Composite positive electrode material coated with metal synergistic lithium supplement polyanion and preparation method of composite positive electrode material

Abstract

The invention discloses a composite positive electrode material coated with metal and lithium supplement polyanions and a preparation method, and belongs to the field of lithium ion batteries. The structure of the composite positive electrode material is as follows: a layer of synergistic transition metal decomposed by phosphoric acid transition metal salt is doped into a transition metal oxide positive electrode material bulk phase to form a synergistic transition metal doped layer on the surface layer of the transition metal oxide positive electrode material; phosphoric acid is combined with a lithium source on the surface of the transition metal oxide positive electrode material outside the synergistic transition metal doped layer to generate a lithium phosphate coating layer; the transition metal in the phosphoric acid transition metal salt is the transition metal with various valence states in cooperation with the transition metal cations. The phosphoric acid transition metal salt and the transition metal oxide positive electrode material are sequentially subjected to sanding, drying and heat treatment together to obtain the composite positive electrode material. And the cycling stability and the capacity retention ratio of the battery are greatly improved.

Description

Technical Field

[0001] This invention relates to a composite cathode material with metal-synergistic lithium supplementation and polyanion coating, and its preparation method, belonging to the field of lithium-ion battery preparation technology. Background Technology

[0002] Lithium-ion batteries, as a core technology in the current energy storage field, directly determine the performance boundaries of electric vehicles, portable electronic devices, and large-scale energy storage systems through their energy density, cycle life, and safety. Cathode materials, as the core component of the battery, bear the crucial function of lithium-ion storage and release. However, with the increasing market demand for high energy density (>300Wh / kg) and long cycle life (>2000 cycles), traditional cathode materials (such as lithium cobalt oxide, lithium iron phosphate, and ternary materials) are gradually revealing the following bottlenecks:

[0003] Capacity decay mechanism: Irreversible loss of active lithium during cycling (such as SEI film formation and transition metal dissolution) leads to a rapid decrease in capacity.

[0004] Insufficient high voltage stability: When the working voltage is increased to above 4.5V, the electrolyte decomposition intensifies, and the risk of the positive electrode material structure collapses increases.

[0005] Limitations of lithium replenishment technology: Existing pre-lithiation processes rely on external lithium replenishment agents (such as Li5FeO4), which increases manufacturing costs and is prone to side reactions.

[0006] To address the aforementioned issues, lithium-rich manganese-based materials (LRMs) are considered candidates for next-generation high-energy-density cathode materials due to their high specific capacity (>250 mAh / g) and low cost. However, LRMs still suffer from problems such as low initial efficiency (<85%), lattice oxygen evolution during cycling, and transition metal migration, which severely restrict their commercialization process.

[0007] However, existing technical solutions have many limitations.

[0008] Coating modification technology

[0009] Coatings are widely used to improve the interfacial stability of cathode materials, but existing technologies have significant shortcomings:

[0010] Limited material selection: While mainstream coating materials (such as Al2O3 and LiF) can inhibit electrolyte corrosion, they lack lithium replenishment capabilities. For example, patent CN117121228A discloses a "double-layer coating structure (metal oxide + fluoride)," but its coating layer only serves as a physical barrier and cannot compensate for the loss of active lithium.

[0011] Poor process compatibility: High-temperature sintering (>500℃) or chemical vapor deposition (CVD) processes can easily lead to uneven coating and damage the material's bulk structure.

[0012] Lithium replenishment technology

[0013] Pre-lithiation additives, such as Li5FeO4 and Li2S, require an additional mixing step, and the additives react with the electrolyte to generate gas (patent CN118431411A).

[0014] Oxygen redox lithium replenishment: utilizing the reversible oxidation (O2) of lattice oxygen in lithium-rich materials. 2 -→O-), but accompanied by oxygen evolution (O2↑) and structural distortion (patent CN202411944032).

[0015] Transition Metal Collaborative Design

[0016] Limited metal types: Existing technologies mostly focus on common metals such as Mn, Co, Ni, and Fe, which have limited redox activity (e.g., Mn). 3+ / Mn 4+ Only 0.5-1 Li is released. + / atom).

[0017] The synergistic mechanism is unclear: Patent CN120000000X proposes "Mn-Co dual doping", but does not explain the intermetallic electron transfer path, resulting in low lithium replenishment efficiency.

[0018] Transition metal phosphates possess a similar olivine structure and exhibit high safety and stability. Furthermore, after recombination, transition metal phosphates can achieve transition metal doping and form a phosphate fast-ion conductor coating layer on the surface of transition metal oxides. This transition metal doping undergoes a transition from a low valence state to a high valence state during charging, releasing more Li to meet charge conservation requirements. + To achieve lithium replenishment, and simultaneously, due to the effect of transition metal phosphate salts, a fast-ion conductor coating layer formed on the surface of the transition metal oxide can suppress the electrolyte's erosion of the cathode material while also improving Li-energy efficiency. + This improves the material's cycle stability and rate performance through transmission. Summary of the Invention

[0019] To address the issue of electrolyte directly corroding the cathode material, leading to premature structural changes, transition metal dissolution, and significantly reduced cycle stability and capacity retention, this invention proposes a metal-synergistic lithium-supplementing polyanion-coated composite cathode material and its preparation method.

[0020] To achieve the purpose of the invention, the present invention adopts the following technical solution:

[0021] One objective of this invention is to provide a composite cathode material with metal-coated lithium-ion polyanion coating. The composite cathode material is characterized by the following structure: a co-transition metal doping layer is formed on the surface of the transition metal oxide cathode material by the co-transition metal salt obtained from the decomposition of the transition metal phosphate and the co-transition metal doping layer formed by the co-transition metal salt obtained from the decomposition of the transition metal salt and the lithium source on the surface of the transition metal oxide cathode material. Outside the co-transition metal doping layer, there is a lithium phosphate coating layer formed by the combination of phosphoric acid obtained from the decomposition of the transition metal salt and the lithium source on the surface of the transition metal oxide cathode material.

[0022] Transition metal phosphate decomposes to form a co-transition metal and phosphoric acid. The transition metal in the transition metal phosphate, i.e. the co-transition metal cation, has multiple valence states, including titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), etc.

[0023] The phosphate transition metal salt includes any one or a combination of at least two of the following: titanium phosphate, vanadium phosphate, chromium phosphate, manganese phosphate, iron phosphate, cobalt phosphate, nickel phosphate, nickel phosphate, copper phosphate, molybdenum phosphate, ruthenium phosphate, rhodium phosphate, palladium phosphate, cadmium phosphate, hafnium phosphate, tantalum phosphate, tungsten phosphate, rhenium phosphate, osmium phosphate, and iridium phosphate. However, not only the combinations listed herein, but also other unlisted combinations within this range are applicable. As a preferred embodiment of the present invention, the phosphate transition metal salt is preferably iron phosphate. Iron phosphate is inexpensive and suitable for large-scale industrial production. Furthermore, the iron in iron phosphate is in the +2 valence state, making it easier to oxidize to a higher valence state during charging, releasing more Li ions.

[0024] The thickness of the lithium phosphate coating is 1–500 nm.

[0025] After heat treatment, the surface transition metal phosphate salt of this composite cathode material decomposes into phosphate ions and transition metal ions. The transition metal ions are incorporated into the bulk phase of the transition metal oxide, while the phosphate ions combine with the lithium source near the surface of the transition metal oxide cathode material to form a lithium phosphate coating. During charging, the transition metal incorporated into the bulk phase undergoes oxidation, releasing more lithium source to maintain charge balance and improve the battery's rate performance. Simultaneously, the stronger bonding formed by the incorporated transition metal suppresses the dissolution of the original transition metal oxide and the release of gas. Furthermore, the lithium phosphate coating formed on the surface enhances both the lithium content and the efficiency of the lithium-ion battery. + The transmission of electrons can reduce side reactions between the electrolyte and the composite cathode material, protect the composite cathode material, suppress electron loss, and improve battery cycle performance and thermal stability.

[0026] As a preferred technical solution of the present invention, the transition metal oxide cathode material includes any one or a combination of at least two of ternary cathode materials, lithium-rich cathode materials, or lithium nickel manganese oxide spinel materials. The combination can be ternary cathode material and lithium-rich cathode material, lithium-rich cathode material and lithium nickel manganese oxide spinel material, or ternary cathode material and lithium nickel manganese oxide spinel material, etc., but not only the combinations listed herein, but other unlisted combinations within this range are also applicable.

[0027] In a preferred embodiment of the present invention, the metal-coated lithium-supplemented polyanion-coated composite cathode material is a heat-treated cathode material. The composite cathode material has a Li3PO4 coating layer on its surface, beneath which lies a transition metal oxide. The bulk phase of the transition metal oxide contains a transition metal phosphate salt. Due to the presence of the surface coating layer, the composite cathode material can effectively inhibit electrolyte decomposition and prevent electrolyte attack on the cathode material. Furthermore, the presence of Li3PO4, a fast ion conductor, can effectively improve the rate performance of the material. Simultaneously, because the transition metal phosphate salt is doped into the bulk phase of the transition metal oxide, it provides more lithium source during charging, thereby increasing the battery's discharge capacity. The doped transition metal can also form stronger valence bonds, reducing gas generation in the battery.

[0028] The second objective of this invention is to provide a method for preparing the composite cathode material as described in the first objective, the method comprising the following steps: sequentially milling, drying and heat-treating a transition metal phosphate salt and a transition metal oxide cathode material to obtain the composite cathode material.

[0029] In a preferred embodiment of this invention, taking the composite cathode material as 100% by mass, the mass fraction of the transition metal oxide cathode material is 0.5% to 99.9%. This mass fraction can be 0.5%, 1%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or 99.5%, etc. However, not only the values ​​listed herein, but other unlisted values ​​within this range are also applicable, with 90% to 99.9% being preferred. Excessive content of the transition metal oxide cathode material will result in an insufficient proportion of the transition metal phosphate salt in the composite cathode material, failing to play a role in stabilizing the structure; insufficient content of the transition metal oxide cathode material will cause a decrease in the specific capacity of the composite cathode material. As a preferred embodiment of the present invention, the mass percentage content of the transition metal phosphate salt in the composite material is 0.1% to 99.5%, preferably 0.1% to 10%. Excessive content of the transition metal phosphate salt will cause a decrease in the rate performance of the composite cathode material due to the inactive nature of the transition metal phosphate salt; insufficient content will fail to protect the transition metal oxide structure from damage caused by electrolyte side reactions.

[0030] As a preferred technical solution of the present invention, the sand milling process involves placing the transition metal phosphate salt and the transition metal oxide cathode material in a certain amount of ethanol solvent and performing sand milling. The sand milling process can grind the transition metal phosphate salt into fine particles. Since the transition metal oxide has high enough mechanical strength, it can maintain its original state, while the transition metal phosphate salt is coated on the surface of the transition metal oxide.

[0031] Preferably, the amount of ethanol is 1L of ethanol solvent per 100g of powder (total amount of transition metal phosphate and transition metal oxide cathode material);

[0032] Preferably, the milling speed is 50–2000 rpm; more preferably, the milling time is 60–120 min. Excessive milling speed will cause damage to the composite cathode material, while insufficient speed will prevent the transition metal phosphate salt from adhering tightly to the transition metal oxide material.

[0033] As a preferred embodiment of the present invention, the drying process involves placing the milled material into a vacuum oven for drying. Preferably, the drying temperature is 80–120°C; more preferably, the drying time is 18–24 hours.

[0034] As a preferred embodiment of the present invention, the heat treatment temperature is 100-900℃, preferably higher than the decomposition temperature of the corresponding transition metal phosphate salt.

[0035] Preferably, the heat treatment time is 3 to 5 hours;

[0036] Preferably, the atmosphere for the heat treatment is an inert atmosphere, and more preferably an argon atmosphere.

[0037] If the heat treatment temperature described in this invention is too low, the transition metal phosphate salt will not decompose, thus preventing the transition metal from entering the bulk phase of the material.

[0038] This invention discloses a composite cathode material with metal-synergistic lithium supplementation and polyanion coating, and its preparation method. The specific steps of the method include:

[0039] (1) Place 396g of transition metal oxide cathode material and 4g of transition metal phosphate into a sand mill. The solvent is ethanol. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain a composite cathode material mixture.

[0040] (2) Drying treatment of composite cathode material: The composite cathode material mixture obtained in the first step is placed in a vacuum drying oven at 120°C and dried for 24 hours to obtain the composite cathode material;

[0041] (3) The composite cathode material is placed in a tube furnace under an argon atmosphere for heat treatment at a temperature of 900°C for 3 hours to obtain the composite cathode material with metal synergistic lithium supplementation and polyanion coating.

[0042] Preparation of a lithium-ion battery:

[0043] Step 1, Preparation of composite positive electrode:

[0044] (1) Prepare a slurry by mixing the composite positive electrode material, binder and conductive agent obtained in the present invention in a certain proportion;

[0045] (2) Take a certain amount of the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry.

[0046] (3) Apply the mixed slurry to the aluminum foil and smooth it with a scraper;

[0047] (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours.

[0048] The second step is battery assembly:

[0049] (1) The dried electrode sheet is punched into an electrode sheet with a diameter of 12mm using a punching machine;

[0050] (2) The battery assembly operation is carried out in the glove box. The battery assembly sequence is negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, electrolyte, lithium sheet, positive electrode shell, and finally the battery is pressed tightly with a sealing machine.

[0051] (3) The assembled battery is tested for electrochemical performance on a battery testing platform.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) Significantly improves first charge / discharge efficiency and reversible capacity

[0054] Traditional transition metal oxides typically suffer from first-efficiency (FAE) below 85% due to lattice oxygen activity and transition metal dissolution issues. However, this invention achieves a significant improvement in FAE through a combination of a metal-synergistic lithium replenishment mechanism and a polyanion coating layer.

[0055] Lithium supplementation through iron (Fe) oxidation: During charging, it oxidizes into Each mole of Fe oxidation releases 1 mol of lithium ions, dynamically compensating for lithium loss.

[0056] High voltage compatibility: The phosphate transition metal salt coating (such as Li3PO4) remains stable at a high voltage of 4.8V.

[0057] (2) Long-cycle stability is achieved in this invention through the following design:

[0058] Uniform nano-coating layer: A dense phosphate coating layer with a thickness of 1-500 nm is formed by sand milling (500-2000 rpm) combined with high-temperature heat treatment (100-900℃). This coating layer effectively blocks electrolyte corrosion.

[0059] Metal synergistic suppression of phase transition: Fe doping creates a "pinning effect" that suppresses the transformation of the layered structure to the spinel phase during charging and discharging.

[0060] (3) Technological innovation reduces energy consumption and costs:

[0061] Traditional coating processes rely on solid-state coating, which can easily damage the material structure. The preparation method of this invention achieves green and efficient production through the following optimizations:

[0062] Sand milling-heat treatment process chain: The sand milling stage adopts high-energy ball milling (speed 500~2000rpm) to complete the curing of the coating layer and the doping of transition metals at high temperature (100~900℃) and avoid material damage.

[0063] Improved raw material utilization: By precisely controlling the mass ratio of transition metal oxides to polyanions, the amount of precious transition metals used is reduced, material costs decrease, and industrialization becomes easier. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the preparation process of a composite cathode material with metal-synergistic lithium supplementation and polyanion coating.

[0065] Figure 2 This is a TEM image of the surface coating layer in Example 1.

[0066] Figure 3 XPS diagram of transition metal elements in Example 1.

[0067] Figure 4 The image shows the TOF-SIMS diagram of the composite cathode material in Example 1. Detailed Implementation

[0068] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0069] Example 1

[0070] This embodiment describes a method for preparing a composite cathode material with metal-synergistic lithium-supplementing polyanion coating, as follows:

[0071] The first step involves using LNCM material as a substrate and Fe3(PO4)2 as a composite material to prepare a metal-synergistic lithium-supplementing polyanion-coated composite cathode material:

[0072] (1) Add 396g of LNCM material, 4g of Fe3(PO4)2 and 4L of ethanol to a sand mill for sand milling. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain composite cathode material mixture.

[0073] (2) Drying the composite cathode material mixture: Place the composite cathode material mixture in a vacuum drying oven at 120°C for 24 hours to dry it, and you will get the dried composite cathode material.

[0074] (3) The dried composite cathode material was placed in a tube furnace under an argon atmosphere for heat treatment. The heat treatment temperature was 900℃ and the heat treatment time was 3h to obtain a composite cathode material with metal synergistic lithium supplementation polyanion coating.

[0075] The second step is the preparation of the composite positive electrode:

[0076] (1) Prepare the composite cathode material (approximately 1% Fe3(PO4)2@LNCM), binder (PVDF), and conductive agent (C) in a ratio of 8:1:1 and place them in a mixing tank. You can take 250 mg of composite cathode material, 31.25 mg of PVDF, and 31.25 mg of C.

[0077] (2) Take the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times, each time for 12 minutes, so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry.

[0078] (3) Apply the mixed slurry onto the aluminum foil and smooth it with a 400mm thick scraper;

[0079] (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours.

[0080] The third step is battery assembly:

[0081] (1) The dried electrode sheet is punched into a circular electrode sheet with a diameter of 12mm using a punching machine;

[0082] (2) Roll pressing the electrode sheets;

[0083] (3) Weigh the rolled electrode, calculate and record the amount of active material. For example, if the mass of the electrode is 8.4 mg, then the amount of active material = (mass of electrode - mass of aluminum foil) * 0.8;

[0084] (4) The battery assembly operation is carried out in the glove box. The assembly sequence of the battery is as follows: negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, ENCHEM electrolyte, lithium sheet, positive electrode shell. Finally, the battery is pressed tightly with a sealing machine at a pressure of 50MPa.

[0085] (5) Place the assembled battery into the battery testing platform to test its electrochemical performance.

[0086] The preparation process flow of this embodiment is as follows: Figure 1 As shown, Figure 1 The entire process of preparing the composite cathode (milling, drying, and heat treatment) is demonstrated. The composite cathode obtained in this embodiment was characterized by TEM and XPS, as shown below. Figure 2 and Figure 3 As shown, Figure 2 The image clearly shows a coating layer approximately 10 nm thick on the surface of the LNCM material. This coating layer is a Li3PO4 fast ion conductor coating layer formed after heat treatment. This coating layer can improve the rate performance of the battery and inhibit the erosion of LNCM by the electrolyte. Figure 3 For XPS etching test, Figure 3The curves in the figure represent the Fe content in LNCM materials etched at different depths (how this is shown). As can be seen from the figure, Fe is doped into the bulk phase of the LNCM material (explained in more detail), achieving the purpose of synergistic lithium replenishment with metal. Figure 4 The figure shows the distribution of Li elements on the surface of the composite cathode material using TOF-SIMS characterization. The brighter areas in the figure represent Li elements, which are distributed in a spherical shape on the surface of the material. This indicates that the surface coating layer contains Li. Therefore, it is shown that the phosphate ions in the decomposed transition metal phosphate salt and the Li near the surface of the transition metal oxide form a Li3PO4 coating layer on the surface of the material.

[0087] Its electrochemical performance is shown in Table 1. The battery was tested in a voltage window of 2–4.8V. Its first-cycle discharge specific capacity was 225.5 mAh / g. After cycling at 25℃ and 1C rate, its capacity retention after 300 cycles was 89.8%, showing a significant improvement in rate performance compared to Comparative Example 1. This improvement is attributed to the oxidation of Fe, which releases more Li to maintain charge balance. + This improves the discharge specific capacity of the material.

[0088] Example 2

[0089] This embodiment describes a method for preparing a composite cathode material with metal-synergistic lithium-supplementing polyanion coating, as follows:

[0090] The first step involves using LNCM material as a substrate and Fe3(PO4)2 as a composite material to prepare a metal-synergistic lithium-supplementing polyanion-coated composite cathode material:

[0091] (1) Add 392g of LNCM material, 8g of Fe3(PO4)2 and 4L of ethanol to a sand mill for sand milling. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain composite cathode material mixture.

[0092] (2) Drying the composite cathode material mixture: Place the composite cathode material mixture in a vacuum drying oven at 120°C for 24 hours to dry it, and you will get the dried composite cathode material.

[0093] (3) The dried composite cathode material was placed in a tube furnace under an argon atmosphere for heat treatment. The heat treatment temperature was 900℃ and the heat treatment time was 3h to obtain a composite cathode material with metal synergistic lithium supplementation polyanion coating.

[0094] The second step is the preparation of the composite positive electrode:

[0095] (1) Prepare the composite cathode material (approximately 2% Fe3(PO4)2@LNCM), binder (PVDF), and conductive agent (C) in a ratio of 8:1:1 and place them in a mixing tank. You can take 250 mg of composite cathode material, 31.25 mg of PVDF, and 31.25 mg of C.

[0096] (2) Take the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times, each time for 12 minutes, so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry.

[0097] (3) Apply the mixed slurry onto the aluminum foil and smooth it with a 400mm thick scraper;

[0098] (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours.

[0099] The third step is battery assembly:

[0100] (1) The dried electrode sheet is punched into a circular electrode sheet with a diameter of 12mm using a punching machine;

[0101] (2) Roll pressing the electrode sheets;

[0102] (3) Weigh the rolled electrode, calculate and record the amount of active material. For example, if the mass of the electrode is 8.4 mg, then the amount of active material = (mass of electrode - mass of aluminum foil) * 0.8;

[0103] (4) The battery assembly operation is carried out in the glove box. The assembly sequence of the battery is as follows: negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, ENCHEM electrolyte, lithium sheet, positive electrode shell. Finally, the battery is pressed tightly with a sealing machine at a pressure of 50MPa.

[0104] (5) Place the assembled battery into the battery testing platform to test its electrochemical performance.

[0105] The preparation process flow of this embodiment is as follows: Figure 1 As shown, Figure 1 The entire process of preparing the composite cathode (milling, drying, and heat treatment) is demonstrated. The composite cathode obtained in this embodiment was characterized by TEM and XPS, as shown below. Figure 2 and Figure 3 As shown, Figure 2 The image clearly shows a coating layer approximately 10 nm thick on the surface of the LNCM material. This coating layer is a Li3PO4 fast ion conductor coating layer formed after heat treatment. This coating layer can improve the rate performance of the battery and inhibit the erosion of LNCM by the electrolyte. Figure 3 For XPS etching test, Figure 3The curves in the figure represent the Fe content in LNCM materials etched at different depths. As can be seen from the figure, Fe is doped into the bulk phase of the LNCM material, achieving the purpose of synergistic lithium replenishment by metal.

[0106] Its electrochemical performance is shown in Table 1. Its initial discharge specific capacity is 221.3 mAh / g. After cycling at 25℃ and 1C rate, its capacity retention after 300 cycles is 90.2%, showing a significant improvement in rate performance compared to Comparative Example 1. This is attributed to the oxidation of Fe, which releases more Li to maintain charge balance. + This improves the discharge specific capacity of the material.

[0107] Example 3

[0108] This embodiment describes a method for preparing a composite cathode material with metal-synergistic lithium-supplementing polyanion coating, as follows:

[0109] The first step involves using LNCM material as a substrate and VPO4 as a composite material to prepare a metal-synergistic lithium-supplemented polyanion-coated composite cathode material:

[0110] (1) Add 396g of LNCM material, 4g of VPO4 and 4L of ethanol to a sand mill for sand milling. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain composite cathode material mixture.

[0111] (2) Drying the composite cathode material mixture: Place the composite cathode material mixture in a vacuum drying oven at 120°C for 24 hours to dry it, and you will get the dried composite cathode material.

[0112] (3) The dried composite cathode material was placed in a tube furnace under an argon atmosphere for heat treatment. The heat treatment temperature was 900℃ and the heat treatment time was 3h to obtain a composite cathode material with metal synergistic lithium supplementation polyanion coating.

[0113] The second step is the preparation of the composite positive electrode:

[0114] (1) Prepare the composite cathode material (about 1% VPO4@LNCM), binder (PVDF), and conductive agent (C) in a ratio of 8:1:1 and put them into a mixing tank. You can take 250 mg of composite cathode material, 31.25 mg of PVDF, and 31.25 mg of C.

[0115] (2) Take the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times, each time for 12 minutes, so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry.

[0116] (3) Apply the mixed slurry onto the aluminum foil and smooth it with a 400mm thick scraper;

[0117] (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours.

[0118] The third step is battery assembly:

[0119] (1) The dried electrode sheet is punched into a circular electrode sheet with a diameter of 12mm using a punching machine;

[0120] (2) Roll pressing the electrode sheets;

[0121] (3) Weigh the rolled electrode, calculate and record the amount of active material. For example, if the mass of the electrode is 8.4 mg, then the amount of active material = (mass of electrode - mass of aluminum foil) * 0.8;

[0122] (4) The battery assembly operation is carried out in the glove box. The assembly sequence of the battery is as follows: negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, ENCHEM electrolyte, lithium sheet, positive electrode shell. Finally, the battery is pressed tightly with a sealing machine at a pressure of 50MPa.

[0123] (5) Place the assembled battery into the battery testing platform to test its electrochemical performance.

[0124] Its electrochemical performance is shown in Table 1. Its initial discharge specific capacity is 224.8 mAh / g. After cycling at 25℃ and 1C rate, its capacity retention after 300 cycles is 92.6%, showing a significant improvement in rate performance compared to Comparative Example 1. This is attributed to the oxidation of V, which releases more Li to maintain charge balance. + This improves the discharge specific capacity of the material.

[0125] Comparative Example 1

[0126] This example is a comparative example, as follows:

[0127] The first step is to use LNCM material as a substrate to prepare the cathode material:

[0128] (1) Add 400g of LNCM material and 4L of ethanol to a sand mill for sand milling. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain the positive electrode material mixture.

[0129] (2) Drying the cathode material mixture: Place the cathode material mixture in a vacuum drying oven at 120°C for 24 hours to dry it, and you will get the dried cathode material.

[0130] (3) The dried composite cathode material is placed in a tube furnace under an argon atmosphere for heat treatment. The heat treatment temperature is 900℃ and the heat treatment time is 3h to obtain the heat-treated cathode material.

[0131] The second step is the preparation of the positive electrode sheet:

[0132] (1) Prepare the positive electrode material (LNCM), binder (PVDF), and conductive agent (C) in a ratio of 8:1:1 and put them into a mixing tank. You can take 250 mg of positive electrode material, 31.25 mg of PVDF, and 31.25 mg of C.

[0133] (2) Take the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times, each time for 12 minutes, so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry.

[0134] (3) Apply the mixed slurry onto the aluminum foil and smooth it with a 400mm thick scraper;

[0135] (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours.

[0136] The third step is battery assembly:

[0137] (1) The dried electrode sheet is punched into a circular electrode sheet with a diameter of 12mm using a punching machine;

[0138] (2) Roll pressing the electrode sheets;

[0139] (3) Weigh the rolled electrode, calculate and record the amount of active material. For example, if the mass of the electrode is 8.4 mg, then the amount of active material = (mass of electrode - mass of aluminum foil) * 0.8;

[0140] (4) The battery assembly operation is carried out in the glove box. The assembly sequence of the battery is as follows: negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, ENCHEM electrolyte, lithium sheet, positive electrode shell. Finally, the battery is pressed tightly with a sealing machine at a pressure of 50MPa.

[0141] (5) Place the assembled battery into the battery testing platform to test its electrochemical performance.

[0142] Its electrochemical performance is shown in Table 1. Its first-cycle discharge specific capacity is 208.28 mAh / g. Under the conditions of 25℃ and 1C rate, the capacity retention rate after 300 cycles is 60.2%. Because there is no change in the valence state of the transition metal, the amount of released Li+ is reduced. Therefore, the discharge specific capacity of the material is lower than that of Examples 1, 2 and 3. At the same time, since the surface of the material in Comparative Example 1 is not protected by the coating layer, it cannot suppress the erosion of the positive electrode material by the electrolyte, which leads to the premature collapse of the positive electrode material structure. Therefore, the capacity retention rate of Comparative Example 1 is poor.

[0143] Table 1 Comparison of battery performance of coin cells assembled from different modified samples

[0144]

[0145] Example 1 achieved metal-synergistic lithium replenishment through polyanionic coating by heat treatment at 900°C for 3 hours using a composite of 1% Fe3(PO4)2 and LNCM. Example 2 improved cycle stability by increasing the ratio of 2% Fe3(PO4)2 and LNCM. Example 3 achieved metal-synergistic lithium replenishment by using a composite of 1% VPO4 and LNCM with different transition metal phosphate salts. The difference between Examples 1 and 2 is that different ratios of transition metal phosphate salts were used, while Example 3 used a different transition metal phosphate salt. The only difference between Examples 1-3 and Comparative Example 1 is that the comparative example only used transition metal oxides and did not use transition metal phosphate salts for composite formation.

[0146] The foregoing basic examples and their further alternative examples of the present invention can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and are claimed by the present invention. In the present invention, each alternative example can be arbitrarily combined with any other basic example and alternative example. Those skilled in the art will recognize numerous combinations. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cathode material with metal-synergistic lithium supplementation and polyanion coating, characterized in that, The composite cathode material structure consists of a transition metal oxide cathode material surface layer with a synergistic transition metal doping layer formed by the synergistic transition metal obtained from the decomposition of a transition metal phosphate salt and its doping into the bulk phase of the transition metal oxide cathode material. Outside the synergistic transition metal doping layer, there is a lithium phosphate coating layer formed by the combination of phosphoric acid obtained from the decomposition of the transition metal phosphate salt and the lithium source on the surface of the transition metal oxide cathode material. The transition metal in the transition metal phosphate salt is decomposed to form a synergistic transition metal and phosphoric acid. The transition metal in the transition metal phosphate salt, i.e. the synergistic transition metal cation, has multiple valence states.

2. The composite cathode material with metal-synergistic lithium supplementation and polyanion coating according to claim 1, characterized in that, The transition metals in transition metal phosphate salts, namely co-transition metals, include one or more of the following: titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), and iridium (Ir).

3. The composite cathode material with metal-synergistic lithium supplementation and polyanion coating according to claim 1, characterized in that, The thickness of the lithium phosphate coating is 1–500 nm.

4. The composite cathode material with metal-synergistic lithium supplementation and polyanion coating according to claim 1, characterized in that, The transition metal oxide cathode material includes any one or a combination of at least two of the following: ternary cathode material, lithium-rich cathode material, or lithium nickel manganese oxide spinel material. The combination can be ternary cathode material with lithium-rich cathode material, lithium-rich cathode material with lithium nickel manganese oxide spinel material, or ternary cathode material with lithium nickel manganese oxide spinel material, etc. However, not only the combinations listed herein, but other unlisted combinations within this range are also applicable.

5. A method for preparing the composite cathode material according to any one of claims 1-4, characterized in that, The composite cathode material is obtained by sequentially milling, drying, and heat-treating transition metal phosphate salts and transition metal oxide cathode materials.

6. The method according to claim 5, characterized in that, Based on the mass of the composite cathode material as 100%, the mass fraction of the transition metal oxide cathode material is 0.5-99.9%, preferably 90-99.9%; the mass percentage content of the transition metal phosphate salt in the composite material is 0.1-99.5%, preferably 0.1-10%; the transition metal phosphate salt includes any one or a combination of at least two of the following: titanium phosphate, vanadium phosphate, chromium phosphate, manganese phosphate, iron phosphate, cobalt phosphate, nickel phosphate, nickel phosphate, copper phosphate, molybdenum phosphate, ruthenium phosphate, rhodium phosphate, palladium phosphate, cadmium phosphate, hafnium phosphate, tantalum phosphate, tungsten phosphate, rhenium phosphate, osmium phosphate, and iridium phosphate.

7. The method according to claim 5, characterized in that, The aforementioned sand milling process involves placing the transition metal phosphate salt and the transition metal oxide cathode material in a certain amount of ethanol solvent and then performing sand milling. The sand milling process can grind the transition metal phosphate salt into fine particles. Since the transition metal oxide has high enough mechanical strength, it can maintain its original state, while simultaneously coating the transition metal phosphate salt onto the surface of the transition metal oxide. The amount of ethanol is 1L of ethanol solvent per 100g of powder; The grinding speed is 50–2000 rpm; the grinding time is 60–120 min; The drying process involves placing the milled material into a vacuum oven for drying; preferably, the drying temperature is 80–120°C; more preferably, the drying time is 18–24 hours. The heat treatment temperature is 100–900°C, preferably higher than the decomposition temperature of the corresponding transition metal phosphate salt; The heat treatment time is 3 to 5 hours; The heat treatment atmosphere is an inert atmosphere, preferably an argon atmosphere.

8. The method according to claim 5, characterized in that, Includes the following steps: (1) Place 396g of transition metal oxide cathode material and 4g of transition metal phosphate into a sand mill. The solvent is ethanol. First, premix at 500rpm for 1h, then sand mill at 2000rpm for 120min to obtain a composite cathode material mixture. (2) Drying treatment of composite cathode material: The composite cathode material mixture obtained in the first step is placed in a vacuum drying oven at 120°C and dried for 24 hours to obtain the composite cathode material; (3) The composite cathode material is placed in a tube furnace under an argon atmosphere for heat treatment at a temperature of 900°C for 3 hours to obtain the composite cathode material with metal synergistic lithium supplementation and polyanion coating.

9. A lithium-ion battery, characterized in that, Includes the composite cathode material as described in any one of claims 1-4.

10. A method for preparing a lithium-ion battery, characterized in that, Includes the following steps: Step 1, Preparation of composite positive electrode: (1) Prepare a slurry by mixing the composite cathode material, binder and conductive agent as described in any one of claims 1-4; (2) Take a certain amount of the above-prepared materials and put them into a degassing machine for mixing. Use the degassing machine to mix the materials three times so that the composite positive electrode material, binder and conductive agent are evenly mixed together to obtain a uniformly mixed slurry. (3) Apply the mixed slurry to the aluminum foil and smooth it with a scraper; (4) Place the flattened electrode in a vacuum drying oven at 120℃ and dry for 12 hours. The second step is battery assembly: (1) The dried electrode sheet is punched into an electrode sheet with a diameter of 12mm using a punching machine; (2) The battery assembly operation is carried out in the glove box. The assembly sequence of the battery is negative electrode shell, spring sheet, 1mm thick gasket, composite positive electrode sheet, separator, electrolyte, lithium sheet, positive electrode shell, and finally the battery is pressed tightly with a sealing machine.

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