Quenching liquid, preparation method of surface-stabilized lithium-rich manganese-based positive electrode material and secondary battery

Abstract

The invention discloses quenching liquid, a preparation method of a surface-stabilized lithium-rich manganese-based positive electrode material and a secondary battery. The quenching liquid comprises a solvent, lithium hydroxide or lithium salt, a reducing agent and phosphate, the lithium-rich manganese-based positive electrode material is treated through a quenching liquid quenching method, the first-effect coulombic efficiency and the cycling stability of the battery are improved, and voltage attenuation is relieved.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a quenching liquid, a method for preparing a surface-stabilized lithium-rich manganese-based cathode material, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in electronic devices, electric vehicles, energy storage systems, and other fields due to their high plateau voltage, low self-discharge, and long cycle life. Cathode materials, as one of the key materials in lithium-ion batteries, directly affect the battery's energy density, safety performance, and cycle performance. However, the specific capacity of traditional cathode materials, including lithium cobalt oxide, lithium manganese oxide, ternary cathode materials, and lithium iron phosphate cathode materials, still needs improvement. Lithium-rich manganese-based cathode materials are currently the lithium-ion battery cathode materials with the highest specific capacity discovered, achieving a specific capacity of over 300 mAh / g. This material also has advantages such as low raw material cost and environmental friendliness, thus possessing great development potential and application value.

[0003] Although lithium-rich manganese-based cathode materials have the advantage of high specific capacity, they suffer from the following problems in practical applications: low initial coulombic efficiency; poor cycle performance; and severe voltage decay during cycling. The initial charging process of lithium-rich manganese-based cathode materials can be divided into two steps. The first step, when the voltage is less than 4.5V, mainly involves the delithiation of the LiMnO2 phase. This process involves charge compensation through the loss of electrons by transition metal cations, similar to the initial charging process of existing ternary cathode materials. The second step, when the voltage is higher than 4.5V, involves the joint delithiation of lithium ions from both the lithium layer and the transition metal layer. At this stage, charge compensation is mainly achieved through the oxidation reaction of oxygen anions. However, the delithiation of lithium from the transition metal layer and the loss of electrons by oxygen cause the collapse of the original structure. After oxidation, oxygen ions easily escape from the structure as oxygen on the surface. During subsequent discharge, due to the release of oxygen and the collapse of the original structure, lithium ions cannot completely return to the lattice of the lithium-rich manganese-based cathode material, resulting in low initial charge-discharge efficiency. To achieve high capacity, lithium-rich manganese-based cathode materials require a wider charge-discharge voltage window. During high-charge states, the high-valence transition metals in the material exhibit strong oxidizing properties, readily reacting with the electrolyte and causing irreversible transformation of the crystal structure from layered to spinel phase, as well as deterioration of the interface film. This leads to capacity decay and increased interfacial impedance. Simultaneously, the dissolution of transition metal ions at the electrode / electrolyte interface during charge-discharge is also a significant factor contributing to poor cycle performance. Voltage decay in lithium-rich manganese-based cathode materials is more pronounced in the first few weeks, gradually slowing down thereafter. It is widely believed that the irreversible oxygen release during the reaction, causing a phase transition in the material structure, is the primary cause of voltage decay. After oxygen release, during discharge, lithium ions re-enter the cathode structure. Oxygen loss necessitates electron absorption by the transition metals to balance the charge state. As the transition metals accept electrons, the material's potential decreases, resulting in a drop in overall voltage. Throughout the battery cycle, oxygen is continuously released, thus causing the material's potential to continuously decline.

[0004] Currently, the main methods for solving this problem include surface coating, bulk doping, surface modification, and particle nanostructuring. However, existing technologies still cannot effectively solve the problems of low initial coulombic efficiency, severe voltage decay, and poor cycle performance of lithium-rich manganese-based cathode materials. Summary of the Invention

[0005] This invention addresses the problems in existing technologies by providing a quenching fluid, a surface-stabilized treatment method for preparing lithium-rich manganese-based cathode materials, and their applications. The lithium-rich manganese-based cathode material is treated with a quenching fluid to achieve a high first-efficiency coulombic efficiency, while simultaneously improving cycle life and mitigating voltage decay.

[0006] Firstly, this application provides a quenching fluid.

[0007] In some embodiments, the quenching fluid includes a solvent, lithium hydroxide or lithium salt, a reducing agent, or a phosphate.

[0008] In some embodiments, the solvent is pure water or other liquids that facilitate the dissolution of lithium hydroxide or lithium salts, reducing agents, or phosphates and do not undergo side reactions with lithium hydroxide or lithium salts, reducing agents, or phosphates.

[0009] In some embodiments, the lithium salt is a soluble lithium salt, selectable from organic or inorganic lithium salts. The organic lithium salt may be selected from one or more of lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, and lithium bis(trifluoromethanesulfonyl)imide; the inorganic lithium salt may be selected from one or more of lithium nitrate, lithium hexafluorophosphate, lithium acetate, lithium sulfide, and lithium perchlorate. Preferably, lithium hydroxide or a soluble inorganic lithium salt is used.

[0010] In some embodiments, the reducing agent is a substance with strong reducing properties, selected from metal hydrides, vitamins, or citric acid. The metal hydride may be selected from one or more of lithium aluminum hydride (LiAlH4), potassium borohydride (KBH4), sodium borohydride (NaBH4), and lithium borohydride (LiBH4); the vitamin may be selected from one or more of vitamin A, vitamin C, and vitamin E. Preferably, the reducing agent in this application is selected from metal hydrides. More preferably, the reducing agent is selected from lithium aluminum hydride.

[0011] In some embodiments, the phosphate is a highly soluble phosphate, selected from dihydrogen phosphate, hydrogen phosphate, or orthophosphate. The dihydrogen phosphate may be selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; the hydrogen phosphate may be selected from sodium hydrogen phosphate, potassium hydrogen phosphate, and ammonium hydrogen phosphate; and the orthophosphate may be selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate. Preferably, the phosphate is selected from dihydrogen phosphate.

[0012] In some embodiments, the amount of lithium hydroxide or lithium salt added, in terms of lithium ion concentration, is 0.02 to 0.1 mol / L.

[0013] In some embodiments, the amount of reducing agent added is 3.0% to 15.0% of the solvent mass.

[0014] In some embodiments, the amount of phosphate added is 0.5% to 2.0% of the solvent mass.

[0015] Preferably, the quenching fluid further includes a solid electrolyte.

[0016] In some embodiments, the solid electrolyte may be selected from one or more of lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanate (LLTO), and polyethylene oxide (PEO).

[0017] In some embodiments, the addition amount of the solid electrolyte is 0.5% - 2.0% of the mass of the solvent.

[0018] In a second aspect, the present application provides a preparation method for a surface-stabilized lithium-rich manganese-based cathode material.

[0019] In some embodiments, the preparation method includes a step of quenching a first-fired material of the lithium-rich manganese-based cathode material in the quenching liquid of the first aspect.

[0020] In some embodiments, the first-fired material of the lithium-rich manganese-based cathode material is a material having the basic active properties of a cathode material obtained by mixing a lithium-rich manganese-based precursor material with lithium hydroxide or a lithium salt and performing solid-phase sintering. Specifically, the chemical formula of the first-fired material of the lithium-rich manganese-based cathode material is xLi2MnO3·(1 - x)LiMO2, where 0.6 < x < 0.8, and M is one or more of Ni, Co, Mn, Al, Zr, Cr, Y, Nb, Ta, La, W, Mg.

[0021] In some embodiments, in the mixture of the lithium-rich manganese-based precursor material and lithium hydroxide or a lithium salt, the molar ratio of lithium ions to other metals is 1.2 - 1.4.

[0022] In some embodiments, the solid-phase sintering temperature of the first-fired material of the lithium-rich manganese-based cathode material is 800 - 850°C.

[0023] In some embodiments, the quenching process is to heat the first-fired material of the lithium-rich manganese-based cathode material to 150 - 300°C, and then pour it into the quenching liquid for cooling, where the temperature difference is greater than 100°C. Preferably, the temperature of the quenching liquid is room temperature or 10 - 30°C.

[0024] In some embodiments, the mass ratio of the first-fired material of the lithium-rich manganese-based cathode material to the quenching liquid is 1:(1 - 3). In some embodiments, in order to improve the quenching effect, after the first-fired material of the lithium-rich manganese-based cathode material is heated to 150 - 300°C, it is kept warm for 2 - 5 h.

[0025] Furthermore, the material after quenching and cooling is filtered and dried to obtain a dry pretreated material.

[0026] In some embodiments, the drying temperature is 100 - 150°C, and the drying time is 5 - 10 h.

[0027] Furthermore, the pretreated material is subjected to secondary sintering, the sintering temperature is 300 - 500°C, and the sintering time is 5 - 15 h.

[0028] In a third aspect, the present application provides a secondary battery, including the surface-stabilized lithium-rich manganese-based cathode material obtained by the preparation method provided in the second aspect of the present application.

[0029] Beneficial effects of the present invention

[0030] First, rapid quenching induces a phase transition on the material surface, forming a spinel-like structure that enhances ion migration and electronic conductivity, thereby improving the material's specific capacity and cycle stability. A suitable quenching fluid composition mitigates the adaptability issues caused by the sudden temperature drop and drastic structural changes during quenching, while simultaneously achieving performance improvements. Adding a small amount of lithium hydroxide or lithium salt to the quenching fluid can regulate the balance of lithium content on the material surface, effectively compensating for surface lithium loss during quenching and thus mitigating voltage decay caused by lithium loss. Reduction of the material surface with a reducing agent during quenching creates surface oxygen vacancies. This enhances surface lithium ion migration and electronic conductivity, increasing battery specific capacity, and reduces oxygen release during charging and discharging, mitigating side reaction gas generation and effectively improving the material's first-efficiency coulombic efficiency. Phosphate exhibits excellent lithium-ion and electronic conductivity. As a repair agent, it penetrates the material's surface crystal structure during quenching, mitigating phase transitions during cyclic charging and discharging, thus improving cycle stability. Simultaneously, it synergistically enhances the battery's initial coulombic efficiency with reducing agents and mitigates voltage decay during cyclic charging and discharging in conjunction with lithium hydroxide or lithium salts. Furthermore, solid-state electrolytes possess excellent ionic conductivity and are uniformly and stably coated onto the material surface through quenching, reducing side reactions between the cathode material and the electrolyte. Therefore, this surface-stabilized lithium-rich manganese-based cathode material exhibits high initial coulombic efficiency and good cycle stability. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 These are the XRD patterns of Example 1 and Comparative Example 5.

[0033] Figure 2 These are SEM images of Example 1 and Comparative Example 1.

[0034] Figure 3 This is a comparison chart of the discharge specific capacity of the lithium-rich manganese-based cathode materials prepared in Examples 1-3 and Comparative Examples 1, 2, and 4 under 100 long-cycle performance.

[0035] Figure 4This is a voltage decay trend graph of the lithium-rich manganese-based cathode materials prepared in Example 1 and Comparative Example 3 under 100 long-cycle performance.

[0036] Figure 5 These are diagrams showing the bulge conditions of Example 1 and Comparative Example 4. Detailed Implementation

[0037] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having" and any variations thereof in the specification, claims and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0039] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0040] In the description of this application, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two), and "at least one" refers to one or more (including one, two, three, etc.).

[0041] In a first aspect, this application provides a quenching fluid. The quenching fluid includes a solvent, lithium hydroxide or lithium salt, a reducing agent, and a phosphate.

[0042] Adding lithium hydroxide or lithium salts to the quenching solution can effectively compensate for surface lithium loss during the quenching process, thereby mitigating voltage decay caused by lithium loss. Reducing agents reduce the material surface, creating surface oxygen vacancies. This improves the migration ability and electronic conductivity of surface lithium ions, increasing the battery's specific capacity. It also reduces oxygen release during charging and discharging, alleviating side reaction gas generation problems and effectively improving the material's first-efficiency coulombic efficiency. Phosphates, with their excellent lithium-ion and electronic conductivity, act as a repair agent, entering the material's surface crystal structure during quenching. This slows down phase transitions during cyclic charging and discharging, thus improving the battery's cycle stability.

[0043] During the quenching process, the structural support of phosphates can overcome the surface structural instability caused by oxygen vacancies created by the reducing agent. Simultaneously, it synergistically improves the initial coulombic efficiency of the battery and, in conjunction with lithium hydroxide or lithium salts, mitigates voltage decay during battery cycling. Therefore, quenching lithium-rich manganese-based cathode materials using the aforementioned quenching solution can effectively improve the initial coulombic efficiency and cycle stability of the material while mitigating voltage decay.

[0044] In some embodiments, the solvent is pure water or other liquids that facilitate the dissolution of lithium hydroxide or lithium salts, reducing agents, or phosphates and do not undergo side reactions with lithium hydroxide or lithium salts, reducing agents, or phosphates.

[0045] In some embodiments, the lithium salt is a soluble lithium salt, which may be selected from organic or inorganic lithium salts. The organic lithium salt may be selected from one or more of lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, and lithium bis(trifluoromethanesulfonyl)imide; the inorganic lithium salt may be selected from one or more of lithium nitrate, lithium hexafluorophosphate, lithium acetate, lithium sulfide, and lithium perchlorate. Preferably, using lithium hydroxide or a soluble inorganic lithium salt helps reduce complexation during the quenching process and promotes the migration and anchoring of lithium to the surface of the lithium-rich manganese-based cathode material.

[0046] In some embodiments, the reducing agent is a substance with strong reducing properties, selected from metal hydrides, vitamins, or citric acid. The metal hydride may be selected from one or more of lithium aluminum hydride (LiAlH4), potassium borohydride (KBH4), sodium borohydride (NaBH4), and lithium borohydride (LiBH4); the vitamin may be selected from one or more of vitamin A, vitamin C, and vitamin E. Preferably, the reducing agent in this application is selected from metal hydrides. More preferably, the reducing agent in this application is selected from lithium aluminum hydride. Metal hydrides have a stronger defect-building ability for lithium-rich manganese-based cathode materials, and can also supplement a small amount of active metal, which is beneficial to the structural stability of the phase transition process on the surface of the lithium-rich manganese-based cathode material.

[0047] In some embodiments, the phosphate is a highly soluble phosphate, selected from dihydrogen phosphate, hydrogen phosphate, or orthophosphate. The dihydrogen phosphate may be selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; the hydrogen phosphate may be selected from sodium hydrogen phosphate, potassium hydrogen phosphate, and ammonium hydrogen phosphate; and the orthophosphate may be selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate. Preferably, the phosphate in this application is selected from dihydrogen phosphate, which provides higher reactivity during rapid quenching.

[0048] In some embodiments, the amount of lithium hydroxide or lithium salt added, expressed as lithium ion concentration, is 0.02–0.1 mol / L. Within this concentration range, the lithium salt can effectively regulate the lithium content on the surface of the cathode material. If the concentration is too high, it may exacerbate the side reactions that degrade the material due to residual alkali on the material surface; if the concentration is too low, it may not be able to compensate for the structural lithium release caused by lithium loss from the material surface.

[0049] In some embodiments, the amount of reducing agent added is 3.0% to 15.0% of the solvent mass. Within this range, the reducing agent concentration can effectively regulate the surface structure of the material. If the concentration is too high, it may lead to a decrease in the material's discharge specific capacity; if the concentration is too low, it may not effectively alleviate the problem of gas generation from side reactions.

[0050] In some embodiments, the amount of phosphate added is 0.5% to 2.0% of the solvent mass. Within this range, the phosphate concentration can effectively maintain the surface crystal structure of the material.

[0051] Preferably, the quenching fluid further includes a solid electrolyte. The solid electrolyte is different from the lithium salt.

[0052] Solid electrolytes possess excellent ionic conductivity. Through quenching and secondary sintering, solid electrolytes are uniformly and stably coated on the material surface, improving the ion conductivity of the phase change layer on the surface of lithium-rich manganese-based cathode materials and reducing side reactions between the cathode material and the electrolyte. Therefore, adding solid electrolytes to the quenching solution can better enhance the cycling stability of the material.

[0053] In some embodiments, the solid electrolyte may be selected from one or more of lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanate (LLTO), and polyethylene oxide (PEO).

[0054] In some embodiments, the amount of solid electrolyte added is 0.5% to 2.0% of the solvent mass. Within this range, the solid electrolyte can form a good ion conduction network.

[0055] Secondly, this application provides a method for preparing a surface-stabilized lithium-rich manganese-based cathode material.

[0056] In some embodiments, the preparation method includes the step of quenching a lithium-rich manganese-based cathode material in a quenching solution in the first aspect.

[0057] In some embodiments, the first-fired material of the lithium-rich manganese-based cathode material is a material with the basic active properties of the cathode material obtained by mixing a lithium-rich manganese-based precursor material with lithium hydroxide or a lithium salt and performing solid-phase sintering. The lithium-rich manganese-based precursor material is a precursor material for preparing the lithium-rich manganese-based cathode material and can be selected from manganese-containing metal compounds. Specifically, the chemical formula of the first-fired material of the lithium-rich manganese-based cathode material is xLi2MnO3·(1 - x)LiMO2, where 0.6 < x < 0.8, and M is one or more of Ni, Co, Mn, Al, Zr, Cr, Y, Nb, Ta, La, W, Mg.

[0058] In some embodiments, in the mixture of the lithium-rich manganese-based precursor material and lithium hydroxide or the lithium salt, the molar ratio of lithium ions to other metals is 1.2 to 1.4.

[0059] In some embodiments, the solid-phase sintering temperature of the first-fired material of the lithium-rich manganese-based cathode material is 800 to 850 °C.

[0060] In some embodiments, the quenching process is to heat the first-fired material of the lithium-rich manganese-based cathode material to 150 to 300 °C and then pour it into a quenching liquid for cooling, where the temperature difference is greater than 100 °C. Preferably, the temperature of the quenching liquid is room temperature or 10 to 30 °C.

[0061] The rapid quenching causes a phase change on the material surface, generating a layer of spinel-like structure on the surface, which can enhance the ion migration ability and electron conductivity, and improve the specific capacity and cycle stability of the material.

[0062] In some embodiments, the mass ratio of the first-fired material of the lithium-rich manganese-based cathode material to the quenching liquid is 1:(1 to 3). A suitable ratio is beneficial for sufficient quenching and reducing the waste of the quenching liquid.

[0063] In some embodiments, in order to improve the quenching effect, after the first-fired material of the lithium-rich manganese-based cathode material is heated to 150 to 300 °C, it is kept warm for 2 to 5 h.

[0064] In some embodiments, the time interval from taking out the first-fired material of the lithium-rich manganese-based cathode material after heating to adding it into the quenching liquid is less than 5 min. Preferably, the time interval is less than 1 min. During the quenching process, the quenching liquid is preferably in a continuous stirring state, the stirring speed is greater than 250 r / min, and the stirring time is 5 to 30 min. This is beneficial for the uniformity of the components in the quenching liquid and the temperature distribution.

[0065] Further, the material after quenching and cooling is filtered and dried to obtain a dried pre-treatment material.

[0066] In some embodiments, the drying temperature is 100 to 150 °C, and the drying time is 5 to 10 h.

[0067] Furthermore, the pretreated material undergoes secondary sintering at a temperature of 300–500℃ for 5–15 hours. This secondary sintering allows the coating layer to be distributed more evenly and stably on the material surface.

[0068] Thirdly, this application provides a secondary battery, including a surface-stabilized lithium-rich manganese-based cathode material obtained by the preparation method provided in the second aspect of this application.

[0069] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. The separator, positioned between the positive and negative electrode plates, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0070] In some embodiments, the positive electrode includes a current collector and a positive electrode active layer bonded to the current collector. The positive electrode active layer contains a surface-stabilized lithium-rich manganese-based positive electrode material prepared by the preparation method provided in the second aspect of this application.

[0071] In some implementations, the current collector for the positive electrode is also called the positive electrode current collector, and can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil.

[0072] In some embodiments, the negative electrode includes a current collector and a negative electrode active layer bonded to the current collector. The current collector of the negative electrode, also known as the negative electrode current collector, can be a metal foil or a composite current collector. The negative electrode active material of the negative electrode active layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc.

[0073] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application.

[0074] This should not be construed as a limitation of this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0075] Example 1

[0076] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 15g of citric acid, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0077] According to the molar ratio of Li / Me (Me: metals other than Li) = 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0078] Example 2

[0079] Referring to Example 1, different holding temperatures were selected, followed by quenching. The specific schemes are as follows:

[0080] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 15g of citric acid, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0081] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 300℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0082] Example 3

[0083] Referring to Example 1, different contents of phosphate and solid electrolyte were selected, and the specific schemes are as follows:

[0084] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 15g of citric acid, 2.5g of ammonium dihydrogen phosphate, and 10g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0085] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0086] Example 4

[0087] Referring to Example 1, different types and amounts of lithium salts were selected, and the specific scheme is as follows:

[0088] Weigh 500g of room temperature pure water as a solvent, and weigh 2g of lithium nitrate, 15g of citric acid, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0089] Ni was weighed according to the Li / Me molar ratio of 1.33. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0090] Example 5

[0091] Referring to Example 1, different reducing agents and different reducing agent contents were selected, and the specific schemes are as follows:

[0092] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 20g of NaBH4, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0093] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0094] Example 6

[0095] Referring to Example 1, without using a solid electrolyte, the specific scheme is as follows:

[0096] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 15g of citric acid, and 5g of ammonium dihydrogen phosphate. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching liquid.

[0097] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0098] Comparative Example 1

[0099] Referring to Example 1, without using quenching fluid, the specific solution is as follows:

[0100] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.651000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain the first sintered lithium-rich manganese-based cathode material. After cooling, the material was placed in a furnace for secondary sintering at 300℃ for 8 hours. After being removed from the furnace, the material was sieved to obtain the first sintered lithium-rich manganese-based cathode material.

[0101] Comparative Example 2

[0102] Referring to Example 1, without using phosphates, the specific scheme is as follows:

[0103] Weigh 500g of room temperature pure water as a solvent, weigh 1g of lithium hydroxide, 15g of citric acid, and 5g of LATP, add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0104] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0105] Comparative Example 3

[0106] Referring to Example 1, without using lithium hydroxide or lithium salts, the specific scheme is as follows:

[0107] Weigh 500g of room temperature pure water as a solvent, and weigh 15g of citric acid, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0108] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.651000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0109] Comparative Example 4

[0110] Referring to Example 1, without using a reducing agent, the specific scheme is as follows:

[0111] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0112] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.65 1000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of the lithium-rich manganese-based cathode material 1 sintering material was taken, placed in a mortar, and heated in a furnace at 200℃ for 3 hours. After heating, the material was directly discharged into a quenching liquid for quenching. The mixture was stirred for 10 minutes to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered and dried at 100℃ for 5 hours. After drying, the material was placed in a mortar again and sintered in a furnace at 300℃ for 8 hours. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0113] Comparative Example 5

[0114] Referring to Example 1, quenching is not performed; the specific scheme is as follows:

[0115] Weigh 500g of room temperature pure water as a solvent, and weigh 1g of lithium hydroxide, 15g of citric acid, 5g of ammonium dihydrogen phosphate, and 5g of LATP. Add them to the pure water and stir for 10 minutes to dissolve and obtain the required quenching solution.

[0116] According to the Li / Me molar ratio of 1.33, Ni was weighed separately. 0.35 Mn 0.651000g of CO3-rich manganese precursor and 405g of lithium carbonate were mixed and then solid-state sintered at 820℃ to obtain lithium-rich manganese-based cathode material sintering material 1. 500g of lithium-rich manganese-based cathode material 1 sintering material 1 was added to the prepared quenching liquid and stirred for 10min to ensure that the quenching liquid and the material were fully mixed. Then, it was filtered, dried at 100℃ for 5h, and after drying, the material was put into a bowl and sintered in a furnace at 300℃ for 8h. After sintering, the material was sieved to obtain lithium-rich manganese-based cathode material.

[0117] To further verify whether the surface stabilization treatment of the lithium-rich manganese-based cathode material described in this invention improves the electrochemical performance, lithium-ion batteries were prepared using the lithium-rich manganese-based cathode materials obtained in the examples and comparative examples, and their performance was tested.

[0118] Preparation method: The test sample, conductive agent SP and binder PVDF are mixed at a mass ratio of 90:5:5. An appropriate amount of N-vinylpyrrolidone is added as a solvent to form a uniform slurry. The slurry is coated on aluminum foil, vacuum dried and rolled to prepare a positive electrode sheet. Lithium metal is used as the negative electrode. The electrolyte is formed by mixing 1 mol / L lithium hexafluorophosphate (LiPF6) and a three-component mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): potassium ethyl carbonate (EMC) = 1:1:1 (v / v). A polypropylene microporous membrane is used as the separator. The CR2032 coin cell is assembled in an inert gas-filled glove box.

[0119] The CR2032 coin cells prepared in the above embodiments and comparative examples were subjected to first-efficiency charge-discharge tests and cycle performance tests, respectively.

[0120] (1) The test was conducted at room temperature of 25℃. The first test voltage was 2.5~4.8V, the nominal capacity was 270mAh / g, and the current density was 0.1C. This test method was used to calibrate the first charge and discharge capacity and first efficiency of the material.

[0121] (2) The test was conducted at room temperature of 25℃. The voltage of the first test was 2.5~4.6V, the nominal capacity was 270mAh / g, the current density was 1.0C, and the cycle retention rate and voltage decay performance of the material were calibrated by 100 cycles.

[0122] Cycle retention rate and voltage decay are calculated as follows.

[0123] Cycle retention rate = Capacity on the 100th cycle ÷ Capacity on the 1st cycle × 100%

[0124] Voltage decay = Plateau voltage of cycle 1 - Plateau voltage of cycle 100

[0125] The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128] The data results from Examples 1-6 and Comparative Example 1 verify that quenching lithium-rich manganese-based cathode material in a quenching liquid can improve the first-efficiency coulombic efficiency and cycle stability of the battery and alleviate voltage decay. Figure 2 These are SEM images of Example 1 and Comparative Example 1. The comparison shows that after quenching in the quenching liquid, the material exhibits a unique structure where the primary particles on the surface change from a transverse to a radial arrangement. This structure, along with the wetting of the electrolyte and the deintercalation / extraction of lithium ions, effectively improves the material's initial efficiency. Simultaneously, a solid electrolyte coating formed after quenching can be observed on the surface of the secondary particles. During cycling, this solid electrolyte acts as an isolation barrier between the positive electrode particle surface and the electrolyte, reducing side reactions in the material.

[0129] This invention utilizes the synergistic effect of various components in the quenching fluid to comprehensively improve and stabilize the properties of the material after quenching. As seen in Comparative Examples 1-4, the improvement in battery performance is unpredictable for materials quenched using only some of the quenching fluid components (Comparative Examples 2-4). Compared to untreated materials (Comparative Example 1), only a limited improvement is achieved (Comparative Example 4), and it may even further degrade battery performance (Comparative Examples 2 and 3). This indicates that using only some of the quenching fluid components is insufficient to comprehensively improve the battery's initial coulombic efficiency, cycle stability, and mitigate voltage decay.

[0130] The data results from Examples 1-6 and Comparative Example 3 and Figure 4 The cyclic voltage decay curves in the data verify that adding lithium hydroxide or lithium salts to the quenching solution can effectively compensate for the surface lithium loss during the quenching process, thereby alleviating the voltage decay caused by lithium loss. One of the main reasons is that the loss of surface lithium during the quenching process causes structural lithium to migrate from the structure to the surface, forming a new lithium-containing surface layer. The charge imbalance caused by the loss of structural lithium is compensated by the loss of electrons by the transition metal. During battery charging, due to the original electron loss of the transition metal, the redox reaction of oxygen anions is accelerated for charge compensation, thereby exacerbating the material phase transition and voltage decay.

[0131] Reducing agents can create surface oxygen vacancies, which on the one hand improves the migration ability and electronic conductivity of lithium ions on the surface, and on the other hand reduces oxygen release during battery charging and discharging, alleviating the problem of gas generation from side reactions. Figure 5 The bulging diagrams of Example 1 and Comparative Example 4 show that the gas generation problem of the material was significantly alleviated after adding a reducing agent to the quenching liquid. This is based on the data results from Examples 1-6 and Comparative Example 4. Figure 3The comparison chart of discharge specific capacity under medium and long cycle performance verifies that adding a reducing agent to the quenching fluid can improve the discharge specific capacity of the battery, thereby improving the first-efficiency coulombic efficiency.

[0132] Phosphate enters the material's surface crystal structure during quenching, which can slow down the phase transition during cyclic charge-discharge processes. This is based on data from Examples 1-6 and Comparative Example 2. Figure 3 The comparison chart of discharge specific capacity under medium and long cycle performance verifies that adding phosphate to the quenching fluid can effectively improve the cycle stability of the battery. The comparison of data from Comparative Examples 2, 3, and 4 verifies that phosphate can also synergistically improve the battery's initial coulombic efficiency with the reducing agent and synergistically alleviate voltage decay during battery cycle charging and discharging with lithium salt.

[0133] pass Figure 1 The XRD patterns of Example 1 and Comparative Example 5 show that a small peak appears between 15 and 16° after quenching of the lithium-rich manganese-based cathode material. Figure 1 The spinel-like phase peaks (marked by the middle arrow) show a shift in the 003 peak position towards a smaller angle, indicating an increase in the lattice constant. Data from Examples 1-5 and Comparative Example 5 verify that rapid quenching causes a phase transformation on the material surface, generating a spinel-like structure that improves the material's specific capacity and cycle stability.

[0134] Solid electrolytes are uniformly and stably coated onto the material surface through quenching, which can reduce side reactions between the cathode material and the electrolyte. A comparison of the data from Examples 1-5 and Example 6 verifies that adding a solid electrolyte to the quenching solution can effectively improve the cycling stability of the material.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A quenching fluid, characterized in that, The quenching liquid includes a solvent, lithium hydroxide or a lithium salt, a reducing agent, and a phosphate.

2. The quenching fluid according to claim 1, characterized in that, The solvent is pure water or other liquid that is conducive to the dissolution of lithium hydroxide or a lithium salt, a reducing agent, and a phosphate and does not undergo side reactions with lithium hydroxide or a lithium salt, a reducing agent, and a phosphate; The lithium salt is a soluble lithium salt, selected from organic lithium salts or inorganic lithium salts. The organic lithium salt is preferably selected from one or more of lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, and lithium bis(trifluoromethanesulfonyl)imide. The inorganic lithium salt is preferably selected from one or more of lithium nitrate, lithium hexafluorophosphate, lithium acetate, lithium sulfide, and lithium perchlorate; The reducing agent is selected from metal hydrides, vitamins, or citric acid. Among them, the metal hydride is preferably selected from one or more of lithium aluminum hydride (LiAlH4), potassium borohydride (KBH4), sodium borohydride (NaBH4), and lithium borohydride (LiBH4). The vitamin is preferably selected from one or more of vitamin A, vitamin C, and vitamin E. The phosphate is selected from dihydrogen phosphates, hydrogen phosphates, or orthophosphates. Among them, the dihydrogen phosphate is preferably selected from one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate. The hydrogen phosphate is preferably selected from sodium hydrogen phosphate, potassium hydrogen phosphate, and ammonium hydrogen phosphate. The orthophosphate is preferably selected from one or more of sodium phosphate, potassium phosphate, and ammonium phosphate.

3. The quenching fluid according to claim 1, characterized in that, The addition amount of lithium hydroxide or a lithium salt is 0.02 - 0.1 mol / L in terms of lithium ion concentration; the addition amount of the reducing agent is 3.0% - 15.0% of the mass of the solvent; the addition amount of the phosphate is 0.5% - 2.0% of the mass of the solvent.

4. The quenching fluid according to claim 1, characterized in that, The quenching liquid further includes a solid electrolyte, which is preferably selected from one or more of lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanate (LLTO), and polyethylene oxide (PEO). The addition amount of the solid electrolyte is preferably 0.5% - 2.0% of the mass of the solvent.

5. A method for preparing a surface-stabilized lithium-rich manganese-based cathode material, characterized in that, The preparation method includes the step of quenching the first - fired material of the lithium - rich manganese - based cathode material in the quenching liquid according to any one of claims 1 - 4.

6. The method for preparing the surface-stabilized lithium-rich manganese-based cathode material according to claim 5, characterized in that, The first - fired material of the lithium - rich manganese - based cathode material is a material obtained by mixing a lithium - rich manganese - based precursor material with lithium hydroxide or a lithium salt and performing solid - phase sintering, which has the basic active properties of a cathode material. Preferably, the chemical formula of the first - fired material of the lithium - rich manganese - based cathode material is xLi2MnO3·(1 - x)LiMO2, where 0.6 < x < 0.8, and M is one or more of Ni, Co, Mn, Al, Zr, Cr, Y, Nb, Ta, La, W, Mg. Preferably, the solid - phase sintering temperature of the first - fired material of the lithium - rich manganese - based cathode material is 800 - 850 °C.

7. The method for preparing the surface-stabilized lithium-rich manganese-based cathode material according to claim 5, characterized in that, The mass ratio of the first - fired material of the lithium - rich manganese - based cathode material to the quenching liquid is 1:(1 - 3).

8. The method for preparing the surface-stabilized lithium-rich manganese-based cathode material according to claim 5, characterized in that, The quenching process is to heat the first - fired material of the lithium - rich manganese - based cathode material to 150 - 300 °C, and then pour it into the quenching liquid for cooling, where the temperature difference is greater than 100 °C. Preferably, the temperature of the quenching liquid is room temperature or 10 - 30 °C.

9. The method for preparing the surface-stabilized lithium-rich manganese-based cathode material according to claim 5, characterized in that, The quenched and cooled material is filtered and dried to obtain a dry pretreated material. The pretreated material is then subjected to secondary sintering at a temperature of 300–500℃ for 5–15 hours.

10. A secondary battery, characterized in that, Including the surface-stabilized lithium-rich manganese-based cathode material obtained by the preparation method according to any one of claims 5 to 9.

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