Positive electrode active material, positive electrode, battery, and device

Abstract

A positive electrode active material, a positive electrode, a battery and a device. The positive electrode active material comprises first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles, wherein the particle size D50 of the first lithium manganese iron phosphate particles is less than the particle size D50 of the second lithium manganese iron phosphate particles; and the Mn / (Mn+Fe) molar ratio of the first lithium manganese iron phosphate particles is x, the Mn / (Mn+Fe) molar ratio of the second lithium manganese iron phosphate particles is y, and x>y.

Description

Positive electrode active material, positive electrode, battery and device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311872054.2 and titled “Positive Electrode Active Materials, Positive Electrodes, Batteries and Devices,” the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a positive electrode active material, a positive electrode, a battery and a device. Background Art

[0003] Among the existing positive electrode active materials, among the polyanionic phosphate materials with olivine structure, lithium manganese iron phosphate (LiMn x Fe (1-x) PO4) has a higher operating voltage platform and therefore has a higher theoretical energy density.

[0004] However, the introduction of manganese reduces the intrinsic ionic conductivity of the active material, affecting the battery's rate performance. To overcome this technical issue, the particle size of the lithium iron manganese phosphate primary particles is typically reduced to shorten the ion migration path. However, this reduction in particle size also reduces the material's compaction density, affecting the battery's energy density. Therefore, maintaining the battery's rate performance while also increasing its compaction density is a significant challenge.

[0005] Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a positive electrode active material, a positive electrode, a battery and a device to take into account both battery rate performance and energy density.

[0007] In a first aspect, the present application provides a positive electrode active material, comprising a first lithium iron manganese phosphate particle and a second lithium iron manganese phosphate particle, wherein the D 50 The particle size is smaller than that of the second lithium manganese iron phosphate particle D 50 The particle size is 0.0447mm, and the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particles is x, the molar ratio of Mn / (Mn+Fe) in the second lithium manganese iron phosphate particles is y, and x>y.

[0008] The ion migration path of the small-particle lithium manganese iron phosphate particles is short, which can reduce impedance and improve the specific capacity of the active material, which is beneficial to improving the rate performance of the battery. At the same time, the large-particle lithium manganese iron phosphate particles have a smaller specific surface area and relatively good processing performance, which can increase the compaction density of the active material, which is beneficial to improving the energy density of the battery. The active material of the present application is doped with first lithium manganese iron phosphate particles with small particle size and second lithium manganese iron phosphate particles with large particle size to take into account the rate performance and compaction density of the battery. At the same time, since the introduction of manganese element causes the intrinsic ionic conductivity of lithium manganese iron phosphate to decrease, the present application further makes the molar content of manganese element in the first lithium manganese iron phosphate with small particle size higher than the molar content of manganese element in the second lithium manganese iron phosphate particles with large particle size, thereby improving the energy density of the active material.

[0009] That is, the active material of the present application is composed of two types of lithium manganese iron phosphate particles with different particle sizes and different Mn / (Mn+Fe) molar ratios. The small-sized first lithium manganese iron phosphate particles with a high Mn / (Mn+Fe) molar ratio can bear the high power output of the battery during high-rate discharge, thereby improving the battery's rate performance. The large-sized second lithium manganese iron phosphate particles with a lower Mn / (Mn+Fe) molar ratio have a higher compaction density, thereby improving the volumetric energy density of the battery.

[0010] In one embodiment, the D of the first lithium manganese iron phosphate particles 50 The particle size range is between 50nm and 350nm. The D 50 The particle size range is between 500nm and 2000nm.

[0011] In one embodiment, 0.7≤x≤0.85, 0.3≤y≤0.65.

[0012] In one embodiment, in the positive electrode active material, the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is between 0.2 and 1.

[0013] In one embodiment, 0.7≤x≤0.8, 0.4≤y≤0.6.

[0014] In one embodiment, in the positive electrode active material, the molar ratio of Mn / (Mn+Fe) is between 0.36 and 0.75.

[0015] In one embodiment, the material of the first lithium manganese iron phosphate particles includes LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 At least one of PO4.

[0016] In one embodiment, the material of the second lithium manganese iron phosphate particles includes LiMn 0.55 Fe 0.45 PO4、LiMn 0.4 Fe 0.6 At least one of PO4.

[0017] In a second aspect, the present application provides a positive electrode comprising the positive electrode active material in any one of the above embodiments.

[0018] It can be understood that the positive electrode provided in the second aspect of the present application also has all the beneficial effects that can be achieved in any embodiment of the first aspect of the present application because it adopts the positive electrode active material provided in the first aspect of the present application.

[0019] In one embodiment, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer includes the positive electrode active material; the compaction density of the positive electrode active material layer is between 2.35 g / cm 3 ~2.62g / cm 3 between.

[0020] In a third aspect, the present application further provides a battery, which includes the positive electrode provided in any embodiment of the second aspect of the present application.

[0021] In a fourth aspect, the present application further provides a device, which includes the battery provided in any embodiment of the third aspect of the present application, and the device includes an electrical device or an energy storage system.

[0022] It can be understood that the battery provided in the third aspect of the present application and the device provided in the fourth aspect both adopt the positive electrode provided in the second aspect of the present application, and therefore also have all the beneficial effects that can be achieved in all the embodiments of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation methods or the description of the prior art. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] FIG1 is a schematic diagram of a cross-sectional structure of a battery provided in one embodiment of the present application;

[0025] FIG2 is a schematic structural diagram of a positive electrode provided in one embodiment of the present application;

[0026] FIG3 is a schematic diagram of the structure of the positive electrode active material in one embodiment of the present application;

[0027] FIG4 is a cross-sectional model diagram of a first lithium iron manganese phosphate particle and a second lithium iron manganese phosphate particle filled with each other in one embodiment of the present application.

[0028] Reference numerals: 300 - battery; 301 - negative electrode; 302 - insulating separator; 200 - positive electrode; 201 - current collector; 202 - positive electrode active material layer; 100 - positive electrode active material; 10 - first lithium iron manganese phosphate particles; 20 - second lithium iron manganese phosphate particles. Specific embodiments

[0029] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0030] The following descriptions of the embodiments are with reference to the attached diagrams to illustrate specific embodiments that the present application can be used to implement. The serial numbers of the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in the present application include direct and indirect connections (couplings) unless otherwise specified. The directional terms mentioned in the present application, such as "up", "down", "front", "back", "left", "right", "inside", "outside", "side", etc., are only with reference to the directions of the attached drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0031] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections, indirect connections through an intermediary, or internal connections between two components. A person of ordinary skill in the art will understand the specific meanings of these terms in this application based on the specific circumstances. It should be noted that the terms "first," "second," and so on, in the specification, claims, and drawings of this application are used to distinguish between different objects, not to describe a specific order. Furthermore, the terms "include," "may include," "comprise," or "may include" as used in this application indicate the presence of the corresponding functions, operations, components, etc. disclosed, and do not limit the presence or absence of one or more additional functions, operations, components, etc. Furthermore, the terms "include" or "comprising" indicate the presence of the corresponding features, numbers, steps, operations, elements, components, or combinations thereof disclosed in the specification, and do not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, and are intended to cover non-exclusive inclusions.

[0032] Please refer to FIG1 , which is a schematic cross-sectional view of a battery 300 according to an embodiment of the present application.

[0033] As shown in Figure 1, the battery 300 of the present application includes a negative electrode 301, an insulating separator 302, and a positive electrode 200. The negative electrode 301, the insulating separator 302, and the positive electrode 200 are stacked in sequence to form a single battery 300. The insulating separator 302 is used to separate the positive electrode 200 and the negative electrode 301 to prevent conduction between the positive and negative electrodes. In one embodiment, the battery 300 also includes an electrolyte (not shown in the figure), and the negative electrode 301, the insulating separator 302, and the positive electrode 200 are all immersed in the electrolyte. The electrolyte acts as a medium to transport ions and conduct current between the positive electrode 200 and the negative electrode 301.

[0034] Please refer to FIG. 2 , which is a schematic structural diagram of a positive electrode 200 provided in an embodiment of the present application.

[0035] As shown in FIG2 , the positive electrode 200 of the present application includes a current collector 201 and a positive electrode active material layer 202. The positive electrode active material layer 202 includes a positive electrode active material 100 and is distributed on the surface of the current collector 201. The current collector 201 is made of a conductive material. The current collector 201 not only serves as a carrier for the positive electrode active material 100, but also collects and conducts the current generated by the positive electrode active material 100 to the outside of the battery 300. It is understood that in one embodiment, the current collector 201 can be made of a conductive material such as aluminum foil, copper foil, or composite copper / aluminum foil, and this application does not specifically limit this.

[0036] Please refer to FIG3 , which is a schematic structural diagram of a positive electrode active material 100 in an embodiment of the present application.

[0037] As shown in FIG3 , the positive electrode active material 100 of the present application includes a first lithium iron manganese phosphate particle 10 and a second lithium iron manganese phosphate particle 20 . 50 The particle size is smaller than that of the second lithium manganese iron phosphate particle 20. 50 Particle size. The first lithium iron manganese phosphate particles 10 within a small particle size range can be filled into the gaps between the second lithium iron manganese phosphate particles 20 within a large particle size range (please refer to Figure 4, which is a cross-sectional model diagram of the first lithium iron manganese phosphate particles 10 and the second lithium iron manganese phosphate particles 20 filling each other in one embodiment of the present application).

[0038] It should be noted that when only one type of lithium iron manganese phosphate particles is used as the positive electrode active material 100 of the positive electrode 200, that is, only lithium iron manganese phosphate particles within a small particle size range or only lithium iron manganese phosphate particles within a large particle size range are used, the single small-sized lithium iron manganese phosphate has a large specific surface area, relatively poor processing performance, and a low compaction density, thereby affecting the energy density of the battery 300. The single large-sized lithium iron manganese phosphate has a long ion migration path and increased impedance, which affects the rate performance of the battery 300. In other words, using only one type of lithium iron manganese phosphate particle cannot simultaneously achieve high rate performance and high energy density.

[0039] The positive electrode active material 100 of the present application uses a first lithium manganese iron phosphate particle 10 with a small particle size and a second lithium manganese iron phosphate particle 20 with a large particle size to be doped and filled to simultaneously ensure the rate performance and energy density of the battery 300. At the same time, due to the introduction of manganese, the intrinsic ionic conductivity of lithium manganese iron phosphate decreases. In the present application, the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particle is x, and the molar ratio of Mn / (Mn+Fe) in the second lithium manganese iron phosphate particle is y, where x>y. In the present application, the molar ratio of Mn / (Mn+Fe) refers to the percentage of the amount of Mn element in the lithium manganese iron phosphate based on the sum of the amounts of Mn and Fe elements. Specifically, x refers to the percentage of the amount of Mn element in the first lithium manganese iron phosphate material based on the sum of the amounts of Mn and Fe elements; y refers to the percentage of the amount of Mn element in the second lithium manganese iron phosphate material based on the sum of the amounts of Mn and Fe elements. The amount of substance represents a collection of particles of a certain number. The unit of the amount of substance is mole, symbolized by mol. The molar content of manganese in the first lithium manganese iron phosphate particles 20 with a small particle size is set to be higher than the molar content of manganese in the second lithium manganese iron phosphate particles 20, thereby increasing the energy density of the positive electrode active material 100.

[0040] That is, the positive electrode active material 100 of the present application adopts two different D 50 The composite composition comprises lithium manganese iron phosphate particles of different particle sizes and Mn / (Mn+Fe) molar ratios. The first lithium manganese iron phosphate particles 10 with a small particle size and a high Mn / (Mn+Fe) molar ratio can bear the instantaneous high power output of the battery 300 during high-rate discharge, thereby improving the rate performance of the battery 300. The second lithium manganese iron phosphate particles 20 with a large particle size and a lower Mn / (Mn+Fe) molar ratio can increase the compaction density of the positive electrode 200, thereby improving the volumetric energy density of the battery 300.

[0041] In the present application, the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles can be tested using an inductively coupled plasma spectrometer (ICP).

[0042] In one embodiment, the D of the first lithium manganese iron phosphate particle 10 is 50 The particle size range is between 50nm and 350nm. The D of the second lithium manganese iron phosphate particle 20 is 50 The particle size range is between 500nm and 2000nm.

[0043] It should be noted that the D of the first lithium manganese iron phosphate particle 10 50 The particle size range is between 50nm and 350nm, which refers to the median particle size D of the first lithium manganese iron phosphate particle 10. 50 The median particle size D of the first lithium manganese iron phosphate particle 10 is between 50 nm and 350 nm. 50 It is 50nm~150nm, 100nm~200nm, 200nm~350nm, etc.

[0044] Similarly, the particle size of the second lithium manganese iron phosphate particles 20 ranges from 500 nm to 2000 nm, which refers to the median particle size D of the second lithium manganese iron phosphate particles 20. 50 The range is between 500nm and 2000nm. Optionally, the median particle size D of the second lithium manganese iron phosphate particles 20 is 50 It is 600nm~1000nm, 700nm~1500nm, 1200nm~2000nm, etc.

[0045] Among them, the median particle size D 50 , also known as volume average particle size, represents the particle size at which the cumulative volume distribution percentage of a material reaches 50%. This can be measured using, for example, a Malvern laser particle size analyzer, referring to the particle size distribution laser diffraction method in accordance with GB / T 19077-2016.

[0046] It is understood that in this embodiment, setting the median particle size of the first lithium iron manganese phosphate particles 10 to be between 50 nm and 350 nm, and setting the median particle size of the second lithium iron manganese phosphate particles 20 to be between 500 nm and 2000 nm, can improve the processing performance of the positive electrode active material 100, reduce the physical gel phenomenon, and improve the overall consistency of the positive electrode active material 100. In addition, it can also improve the transport performance of ions in the positive electrode active material 100, which is conducive to further improving the cycle performance of the battery 300.

[0047] In one embodiment, the Mn / (Mn+Fe) molar ratio x in the first lithium manganese iron phosphate particles 10 is between 70% and 85%, and the Mn / (Mn+Fe) molar ratio y in the second lithium manganese iron phosphate particles 20 is between 30% and 65%.

[0048] As can be understood, by setting the Mn / (Mn+Fe) molar ratio x in the first lithium manganese iron phosphate particles between 70% and 85%, the active material can have a high operating voltage platform and certain rate performance. By setting the Mn / (Mn+Fe) molar ratio y in the second lithium manganese iron phosphate particles between 30% and 65%, the active material can have a low intrinsic impedance and good gram capacity. Gram capacity refers to the amount of electricity released per gram of active material, measured in mAh / g. Setting the Mn / (Mn+Fe) molar ratios x and y in the first and second lithium manganese iron phosphate particles 10 and 20, respectively, between 0.7 and 0.85 and 0.30 and 0.65 can prevent excessive manganese content from affecting the conductivity of the positive electrode active material 100 and reducing the rate performance of the battery 300. It can also prevent excessive manganese content from leading to a low operating voltage platform and reducing the energy density of the battery 300.

[0049] In one embodiment, in the positive electrode active material 100 , the mass ratio of the first lithium iron manganese phosphate particles 10 to the second lithium iron manganese phosphate particles 20 is 0.2-1.

[0050] Further optionally, the mass ratio of the first lithium iron manganese phosphate particles 10 to the second lithium iron manganese phosphate particles 20 can be, for example, 1:4, 1:3, 3:7, etc. It will be appreciated that setting the mass ratio of the first lithium iron manganese phosphate particles 10 to the second lithium iron manganese phosphate particles 20 within the above range ensures a mixed filling effect of the first lithium iron manganese phosphate particles 10 and the second lithium iron manganese phosphate particles 20, thereby enabling the battery 300 to have a higher compression density and higher rate performance.

[0051] In one embodiment, the molar ratios x and y of Mn / (Mn+Fe) in the first and second lithium manganese iron phosphate particles 10 and 20 satisfy 0.7≤x≤0.8 and 0.4≤y≤0.6.

[0052] In one embodiment, in the positive electrode active material, the molar ratio of Mn / (Mn+Fe) is between 0.36 and 0.75. That is, if the sum of the amount of Mn and Fe in the first lithium manganese iron phosphate and the amount of Mn and Fe in the second lithium manganese iron phosphate in the positive electrode active material is recorded as N 总 The sum of the amount of manganese in the first lithium manganese iron phosphate and the amount of manganese in the second lithium manganese iron phosphate in the positive electrode active material is recorded as n 总 , n 总 / N 总 Between 0.36 and 0.75.

[0053] In this embodiment, after setting up the mixed filling of two kinds of particles, the ratio of the sum of the molar contents of the total manganese element to the molar contents of Mn and Fe in the first lithium manganese iron phosphate and the sum of the molar contents of Mn and Fe in the second lithium manganese iron phosphate is between 0.36 and 0.75, so as to better alleviate the increase in impedance caused by excessive manganese elements, affecting the rate performance of the battery 300, and at the same time better alleviate the decrease in voltage caused by too low manganese elements, affecting the theoretical energy density of the battery 300.

[0054] In one embodiment, the material of the first lithium manganese iron phosphate particle 10 includes LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 At least one of PO4.

[0055] In this embodiment, the material of the first lithium manganese iron phosphate particles 10 can be LiMn 0.8 Fe 0.2 PO4 or LiMn 0.7 Fe 0.3 In PO4, LiMn can also be 0.8 Fe 0.2 PO4 and LiMn 0.7 Fe 0.3 It is understood that the redox potential of manganese ions is higher than that of iron ions, and the material of the first lithium manganese iron phosphate particle 10 can be LiMn 0.8 Fe 0.2 PO4、LiMn 0.7 Fe 0.3 PO4, so that the manganese element and the iron element in the first lithium manganese iron phosphate particle 10 have a suitable ratio, thereby ensuring that the first lithium manganese iron phosphate particle 10 has a higher voltage platform without reducing the specific capacity of the positive electrode active material 100.

[0056] In one embodiment, the material of the second lithium manganese iron phosphate particles 20 includes LiMn 0.55 Fe 0.45 PO4、LiMn 0.4 Fe 0.6 At least one of PO4.

[0057] In this embodiment, the material of the second lithium manganese iron phosphate particles 20 can be LiMn 0.55 Fe 0.45 PO4 or LiMn 0.4 Fe 0.6 PO4, or LiMn 0.55 Fe 0.45 PO4 and LiMn 0.4 Fe 0.6 PO4 combination.

[0058] In one embodiment, the first lithium manganese iron phosphate particles 10 include a first particle group and a second particle group, and the D of the first lithium manganese iron phosphate particles 10 in the first particle group is 50 The particle size is smaller than that of the first lithium manganese iron phosphate particle 10 in the second particle group. 50 The particle size is 200 nm, and the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particles 10 in the first particle group is greater than the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particles 10 in the second particle group.

[0059] It can be understood that two groups of particles with different particle sizes and manganese content elements are set in the first lithium manganese iron phosphate particles 10, so as to compound lithium manganese iron phosphate particles with a variety of different particle sizes and a variety of different Mn / (Mn+Fe) molar ratios, thereby achieving uniform filling and ensuring uniform current distribution inside the positive electrode active material 100, so as to further improve the overall compaction density of the positive electrode active material 100, and at the same time avoid the different degrees of internal deterioration of the battery 300 due to uneven current distribution, which leads to capacity decay of the battery 300.

[0060] In one embodiment, the second lithium manganese iron phosphate particles 20 include a third particle group and a fourth particle group, and the D of the second lithium manganese iron phosphate particles 20 in the third particle group is 50 The particle size is smaller than that of the second lithium manganese iron phosphate particles 20 in the fourth particle group. 50 The particle size is 200 nm, and the molar ratio of Mn / (Mn+Fe) in the second lithium manganese iron phosphate particles 20 in the third particle group is greater than the molar ratio of Mn / (Mn+Fe) in the second lithium manganese iron phosphate particles 20 in the fourth particle group.

[0061] It can be understood that in this embodiment, two groups of particles with different particle sizes and manganese content elements are provided in the second lithium manganese iron phosphate particles 20, so as to compound lithium manganese iron phosphate particles with a variety of different particle sizes and a variety of different Mn / (Mn+Fe) molar ratios, thereby achieving uniform filling and ensuring uniform current distribution inside the positive electrode active material 100, so as to further improve the overall compaction density of the positive electrode active material 100, and at the same time avoid the different degrees of internal degradation of the battery 300 due to uneven current distribution, which leads to capacity attenuation of the battery 300.

[0062] In one embodiment, the positive electrode 200 further includes a dispersant, a conductive agent and a binder (not shown). By providing a dispersant, the positive electrode active material 100 can be evenly distributed. It can be understood that a conductive agent is provided to collect current between the lithium iron manganese phosphate particles and between the lithium iron manganese phosphate particles and the current collector 201, thereby reducing the contact resistance of the electrode and accelerating the movement rate of electrons. At the same time, it can also effectively increase the migration rate of lithium ions in the lithium iron manganese phosphate particles, thereby improving the charge and discharge efficiency of the battery 300. The provision of a binder can then bond and fix the lithium iron manganese phosphate particles and give the lithium iron manganese phosphate particles a certain structural strength. Based on the fact that the binder is usually in powder form, during the production process of the positive electrode 200, the binder needs to be dissolved in the dispersant so that it is in full contact with the lithium iron manganese phosphate particles, the conductive agent, etc. and is evenly dispersed therein. Among them, the dispersant, the binder, and the conductive agents can be conventional choices in the battery field. For example, the conductive agent can be selected from one or more of conductive carbon black (such as acetylene black, Ketjen black, Super-P, 350G carbon black, etc.), carbon nanotubes (single-walled carbon nanotubes or multi-walled carbon nanotubes), graphene, carbon fibers, ordered mesoporous carbon, etc. The binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyolefins (such as polyethylene (PE), polypropylene (PP)), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyacrylate, polyimide (PI), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate (SA), gelatin, etc., but is not limited thereto.

[0063] In one embodiment, the positive electrode 200 further includes a current collector 201. The positive electrode active material 100 is mixed with a dispersant, a conductive agent, and a binder and then coated on the surface of the current collector. The current collector 201 is used to collect and conduct the current generated by the positive electrode active material 100.

[0064] The current collector 201 may include, but is not limited to, aluminum foil, aluminum alloy foil, polymer film coated with metal aluminum, or the aforementioned materials with carbon coating on the surface, etc. In some embodiments of the present application, the current collector 201 is aluminum foil, or carbon-coated aluminum foil.

[0065] In one embodiment, the compaction density of the positive electrode 200 is between 2.35 g / cm3 ~2.62g / cm 3 between.

[0066] In this application, the negative electrode 301 of the battery 300 generally includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer generally contains a negative electrode active material, a conductive agent, and a binder. In embodiments of this application, the negative electrode active material for the lithium battery can be selected from one or more of hard carbon, soft carbon, graphite, mesocarbon microbeads, and silicon-carbon composite materials.

[0067] The insulating diaphragm 302 is used to separate the positive electrode 200 and the negative electrode 301, maintaining the insulation and liquid retention properties between the two. The insulating diaphragm 302, the positive electrode 200, and the negative electrode 301 together constitute the electrode core of the battery 300. The electrode core is housed in the battery casing and is soaked by the electrolyte contained in the casing. In some embodiments of the present application, the lithium battery can be assembled by the following method: the positive electrode, the diaphragm, and the negative electrode are stacked in sequence to form the electrode core; the electrode core is housed in the battery casing, and the electrolyte is injected, and the battery casing is sealed to obtain the battery. The battery cell can be a wound type or a laminated type.

[0068] In this application, the insulating separator 302 may be any separator material used in a battery. For example, the insulating separator 302 may include, but is not limited to, polymer separators such as single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP, or non-woven fabrics. The electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and organic solvent are conventional in the battery field and can be selected based on actual needs.

[0069] In one embodiment, the discharge capacity of the battery 300 at a 5C rate is greater than or equal to 105 mAh / g; the volumetric energy density of the battery 300 is greater than or equal to 1364.5 mWh / cm 3 .

[0070] In this application, the D of the first lithium iron manganese phosphate particle and the second lithium iron manganese phosphate particle is 50 The test method for the Mn / (Mn+Fe) molar ratio is as follows:

[0071] After the lithium-ion battery is fully discharged, it is disassembled to obtain the positive electrode, and the positive electrode is placed in a solvent dimethyl carbonate (DMC) and soaked for 10-20 minutes to clean the residual electrolyte. After the positive electrode is dried, it is soaked in water to inactivate the binder so that the dressing layer can be peeled off from the positive electrode current collector. The dressing layer is then dissolved in a solvent N-methylpyrrolidone (NMP) and heated at 80°C to accelerate dissolution. The dissolved material is filtered to separate the solid material, and the solid material is washed with NMP. The obtained mixture containing the solid material and NMP is then centrifuged at 5000 rpm, and the upper layer containing the conductive agent is discarded, and the lower layer containing lithium manganese iron phosphate (LMFP) is collected. The material containing LMFP is washed and centrifuged with NMP 6 times. Due to the two LMFP materials D 50 The difference is large, and further separation can be achieved by reducing the rotation speed. The rotation speed is then adjusted to 3000 rpm for centrifugal treatment, and the second LMFP material can be precipitated to the lower layer. The upper liquid is filtered to obtain the first LMFP material.

[0072] The two separated LMFP powders can be subjected to laser particle size test respectively. 50 And ICP test Mn / (Mn+Fe) molar ratio. Specifically, D 50 The test can refer to GB / T19077-2016 particle size distribution laser diffraction method and be performed using, for example, a Malvern laser particle size analyzer.

[0073] In addition, the Mn / Fe content can also be tested directly through SEM-EDS. For example, a certain volume of electrode can be cross-sectioned or polished using an argon ion beam to obtain a cross-section of the electrode. SEM-EDS scans of large-particle and small-particle LMFP materials can be performed separately to obtain the Mn / Fe mass ratio, which can then be further calculated to obtain the Mn / (Mn+Fe) molar ratio.

[0074] The test method for the Mn / (Mn+Fe) molar ratio in the positive electrode active material is as follows: the lithium-ion battery is completely discharged and disassembled to obtain the positive electrode, and the positive electrode is placed in the solvent DMC and soaked for 10-20 minutes to clean the residual electrolyte. After the positive electrode is dried, it is soaked in water to inactivate the binder so that the dressing layer can be peeled off from the positive electrode current collector. The dressing layer is then dissolved in the solvent N-methylpyrrolidone (NMP) and heated at 80°C to accelerate dissolution. The dissolved material is filtered to separate the solid material, and the solid material is washed with NMP. The obtained mixture containing the solid material and NMP is then centrifuged at 5000 rpm, and the upper layer material containing the conductive agent is discarded and the lower layer material containing lithium manganese iron phosphate (LMFP) is collected. The Mn / (Mn+Fe) molar ratio is tested by ICP.

[0075] The following is a comparative explanation of the beneficial effects that may be achieved by the positive electrode active material 100 of the present application, in combination with some embodiments of the positive electrode active material 100 of the present application and some embodiments in the prior art.

[0076] Example 1

[0077] In Example 1, the material of the first lithium manganese iron phosphate particles is LiMn 0.8 Fe 0.2 PO4, and its particle size D 50 The second lithium manganese iron phosphate particle LiMn 0.6 Fe 0.4 PO4, and its particle size D 50 The mass ratio of the first lithium iron manganese phosphate particles to the second lithium iron manganese phosphate particles is 0.25.

[0078] Example 2

[0079] The difference between the positive electrode active material provided in Example 2 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 2, the particle size D of the first lithium manganese iron phosphate particles is 50 is 300nm.

[0080] Example 3

[0081] The difference between the positive electrode active material provided in Example 3 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 3, the material of the first lithium manganese iron phosphate particle is LiMn 0.7 Fe 0.3 PO4.

[0082] Example 4

[0083] The difference between the positive electrode active material provided in Example 4 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 4, the material of the second lithium manganese iron phosphate particles is LiMn 0.5 Fe 0.5 PO4, and its particle size D 50 is 1500nm.

[0084] Example 5

[0085] The difference between the positive electrode active material provided in Example 5 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 5, the mass compounding ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.5.

[0086] Example 6

[0087] The difference between the positive electrode active material provided in Example 6 and the positive electrode active material in Example 1 is that, in the positive electrode active material provided in Example 6, the mass compounding ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 1.

[0088] Example 7

[0089] The difference between the positive electrode active material provided in Example 7 and the positive electrode active material in Example 1 is that, in the positive electrode active material provided in Example 7, the mass compounding ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.2.

[0090] Example 8

[0091] The difference between the positive electrode active material provided in Example 8 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 8, the first lithium manganese iron phosphate particles D 50 The second lithium manganese iron phosphate particle D is 350nm. 50 is 2000nm.

[0092] Example 9

[0093] The difference between the positive electrode active material provided in Example 9 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 9, the particle size D of the first lithium manganese iron phosphate particles is 50 The particle size D of the second lithium manganese iron phosphate particle is 50 nm. 50 is 500nm.

[0094] Example 10

[0095] The difference between the positive electrode active material provided in Example 10 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 10, the material of the first lithium manganese iron phosphate particle is LiMn0.85 Fe 0.15 PO4, the material of the second lithium manganese iron phosphate particles is LiMn 0.65 Fe 0.35 PO4.

[0096] Example 11

[0097] The difference between the positive electrode active material provided in Example 11 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 11, the material of the first lithium manganese iron phosphate particle is LiMn 0.7 Fe 0.3 PO4, the material of the second lithium manganese iron phosphate particles is LiMn 0.3 Fe 0.7 PO4.

[0098] Example 12

[0099] The difference between the positive electrode active material provided in Example 12 and the positive electrode active material in Example 1 is that, in the positive electrode active material provided in Example 12, the mass compounding ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 1.2.

[0100] Example 13

[0101] The difference between the positive electrode active material provided in Example 13 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 13, the material of the second lithium manganese iron phosphate particles is LiMn 0.55 Fe 0.45 PO4, the mass compounding ratio of the first lithium iron manganese phosphate particles to the second lithium iron manganese phosphate particles is 0.1.

[0102] Example 14

[0103] The difference between the positive electrode active material provided in Example 14 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 14, the material of the first lithium manganese iron phosphate particle is LiMn 0.4 Fe 0.6 PO4, the material of the second lithium manganese iron phosphate particles is LiMn 0.2 Fe 0.8 PO4, the mass compounding ratio of the first lithium iron manganese phosphate particles to the second lithium iron manganese phosphate particles is 0.2.

[0104] Example 15

[0105] The difference between the positive electrode active material provided in Example 15 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 15, the particle size D of the first lithium manganese iron phosphate particles is 50The particle size D of the second lithium manganese iron phosphate particle is 400 nm. 50 The particle size of the first lithium iron manganese phosphate particle is 2000 nm, and the mass ratio of the first lithium iron manganese phosphate particle to the second lithium iron manganese phosphate particle is 0.3.

[0106] Example 16

[0107] The difference between the positive electrode active material provided in Example 16 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Example 16, the particle size D of the first lithium manganese iron phosphate particles is 50 The particle size D of the second lithium manganese iron phosphate particle is 40 nm. 50 The particle size is 450 nm, and the mass ratio of the first lithium iron manganese phosphate particle to the second lithium iron manganese phosphate particle is 0.3.

[0108] Comparative Example 1

[0109] The difference between the positive electrode active material provided in Comparative Example 1 and the positive electrode active material in Example 1 is that in the positive electrode active material provided in Comparative Example 1, the material of the first lithium manganese iron phosphate particle is LiMn 0.4 Fe 0.6 PO4, the material of the second lithium manganese iron phosphate particles is LiMn 0.8 Fe 0.2 PO4.

[0110] Comparative Example 2

[0111] In Comparative Example 2, the positive electrode active material only includes the first lithium iron manganese phosphate particles, without the second lithium iron manganese phosphate particles. The material of the first lithium iron manganese phosphate particles is LiMn 0.8 Fe 0.2 PO4, and its particle size D 50 is 150nm.

[0112] Comparative Example 3

[0113] In Comparative Example 3, the positive electrode active material only includes the first lithium iron manganese phosphate particles, without the second lithium iron manganese phosphate particles. The material of the first lithium iron manganese phosphate particles is LiMn 0.7 Fe 0.3 PO4, and its particle size D 50 is 300nm.

[0114] Comparative Example 4

[0115] In Comparative Example 4, the positive electrode active material only contains the second lithium iron manganese phosphate particles without the first lithium iron manganese phosphate particles. The material of the second lithium iron manganese phosphate particles is LiMn 0.6 Fe 0.4 PO4, and its particle size D 50 It is 700nm.

[0116] Comparative Example 5

[0117] In Comparative Example 5, the positive electrode active material only contains the second lithium iron manganese phosphate particles, without the first lithium iron manganese phosphate particles. The material of the second lithium iron manganese phosphate particles is LiMn 0.5 Fe 0.5 PO4, and its particle size D 50 is 1000nm.

[0118] The molar content and particle size D of the first lithium manganese iron phosphate particles (LMFP-1) of the positive electrode active material in the above examples and comparative examples are 50 , the molar content and particle size of manganese element in the second lithium manganese iron phosphate particles (LMFP-2) 50 The mass ratio of the first lithium manganese iron phosphate particle (LMFP-1) and the second lithium manganese iron phosphate particle (LMFP-2), and the ratio of the manganese content in the first lithium manganese iron phosphate particle (LMFP-1) and the second lithium manganese iron phosphate particle (LMFP-2) to the content of other elements were statistically analyzed. The results are shown in Table 1:

[0119] Table 1: Parameter design of each embodiment and comparative example

[0120] The positive electrode active materials provided in Examples 1 to 11 and the positive electrode active materials provided in Comparative Examples 1 to 5 were assembled into positive electrode sheets and batteries according to the following methods.

[0121] The preparation method of the positive electrode sheet includes:

[0122] The positive electrode active material, binder PVDF, conductive agent carbon black, and solvent NMP were prepared in a mass ratio of 100:2:2:60 to prepare a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil with a single-side surface density of 200 g / m 2 , dried, and roll-pressed to obtain a positive electrode sheet.

[0123] The battery preparation method includes:

[0124] 1. Cut the rolled positive electrode sheet into discs with a diameter of 1.5 cm and weigh them to obtain the electrode mass m 正极 Weigh the mass m of aluminum foil of the same area Al , subtract the two parameters to obtain the dressing weight m 敷料 =m 正极 -m Al The weight of LMFP material in the positive electrode is m=m 敷料 ×96.15%.

[0125] 2. Cut the positive electrode sheet into 1.5cm diameter discs and bake them in a 105°C oven for 24 hours to remove moisture. Then, assemble the CR2016 button-type half-cell by sequentially assembling the positive electrode sheet, PP separator, lithium sheet, and nickel foam into the shell and pressing them together to form the button-type cell.

[0126] The compaction density of the positive electrode sheet and the electrochemical performance of the battery were tested as shown in Table 2. The test results are shown in Table 2. The test methods for each parameter are as follows:

[0127] Pole compaction density test method: Measure the thickness of the positive electrode and aluminum foil to obtain the dressing thickness h, and the pole compaction density D = m 敷料 / (π×(1.5 / 2)cm×(1.5 / 2)cm×h);

[0128] Average voltage and 0.1C discharge capacity test method: Calibrate the button-type half-cell's room-temperature capacity. Specifically, at room temperature (25°C), charge at a constant current and voltage of 0.1C to an upper voltage limit of 4.35V. Then, charge at a constant voltage of 4.35V to a cutoff current of 0.05C, and rest for 30 minutes. Then, discharge at a constant current of 0.1C to a lower voltage limit of 2.5V, and rest for 30 minutes. Repeat these charge and discharge steps three times. The capacity discharged during the third discharge is recorded as C0 (Ah). The average discharge voltage during the third discharge is also recorded. C0 is the room-temperature calibrated capacity of the positive button-type half-cell. 0.1C discharge capacity = C0 / total mass of the positive active material in a single cell.

[0129] 5C discharge specific capacity test method: With C0 as the rated capacity of the battery, charge at 0.1C0 constant current and constant voltage to an upper limit voltage of 4.35V, then charge at 4.35V constant voltage to a cutoff current of 0.05C0, and leave it for 30 minutes; then discharge at 5C0 constant current to a lower limit voltage of 2.5V, and leave it for 30 minutes; record the discharge capacity C1, which is the battery's 5C discharge capacity. Similarly, 5C discharge specific capacity = C1 / total mass of positive electrode active material in a single battery.

[0130] 5C discharge specific capacity mainly characterizes the rate performance of the battery;

[0131] Mass specific energy = 0.1C discharge specific capacity × average discharge voltage;

[0132] Volumetric energy = mass specific energy × compaction density; volumetric energy mainly represents the energy density of the battery.

[0133] Table 2: Performance comparison of various examples and comparative examples

[0134] Combining Table 1 and Table 2:

[0135] By comparing the results of Examples 1-16 and Comparative Examples 2-5, it can be seen that the battery made of large-particle-sized lithium iron manganese phosphate particles in the comparative example not only has a low energy density, but also has poor rate performance; while the battery made of small-particle-sized lithium iron manganese phosphate particles has a better rate performance than the battery made of large-particle-sized lithium iron manganese phosphate particles alone, but its energy density is reduced. That is, the battery made of lithium iron manganese phosphate particles with a single particle size cannot take into account both its rate performance and energy density, and its comprehensive electrochemical performance is relatively poor. In contrast, in the embodiments of the present application, the first lithium iron manganese phosphate particles and the second lithium iron manganese phosphate particles with different particle sizes are mixed and filled with each other, which can increase the compaction density of the positive electrode sheet and ensure that the battery has a higher discharge specific capacity, that is, it can improve both the energy density of the battery and the rate performance of the battery, thereby making the comprehensive electrochemical performance of the battery more excellent.

[0136] By comparing the results of Examples 1-16 and Comparative Example 1, it can be seen that the embodiments of the present application use small-particle lithium manganese phosphate particles with a high manganese content doped with large-particle lithium manganese phosphate particles with a low manganese content. Compared with the comparative example 1 in which low manganese content and small-particle lithium manganese phosphate particles are doped with high manganese content and large-particle lithium manganese phosphate particles, the embodiments of the present application have more excellent rate performance and energy density, thereby greatly improving the comprehensive electrochemical performance of the battery.

[0137] By comparing the results of Example 1, Example 2, Example 8, Example 9, Example 15, and Example 16, it can be seen that the comprehensive electrochemical performance of the battery can be optimized by regulating the respective particle sizes of the first lithium iron manganese phosphate particles and the second lithium iron manganese phosphate particles within an appropriate range.

[0138] It can be seen from the results of Comparative Examples 1, 3, 4, 10, 11 and 14 that the comprehensive electrochemical performance of the battery can also be optimized by regulating the relative content of manganese elements in the first lithium iron manganese phosphate particles and the second lithium iron manganese phosphate particles within an appropriate range.

[0139] It can be seen from the results of Comparative Examples 1, 5, 6, 7, 12 and 13 that by regulating the compounding ratio of the first lithium iron manganese phosphate particles and the second lithium iron manganese phosphate particles within an appropriate range, the compaction density and gram capacity of the battery can be optimized, thereby improving the comprehensive electrochemical performance of the battery.

[0140] In summary, in the present application, by setting the first lithium manganese iron phosphate particles with small particle size to have a higher manganese content and the second lithium manganese iron phosphate particles with large particle size to have a lower manganese content, the battery can have both better rate performance and energy density, that is, the comprehensive electrochemical performance of the battery can be optimized.

[0141] It should be understood that the terms "first," "second," etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "plurality" means two or more, unless otherwise specifically defined.

[0142] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, 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 any one or more embodiments or examples.

[0143] It should be understood that the application of this application is not limited to the above examples. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the scope of protection of the claims appended to this application. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments and making equivalent changes in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A positive electrode active material, wherein, It includes a first lithium iron manganese phosphate particle 10 and a second lithium iron manganese phosphate particle 20, and the D of the first lithium iron manganese phosphate particle 10 50 particle size is smaller than the D of the second lithium iron manganese phosphate particle 20 50 particle size, and the molar ratio of Mn / (Mn + Fe) in the first lithium iron manganese phosphate particle 10 is x, and the molar ratio of Mn / (Mn + Fe) in the second lithium iron manganese phosphate particle 20 is y, where x > y.

2. The positive electrode active material according to claim 1, wherein The D of the first lithium iron manganese phosphate particle 10 50 particle size range is between 50 nm and 350 nm, and the D of the second lithium iron manganese phosphate particle 20 50 particle size range is between 500 nm and 2000 nm.

3. The positive electrode active material according to claim 1 or 2, wherein, 0.7 ≤ x ≤ 0.85, 0.3 ≤ y ≤ 0.

65.

4. The positive electrode active material according to any one of claims 1 to 3, wherein, In the positive electrode active material, the mass ratio of the first lithium iron manganese phosphate particles 10 to the second lithium iron manganese phosphate particles 20 is 0.2 to 1.

5. The positive electrode active material according to any one of claims 1 to 4, wherein, 0.7 ≤ x ≤ 0.8, 0.4 ≤ y ≤ 0.

6.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, In the positive electrode active material 100, the molar ratio of Mn / (Mn + Fe) is between 0.36 and 0.

75.

7. The positive electrode active material according to any one of claims 1 to 6, wherein, The material of the first lithium iron manganese phosphate particle 10 includes LiMn 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 PO4, at least one of them; and / or, The material of the second lithium iron manganese phosphate particle 20 includes LiMn 0.55 Fe 0.45 PO4, LiMn 0.4 Fe 0.6 at least one of PO4.

8. The positive electrode active material according to any one of claims 1 to 6, wherein, The first lithium iron manganese phosphate particle 10 includes a first particle group and a second particle group. The D of the first lithium iron manganese phosphate particle 10 in the first particle group 50 particle size is smaller than the D of the first lithium iron manganese phosphate particle 10 in the second particle group 50 particle size, and the Mn / (Mn + Fe) molar ratio in the first lithium iron manganese phosphate particle 10 in the first particle group is greater than the Mn / (Mn + Fe) molar ratio in the first lithium iron manganese phosphate particle 10 in the second particle group.

9. The positive electrode active material according to any one of claims 1 to 6, wherein, The second lithium iron manganese phosphate particle 20 includes a third particle group and a fourth particle group, and the D 50 particle size of the lithium iron manganese phosphate particle 20 in the third particle group is smaller than the D 50 particle size of the lithium iron manganese phosphate particle in the fourth particle group, and the Mn / (Mn + Fe) molar ratio in the lithium iron manganese phosphate particle 20 in the third particle group is greater than the Mn / (Mn + Fe) molar ratio in the lithium iron manganese phosphate particle 20 in the fourth particle group.

10. A positive electrode, wherein, It includes the positive electrode active material 100 according to any one of claims 1 to 9.

11. The positive electrode according to claim 10, wherein, The positive electrode includes a current collector 201 and a positive electrode active material layer 202 provided on the current collector 201, and the positive electrode active material layer 202 includes the positive electrode active material 100; the tap density of the positive electrode active material layer 202 is between 3 2.35 g / cm 3 and 2.62 g / cm.

12. A battery, wherein, It includes the positive electrode 200 according to claim 10 or 11.

13. A device, wherein, It includes the battery 300 according to claim 12, and the device includes an electrical equipment or an energy storage system.

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