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

Abstract

The application provides a positive electrode active material, a positive electrode, a battery and a device, wherein the positive electrode active material comprises first lithium iron manganese phosphate particles and second lithium iron manganese phosphate particles, the D 50 particle size of the first lithium iron manganese phosphate particles is less than the D 50 particle size of the second lithium iron manganese phosphate particles, and the molar ratio of Mn / (Mn+Fe) in the first lithium iron manganese phosphate particles is x, the molar ratio of Mn / (Mn+Fe) in the second lithium iron manganese phosphate particles is y, and x>y. The positive electrode active material of the application is composed of two kinds of lithium iron manganese phosphate particles with different particle size ranges and different manganese contents, and the first lithium iron manganese phosphate particles with high manganese content and small particle size can bear the instantaneous high power output of the battery during high-rate discharge, thereby improving the rate performance of the battery. The second lithium iron manganese phosphate particles with low manganese content and large particle size can improve the gram capacity of the active material, improve the compaction density, and improve the energy density of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode active material, a positive electrode, a battery and a device. BACKGROUND

[0002] In the existing positive electrode active material, among the polyanion type phosphate materials with olivine structure, the working voltage platform of lithium manganese iron phosphate (LiMn x Fe (1-x) PO4) is relatively high (4.1V), and has a relatively high theoretical energy density.

[0003] However, the introduction of manganese elements will cause the intrinsic ion conductivity of the active material to decrease, affecting the rate performance of the battery. In order to overcome this technical problem, the particle size of the lithium manganese iron phosphate primary particles can be currently reduced to shorten the ion migration path. However, the reduction of the particle size will also reduce the material compaction density, affecting the energy density of the battery. Therefore, it is a great challenge to ensure the rate performance of the battery while improving the compaction density of the battery. SUMMARY

[0004] In view of the deficiencies of the prior art described above, the purpose of the present application is to provide a positive electrode active material, a positive electrode, a battery and a device to balance the rate performance and energy density of the battery.

[0005] In a first aspect, the present application provides a positive electrode active material, comprising first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles, the D 50 particle size of the first lithium manganese iron phosphate particles is smaller than the D 50 particle size of the second lithium manganese iron phosphate particles, and the Mn / (Mn+Fe) molar ratio in the first lithium manganese iron phosphate particles is x, the Mn / (Mn+Fe) molar ratio in the second lithium manganese iron phosphate particles is y, and x>y.

[0006] The ion migration path of the small particle size lithium manganese iron phosphate particles can reduce the impedance and improve the gram capacity of the active material, which is beneficial to improve the rate performance of the battery. At the same time, the specific surface area of the large particle size lithium manganese iron phosphate particles is relatively small, and the processing performance is relatively good, which can improve the compaction density of the active material and is beneficial to improve the energy density of the battery. The active material of the present application adopts the small particle size first lithium manganese iron phosphate particles and the large particle size second lithium manganese iron phosphate particles to balance the rate performance and compaction density of the battery. At the same time, based on the high working voltage platform of manganese elements but the influence on the conductivity of the material ions, by setting the molar content of manganese elements in the first lithium manganese iron phosphate particles to be higher than the molar content of manganese elements in the second lithium manganese iron phosphate particles, the energy density of the active material is improved.

[0007] That is, the active material of the present application is composed of two kinds of lithium manganese iron phosphate particles with different particle sizes and different Mn / (Mn+Fe) molar ratios, wherein the first lithium manganese iron phosphate particles with small particle size and high Mn / (Mn+Fe) molar ratio can bear the instantaneous high power output of the battery during high-rate discharge, thereby improving the rate performance of the battery. The second lithium manganese iron phosphate particles with large particle size and low Mn / (Mn+Fe) molar ratio have high tap density, thereby improving the volumetric energy density of the battery.

[0008] In an embodiment, the D 50 of the first lithium manganese iron phosphate particles ranges from 50 nm to 350 nm, and the D 50 of the second lithium manganese iron phosphate particles ranges from 500 nm to 2000 nm.

[0009] In an embodiment, 0.7≤x≤0.85, 0.3≤y≤0.65.

[0010] In an embodiment, the mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles in the positive electrode active material is between 0.2 and 1.

[0011] In an embodiment, 0.7≤x≤0.8, 0.4≤y≤0.6.

[0012] In an embodiment, the Mn / (Mn+Fe) molar ratio in the positive electrode active material is between 0.36 and 0.75.

[0013] In an embodiment, the material of the first lithium manganese iron phosphate particles comprises at least one of LiMn 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 PO4.

[0014] In an embodiment, the material of the second lithium manganese iron phosphate particles comprises at least one of LiMn 0.55 Fe 0.45 PO4, LiMn 0.4 Fe 0.6 PO4.

[0015] In a second aspect, the present application provides a positive electrode comprising the positive electrode active material in any of the above embodiments.

[0016] 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 of the embodiments of the first aspect of the present application, since the positive electrode provided in the second aspect of the present application employs the positive electrode active material provided in the first aspect of the present application.

[0017] In one embodiment, the positive electrode comprises a current collector and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer comprising the positive electrode active material; the positive electrode active material layer has a compacted density of 2.35 g / cm 3 ~ 2.62 g / cm 3 .

[0018] In a third aspect, the application further provides a battery, which comprises the positive electrode provided in any one of the embodiments of the second aspect of the application.

[0019] In a fourth aspect, the application further provides a device, which comprises the battery provided in any one of the embodiments of the third aspect of the application, and the device comprises an electrical equipment or an energy storage system.

[0020] It can be understood that the battery provided in the third aspect of the application and the device provided in the fourth aspect of the application both adopt the positive electrode provided in the second aspect of the application, and thus have all the beneficial effects that can be achieved in all the embodiments of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A schematic diagram of the cross-sectional structure of the battery provided in one embodiment of the application;

[0022] Figure 2 A schematic diagram of the structure of the positive electrode provided in one embodiment of the application;

[0023] Figure 3 A schematic diagram of the structure of the positive electrode active material provided in one embodiment of the application;

[0024] Figure 4 A cross-sectional model diagram of the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles filling each other provided in one embodiment of the application.

[0025] FIG. 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 manganese iron phosphate particles; 20- second lithium manganese iron phosphate particles. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the application, the application will be described more fully below with reference to the accompanying drawings. The preferred embodiments of the application are shown in the drawings. However, the application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the application can be more thoroughly and completely understood.

[0027] The following description of the embodiments is provided as an example to illustrate the specific embodiments that can be implemented by the present application. The serial numbers of the components in the present application, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any sequential or technical meaning. The "connection" and "coupling" in the present application, unless otherwise specified, include direct and indirect connections (couplings). The direction terms mentioned in the present application, such as "up", "down", "front", "back", "left", "right", "inner", "outer", "side", etc., are only the direction of the attached drawings, therefore, the direction terms used are for better, clearer illustration and understanding of the present application, and are not indicative or implied that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0028] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "coupling" should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected; can be directly connected, or indirectly connected through an intermediate medium; can be the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the drawings are used to distinguish different objects, and are not used to describe a specific order. In addition, the terms "include", "may include", "contain" or "may contain" used in the present application represent the existence of the corresponding functions, operations, elements, etc. disclosed, and do not limit other one or more functions, operations, elements, etc. In addition, the terms "include" or "contain" represent the existence of the corresponding features, numbers, steps, operations, elements, components or combinations thereof disclosed in the specification, and do not exclude the existence or addition of one or more other features, numbers, steps, operations, elements, components or combinations thereof, and are intended to cover non-exclusive inclusion.

[0029] Please refer to Figure 1 , Figure 1 The cross-sectional structure schematic diagram of the battery 300 provided by an embodiment of the present application is shown in the figure.

[0030] As Figure 1As shown, the battery 300 of the present application comprises 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 avoid the positive and negative electrodes being in conduction. In an embodiment, the battery 300 further comprises 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, which serves as a medium to transport ions and conduct current between the positive electrode 200 and the negative electrode 301.

[0031] As shown, Figure 2 , Figure 2 A structural schematic diagram of the positive electrode 200 according to an embodiment of the present application is shown.

[0032] As shown, Figure 2 , the positive electrode 200 of the present application comprises a current collector 201 and a positive electrode active material layer 202. The positive electrode active material layer 202 comprises the positive electrode active material 100 and is distributed on the surface of the current collector 201. The current collector 201 is made of an electrically conductive material, and 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 can be understood that, in an embodiment, the current collector 201 can be made of an electrically conductive material such as an aluminum foil or a copper foil or a composite copper / aluminum foil, and the present application does not make a special limitation in this regard.

[0033] As shown, Figure 3 , Figure 3 A structural schematic diagram of the positive electrode active material 100 according to an embodiment of the present application is shown.

[0034] As shown, Figure 3 , the positive electrode active material 100 of the present application comprises first lithium manganese iron phosphate particles 10 and second lithium manganese iron phosphate particles 20. The D 50 particle size of the first lithium manganese iron phosphate particles 10 is smaller than the D 50 particle size of the second lithium manganese iron phosphate particles 20. The first lithium manganese iron phosphate particles 10 in the small particle size range can be filled into the gaps between the second lithium manganese iron phosphate particles 20 in the large particle size range (see Figure 4 , Figure 4 A cross-sectional model diagram of the mutual filling of the first lithium manganese iron phosphate particles 10 and the second lithium manganese iron phosphate particles 20 according to an embodiment of the present application is shown.

[0035] It should be noted that when only one kind of lithium manganese iron phosphate particle is used as the positive electrode active material 100 of the positive electrode 200, that is, only lithium manganese iron phosphate particles in a small particle size range or only lithium manganese iron phosphate particles in a large particle size range are used, however, single small particle size lithium manganese iron phosphate has a relatively large specific surface area, relatively poor processability and low compaction density, thereby affecting the energy density of the battery 300. Single large particle size lithium manganese iron phosphate has a long ion migration path, which increases impedance and affects the rate performance of the battery 300. That is, only one kind of lithium manganese iron phosphate particle cannot simultaneously satisfy high rate performance and high energy density.

[0036] However, the positive electrode active material 100 of the present application uses small particle size first lithium manganese iron phosphate particles 10 and large particle size second lithium manganese iron phosphate particles 20 to mutually dope and fill, so as to simultaneously ensure the rate performance and compaction density of the battery 300. Meanwhile, based on the high working voltage platform of the manganese element but the influence on the conductivity of the material ions, the Mn / (Mn+Fe) molar ratio in the first lithium manganese iron phosphate particles is x, the Mn / (Mn+Fe) molar ratio in the second lithium manganese iron phosphate particles is y, and x>y. In the present application, the Mn / (Mn+Fe) molar ratio refers to the mass fraction of Mn element based on the sum of the mass of Mn element and Fe element in lithium manganese iron phosphate. Specifically, x refers to the mass fraction of Mn element based on the sum of the mass of Mn element and Fe element in the first lithium manganese iron phosphate material; y refers to the mass fraction of Mn element based on the sum of the mass of Mn element and Fe element in the second lithium manganese iron phosphate material. The positive electrode active material 100 is arranged to have a higher molar content of manganese element in the first lithium manganese iron phosphate particles than in the second lithium manganese iron phosphate particles 20, thereby improving the energy density of the positive electrode active material 100.

[0037] That is, the positive electrode active material 100 of the present application is composed of two different D 50 particle size and different Mn / (Mn+Fe) molar ratio lithium manganese iron phosphate particles, wherein the small particle size first lithium manganese iron phosphate particles 10 with high Mn / (Mn+Fe) molar ratio can bear the instantaneous high power output of the battery 300 during large rate discharge, thereby improving the rate performance of the battery 300. The large particle size second lithium manganese iron phosphate particles 20 with lower Mn / (Mn+Fe) molar ratio can improve the compaction density of the positive electrode 200, thereby improving the volume energy density of the battery 300.

[0038] In the present application, the Mn / (Mn+Fe) molar ratio in the above first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles can be tested by an inductively coupled plasma spectrometer (ICP).

[0039] In one embodiment, the D50 The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm. 50 The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm.

[0040] It should be noted that the particle size range of the first manganese iron phosphate particles 10 is between 50nm and 350nm, which refers to the median particle size D 50 The particle size range of the first manganese iron phosphate particles 10 is between 50nm and 350nm, which refers to the median particle size D 50 The particle size range of the first manganese iron phosphate particles 10 is between 50nm and 350nm, which refers to the median particle size D 50 The particle size range of the first manganese iron phosphate particles 10 is between 50nm and 350nm, which refers to the median particle size D

[0041] The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm, which refers to the median particle size D 50 The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm, which refers to the median particle size D 50 The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm, which refers to the median particle size D

[0042] The particle size range of the second manganese iron phosphate particles 20 is between 500nm and 2000nm, which refers to the median particle size D 50 The median particle size D

[0043] It can be understood that in the present embodiment, the median particle size range of the first manganese iron phosphate particles 10 is set between 50nm and 350nm, and the median particle size range of the second manganese iron phosphate particles 20 is set between 500nm and 2000nm, which can improve the processing performance of the positive active material 100, reduce the physical gel phenomenon, and improve the overall consistency of the positive active material 100. In addition, it can also improve the ion transmission performance in the positive active material 100, which is beneficial to further improve the cycle performance of the battery 300.

[0044] In one embodiment, the Mn / (Mn+Fe) molar ratio x in the first manganese iron phosphate particles 10 is between 70% and 85%, and the Mn / (Mn+Fe) molar ratio y in the second manganese iron phosphate particles 20 is between 30% and 65%.

[0045] It can be understood that by setting the Mn / (Mn+Fe) molar ratio x of the first lithium manganese iron phosphate particles to be between 70% and 85%, the active material has a relatively high working voltage platform and certain rate performance; by setting the Mn / (Mn+Fe) molar ratio y of the second lithium manganese iron phosphate particles to be between 30% and 65%, the active material has a relatively low intrinsic impedance and good specific capacity. The specific capacity refers to the electric capacity released per gram of active material, and the unit is mAh / g. By setting the Mn / (Mn+Fe) molar ratios x and y of the first lithium manganese iron phosphate particles 10 and the second lithium manganese iron phosphate particles 20 to be between 0.7 and 0.85 and between 0.30 and 0.65 respectively, the content of manganese element can be prevented from being too high to affect the conductivity of the positive active material 100, and the rate performance of the battery 300 can be reduced. At the same time, the content of manganese element can also be prevented from being too low, which leads to a relatively low working voltage platform and reduces the energy density of the battery 300.

[0046] In an embodiment, the mass ratio of the first lithium manganese iron phosphate particles 10 to the second lithium manganese iron phosphate particles 20 in the positive active material 100 is 0.2 to 1.

[0047] Further optionally, the mass ratio of the first lithium manganese iron phosphate particles 10 to the second lithium manganese iron phosphate particles 20 can be, for example, 1:4, 1:3, 3:7, etc. It can be understood that by setting the mass ratio of the first lithium manganese iron phosphate particles 10 to the second lithium manganese iron phosphate particles 20 within the above range, the mixed filling effect of the first lithium manganese iron phosphate particles 10 and the second lithium manganese iron phosphate particles 20 can be ensured, so that the battery 300 has a higher pressure density and higher rate performance.

[0048] In an embodiment, the Mn / (Mn+Fe) molar ratios x and y of the first lithium manganese iron phosphate particles 10 and the second lithium manganese iron phosphate particles 20 satisfy 0.7≤x≤0.8 and 0.4≤y≤0.6.

[0049] In an embodiment, the Mn / (Mn+Fe) molar ratio in the positive active material is between 0.36 and 0.75. That is, if the sum of the amount of substance of Mn and Fe in the first lithium manganese iron phosphate and the amount of substance of Mn and Fe in the second lithium manganese iron phosphate in the positive active material is denoted as N 总 , the sum of the amount of substance of manganese element in the first lithium manganese iron phosphate and the amount of substance of manganese element in the second lithium manganese iron phosphate in the positive active material is denoted as n 总 , n 总 / N 总 is between 0.36 and 0.75.

[0050] In this embodiment, by setting the total molar content of manganese element after mixing and filling the two types of particles, the ratio of the total molar content of manganese element to the molar content of Mn and Fe in the first lithium manganese iron phosphate and the molar content of Mn and Fe in the second lithium manganese iron phosphate is between 0.36 and 0.75. This is to avoid the increased impedance caused by excessive manganese element, which would affect the rate performance of battery 300, and at the same time, to avoid the voltage drop caused by excessive manganese element, which would affect the theoretical energy density of battery 300.

[0051] 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.

[0052] In this embodiment, the material of the first lithium manganese iron phosphate particle 10 can be LiMn. 0.8 Fe 0.2 PO4 could be LiMn 0.7 Fe 0.3 In PO4, it can also be LiMn 0.8 Fe 0.2 PO4 and LiMn 0.7 Fe 0.3 The combination in PO4. Understandably, given that the redox potential of manganese ions is higher than that of iron ions, the material for setting the first lithium manganese iron phosphate particle 10 can be LiMn. 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 At least one of PO4 is used to ensure that the manganese and iron elements in the first lithium manganese iron phosphate particles 10 have a suitable ratio, thereby ensuring that the first lithium manganese iron phosphate particles 10 have a high voltage platform without reducing the theoretical specific capacity of the positive electrode active material 100.

[0053] In one embodiment, the material of the second lithium manganese iron phosphate particle 20 includes LiMn. 0.55 Fe 0.45 PO4, LiMn 0.4 Fe 0.6 At least one of PO4.

[0054] In this embodiment, the material of the second lithium manganese iron phosphate particle 20 can be LiMn. 0.55 Fe 0.45 PO4 could be LiMn 0.4 Fe 0.6 PO4 can also be LiMn 0.55 Fe 0.45 PO4 and LiMn0.4 Fe 0.6 A combination of PO4.

[0055] In one embodiment, the first lithium manganese iron phosphate particles 10 include a first particle group and a second particle group, wherein the first lithium manganese iron phosphate particles 10 in the first particle group have a D 50 The particle size is smaller than that of the first lithium manganese iron phosphate particles in the second particle group by 10 D 50 The particle size is such that the Mn / (Mn+Fe) molar ratio in the first lithium manganese iron phosphate particle 10 in the first particle group is greater than the Mn / (Mn+Fe) molar ratio in the first lithium manganese iron phosphate particle 10 in the second particle group.

[0056] Understandably, setting two groups of particles with different particle sizes and manganese content in the first lithium manganese iron phosphate particles 10, so as to use a variety of lithium manganese iron phosphate particles with different particle sizes and different Mn / (Mn+Fe) molar ratios for compounding, can achieve uniform filling and ensure uniform current distribution inside the positive electrode active material 100, thereby further improving the overall compaction density of the positive electrode active material 100, and avoiding the capacity decay of the battery 300 caused by uneven current distribution leading to different degrees of internal degradation.

[0057] In one embodiment, the second lithium manganese iron phosphate particles 20 include a third particle group and a fourth particle group, wherein the second lithium manganese iron phosphate particles 20 in the third particle group have a D 50 The particle size is smaller than that of the second lithium manganese iron phosphate particle 20 in the fourth particle group. 50 The particle size is such that the Mn / (Mn+Fe) molar ratio in the second lithium manganese iron phosphate particle 20 in the third particle group is greater than the Mn / (Mn+Fe) molar ratio in the second lithium manganese iron phosphate particle 20 in the fourth particle group.

[0058] Understandably, in this embodiment, two groups of particles with different particle sizes and manganese content are set in the second lithium manganese iron phosphate particles 20. By using lithium manganese iron phosphate particles with different particle sizes and different Mn / (Mn+Fe) molar ratios for compounding, uniform filling can be achieved and the current distribution inside the positive electrode active material 100 can be ensured to be uniform, thereby further improving the overall compaction density of the positive electrode active material 100. At the same time, it avoids the capacity decay of the battery 300 caused by uneven current distribution leading to different degrees of internal degradation.

[0059] In one embodiment, the cathode 200 further comprises a dispersant, a conductive agent and a binder (not shown in the figure). The dispersant is provided to make the cathode active material 100 uniformly distributed. It can be understood that the conductive agent is provided to collect current between lithium iron manganese phosphate particles, between lithium iron manganese phosphate particles and the current collector 201, so as to reduce the contact resistance of the electrode, accelerate the moving speed of electrons, effectively improve the migration rate of lithium ions in lithium iron manganese phosphate particles, and improve the charge and discharge efficiency of the battery 300. The binder is provided to bind and fix the lithium iron manganese phosphate particles and make the lithium iron manganese phosphate particles have a certain structural strength. Since the binder is usually in a powder form, the binder needs to be dissolved in the dispersant during the manufacturing process of the cathode 200, so that the binder is in full contact with the lithium iron manganese phosphate particles, the conductive agent and the like and is uniformly dispersed therein. The dispersant, the binder and the conductive agent 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), polyolefin (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.

[0060] In one embodiment, the cathode 200 further comprises a current collector 201. The cathode active material 100 is coated on the surface of the current collector after being mixed with the dispersant, the conductive agent and the binder, and the current collector 201 is used to collect and lead out the current generated by the cathode active material 100.

[0061] The current collector 201 can include, but is not limited to, an aluminum foil, an aluminum alloy foil, a polymer film coated with metal aluminum or the aforementioned material coated with carbon on the surface, etc. In some embodiments of the present application, the current collector 201 is an aluminum foil or a carbon-coated aluminum foil.

[0062] In one embodiment, the compacted density of the cathode 200 is between 2.35 g / cm 3 and 2.62 g / cm 3 .

[0063] In the present application, the anode 301 of the battery 300 generally comprises an anode current collector and an anode material layer provided on at least one side surface of the anode current collector. The anode material layer generally contains an anode active material, a conductive agent and a binder. In the embodiments of the present application, the anode active material for lithium batteries can be selected from one or more of hard carbon, soft carbon, graphite, mesocarbon microbeads, silicon-carbon composite material, etc.

[0064] The insulating separator 302 is used to separate the positive electrode 200 and the negative electrode 301, maintain the insulation and liquid retention properties between the two; the insulating separator 302, together with the positive electrode 200 and the negative electrode 301, forms the electrode core of the battery 300, which is contained in the battery shell and is infiltrated by the electrolyte contained in the shell. In some embodiments of the present application, the lithium battery can be assembled by the following method: the positive electrode, the separator and the negative electrode are sequentially stacked to form an electrode core; the electrode core is contained in the battery shell, and the electrolyte is injected, then the battery shell is sealed to obtain the battery. The electrode core can be a winding type or a laminated type, etc.

[0065] In the present application, the insulating separator 302 can use any separator material in the battery. For example, the insulating separator 302 can include but is not limited to single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer film PP / PE, double-layer film PP / PP, and three-layer PP / PE / PP polymer separator, or non-woven fabric, etc. The electrolyte includes electrolyte salt and organic solvent, and the specific types and compositions of electrolyte salt and organic solvent are conventional choices in the battery field, which can be selected according to actual needs.

[0066] In one embodiment, the battery 300 has a discharge specific capacity greater than or equal to 105 mAh / g at a 5C rate; the volumetric energy of the battery 300 is greater than or equal to 1364.5 mWh / cm 3 .

[0067] In the present application, the D 50 The test method of the D

[0068] After the lithium ion battery is completely discharged, the positive electrode is obtained, and the positive electrode is soaked in the solvent dimethyl carbonate (English abbreviation is DMC) for 10-20 min to clean the residual electrolyte. After the positive electrode is dried, it is soaked in water to make the binder ineffective, so that the coating layer can be peeled off from the positive electrode current collector. Then the coating layer is dissolved in the solvent N-methyl pyrrolidone (NMP) and heated at 80°C to accelerate the dissolution. The dissolved material is suction filtered to separate the solid material, and the solid material is washed with NMP, then the obtained mixture containing solid material and NMP is centrifuged at a speed of 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 LMFP-containing material is washed with NMP for 6 times-centrifugation. Since the two LMFP materials D 50The centrifugal speed is further adjusted to 3000 rpm for centrifugal treatment, and the second LMFP material can be precipitated to the lower layer, and the upper liquid is filtered to obtain the first LMFP material.

[0069] The two separated LMFP powders can be respectively subjected to laser particle size testing D 50 and ICP testing of the Mn / (Mn+Fe) molar ratio. Specifically, the D 50 testing can refer to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, and a Malvern laser particle size analyzer can be used for testing.

[0070] In addition, the Mn / Fe content can also be directly tested by SEM-EDS, for example, the CP (Ar ion thinning) treatment is used on the pole piece to obtain a pole piece cross section, and SEM-EDS scanning is performed on the large-particle and small-particle LMFP materials respectively, so that the Mn / Fe mass ratio can be obtained, and the Mn / (Mn+Fe) molar ratio can be further calculated.

[0071] In the positive electrode active material, the testing method of the Mn / (Mn+Fe) molar ratio is as follows: after the lithium ion battery is completely discharged, the positive electrode is obtained by disassembling, and the positive electrode is soaked in the solvent DMC for 10-20 min to clean the residual electrolyte. After the positive electrode is dried, it is soaked in water to make the binder ineffective, so that the coating layer can be peeled off from the positive electrode current collector. Then the coating layer is dissolved in the solvent N-methyl pyrrolidone (NMP), and heated at 80°C to accelerate the dissolution. The dissolved material is filtered to separate the solid material, and the solid material is washed with NMP, and then the obtained mixture containing the solid material and NMP is subjected to centrifugal treatment at a speed of 5000 rpm, and the upper material containing the conductive agent is discarded, and the lower material containing the lithium manganese iron phosphate (LMFP) is collected. The Mn / (Mn+Fe) molar ratio is tested by ICP.

[0072] The beneficial effects that can be achieved by the positive electrode active material 100 of the present application are compared and explained below in combination with some embodiments of the positive electrode active material 100 of the present application and some embodiments of the prior art.

[0073] Embodiment 1

[0074] In embodiment 1, the first lithium manganese iron phosphate particle material is LiMn 0.8 Fe 0.2 PO4, and the particle size D 50 is 150 nm. The second lithium manganese iron phosphate particle LiMn 0.6 Fe 0.4 PO4, and the particle size D 50is 1000 nm. The mass compounding ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.25.

[0075] Example 2

[0076] The positive electrode active material provided in Example 2 is different from the positive electrode active material in Example 1 in that, in the positive electrode active material provided in Example 2, the particle size D 50 is 300 nm.

[0077] Example 3

[0078] The positive electrode active material provided in Example 3 is different from the positive electrode active material in Example 1 in that, in the positive electrode active material provided in Example 3, the material of the first lithium manganese iron phosphate particles is LiMn 0.7 Fe 0.3 PO4.

[0079] Example 4

[0080] The positive electrode active material provided in Example 4 is different from the positive electrode active material in Example 1 in 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 the particle size D 50 is 1500 nm.

[0081] Example 5

[0082] The positive electrode active material provided in Example 5 is different from the positive electrode active material in Example 1 in 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.

[0083] Example 6

[0084] The positive electrode active material provided in Example 6 is different from the positive electrode active material in Example 1 in 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.

[0085] Example 7

[0086] The positive electrode active material provided in Example 7 is different from the positive electrode active material in Example 1 in 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.

[0087] Example 8

[0088] The positive electrode active material provided in Example 8 is different from the positive electrode active material in Example 1 in that, in the positive electrode active material provided in Example 8, the particle size D of the first lithium manganese iron phosphate particles is 350 nm 50 , the particle size D of the second lithium manganese iron phosphate particles is 2000 nm. 50

[0089] Example 9

[0090] The positive electrode active material provided in Example 9 is different from the positive electrode active material in Example 1 in 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 nm 50 , the particle size D of the second lithium manganese iron phosphate particles is 500 nm. 50

[0091] Example 10

[0092] The positive electrode active material provided in Example 10 is different from the positive electrode active material in Example 1 in that, in the positive electrode active material provided in Example 10, the material of the first lithium manganese iron phosphate particles is LiMn 0.85 Fe 0.15 PO4, and the material of the second lithium manganese iron phosphate particles is LiMn 0.65 Fe 0.35 PO4.

[0093] Example 11

[0094] The positive electrode active material provided in Example 11 is different from the positive electrode active material in Example 1 in that, in the positive electrode active material provided in Example 11, the material of the first lithium manganese iron phosphate particles is LiMn 0.7 Fe 0.3 PO4, and the material of the second lithium manganese iron phosphate particles is LiMn 0.3 Fe 0.7 PO4.

[0095] Example 12

[0096] The positive electrode active material provided in Example 12 is different from the positive electrode active material in Example 1 in 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.

[0097] Example 13

[0098] The positive electrode active material provided in Example 13 is different from the positive electrode active material in Example 1 in 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 ​​The mass ratio of PO4, first lithium manganese iron phosphate particles to second lithium manganese iron phosphate particles is 0.1.

[0099] Example 14

[0100] The difference between the positive electrode active material provided in Example 14 and the positive electrode active material in Example 1 is that the material of the first lithium manganese iron phosphate particle in the positive electrode active material provided in Example 14 is LiMn. 0.4 Fe 0.6 PO4, the material of the lithium iron phosphate second manganese phosphate particles is LiMn 0.2 Fe 0.8 The mass ratio of the first lithium manganese iron phosphate particles to the second lithium manganese iron phosphate particles is 0.2.

[0101] Example 15

[0102] The difference between the positive electrode active material provided in Example 15 and the positive electrode active material in Example 1 is that the particle size D of the first lithium manganese iron phosphate particles in the positive electrode active material provided in Example 15 is... 50 The particle size D of the second lithium manganese iron phosphate particles is 400 nm. 50 The size is 2000nm, and the mass ratio of the first lithium manganese iron phosphate particle to the second lithium manganese iron phosphate particle is 0.3.

[0103] Example 16

[0104] The difference between the positive electrode active material provided in Example 16 and the positive electrode active material in Example 1 is that the particle size D of the first lithium manganese iron phosphate particles in the positive electrode active material provided in Example 16 is... 50 The particle size D of the second lithium manganese iron phosphate particles is 40 nm. 50 The size is 450nm, and the mass ratio of the first lithium manganese iron phosphate particle to the second lithium manganese iron phosphate particle is 0.3.

[0105] Comparative Example 1

[0106] The difference between the positive electrode active material provided in Comparative Example 1 and the positive electrode active material in Example 1 is that the material of the first lithium manganese iron phosphate particle in the positive electrode active material provided in Comparative Example 1 is LiMn. 0.4 Fe 0.6 PO4, the material of the lithium iron phosphate second manganese phosphate particles is LiMn 0.8 Fe 0.2 PO4.

[0107] Comparative Example 2

[0108] In Comparative Example 2, the positive electrode active material contained only first lithium manganese iron phosphate particles, without any second lithium manganese iron phosphate particles. The first lithium manganese iron phosphate particles were made of LiMn.0.8 Fe 0.2 PO4, and the particle size D 50 is 150 nm.

[0109] Comparative Example 3

[0110] In Comparative Example 3, the positive active material only contains the first lithium manganese iron phosphate particles, without doping the second lithium manganese iron phosphate particles. The material of the first lithium manganese iron phosphate particles is LiMn 0.7 Fe 0.3 PO4, and the particle size D 50 is 300 nm.

[0111] Comparative Example 4

[0112] In Comparative Example 4, the positive active material only contains the second lithium manganese iron phosphate particles, without doping the first lithium manganese iron phosphate particles. The material of the second lithium manganese iron phosphate particles is LiMn 0.6 Fe 0.4 PO4, and the particle size D 50 is 700 nm.

[0113] Comparative Example 5

[0114] In Comparative Example 5, the positive active material only contains the second lithium manganese iron phosphate particles, without doping the first lithium manganese iron phosphate particles. The material of the second lithium manganese iron phosphate particles is LiMn 0.5 Fe 0.5 PO4, and the particle size D 50 is 1000 nm.

[0115] The molar content of manganese element and the particle size D 50 of the first lithium manganese iron phosphate particles (LMFP-1) and the molar content of manganese element and the particle size D 50 of the second lithium manganese iron phosphate particles (LMFP-2) in the positive active materials in the above examples and comparative examples, the mass compounding ratio of the first lithium manganese iron phosphate particles (LMFP-1) and the second lithium manganese iron phosphate particles (LMFP-2), and the ratio of the content of manganese element in the first lithium manganese iron phosphate particles (LMFP-1) and the second lithium manganese iron phosphate particles (LMFP-2) to the content of other elements are counted, and the results are shown in Table 1.

[0116] Table 1: Parameter design of each example and comparative example

[0117]

[0118]

[0119]

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

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

[0122] The positive electrode active material, the binder PVDF, the conductive agent carbon black and the solvent NMP were prepared into a positive electrode slurry in a mass ratio of 100:2:2:60. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil, the single-sided area density was 200 g / m2, dried, rolled to obtain the positive electrode sheet.

[0123] The preparation method of the battery comprises:

[0124] 1. The rolled positive electrode sheet was cut into a circular sheet with a diameter of 1.5 cm and weighed to obtain the sheet mass m 正极 . The same area of aluminum foil was weighed to obtain the weighed mass m Al , and the two parameters were subtracted to obtain the coating weight m 敷料 = m 正极 -m Al . The weight of the LMFP material in the single positive electrode was m = m 敷料 ×96.15%.

[0125] 2. The positive electrode sheet cut into a circular sheet with a diameter of 1.5 cm was baked in a 105°C oven for 24h to remove moisture. Subsequently, the assembly of CR2016 button-type half-batteries was carried out, and the positive electrode sheet-PP separator-lithium sheet-foam nickel were assembled in order and pressed into the shell to form a button-type battery.

[0126] The compaction density of the above positive electrode sheet and the electrochemical performance of the battery were respectively tested according to the performance test in Table 2, and the test results are shown in Table 2. Among them, the test method of each parameter is as follows:

[0127] The test method of the sheet compaction density: the thickness of the positive electrode sheet and the aluminum foil was measured to obtain the coating thickness h, and the sheet compaction density D = m 敷料 / (π×1.5cm×1.5cm×h);

[0128] Average voltage and 0.1C specific discharge capacity test method: the battery capacity of the half-cell was calibrated at room temperature, specifically including: at room temperature (25℃), charged to the upper limit voltage of 4.35V at 0.1C constant current and constant voltage, then charged to the cutoff current of 0.05C at 4.35V constant voltage, and rested for 30min; then discharged to the lower limit voltage of 2.5V at 0.1C constant current, and rested for 30min; repeat the above charge and discharge steps 3 times, the capacity discharged in the 3rd time was recorded as C0, unit is Ah; and the average discharge voltage during the 3rd discharge was recorded. Wherein, the C0 is the room temperature calibrated capacity of the positive electrode half-cell. 0.1C specific discharge capacity = C0 / total mass of positive active material in a single battery.

[0129] 5C specific discharge capacity test method: take C0 as the rated capacity of the battery, 0.1C0 constant current and constant voltage charged to the upper limit voltage of 4.35V, then charged to the cutoff current of 0.05C0 at 4.35V constant voltage, and rested for 30min; then discharged to the lower limit voltage of 2.5V at 5C0 constant current, and rested for 30min; record the discharge capacity C1, which is the 5C discharge capacity of the battery, and similarly, 5C specific discharge capacity = C1 / total mass of positive active material in a single battery.

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

[0131] Specific energy = 0.1C specific discharge capacity x average discharge voltage;

[0132] Volume specific energy = specific energy x compacted density; volume specific energy mainly represents the energy density of the battery.

[0133] Table 2: performance comparison of each example and comparative example

[0134]

[0135]

[0136] In combination with Table 1 and Table 2:

[0137] Comparing the results of Examples 1-16 and Comparative Examples 2-5, it can be seen that the batteries made solely with large-diameter lithium manganese iron phosphate particles in the comparative examples not only have low energy density but also poor rate performance. While the batteries made solely with small-diameter lithium manganese iron phosphate particles have relatively better rate performance than those made solely with large-diameter particles, their energy density is reduced. In other words, batteries made using lithium manganese iron phosphate particles of a single particle size cannot simultaneously achieve good rate performance and energy density, resulting in relatively poor overall electrochemical performance. In contrast, the embodiments of this application use first and second lithium manganese iron phosphate particles of different particle sizes to inter-dope and fill the battery. This increases the compaction density of the positive electrode while ensuring a high discharge specific capacity, thus improving both the energy density and rate performance, resulting in superior overall electrochemical performance.

[0138] Comparing the results of Examples 1-16 and Comparative Example 1, it can be seen that the embodiments of this application, due to the use of small-particle-size lithium manganese iron phosphate particles with high manganese content and doped with large-particle-size lithium manganese iron phosphate particles with low manganese content, have superior rate performance and energy density compared to Comparative Example 1, which uses small-particle-size lithium manganese iron phosphate particles with low manganese content and high manganese content and high-particle-size lithium manganese iron phosphate particles. This greatly improves the overall electrochemical performance of the battery.

[0139] Comparing the results of Examples 1, 2, 8, 9, 15, and 16, it can be seen that by adjusting the particle size of the first and second lithium manganese iron phosphate particles to a suitable range, the overall electrochemical performance of the battery can be optimized.

[0140] The results of comparative examples 1, 3, 4, 10, 11, and 14 show that by adjusting the relative manganese content of the first and second lithium manganese iron phosphate particles within a suitable range, the overall electrochemical performance of the battery can also be optimized.

[0141] The results of comparative examples 1, 5, 6, 7, 12, and 13 show that by adjusting the compounding ratio of the first lithium manganese iron phosphate particles and the second lithium manganese iron phosphate particles within a suitable range, the compaction density and specific capacity of the battery can be optimized, thereby improving the overall electrochemical performance of the battery.

[0142] In summary, this application sets 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, so that the battery can have both better rate performance and energy density, that is, the overall electrochemical performance of the battery can be optimized.

[0143] It is to be understood that the terms "first", "second", and the like, do not imply or mean any relative importance or imply the number of indicated technical features. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of embodiments of the present application, the meaning of "a plurality" is two or more, unless otherwise explicitly specifically limited.

[0144] In the description of the present application, the description referring to the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", or "some examples" etc. means that the specific feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Also, the specific feature, structure, material or characteristic described can be combined in any suitable manner in one or more embodiments or examples.

[0145] It should be understood that the application of the present application is not limited to the above examples, and those of ordinary skill in the art can make improvements or changes according to the above description, and all such improvements and changes shall fall within the scope of protection of the claims of the present application. Those of ordinary skill in the art can understand that all or part of the processes of the above embodiments are implemented, and equivalent changes made in accordance with the claims of the present application, still fall within the scope of the present application.

Claims

1. A positive electrode active material, characterized in that, It is composed of first lithium manganese iron phosphate particles and second lithium manganese iron phosphate particles, wherein the first lithium manganese iron phosphate particles have a D 50 D particles smaller than lithium manganese iron phosphate particles 50 The particle size, and the molar ratio of Mn / (Mn+Fe) in the first lithium manganese iron phosphate particle is x, the molar ratio of Mn / (Mn+Fe) in the second lithium manganese iron phosphate particle is y, x>y, and the D of the first lithium manganese iron phosphate particle 50 The particle size range is between 150nm and 350nm, and the D of the second lithium manganese iron phosphate particles 50 The particle size ranges from 1000 nm to 2000 nm, and the positive electrode active material is used to form the positive electrode active material layer; the compaction density of the positive electrode active material layer is between 2.35 g / cm³. 3 ~2.62g / cm 3 between.

2. The positive electrode active material according to claim 1, characterized in that, 0.7≤x≤0.85, 0.3≤y≤0.

65.

3. The positive electrode active material according to claim 1 or 2, characterized in that, 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 0.2~1.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, 0.7≤x≤0.8, 0.4≤y≤0.

6.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, In the positive electrode active material, the molar ratio of Mn / (Mn+Fe) is between 0.36 and 0.

75.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, The material of the first lithium manganese iron phosphate particle includes LiMn 0.8 Fe 0.2 PO4, LiMn 0.7 Fe 0.3 At least one of PO4; and / or, The material of the second lithium manganese iron phosphate particle includes LiMn 0.55 Fe 0.45 PO4, LiMn 0.4 Fe 0.6 At least one of PO4.

7. A positive electrode, characterized in that, Includes the positive electrode active material as described in any one of claims 1-6.

8. The positive electrode according to claim 7, characterized in that, The positive electrode includes a current collector and a layer of positive electrode active material disposed on the current collector.

9. A battery, characterized in that, Includes the positive electrode as described in claim 7 or 8.

10. An apparatus, characterized in that, The device includes the battery as described in claim 9, and the device includes an electrical appliance or an energy storage system.

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