting in higher impedance of the positive electrode active material. The coating layer described in this application is an ultra-thin coating layer, between 0.5 and 5 nm. Coating layers within this range can effectively cover the surface of the positive electrode material while simultaneously ensuring the material's theoretical energy density and impedance. However, when the coating layer thickness is less than 0.5 nm, it is too thin and cannot completely cover the sample surface, easily causing gaps in the coating and resulting in poor material performance consistency. When the coating layer thickness is greater than 5 nm, it is too thick, reducing the material's theoretical energy density and increasing the material's impedance, as well as the corresponding battery impedance.

[0065] In some embodiments, the material of the coating layer is selected from Li3InF. x Cl (6-x) 、Li3YF x Cl (6-x) Li3ScF x Cl (6-x) Li3MnF x Cl (6-x) ,Li3ZrFxCl (6-x) At least one of the following, where 0 ≤ x ≤ 6.

[0066] In some embodiments, the electrochemical window of the positive electrode active material is above 5.0V, and / or the lithium-ion conductivity of the positive electrode active material is 10. -8 -10 -3 S / cm.

[0067] The electrochemical window can be tested using the linear voltammetry module of an electrochemical workstation. Specifically, the following method can be used: the positive electrode active material to be tested is mixed with the binder PVDF at a mass ratio of 95:5, dissolved in a solvent (e.g., N-methylpyrrolidone (NMP)), the concentration of which is not limited, and then dropped onto the surface of a glassy carbon electrode as the working electrode; then, a battery system (also called an electrolytic cell) is assembled using 1M LiPF6 as a solution and a lithium sheet as the counter electrode. The voltammetry curve of the battery system is then tested, with the voltage range set to 2.5–5V and the scan rate set to 0.5mV / s. The recorded oxidation potential is the electrochemical window.

[0068] The ionic conductivity σ = 1 / ρ, where ρ can be obtained by solving R = h / (ρs); R is the AC impedance, which is measured using an electrochemical workstation impedance testing module. The voltage perturbation mode PEIS is set, the perturbation voltage is 5mV, and the frequency range is 200kHz~30MHz. The impedance of the positive electrode active material sheet is then measured to obtain R; where h is the thickness of the solid electrolyte sheet and s is the area of ​​the solid electrolyte sheet. Furthermore, the solid electrolyte is an ionic conductor and not conductive to electrons. Therefore, before impedance testing, blocked Ag electrodes need to be connected to both sides of the electrolyte sheet, as follows: the two sides of the solid electrolyte are polished to a certain thickness, silver paste is applied to it to draw Ag wires, and then Ag is burned in a muffle furnace to ensure close contact between the Ag electrodes and the electrolyte surface. The measured resistance R = h / (ρs) is used to solve for ρ, and then the ionic conductivity σ is obtained using σ = 1 / ρ.

[0069] In some embodiments, the positive electrode body material is selected from at least one of ternary active materials, lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide.

[0070] The ternary active material is any ternary material used in this field, including, but not limited to, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, etc.

[0071] A second aspect of this application provides a method for preparing a positive electrode active material, the method comprising a coating step, the coating step including:

[0072] (1) Prepare or prepare the positive electrode material;

[0073] (2) Li under an inert atmosphere a MF x Cl (a+n-x) The source is vaporized, optionally at a vaporization temperature of 200-300°C; the vaporized source is adsorbed and deposited on the surface of the positive electrode body material to coat the positive electrode body material, thereby obtaining the positive electrode active material.

[0074] Among them, the molecular formula Li a MF x Cl (a+n-x) middle,

[0075] 1≤a≤3, 0≤x≤a+n; n is the valence state of the M ion, and n is in the range of 2-4.

[0076] M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, and Nb.

[0077] Specifically, starting from the surface of the positive electrode body material, and extending outwards to the outermost part of the coating layer, the F element in the molecular formula Lia MF x Cl (a+n-x) The proportion of Cl in the compound gradually decreases, and the element in the molecular formula Li a MF x Cl (a+n-x) The proportion of these compounds gradually increases.

[0078] The cathode material can be prepared before the coating layer is prepared, or it can be purchased.

[0079] In some embodiments, the method for adsorbing and depositing the vaporized source onto the surface of the cathode material is atomic deposition. Optionally, the number of depositions is m, where m ranges from 1 to 100.

[0080] In some alternative embodiments, in step (2), atomic deposition is used for deposition. Each deposition is called a cycle, and a total of m cycles are performed, where m ranges from h / 0.1 to h / 0.5, and h is defined as described above. The deposition thickness in each cycle is 0.1-0.5 nm. For the k-th cycle, 1 ≤ k ≤ m, Li is used. a MF x Cl (a+n-x) The source is used for deposition, where x is (mk)×(a+n) / m, and a and n are as defined above.

[0081] In some embodiments, the Li a MF x Cl (a+n-x) The sources include lithium sources, M sources, fluorine sources, and chlorine sources, wherein the boiling points of each source are between 70 and 300°C.

[0082] Lithium sources include, but are not limited to, one or more of lithium halides, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester, such as lithium tert-butoxide.

[0083] The sources of M include, but are not limited to, one or more of the alkyl metals, carboxylic acid metals, alcohol metals, and ester metals of element M, with boiling points between 70 and 300 °C.

[0084] Fluorine sources include, but are not limited to, one or more of fluoroalkanes, fluorocarboxylic acids, fluoroalcohols, and fluoroesters. The fluoroesters include fluoroethylene carbonate.

[0085] The chlorine source includes, but is not limited to, one or more of chlorinated alkanes, chlorinated carboxylic acids, chlorinated alcohols, and chlorinated esters. The chlorinated esters include chloroethylene carbonate.

[0086] In this application, the Li a MF x Cl (a+n-x) The source can also be called a "precursor".

[0087] The coating can be achieved using atomic layer deposition (ALD), a method based on ordered surface self-saturation chemical vapor deposition of thin films. AALD can form a deposition layer several atoms thick on the surface of the cathode material to achieve uniform coating. The main steps of this method include: alternately pulsedly introducing gaseous precursors into the reactor, allowing them to chemically adsorb and react on the deposition substrate to form a deposited film. When the precursors reach the surface of the deposition substrate, they chemically adsorb and react on the surface. The AALD reactor needs to be purged with an inert gas between precursor pulses. Therefore, by adjusting the pulse time of the gaseous precursors (e.g., chlorine and fluorine sources) and setting appropriate parameter programs as needed, the deposition ratio of the two halide sources in the coating can be precisely adjusted to form a gradient coating. Each deposition layer is approximately 0.1 nm thick, with a maximum thickness of 0.5 nm. Thus, the coating thickness can be precisely controlled by adjusting the number of deposition cycles.

[0088] Furthermore, for the coating of the cathode bulk material, its coating thickness and uniformity directly affect the performance of the cathode active material. Atomic layer deposition (ALD) allows for precise control of the coating thickness; for example, an ultrathin coating thickness of approximately 0.5 nm can be achieved. In this method, the deposited material (i.e., the aforementioned sources) is vaporized, ensuring complete contact between the vaporized material and the cathode bulk material surface, resulting in more uniform and complete coating and avoiding coating defects. Additionally, the pulse alternation program for the deposited gaseous precursor can be pre-set, allowing for flexible adjustment of the deposited material quantity to create the desired halogen concentration gradient distribution. This method is simple and easy to optimize.

[0089] In some embodiments, after the coating step, the resulting coated positive electrode material is calcined. Optionally, the calcination temperature is 150-300°C and the calcination time is 4-20 hours.

[0090] The calcination can be carried out under an inert atmosphere, such as argon or nitrogen.

[0091] Calcination of the material after coating has the following effects:

[0092] (1) During the calcination process, it helps F elements migrate into the interior of the cathode material, forming a spinel-like transition layer as a connecting link, reducing the interfacial resistance at the interface between the coating layer and the cathode material, and reducing the migration energy of Li ions and stabilizing lattice oxygen.

[0093] (2) Calcination can improve the crystallinity of the coating material and form a cubic dense packing structure (CCP), which helps to form 3D lithium-ion transport channels, thereby reducing material impedance and battery impedance and improving the rate performance and cycle stability of the obtained cell.

[0094] (3) Calcination also helps to achieve better atomic fusion at the junction of the positive electrode and the inner fluoride layer, and at the junction of the inner and outer coatings, forming a transition layer, reducing the grain boundary resistance caused by the coating interface, thereby reducing the impedance of the material and the impedance of the battery.

[0095] (4) High-temperature calcination will further improve the crystallinity and coating stability of crystalline materials.

[0096] One aspect of this application also provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, said positive electrode film layer including the positive electrode active material described in the first aspect of this application or the positive electrode active material prepared by the method described in the second aspect of this application.

[0097] A third aspect of this application provides a secondary battery comprising the positive electrode active material described in the first aspect of this application or the positive electrode active material prepared by the method described in the second aspect of this application. The secondary battery may be in the form of a single battery cell, a battery module, or a battery pack.

[0098] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0099] [Positive electrode plate]

[0100] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application.

[0101] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0102] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the positive electrode body material used for coating may be a known positive electrode active material for batteries. As an example, the positive electrode body material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode body materials may also be used. These positive electrode body materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi1 / 3Co). 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. Optionally, as described above, the cathode body material is selected from at least one of ternary cathode active material systems, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0104] It should be understood that, in addition to using the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method described in the second aspect of this application, other positive electrode active materials known in the art may also be used in the positive electrode sheet.

[0105] 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.

[0106] 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.

[0107] In the positive electrode film layer, the positive electrode active material described in this application accounts for 70-98% by mass, optionally 90% by mass; the binder accounts for 1-15% by mass, and the conductive agent accounts for 1-15% by mass, all based on the total mass of the positive electrode film.

[0108] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0109] [Negative electrode plate]

[0110] 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.

[0111] 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.

[0112] 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.).

[0113] 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, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0114] 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).

[0115] 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, graphene, and carbon nanofibers.

[0116] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0117] In the negative electrode film layer, the mass ratio of the negative electrode material ranges from 70% to 98%, and can be selected as 95% by mass; the mass ratio of the binder ranges from 1% to 15% by mass, and the mass ratio of the conductive agent ranges from 1% to 15% by mass, all based on the total mass of the positive electrode film.

[0118] 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.

[0119] [Electrolytes]

[0120] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0121] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0122] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0123] In some alternative embodiments, the secondary battery includes an electrolyte comprising lithium hexafluorophosphate and / or lithium perchlorate. Optionally, the concentration of lithium hexafluorophosphate and / or lithium perchlorate in the electrolyte ranges from 0.5 to 3 mol / L.

[0124] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0125] 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.

[0126] [Isolation membrane]

[0127] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0128] 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.

[0129] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0130] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0131] 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.

[0132] This application 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 3 This is an example of a square-structured secondary battery 5.

[0133] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or 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.

[0134] Secondary batteries include single-cell battery forms, battery module forms, and battery pack forms. In some embodiments, single-cell battery units can be assembled into battery modules, and the number of single-cell battery units contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module.

[0135] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5In 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.

[0136] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0137] 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.

[0138] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0139] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery 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, 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, energy storage systems, etc.

[0140] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0141] Figure 8 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 high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0142] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0143] Example

[0144] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. 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 this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0145] Example 1

[0146] Preparation of positive electrode active materials

[0147] Step 1: Wrap

[0148] The coating material is Li3InF x Cl (6-x) .

[0149] Lithium source: lithium tert-butoxide; Fluorine source: ethylene fluorocarbonate; Chlorine source: ethylene chlorocarbonate; Source of metallic In: triethylindium

[0150] The specific steps are as follows:

[0151] The NCM 811 positive electrode bulk material powder is placed in a fluidized bed reactor. The reaction chamber is evacuated and Ar gas is introduced for purging. The gas flow rate is controlled to disperse the positive electrode bulk material.

[0152] Before introducing each source into the fluidized bed reactor, lithium tert-butoxide was heated to 165°C, while fluoroethylene carbonate and chloroethylene carbonate were maintained at 200°C. The purge durations between the lithium tert-butoxide injection pulse and the two injection pulses were set to 1 s and 15 s, respectively. The purge durations between the chloroethylene carbonate and fluoroethylene carbonate injection pulses and the two injection pulses were set to 0.1 s and 15 s, respectively. The deposition temperature was 200°C. The injection pulse times of the fluorine and chlorine sources were varied according to a fluorine source:chlorine source volumetric flow rate ratio of x:(6-x), with Ar gas purging for 15 s between pulses. Each completed pulse injection was considered a cycle, and a total of 20 deposition cycles were performed, where x uniformly decreased from 6 to 0, with the ratio decreasing to 6 / 20 in each cycle.

[0153] During the first week of deposition, x was set to 6, and the pulse time of each source was set according to the Li3InF6 ​​ratio.

[0154] During the second week of deposition, x was 5.7, according to Li3InF 5.7 Cl 0.3 The pulse time of each source is set proportionally, and so on.

[0155] During the 20th week of deposition, x was 0, and the pulse time of each source was set according to the proportion of Li3InCl6.

[0156] Each deposition layer is 0.1 nm thick, completing the coating. Afterwards, Ar gas is continuously purged to clean the pipeline. The coated positive electrode active material is then obtained.

[0157] Step 2: Calcination

[0158] The coated positive electrode active material from step 1 is transferred to a tube furnace and calcined using argon as a protective gas at a temperature of 260°C for 4 hours to ensure that the outer coating has better crystallinity.

[0159] A positive electrode active material with a coating layer thickness of 2 nm was prepared.

[0160] Figure 1 This is a surface view of the positive electrode active material obtained in Example 1. Figure 2 for Figure 1 A magnified view of a portion of the positive electrode active material. Figure 1 In the middle, the large particles are the cathode material NCM811, with an outer coating layer. A large field of view shows the cathode particles are completely coated. The coating layer is then magnified. Figure 2 It can be observed that the coating layer is uniform and dense, with no areas where the coating is missing.

[0161] Preparation of the positive electrode sheet

[0162] The positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) prepared in the previous steps are mixed with N-methylpyrrolidone (NMP) in a weight ratio of 90.0:5.0:5.0 to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0163] Preparation of the negative electrode sheet

[0164] The active material artificial graphite, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in deionized water at a weight ratio of 96.0:2.0:2.0 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0165] Preparation of Electrolyte

[0166] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte of Example 1.

[0167]

Isolation Film

[0168] Commercial polypropylene film was used as the separator.

[0169] Fabrication of Stacked Lithium-ion Batteries

[0170] The negative electrode sheet (51×43.5mm), separator (53×46mm), and positive electrode sheet (49.5×42mm) prepared in the previous steps were placed in sequence, stacked, and encapsulated with aluminum-plastic film. 0.5g of electrolyte was added, and after vacuuming, the plates were sealed and left to stand for 2 hours. The plates were then placed in a clamp with a clamping force of 0.4MPa. After formation, the battery cycle performance was tested.

[0171] Examples 2-5

[0172] The battery was prepared in the same manner as in Example 1, except for the coating thickness, the gradient of F and Cl elements, and the corresponding number of cycles. See the table below for details.

[0173] Example 6

[0174] The battery was prepared in the same manner as in Example 1, except for the variation gradient of F and Cl elements, the thickness of each deposition, and the corresponding number of cycles. See the table below for details.

[0175] Example 7

[0176] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3YF. x Cl (6-x) The source of metallic Y is tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid)yttrium, as detailed in the table below.

[0177] Example 8

[0178] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3ScF. x Cl (6-x) The source of the metal Sc is scandium acetate, as detailed in the table below.

[0179] Example 9

[0180] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3MnF. x Cl (6-x) The source of metallic Mn is bis(cyclopentadiyl)manganese, as detailed in the table below.

[0181] Example 10

[0182] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3ZrF. x Cl (6-x)The source of metallic Zr is zirconium acetate, as detailed in the table below.

[0183] Examples 11-13

[0184] The battery was prepared in the same way as in Example 1, except for the changes in the ratio and gradient of F and Cl, as detailed in the table below.

[0185] Examples 14-22

[0186] The battery preparation is the same as in Example 1, except that the calcination temperature and time are different in the calcination step. See the table below for details.

[0187] Comparative Example 1

[0188] The battery fabrication process is the same as in Example 1, except that the NCM 811 positive electrode material is not coated; it is directly used in the fabrication of the positive electrode sheet. See the table below for details.

[0189] Comparative Example 2

[0190] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3InF6, which is chlorine-free, and the F element showed no gradient change. See the table below for details.

[0191] Comparative Example 3

[0192] The battery was prepared in the same manner as in Example 1, except that the coating material was Li3InCl6, which is fluorine-free, and the Cl element showed no gradient change. See the table below for details.

[0193] Comparative Example 4

[0194] The battery fabrication process is the same as in Example 1, except that the coating layer consists of two layers: an inner coating layer with a thickness of 1 nm and coated with Li3InF6, and an outer coating layer with a thickness of 1 nm and coated with Li3InF6, with no gradient change in F and Cl elements. See the table below for details.

[0195] Comparative Example 5

[0196] The battery preparation was the same as in Example 1, except that the changes in the content of F and Cl elements were the same gradient as in Example 1, but in the opposite direction; that is, the F element content gradually increased while the chlorine element content gradually decreased. See the table below for details.

[0197] Comparative Example 6

[0198] The battery was prepared in the same manner as in Example 1, except that the calcination step was omitted. See the table below for details.

[0199] Morphology testing of positive electrode active materials

[0200] The morphology parameter testing process of the positive electrode active materials in the embodiments and comparative examples of this application is as follows:

[0201] The morphology of the positive electrode active material sample of Example 1 was observed using a ZEISS Gemini 360 scanning electron microscope in accordance with standard JY / T010-1996. The test results are shown in Figure 2.

[0202] It should be noted that the shape of the positive electrode matrix material used in this application is not necessarily spherical; it may also be irregular, and can be either primary or secondary particles. It should also be noted that the shape of the coated positive electrode active material obtained in this application is not necessarily spherical; it may also be irregular.

[0203] [Battery Performance Test]

[0204] 1. Battery capacity retention test

[0205] Taking Example 1 as an example, the battery capacity retention rate test process is as follows: At 25°C, the battery corresponding to Example 1 is charged to 4.5V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.5V, left to rest for 5 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity C of the battery after the nth cycle is recorded simultaneously. n Then, the battery capacity retention rate P after each cycle n =C n / C0×100%. The battery capacity retention rate data corresponding to Example 1 in Table 1 are the data obtained after 100 cycles under the above test conditions, i.e., through P 100 =C 100 / C0×100% yields P 100 The value of is the same. The testing process for the comparative model and other embodiments is the same as above.

[0206] 2. Battery AC impedance test

[0207] Taking Example 1 as an example, the fresh positive electrode sheet, polypropylene separator, and 120 μL of electrolyte obtained in Example 1 were assembled into a symmetrical positive electrode cell and placed in a 25°C constant temperature oven for 2 hours to ensure electrolyte wetting. AC impedance testing was performed using an electrochemical workstation impedance testing module with PEIS voltage perturbation mode, a perturbation voltage of 5 mV, a frequency range of 200 kHz to 30 MHz, a voltage range of 0-5 V, and voltage protection of 0-5 V. The impedance test data were then fitted as follows:

[0208] Taking Example 1 as an example, the data from Example 1 was fitted using Z-fit software, and the fitting circuit was R. s +C1 / R SEI +C2 / R ct +W, where R s It is ohmic impedance, mainly related to the conductivity of the positive electrode material; R ct It is the charge transfer impedance, which mainly reflects the lithium-ion insertion / extraction rate in the positive electrode material; C1 is the double-layer capacitance at the SEI-electrolyte interface; R SEI C1 is the SEI film resistance; C2 is the double-layer capacitance at the SEI-graphite interface; W is the Weber impedance. The fitting criteria are: error less than 5%, and the deviation of the intersection point with the real part from the fitted Rs should be less than 5%. Only fitting results that meet these requirements can be accepted. The Rs value in the fitted result... ct With R s Extract and record the data in the table below. The process for processing data in the comparative and other embodiments is the same as above.

[0209]

[0210]

[0211] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. 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 this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized by, A positive electrode body material and a coating layer coated on the surface of the positive electrode body material, characterized in that the coating layer is composed of a compound of a molecular formula Li a MF x Cl (a+n-x) wherein 1≤a≤3, 0≤x≤a+n; n is the valence of M ion, n is in the range of 2-4, M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, Nb, Wherein, taking the surface of the positive electrode body material as the starting point, the content proportion of F element in the compound with the molecular formula of Li a MF x Cl (a+n-x) gradually becomes smaller in the direction of extending outward to the outermost side of the coating layer, and the content proportion of Cl element in the compound with the molecular formula of Li a MF x Cl (a+n-x) gradually becomes larger.

2. The positive electrode active material according to claim 1, characterized by The content of F element changes from large to small in the direction extending outward to the outermost side of the cladding layer, that is, the change gradient of x from a+n→0 is (a+n) / (h / b), wherein h is the thickness of the cladding layer, and b is the minimum thickness where the gradient changes; wherein, h is in the range of 0nm-5nm; b is in the range of 0nm-0.5nm.

3. The positive electrode active material according to claim 1, characterized by The material of the cladding layer is selected from at least one of Li3InF x Cl (6-x) , Li3YF x Cl (6-x) , Li3ScF x Cl (6-x) , Li3MnF x Cl (6-x) , Li3ZrF x Cl (6-x) , wherein 0≤x≤6.

4. The positive electrode active material according to any one of claims 1 to 3, characterized by, The electrochemical window of the positive electrode active material is 5.0 V or more, and / or the lithium ion conductivity of the positive electrode active material is 10 -8 S / cm-10 -3 S / cm.

5. The positive electrode active material according to any one of claims 1 to 3, characterized by, The positive electrode body material is selected from at least one of ternary active material, lithium iron phosphate, lithium manganate, lithium cobaltate.

6. A method for producing a positive electrode active material, characterized by, The method comprises a cladding step, which comprises: (1) preparing or preparing a positive electrode body material; (2) vaporizing Li a MF x Cl (a+n-x) at a temperature of 200-300°C under an inert atmosphere, and depositing the vaporized source on the surface of the positive electrode bulk material to coat the positive electrode bulk material, thereby obtaining the positive electrode active material. wherein the molecular formula Li a MF x Cl (a+n-x) wherein, 1≤a≤3, 0≤x≤a+n; n is the valence of M ion, n is in the range of 2-4, M is selected from one or more of the elements In, Y, Sc, Er, Tb, Yb, Lu, Zr, Al, Ga, La, Ho, Ti, Nb, Wherein, starting from the surface of the positive electrode body material, as extending outward to the direction of the outermost side of the coating layer, the content proportion of F element in the compound with the molecular formula of Li a MF x Cl (a+n-x) gradually becomes smaller, and the content proportion of Cl element in the compound with the molecular formula of Li a MF x Cl (a+n-x) gradually becomes larger.

7. The production method of a positive electrode active material according to claim 6, characterized by, The method for adsorbing and depositing the vaporized source on the surface of the positive electrode body material is atomic deposition, and the number of deposition times is m, m is in the range of 1-100.

8. The production method of a positive electrode active material according to claim 6, characterized by, The Li a MF x Cl (a+n-x) Sources include a lithium source, an M source, a fluorine source, a chlorine source, wherein the boiling point of each source is between 70-300°C. The lithium source includes one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alcoholate, and lithium ester; The M source includes one or more of alkyl metal, carboxylate metal, alcoholate metal, and ester metal of M element; The fluorine source includes one or more of fluoroalkane, fluoro carboxylic acid, fluoro alcohol, and fluoro ester; The chlorine source includes one or more of chloroalkane, chloro carboxylic acid, chloro alcohol, and chloro ester.

9. The production method of a positive electrode active material according to any one of claims 6 to 8, characterized by, After the cladding step, the obtained cladded positive electrode active material is calcined, the calcination temperature is 150°C-300°C, and the calcination time is 4h-20h.

10. A secondary battery comprising the positive electrode active material of claims 1-5 or the positive electrode active material prepared by the method of any one of claims 6-9.

11. The secondary battery according to claim 10, characterized by The secondary battery comprises an electrolyte, and the electrolyte comprises lithium hexafluorophosphate and / or lithium perchlorate.

12. An electrical device, characterized by The secondary battery of claim 10 or 11 is included. The secondary battery of claim 10 or 11 is included.

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