Positive electrode active material, positive electrode sheet, battery, and power using device

Abstract

The application discloses a positive electrode active material, a positive electrode sheet, a battery and a power utilization device. The positive electrode active material comprises: a first active material, wherein the first active material comprises a lithium-rich manganese-based material, and the gram capacity of the first active material in the interval of 2.5 V-4.35 V is not less than 150 mAh / g; and a second active material, wherein the second active material comprises a lithium-containing phosphate. Therefore, the positive electrode active material with high energy density and optimal cycle life can be obtained.

Description

Technical Field

[0001] This application relates to the energy sector, specifically to positive electrode active materials, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] In recent years, with the development of lithium-ion battery technology, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, and have also found wide applications in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Currently, however, there are still many problems to be solved in the industrial production and application of lithium-ion batteries. Summary of the Invention

[0003] In one aspect of this application, a positive electrode active material is proposed, comprising: a first active material comprising a lithium-rich manganese-based material, wherein the specific capacity of the first active material in the 2.5V-4.35V range is not less than 150mAh / g; and a second active material comprising a lithium phosphate. Thus, a positive electrode active material with high energy density and superior cycle life can be obtained.

[0004] According to an embodiment of this application, the chemical formula of the first active material satisfies nLi2MnO3·(1-n)LiNi x Mn (1-x-y) M y O2, wherein 0.1≤n≤0.3, 0.3<x<1, 0<y<0.1, and the element M includes at least one of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta, and Hf. This allows for further improvement of the energy density of the positive electrode active material, achieving a specific capacity of not less than 150 mAh / g for the first active material in the 2.5V-4.35V range.

[0005] According to embodiments of this application, the chemical formula of the lithium-containing phosphate satisfies LiFe 1-a-b Mn a Q b PO4, wherein 0≤a≤1, 0≤b≤0.1, 0≤a+b≤1, and the Q element includes at least one of transition metal elements other than Fe and Mn, as well as non-transition metal elements. This can improve the safety performance of the positive electrode active material and reduce its manufacturing cost.

[0006] According to embodiments of this application, the mass fraction of the first active material in the positive electrode active material is 10wt%-90wt%; further, the mass fraction of the first active material in the positive electrode active material is 25wt%-90wt%. This can further improve the energy density and cycle life of the positive electrode active material.

[0007] According to an embodiment of this application, the Dv50 of the first active material is 4μm-10μm. This is beneficial for increasing the compaction density of the positive electrode active material.

[0008] According to embodiments of this application, the Dv50 of the second active material is 0.5 μm-2 μm. This is beneficial for increasing the compaction density of the positive electrode active material.

[0009] According to embodiments of this application, the discharge voltage plateau of the positive electrode active material is 3.3V-3.8V. This is beneficial for improving the energy density of the positive electrode active material.

[0010] In another aspect of this application, a positive electrode sheet is proposed, comprising a positive current collector and a positive active material layer, wherein the positive active material layer is located on one side of the positive current collector and comprises the aforementioned positive active material. Thus, this positive electrode sheet possesses all the features and advantages of the aforementioned positive active material, which will not be elaborated further here.

[0011] According to an embodiment of this application, the compaction density of the positive electrode sheet is 2.5 g / cm³. 3 -3.1g / cm 3 This is beneficial for obtaining batteries with higher energy density.

[0012] In another aspect, this application proposes a battery comprising a positive electrode plate, wherein the positive electrode plate is the aforementioned positive electrode plate. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode plate, which will not be repeated here.

[0013] In another aspect, this application proposes an electrical device comprising the aforementioned battery. Thus, the electrical device possesses all the features and advantages of the aforementioned battery, which will not be repeated here. Attached Figure Description

[0014] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0015] Figure 1 A schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application is shown;

[0016] Figure 2This is a schematic diagram of a battery according to one embodiment of this application;

[0017] Figure 3 yes Figure 2 An exploded view of a battery according to one embodiment of this application is shown;

[0018] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0019] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0020] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0021] Figure 7 This is a schematic diagram of an electrical device that uses a battery as a power source according to one embodiment of this application;

[0022] Figure 8 This is the charge-discharge curve of the first active material in Example 1 of this application;

[0023] Figure 9 These are the cycle life curves of Embodiment 1, Embodiment 6, and Comparative Example 1 of this application.

[0024] Explanation of reference numerals in the attached figures:

[0025] 1: Battery pack; 2: Upper casing; 3: Lower casing; 4: Battery module; 5: Battery; 10: Positive electrode sheet; 11: Positive current collector; 12: Positive active material layer; 51: Housing; 52: Electrode assembly; 53: Cover plate. Detailed Implementation

[0026] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0027] In one aspect of this application, a positive electrode active material is proposed, comprising: a first active material comprising a lithium-rich manganese-based material, wherein the specific capacity of the first active material in the 2.5V-4.35V range is not less than 150mAh / g; and a second active material comprising a lithium phosphate. Thus, a positive electrode active material possessing high specific capacity, superior cycle life, and high energy density can be obtained. Specific capacity refers to the ratio between the capacitance that an active material can release and the mass of the active material; a higher specific capacity indicates a greater capacitance that a unit mass of active material can deliver.

[0028] To facilitate understanding, the principle behind the aforementioned beneficial effects of the positive electrode active material in this application is explained below:

[0029] While lithium phosphate cathode active materials offer advantages such as low cost and high safety, they also suffer from drawbacks including low specific capacity and rapid early cycle degradation. For example, during the initial charge and discharge of the battery cell, the electrolyte undergoes a reduction decomposition reaction on the negative electrode surface, forming a solid electrolyte interphase (SEI) film. The formation of the SEI film consumes a significant amount of active lithium, resulting in a decrease in the actual energy density of the battery compared to the theoretical calculation. During battery cell cycling, the cracking and fragmentation of lithium phosphate particles, as well as the thickening and repair of the SEI film, continuously consume active lithium, causing a significant decline in the battery's cycle performance.

[0030] Furthermore, while adding lithium-replenishing additives to the positive electrode active material layer can replenish lithium ions inside the battery before it operates, addressing issues such as low energy density, low initial cycle efficiency, and poor cycle life, these additives typically require charging to a relatively high voltage to effectively utilize their replenishing capacity. For example, lithium-rich manganese-based materials, due to their superlattice formed by lithium-rich manganese oxide and layered lithium metal oxides, offer advantages such as high capacity, high energy density, low cost, and long cycle life. However, these materials require charging to 4.5V to effectively utilize their capacity and achieve the replenishing effect, while lithium phosphates typically operate at a lower voltage, usually 3.2-4.2V. If lithium phosphates are mixed with lithium-replenishing additives with a charging upper limit voltage greater than 4.5V to form the positive electrode active material layer, the structure of the lithium phosphate will collapse when the battery is charged to 4.5V, preventing lithium ions from re-intercalating and causing a sharp decline in capacity, resulting in a significant decrease in the battery's cycle performance.

[0031] In this application, by using a lithium-rich manganese-based material with a specific capacity of not less than 150 mAh / g during 0.33C charge-discharge in the 2.5-4.35V range as a lithium replenishing additive and mixing it with lithium-containing phosphate as a positive electrode active material, not only can the energy density of the lithium-containing phosphate be significantly improved (energy density = specific capacity × voltage plateau × compaction density), but the lithium-rich manganese-based material with a specific capacity of not less than 150 mAh / g during 0.33C charge-discharge in the 2.5-4.35V range can also be gradually activated at low voltage, releasing active lithium during cycling to replenish anode lithium consumption, improve the early-stage degradation trend of the phosphate system, and achieve slow degradation. In summary, by combining the high capacity and high voltage characteristics of lithium-rich manganese-based materials with the low cost and high safety advantages of lithium-containing phosphate particles, the electrical performance such as energy density and cycle stability of the lithium-containing phosphate system is greatly improved, resulting in a positive electrode active material with high specific capacity, excellent cycle life, and high energy density. In summary, by using a lithium-rich manganese-based material with a specific capacity of not less than 150 mAh / g, which can be charged and discharged at 0.33C in the 2.5-4.35V range, mixed with lithium phosphate as the positive electrode active material of lithium batteries, the high capacity and high voltage characteristics of the lithium-rich manganese-based material are combined with the low cost and high safety of lithium phosphate particles, which greatly improves the electrical performance of the lithium phosphate system, such as energy density and cycle stability. A positive electrode active material with high capacity, better cycle life, and high energy density is obtained.

[0032] In the description of this application, "first feature" and "second feature" may include one or more of the features.

[0033] According to some embodiments of this application, the first active material is a lithium-rich manganese-based material, and the chemical formula of the first active material can satisfy nLi2MnO3·(1-n)LiNi. x Mn （1-x-y） M y O2, where 0.1≤n≤0.3, 0.3<x<1, 0<y<0.1, and element M includes at least one of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta, and Hf. The element M doped in lithium-rich manganese-based materials can promote the diffusion of lithium ions in the first active material, thereby enhancing the specific capacity of the lithium-rich manganese-based material and thus increasing the battery capacity by improving the kinetic performance of the first active material. Manganese can also improve the crystal structure stability of lithium-rich manganese-based materials, preventing significant structural changes during charge and discharge, and improving the capacity, cycle stability, and cycle life of the lithium-rich manganese-based material. Specifically, LiNi in the first active material... x Mn （1-x-y） M yO2 is the electrochemically active component, which can release capacity during cycling. Li2MnO3 in the primary active material is the inactive component, playing a role in stabilizing LiNi during cycling. x Mn （1-x-y） M y The role of the O2 chemical structure is such that, by controlling the proportion of Li2MnO3 in the first active material to be 0.1-0.3, the specific capacity of the first active material in the 2.5V-4.35V range is not less than 150mAh / g. For example, see [link to relevant documentation]. Figure 8 When the chemical formula of the first active material is 0.2Li2MnO3·0.8LiNi 0.5 Mn 0.5 When O2 is present, the specific capacity of the first active material when charged to 4.35V can exceed 155mAh / g. This is achieved when the chemical formula of the first active material satisfies nLi2MnO3·(1-n)LiNi x Mn （1-x-y） M y When O2 is present and n is less than 0.1, the structure of the first active material is unstable, and the cycle stability of the active component in the first active material is poor; when the chemical formula of the first active material satisfies nLi2MnO3·(1-n)LiNi x Mn （1-x-y） M y When O2 is present and n is greater than 0.3, the specific capacity of the first active material is low, the lithium replenishment effect is poor, and the energy density improvement of the lithium phosphate system is not significant.

[0034] According to some embodiments of this application, the second active material is a lithium-containing phosphate. Specifically, the second active material may include an olivine-type lithium-containing phosphate. The type of lithium-containing phosphate is not particularly limited; for example, the chemical formula of the lithium-containing phosphate may satisfy LiFe... 1-a-b Mn a Q b PO4, wherein 0≤a≤1, 0≤b≤0.1, 0≤a+b≤1, and element Q includes at least one of transition metal elements other than Fe and Mn, as well as non-transition metal elements. Specifically, lithium-containing phosphates may include at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, modified lithium iron phosphate, modified lithium manganese phosphate, and modified lithium manganese iron phosphate. The modifying compounds of the above materials may be used to modify the materials through doping and / or surface coating. Lithium-containing phosphates have the advantages of low cost, superior drop test and nail penetration test results, and higher thermal safety during overcharging, which can effectively reduce the possibility of danger caused by thermal abuse and mechanical abuse of the battery cell.

[0035] According to some embodiments of this application, the mixing ratio of the first active material and the second active material in the positive electrode active material is not particularly limited. For example, the mass fraction of the first active material in the positive electrode active material can be 10wt%-90wt%; further, the mass fraction of the first active material in the positive electrode active material can be 25wt%-90wt%. When the content of the first active material in the positive electrode active material is within the above range, the content of the first active material in the positive electrode active material is relatively high, which can effectively improve the energy density of the positive electrode active material.

[0036] According to some embodiments of this application, the particle sizes of the first and second active materials are not particularly limited. For example, the Dv50 of the first active material can be 4 μm-10 μm; further, the Dv50 of the first active material can be 6-8 μm; the Dv50 of the second active material can be 0.5 μm-2 μm; further, the Dv50 of the second active material can be 0.8-1.5 μm. When the Dv50 of the first and second active materials are within the above ranges, particle gradation can be achieved, further improving the compaction density of the positive electrode active material. The Dv50 of the particles can be tested using a laser particle size analyzer. Specifically, the positive electrode active material powder particles are first dispersed in an appropriate amount of solvent to form a dispersion. Then, the aforementioned dispersion is placed in a laser particle size analyzer to measure the particle size of the positive electrode active material powder.

[0037] According to some embodiments of this application, by mixing lithium-rich manganese-based materials with a charging upper limit voltage of no more than 4.5V and lithium-containing phosphates with a charging upper limit voltage of no more than 4.2V in the aforementioned proportion, the discharge voltage plateau of the resulting positive electrode active material can be 3.3V-3.8V. Specifically, the discharge voltage plateau of the positive electrode active material can be obtained by testing as follows: the positive electrode active material is made into a battery using conventional processes, the residual charge inside the battery is drained, and then it is charged at 1 / 3C to its respective upper limit voltage. Then, it is charged at a constant voltage under the upper limit voltage until the current is ≤0.05C. After standing for 5 minutes, it is discharged at 1 / 3C until the battery voltage is 2.5V. The amount of electricity released by the battery during this discharge process is the discharge capacity, and the energy output by the battery during this discharge process is the discharge energy. The discharge voltage plateau can be calculated using the formula: Discharge voltage plateau = Discharge energy / Discharge capacity. As the proportion of lithium-rich manganese-based materials in the mixed positive electrode active material increases, the discharge voltage plateau of the positive electrode active material gradually rises. When the discharge voltage plateau of the positive electrode active material is within the aforementioned range, compared with a single lithium phosphate positive electrode active material (voltage plateau of approximately 3.2V), the mixed positive electrode active material obtained by mixing the aforementioned proportions in this application, which includes lithium-rich manganese-based materials and lithium phosphate, has a higher energy density.

[0038] In this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may differ by less than 10% or by a difference that is considered reasonable by those skilled in the art, such as 1%, 2%, 3%, 4%, or 5%. In another aspect of this application, reference is made to... Figure 1 This application proposes a positive electrode sheet 10, including a positive current collector 11 and a positive active material layer 12. The positive active material layer 12 is located on one side of the positive current collector 11 and includes the aforementioned positive active material. As an example, the positive current collector 11 has two surfaces opposite each other in its own thickness direction, and the positive active material layer 12 can be disposed on either or both of the two opposite surfaces of the positive current collector 11. Thus, this positive electrode sheet includes all the features and advantages of the aforementioned positive active material, which will not be repeated here.

[0039] According to some embodiments of this application, the positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by depositing metal material on a polymer substrate). For example, the positive electrode current collector can be aluminum foil.

[0040] In another aspect, this application proposes a battery comprising: a positive electrode, wherein the positive electrode is the aforementioned positive electrode. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through. Therefore, this battery exhibits high energy density and superior capacity retention.

[0041] According to some embodiments of this application, there are no particular limitations on the shape of the battery; it can be cylindrical, square, or other arbitrary shapes. For example, Figure 2 This is a square-structured battery 5 as an example. Specifically, refer to... Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0042] In the description of this application, "multiple" means two or more.

[0043] According to some embodiments of this application, the battery may include an outer packaging. This outer packaging is used to encapsulate the positive electrode, negative electrode, and electrolyte. For example, the outer packaging may include a housing and a cover. The housing may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly using a winding process or a stacking process. The electrode assembly is encapsulated in the receiving cavity. The electrolyte may be a liquid electrolyte, which wets the electrode assembly. The number of electrode assemblies contained in the battery may be one or more, adjustable as needed.

[0044] According to some embodiments of this application, batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module. Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple batteries 5 can be fixed in place by fasteners. Battery module 4 may also include a housing with a receiving space in which the multiple batteries 5 are received.

[0045] According to some embodiments of this application, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack. Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0046] According to some embodiments of this application, by mixing a first active material with a Dv50 of 4μm-10μm and a second active material with a Dv50 of 0.5μm-2μm in the aforementioned proportion, the compaction density of the positive electrode sheet can be 2.5g / cm³. 3 -3.1g / cm 3 When the compaction density of the positive electrode sheet is within the aforementioned range, the battery containing the aforementioned positive electrode sheet has a higher energy density.

[0047] In another aspect of this application, an electrical device is proposed, comprising the aforementioned battery. The battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. The electrical device can select the battery, battery module, or battery pack according to its usage requirements.

[0048] According to some embodiments of this application, Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0049] According to some embodiments of this application, the power device can also be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a battery as its power source.

[0050] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0051] Example 1:

[0052] The first method for synthesizing active materials:

[0053] Using manganese sulfate as the manganese source and nickel sulfate as the nickel source, a transition metal salt solution with a concentration of 2 mol / L was prepared according to a Mn:Ni molar ratio of 6:4. A 2 mol / L sodium carbonate solution and a 1 mol / L ammonia solution were also prepared. 20% of the reactor volume of deionized water was added as the reaction base liquid to the reactor. Under a nitrogen atmosphere, the transition metal salt solution, sodium carbonate solution, and ammonia solution were simultaneously pumped into the reactor at flow rates of V1 = 35 mL / h, V2 = 5-50 mL / h, and V3 = 35 mL / h, respectively. The pH of the reaction system was controlled to 9.5 by adjusting the feed flow rate V2 of the sodium carbonate solution. The reaction was carried out for 20 hours at a temperature of 50°C and a stirring speed of 800 rpm. After feeding, the reaction slurry was aged for another 10 hours. The precipitate was then filtered, washed, and dried to obtain the first active material precursor, Ni. 0.4Mn 0.6 CO3. Finally, the above-mentioned first active material precursor powder and lithium source (lithium carbonate) are mixed evenly at a weight ratio of 100:50, and sintered at 800°C for 8 hours in air atmosphere to obtain the first active material.

[0054] The chemical formula of the first active material was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, the first active material was first digested with aqua regia, and then the resulting aqua regia solution containing the first active material was passed through an ICP-AES spectrometer to obtain the absolute content of each element in the first active material, thereby obtaining its chemical composition.

[0055] The chemical formula of the first active material is 0.2Li₂MnO₃·0.8LiNi 0.5 Mn 0.5 O2, the second active material is lithium iron phosphate, wherein the first active material accounts for 50 wt% of the mass of the mixed positive electrode active material, and the remainder is the second active material.

[0056] Preparation of lithium-ion batteries:

[0057] 1. Preparation of positive electrode sheet

[0058] The positive electrode active material, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) are mixed in a weight ratio of 94:4:2. N-methylpyrrolidone solvent is added, and the mixture is thoroughly stirred to obtain a uniform positive electrode slurry. The positive electrode slurry is coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0059] 2. Preparation of negative electrode sheet

[0060] Artificial graphite, conductive agent acetylene black, binder SBR (styrene-butadiene rubber), and binder CMC (sodium carboxymethyl cellulose) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain a uniform negative electrode slurry. The negative electrode slurry was coated onto both surfaces of the negative electrode current collector copper foil, dried, and cold-pressed to 1.65 g / cm³. 3 This yields the negative electrode sheet.

[0061] 3. Preparation of electrolyte

[0062] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (polycarbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC=3:3:3. Then, LiPF6, VC (ethylene carbonate), DTD (ethylene sulfate), and PS (1,3-propanesulfonate lactone) were added and stirred until homogeneous to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1mol / L, and the mass percentages of VC, DTD, and PS were 3wt%, 1wt%, and 1wt%, respectively.

[0063] 4. Preparation of the separating membrane

[0064] Polyethylene porous membrane is used as the separation membrane.

[0065] 5. Preparation of lithium-ion batteries

[0066] The aforementioned positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining a bare cell. The bare cell is placed in an outer package, injected with the aforementioned prepared electrolyte, and encapsulated for formation to obtain a lithium-ion battery.

[0067] Example 2:

[0068] Consistent with Example 1, except that the transition metal salt solution was prepared in a Mn:Ni molar ratio of 6.6:3.4 during the synthesis of the first active material; the chemical formula of the first active material is 0.3Li₂MnO₃·0.7LiNi. 0.5 Mn 0.5 O2.

[0069] Example 3:

[0070] Consistent with Example 1, except that the transition metal salt solution was prepared in a Mn:Ni molar ratio of 5.5:4.5 during the synthesis of the first active material; the chemical formula of the first active material is 0.1Li₂MnO₃·0.9LiNi. 0.5 Mn 0.5 O2.

[0071] Example 4:

[0072] Consistent with Example 1, except that the first active material accounts for 30 wt% of the positive electrode active material.

[0073] Example 5:

[0074] Consistent with Example 1, except that the first active material accounts for 70 wt% of the positive electrode active material.

[0075] Example 6:

[0076] Consistent with Example 1, except that the first active material accounts for 90 wt% of the positive electrode active material.

[0077] Comparative Example 1:

[0078] Consistent with Example 1, except that the positive electrode active material is lithium iron phosphate.

[0079] The batteries in Examples 1-6 and Comparative Example 1 were tested as follows, and the test results are shown in Table 1.

[0080] 1. Battery capacity test:

[0081] In a constant temperature environment of 25℃, the batteries of each embodiment and comparative example were discharged at 1 / 3C to 2.5V to drain the residual charge inside the battery. After standing for 5 minutes, they were charged at 1 / 3C to their respective upper limit voltage. Then, they were charged at the upper limit voltage with constant voltage until the current ≤0.05C. After standing for 5 minutes, they were discharged at 1 / 3C to 2.5V. The amount of charge released by the battery during this discharge process is the discharge capacity, and the energy output by the battery during this discharge process is the discharge energy. The discharge voltage plateau was recorded. The specific calculation method includes recording the discharge energy of the battery during the discharge process and dividing it by the aforementioned discharge capacity to obtain the discharge voltage plateau.

[0082] 2. Cyclic performance test:

[0083] Under constant temperature of 25℃, the battery is charged to the upper limit voltage with a constant current of 1C, then charged at the upper limit voltage until the current drops to 0.05C, and then discharged to 2.5V with a constant current of 1C. The discharge specific capacity of the first cycle (C0) is obtained. This charging and discharging is repeated until the 1000th cycle, and the discharge specific capacity after 1000 cycles is obtained, which is denoted as Cn.

[0084] Capacity retention = Discharge specific capacity after 1000 cycles (C) n ) / First-cycle discharge specific capacity (C0).

[0085] The positive electrode active materials in Examples 1-6 and Comparative Example 1 were tested as follows, and the test results are shown in Table 1.

[0086] 1. Test method for compaction density of positive electrode sheet: First, measure the thickness T of the positive electrode sheet after rolling, and then calculate the compaction density ρ based on the areal density. 压 The calculation formula is as follows: ρ 压 =m / (TT 箔 ), where m is the areal density of the electrode, in g / cm³. 2 T 箔 The thickness of the negative electrode current collector is expressed in cm.

[0087] 2. Test method for specific capacity of positive electrode active material: The specific capacity of positive electrode active material is obtained by dividing the measured battery capacity by the mass of positive electrode active material.

[0088] 3. Test method for specific capacity of the first active material: Prepare positive electrode sheets containing only the first active material in Examples 1-6 as positive electrode active material, and make batteries according to the above steps, and test the battery capacity. The upper limit of charging voltage is shown in Table 1. The specific capacity of the first active material can be obtained by dividing the measured battery capacity by the added mass of the first active material in the positive electrode sheet.

[0089] Table 1

[0090]

[0091] Test results show that by combining the high capacity and high voltage characteristics of lithium-rich manganese-based materials with the advantages of low cost and high safety of lithium phosphate particles, the electrical performance of lithium phosphate system, such as energy density and cycle stability, is greatly improved, resulting in a positive electrode active material with high specific capacity, better cycle life, and high energy density.

[0092] Unless otherwise stated, all technical 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. All patents and publications referenced in this application are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this application but do not exclude other contents.

[0093] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0094] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode active material, characterized by, Comprising: a first active material including a lithium-rich manganese-based material, a specific capacity of the first active material in a range of 2.5 V to 4.35 V is not less than 150 mAh / g, a chemical formula of the first active material satisfies nLi2MnO3·(1-n)LiNi x Mn （1-x-y） M y O2, wherein 0.1≤n≤0.3, 0.3 a second active material comprising a lithium-containing phosphate.

2. The positive electrode active material according to claim 1, characterized by The chemical formula of the lithium-containing phosphate satisfies LiFe 1-a-b Mn a Q b PO4, wherein 0≤a≤1, 0≤b≤0.1, 0≤a+b≤1, the Q element includes at least one of a transition metal element and a non-transition metal element other than Fe and Mn.

3. The positive electrode active material according to claim 1, characterized by The mass fraction of the first active material in the positive electrode active material is 10wt%-90wt%.

4. The positive electrode active material according to claim 3, characterized by The mass fraction of the first active material in the positive electrode active material is 25wt%-90wt%.

5. The positive electrode active material according to claim 1, characterized by The Dv50 of the first active material is 4μm-10μm.

6. The positive electrode active material according to claim 1, characterized by The Dv50 of the second active material is 0.5μm-2μm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized by, The discharge voltage plateau of the positive electrode active material is 3.3V-3.8V.

8. A positive electrode sheet characterized by comprising: The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is located on one side of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1-7.

9. The cathode electrode of claim 8, wherein, The compacted density of the positive electrode plate is 2.5 g / cm 3 - 3.1 g / cm 3 .

10. A battery, characterized by The battery comprises a positive electrode tab, and the positive electrode tab comprises the positive electrode tab according to claim 8 or 9.

11. An electrical device, characterized by The electric device comprises the battery according to claim 10.

Images