Positive electrode active material composition and its application

Abstract

To provide a positive active material composition of a lithium ion secondary battery which improves a rolling density of a positive electrode sheet and increases a volume energy density while improving the conductivity and the rate performance.SOLUTION: A positive electrode active material composition includes a component A as a first active material and a component B as a second active material. In the particle diameter distribution of the first active material and the second active material, a ratio DAmin / DBmin of Dmin is 0.25 to 1.5, a ratio DA10 / DB10 of D10 is 0.1 to 0.6, a ratio DA50 / DB50 of D50 is 0.1 to 0.35, a ratio DA90 / DB90 of D90 is 0.12 to 0.67, and 0.2≤[(DA90-DA10) / DA50] / [(DB90-DB10) / DB50]≤13 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode active material composition and its application. [Background technology]

[0002] Olivine-type cathode materials are widely available and feature low cost and high theoretical capacity. However, the energy density of olivine-type materials, such as lithium iron phosphate and lithium iron manganese phosphate, is much lower than that of other types of cathode materials, such as ternary cathode materials and lithium-rich manganese-based materials. At the same time, olivine-type materials have poor high-temperature cycling performance.

[0003] Lithium-rich lithium manganese-based materials have attracted much attention due to their high discharge specific capacity, low manufacturing cost, and environmental friendliness. However, their low-temperature performance and poor electrical conductivity limit their applications.

[0004] Furthermore, the rolling density of olivine-based materials such as lithium manganese iron phosphate and lithium-rich lithium manganese-based materials is lower than that of conventional ternary materials, which leads to a decrease in the rolling density of electrode sheets manufactured using lithium manganese iron phosphate and lithium-rich lithium manganese-based materials, resulting in a decrease in the volumetric energy density of the battery. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a positive electrode active material composition that can effectively improve the rolling density of a positive electrode sheet while improving the conductivity and rate performance of a lithium ion secondary battery, thereby increasing the volumetric energy density of the lithium ion secondary battery, and applications thereof. [Means for solving the problem]

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions.

[0007] The present invention provides a positive electrode active material composition comprising the following components: Component A as a first active material; Component B as the second active material. Here, the particle size distribution of the first active material and the second active material is D min Ratio of D Amin / D Bmin is 0.25~1.5, D 10 Ratio of D A10 / D B10 is 0.1 to 0.6, D 50 Ratio of D A50 / D B50 is 0.1 to 0.35, D 90 Ratio of D A90 / D B90 is 0.12 to 0.67, and 0.2≦[(D A90 -D A10 ) / D A50 ] / [(D B90 -D B10 ) / D B50 ]≦13.

[0008] In one embodiment of the present invention, the mass ratio of the first active material to the second active material is 50:50 to 90:10.

[0009] In one embodiment of the present invention, the general chemical formula of the first active material is Formula I, where Formula I is Li a Mn x Fe 1-x-y G y PO4, wherein 0.9≦a≦1.10, 0≦x≦1.0, 0≦y≦0.02, 0.5≦x / (1−xy)≦0.9, and element G is one or more of Ti, Mg, Ni, Co, Al, V, Cr, Zr, and Nb.

[0010] In one embodiment of the present invention, the doping amount of element G is 2000 ppm to 5000 ppm.

[0011] In one embodiment of the present invention, the general chemical formula of the second active material is Formula II, where Formula II is Li 1+(b / (2+b)) Mn 2b / (2+b) M (6 / (2+b))-2 O2, where 0.5≦b≦1, and element M is one or more of Ni, Co, Mn, Mg, Al, Ti, Zr, Nb, La, Sr, and W.

[0012] In one embodiment of the present invention, the doping amount of element M is 2000 ppm to 5000 ppm.

[0013] In one embodiment of the present invention, the surface of the first active material is covered with a carbon layer, and the mass of the carbon layer is 1% to 3% of the mass of the first active material.

[0014] The present invention also provides a positive electrode sheet comprising the above-described positive electrode active material composition.

[0015] In one embodiment of the present invention, the rolled density of the positive electrode sheet is 2.47 g / cm 3 ~2.79g / cm 3 is.

[0016] The present invention further provides a lithium ion secondary battery including the above-mentioned positive electrode sheet.

[0017] The present invention further provides an electrochemical device including the above-described lithium ion secondary battery. [Effects of the Invention]

[0018] Therefore, the present invention provides a positive electrode active material composition that can effectively improve the rolling density of a positive electrode sheet, increase the volumetric energy density of a lithium ion secondary battery, and improve the electrical conductivity and ionic conductivity of the lithium ion secondary battery, thereby improving the rate performance and cycle performance of the lithium ion secondary battery, and applications thereof. [Brief explanation of the drawings]

[0019] In order to more clearly describe the technical solutions in the embodiments of the present invention or related technologies, the following description will briefly introduce the accompanying drawings that need to be used to describe the embodiments or related technologies. Obviously, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can obtain other drawings according to these drawings without creative efforts. [Figure 1] 1 is a schematic diagram of a lithium ion secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 1 is a graph showing the cycle performance of lithium batteries in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described below with reference to specific examples, but those skilled in the art will readily understand other advantages and effects of the present invention from the contents disclosed herein. The present invention may be implemented or applied through other different specific embodiments, and the details of the present specification may be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] It should be understood that the present invention can be embodied in different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the following examples, "%" and "parts" mean "% by weight" and "parts by weight," respectively, unless otherwise specified.

[0022] The technical solution of the present invention will be described in more detail below in conjunction with some embodiments and the accompanying drawings. Obviously, the described embodiments are only a part, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0023] Lithium transition metal oxides are expected to be a promising cathode active material for lithium batteries, characterized by low cost and high specific capacity. Lithium ion secondary batteries made of lithium transition metal oxides are widely used in mobile phones, tablet PCs, laptops, digital cameras, and other portable electronic products, as well as vehicles such as electric bicycles and electric vehicles. The present invention provides a cathode active material composition and its applications that can improve the volumetric energy density and rated performance of batteries and can be applied to various electronic products and electric vehicles.

[0024] The present invention provides a positive electrode active material composition comprising component A and component B. Component A is a first active material, component B is a second active material, and the median diameter D of the first active material and the second active material is 50 Ratio of D A50 / D B50 is, for example, 0.1 to 0.35. Furthermore, the median diameter D 50 Ratio of D A50 / D B50 is, for example, 0.2 to 0.3. 50 When the ratio is in this range, the particle gradation effect between the first and second active materials is minimized, and the rolled density of the produced positive electrode sheet is high. Amin is 0.1μm~0.3μm, D A10 is 0.3μm~0.6μm, D A50 is 0.7μm~2.5μm, D A90 The particle size distribution of the second active material is D Bmin is 0.2μm~0.4μm, D B10 is 1μm~3μm, D B50 is 7μm~11μm, D B90 The particle size ratio of the first active material to the second active material is D min Ratio of D Amin / D Bmin is 0.25~1.5, D 10 Ratio of D A10 / D B10 is 0.1 to 0.6, D 50 Ratio of D A50 / D B50is 0.1 to 0.35, D 90 Ratio of D A90 / D B90 is 0.12 to 0.67, and 0.2≦[(D A90 -D A10 ) / D A50 ] / [(D B90 -D B10 ) / D B50 ]≦13. Within the above range, the particle size design of the two active materials becomes more rational, thereby achieving better rolling density and rate performance.

[0025] In one embodiment of the present invention, the first active material is selected from, for example, lithium manganese iron phosphate (LMFP) materials, and the general chemical formula of the first active material is Formula I, which can be, for example, Li a Mn x Fe 1-x-y G y PO4, where 0.9≦a≦1.10, 0≦x≦1.0, 0≦y≦0.02, and 0.5≦x / (1-xy)≦0.9. The element G is, for example, one or more of Ti, Mg, Ni, Co, Al, V, Cr, Zr, and Nb. The element G improves the electrical conductivity and ionic conductivity of the first active material, thereby improving the rate performance of the lithium-ion secondary battery. Furthermore, the doping amount of the element G is 2000 ppm to 5000 ppm, and the doping amount of the element G is defined as the ratio of the mass of the element G to the total mass of the elements Mn, Fe, and G. If the content of the element G is too low, the effect of improving the rate performance of the lithium-ion secondary battery is not significant, while if the content of the element G is too high, the number of active sites decreases, resulting in a decrease in the energy density of the lithium-ion secondary battery.

[0026] In one embodiment of the present invention, for example, the surface of the first active material is coated with a carbon (C) layer, and the amount of carbon coating is, for example, 1% to 3% of the mass of the first active material. Furthermore, the amount of carbon coating is, for example, 1.2% to 2% of the mass of the first active material. When the mass of the carbon coating is within the above range, the conductivity of the first active material is improved, thereby improving the rate characteristics of the battery. At the same time, Mn elution into the first active material is reduced, thereby improving the cycle performance of the battery. If the amount of carbon coating is too small, less than 1% of the mass of the first active material, the coating effect is poor and Mn elution may not be effectively prevented. If the amount of carbon coating is too large, exceeding 3% of the mass of the first active material, the number of active sites is reduced. In one embodiment of the present invention, one or more uniform carbon (C) layers are coated on the surface of the first active material, and the area of ​​the first active material covered by the carbon layer is 100% of the surface area of ​​the first active material. In other embodiments, the area of ​​the first active material covered by the carbon layer may be less than 100% of the surface area of ​​the first active material. In this embodiment, the first active material is, for example, LiMn 0.6 Fe 0.4 PO4 / C, and the carbon coating amount is LiMn 0.6 Fe 0.4 It is 2% of the mass of PO4.

[0027] In one embodiment of the present invention, the second active material includes, for example, a lithium-rich lithium manganese-based material (LMRO). The general chemical formula of the second active material is Formula II, which can be, for example, LLi 1+(b / (2+b)) Mn 2b / (2+b) M (6 / (2+b))-2O2, where 0.5≦b≦1, and element M is one or more of Ni, Co, Mn, Mg, Al, Ti, Zr, Nb, La, Sr, and W. Element M improves the electrical conductivity and ionic conductivity of the second active material, thereby improving the rate characteristics of the lithium ion secondary battery. Furthermore, the doping amount of element M is 2000 ppm to 5000 ppm, and the doping amount of element M is defined as the ratio of the mass of element M to the total mass of elements Mn and M. If the content of element M is too low, the effect of improving the rate characteristics of the lithium ion secondary battery is not significant. If the content of element M is too high, the number of active sites decreases, and the energy density of the lithium ion secondary battery decreases. In this embodiment, the second active material is, for example, Li 1.1 Mn 0.6 Ni 0.4 Selected from O2.

[0028] In one embodiment of the present invention, the mass ratio of the first active material to the second active material is, for example, 50:50 to 90:10. Mixing the first and second active materials to form secondary particles improves the liquid retention of the positive electrode sheet, thereby improving the rate performance of the lithium-ion secondary battery. At the same time, the first active material significantly increases the conductivity of the second active material, and the second active material can increase the rolling density of the first active material. Mixing the first and second active materials in the above mass ratio maximizes the rolling density of the resulting positive electrode sheet, while optimizing the rate performance.

[0029] Referring to FIG. 1, the present invention also provides a positive electrode sheet including the above-described positive electrode active material composition. In one embodiment of the present invention, the positive electrode sheet 100 includes a positive electrode current collector, a conductive agent, a binder, and the above-described positive electrode active material. The positive electrode current collector can be, for example, selected from aluminum foil, a nickel current collector, or a composite current collector. The conductive agent can be, for example, one or more selected from conductive carbon black (SuperP, SP), acetylene black, carbon nanotubes (CNT), and graphene. The binder can be, for example, one or more selected from polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, or polymerized styrene butadiene rubber (SBR).

[0030] Referring to FIG. 1, in this embodiment, the positive electrode current collector is selected from aluminum foil, the conductive agent is selected from SP, the binder is selected from PVDF, and the positive electrode active material is LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 In this example, the median diameter D A50 85% LiMn 0.6 Fe 0.4 PO4 / C with a median diameter of 8 μm, D B50 15% Li with 1.1 Mn 0.6 Ni 0.4 The mixture was mixed with O2 to form secondary spherical particles. The spherical particles, SP, and PVDF were mixed in a weight ratio of, for example, 97:1.5:1.5, and then NMP was added. The mixture was stirred using a vacuum mixer until the system became uniform, yielding a positive electrode slurry. The positive electrode slurry was evenly applied to an aluminum foil, which was then placed in a blast oven and dried at 120°C for 10 minutes. The dried electrode sheet was then rolled and cut to produce a positive electrode sheet 100.

[0031] 1, the present invention also provides a lithium ion secondary battery that can be applied to various electronic devices. The lithium ion secondary battery includes a positive electrode sheet 100, a separator 200, a negative electrode sheet 300, and an electrolyte 400. The positive electrode sheet 100 and the negative electrode sheet 300 are positioned on either side of the separator 200, and the positive electrode sheet 100, the separator 200, and the negative electrode sheet 300 are immersed in the electrolyte 400.

[0032] Referring to FIG. 1 , in one embodiment of the present invention, a negative electrode sheet 300 includes a negative electrode current collector, a conductive agent, a binder, and a negative electrode active material. The negative electrode current collector may be, for example, copper foil. The conductive agent may be, for example, one or more selected from conductive carbon black (SuperP, SP), acetylene black, carbon nanotubes (CNT), and graphene. The binder may be, for example, one or more selected from polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and polymerized styrene butadiene rubber (SBR). The negative electrode active material may be, for example, one or more of natural graphite, artificial graphite, crystalline carbon, amorphous carbon, and a carbon composite material.

[0033] Referring to FIG. 1, in this embodiment, the negative electrode active material is selected from, for example, artificial graphite. The conductive agent is selected from, for example, SP. The binder is selected from, for example, styrene butadiene rubber. The thickener is selected from, for example, sodium carboxymethyl cellulose. In this embodiment, the artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene butadiene rubber are mixed in a mass ratio of 96:1:1:2, and then, for example, deionized water is added and the mixture is mixed in a vacuum mixer. - The negative electrode slurry was obtained by the above reaction. The negative electrode slurry was uniformly applied onto the copper foil of the negative electrode current collector, and the copper foil was placed in a fan drying oven and dried at 120°C for 10 minutes. The dried electrode sheet was then rolled and cut to prepare the negative electrode sheet 300.

[0034] 1, in one embodiment of the present invention, separator 200 is selected from, for example, a polyethylene (PE) film or a polypropylene (PP) film. Separator 200 has a thickness of, for example, 9 μm to 18 μm, an air permeability of, for example, 180 sec / 100 mL to 380 sec / 100 mL, and a porosity of, for example, 30% to 50%.

[0035] 1, in one embodiment of the present invention, the electrolyte solution 400 includes, for example, a lithium salt and an organic solvent. The lithium salt is, for example, one or more selected from lithium hexafluorophosphate (LiPF), lithium difluorophosphate (LiPOF), lithium bis(fluorosulfonyl)imide (LiFSi), lithium tetrafluoroborate (LiBF), lithium difluoro(oxalato)borate(1-) (LiDFOB), and lithium bis(oxalato)borate (LiBOB). In this embodiment, the lithium salt is, for example, LiPF. In one embodiment of the present invention, the content of the lithium salt is, for example, 4% by weight to 24% by weight, based on the mass of the electrolyte solution 400, and the content of the organic solvent is, for example, 96% by weight to 76% by weight, based on the mass of the electrolyte solution 400. The organic solvent is at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and polycarbonate (PC).

[0036] Referring to FIG. 1, in one embodiment of the present invention, a positive electrode sheet 100, a separator 200, and a negative electrode sheet 300 were laminated in this order to insulate the positive and negative electrodes, with the separator 200 positioned between them. The laminated sheets were then wrapped in aluminum plastic film and transferred to a vacuum oven where they were dried at 100°C to 130°C. An electrolyte solution 400 was then injected and sealed. The amount of the electrolyte solution injected was, for example, 3.0 g / Ah. After the electrolyte solution injection, a 4.5 V formation and aging process were performed, and finally a pouch battery with a capacity of 1 Ah, i.e., a lithium-ion secondary battery, was fabricated.

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Appropriate modifications are possible within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0038] Example 1

[0039] Preparation of positive electrode active material composition: Median diameter D of 0.8 μm A50 85% LiMn 0.6 Fe 0.4 PO4 / C and 8μm diameter D B50 15% Li with 1.1 Mn 0.6 Ni 0.4 O2 was mixed to form secondary spherical particles.

[0040] Preparation of positive electrode: The positive electrode active material composition, SP, and PVDF were mixed in a weight ratio of 97:1.5:1.5, and then NMP was added. The mixture was stirred using a vacuum mixer until the mixture was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was evenly applied to aluminum foil, which was then placed in a fan oven and dried at 120°C for 10 minutes. The dried electrode sheet was then rolled and cut to prepare a positive electrode sheet.

[0041] Fabrication of lithium-ion secondary battery: The above-mentioned positive electrode sheet, separator, and negative electrode sheet were stacked in order, and the stacked sheets were covered with an aluminum plastic film, and the electrolyte was injected and sealed. After 4.5 V formation and aging processes, a pouch battery with a capacity of 1 Ah, i.e., a lithium-ion secondary battery, was finally fabricated.

[0042] Example 2

[0043] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0044] Example 3

[0045] LiMn0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0046] Example 4

[0047] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0048] Example 5

[0049] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0050] Example 6

[0051] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0052] Example 7

[0053] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0054] Example 8

[0055] LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D A50 The other operation procedures were the same as in Example 1.

[0056] Example 9

[0057] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50 The other operation procedures were the same as in Example 1.

[0058] Example 10

[0059] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50 The other operation procedures were the same as in Example 1.

[0060] Example 11

[0061] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50 The other operation procedures were the same as in Example 1.

[0062] Example 12

[0063] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50 The other operation procedures were the same as in Example 1.

[0064] Example 13

[0065] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50 The other operation procedures were the same as in Example 1.

[0066] Example 14

[0067] Li 1.1 Mn 0.6 Ni 0.4 O2 median diameter D B50The other operation procedures were the same as in Example 1.

[0068] Example 15

[0069] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 The mass ratio of O2 was changed to 70%:30%, and the other operating procedures were the same as in Example 1.

[0070] Example 16

[0071] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 The mass ratio of O2 was changed to 60%:40%, and the other operating procedures were the same as in Example 1.

[0072] Example 17

[0073] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 The mass ratio of O2 was changed to 50%:50%, and the other operating procedures were the same as in Example 1.

[0074] Example 18

[0075] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 The mass ratio of O2 was changed to 90%:10%, and the other operating procedures were the same as in Example 1.

[0076] Comparative Example 1

[0077] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6Ni 0.4 The mass ratio of O2 was changed to 49%:51%, and the other operating procedures were the same as in Example 1.

[0078] Comparative Example 2

[0079] LiMn 0.6 Fe 0.4 PO4 / C and Li 1.1 Mn 0.6 Ni 0.4 The mass ratio of O2 was changed to 91%:9%, and the other operating procedures were the same as in Example 1.

[0080] Comparative Example 3

[0081] The positive electrode active material has a median diameter D 50 0.8μm LiMn 0.6 Fe 0.4 PO4 / C, and other operating procedures were the same as in Example 1.

[0082] Comparative Example 4

[0083] The positive electrode active material has a median diameter D 50 Li with 8 μm 1.1 Mn 0.6 Ni 0.4 The other operating procedures were the same as in Example 1.

[0084] Rolled density test of electrode sheet: The positive electrode sheet was rolled at 12 MPa to test the rolled density of the positive electrode sheet.

[0085] Cycle test: 500 cycles of charge and discharge were performed at 1C, 45°C, and in the range of 2.5V to 4.2V, and the capacity ratio at the 500th cycle to the 1st cycle was recorded as the capacity retention rate.

[0086] Rate performance test: The rate discharge performance (capacity retention rate) was tested under the conditions of a voltage range of 2.5 V to 4.2 V and a current density of 3 C and 1 / 3 C.

[0087] Low-temperature capacity retention rate: After charging at a constant current and voltage of 1C at 25°C to 4.2V (cut-off current 0.05C), the battery was discharged at a constant current of 1C to 2.0V. Next, the battery was charged again at a constant current and voltage of 1C at 25°C to 4.2V (cut-off current 0.05C), placed at -20°C, and discharged at 1C to 2.0V. The ratio of the discharge capacity to the discharge capacity at 1C at 25°C is the low-temperature capacity retention rate.

[0088] The rolling density of the positive electrode sheets in various examples and comparative examples was tested, and the positive electrode sheets were fabricated into lithium ion secondary batteries, and the performance of the lithium ion secondary batteries was tested. The test results are shown in Table 1. The performance of the lithium ion secondary batteries in the various examples and comparative examples is as follows.

[0089] [Table 1] JPEG0007811199000002.jpg103165

[0090] See Table 1 in combination with Example 1 and Comparative Examples 3-4. In Comparative Example 3, the positive electrode active material was LiMn 0.6 Fe 0.4 PO4 / C, and the battery rate performance was 93.5%, but the rolling density of the electrode sheet was 2.30 g / cm 3 The positive electrode active material of Comparative Example 4 is merely Li 1.2 Mn 0.6 Ni 0.2 O2, and the rolling density of the electrode sheet is 3.08 g / cm 3 The rate performance of the battery was only 86.7%. 0.6 Fe 0.4 When PO4 / C is used alone, the rolling density of the electrode sheet becomes low, which results in problems such as a low volumetric energy density of the battery. 1.2 Mn 0.6 Ni 0.2When O2 is used alone, the problem of reduced conductivity occurs, resulting in a decrease in the battery rate performance. In Example 1, the above two materials are combined, and the rolling density of the electrode sheet is 2.55 g / cm 3 and the rate performance of the battery is 93.7%, and the electrode sheet has a higher rolling density, which improves the volumetric energy density of the battery and also improves the rate performance of the battery.

[0091] 2 and Table 1, in combination with Example 1, Examples 15 to 20, and Comparative Examples 1 and 2, LiMn 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 Compare the mass ratio of O2. 2 According to Example 1, LiMn 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 The mass ratio of LiMnO2 was 85%:15%, and the capacity retention rate of the fabricated lithium battery after 500 cycles was 93.7%. 0.6 Fe 0.4 The PO4 / C content decreased significantly, and LiMn 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 The mass ratio of LiMnO2 was 49%:51%. The capacity retention rate of the fabricated lithium battery was only 90.1% after 500 cycles. 0.6 Fe 0.4 The PO4 / C content increased significantly, and LiMn 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 The mass ratio of O2 was 91%:9%. The rate performance of the lithium battery was maintained at 93.6%, but the rolling density of the electrode sheet was 2.44 g / cm 3 In Examples 15 to 18, LiMn 0.6 Fe 0.4 PO4 / C and Li1.2 Mn 0.6 Ni 0.2 The mass ratio of O2 is in the range of 50%:50% to 90%:10%, and the rolling density of the electrode sheet is higher, with a maximum rolling density of 2.78 g / cm 3 The rate performance was optimal, reaching a maximum of 93.6%. Furthermore, when combined with Examples 1 to 14, LiMn 0.6 Fe 0.4 Median diameter of PO4 / C D 50 is 0.7μm~2.5μm, and Li 1.2 Mn 0.6 Ni 0.2 O2 median diameter D 50 is 7μm to 11μm, and LiMn 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 O2 D 50 The ratio of LiMn is 0.1 to 0.35. 0.6 Fe 0.4 PO4 / C and Li 1.2 Mn 0.6 Ni 0.2 The particle gradation effect between O2 is most suppressed, which increases the rolling density of the sheet and improves the rate performance of the battery.

[0092] As shown in Table 1, the positive electrode active material composition provided by the present invention has a good gradation effect between particles. By preparing the positive electrode active material composition into a positive electrode sheet, the rolled density of the positive electrode sheet is 2.47 g / cm. 3 ~2.79g / cm 3 This improves the performance of the lithium battery, and the rate performance of the fabricated lithium battery can reach 91.0% to 93.7%.

[0093] In summary, the present invention provides a positive electrode active material composition and its applications. Blending two active materials improves the low-temperature performance and electrical conductivity of lithium-ion secondary batteries. Controlling the median diameter ratio of the two active materials within the range of 0.1 to 0.35 enhances the gradation effect of the two types of particles, thereby effectively improving the rolling density of the electrode sheet and, as a result, increasing the volumetric energy density of the lithium-ion secondary battery. Furthermore, doping the two active materials with metal ions improves the electrical conductivity and ionic conductivity of the positive electrode material, thereby improving the rate and cycle characteristics of the lithium-ion secondary battery.

[0094] The above description is merely a preferred embodiment of the present application and merely describes the technical principles employed. Those skilled in the art should understand that the scope of the disclosure contained in the present invention is not limited to the technical solution formed by a specific combination of the above technical features. At the same time, the scope of the disclosure should also include other technical solutions formed by any combination of the above technical features or their equivalents without departing from the concept of the present invention, such as, for example, a technical solution formed by replacing the above features with (but not limited to) technical features disclosed in the present invention having similar functions.

[0095] Except for the technical features described herein, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present invention, the remaining technical features will not be repeated here. [Industrial Applicability]

[0096] The positive electrode active material composition provided by the present invention can be applied to lithium ion secondary batteries. [Explanation of symbols]

[0097] 100: Positive electrode sheet 200: Separator 300: Negative electrode sheet 400: Electrolyte

Claims

1. Component A as a first active material; Component B as a second active material, The general chemical formula of the first active material is LiMn ０．６ Fe ０．４ P.O. ４ and The general chemical formula of the second active material is Formula II, where Formula II is Li １＋（ｂ／（２＋ｂ）） Mn ２ｂ／（２＋ｂ） M （６／（２＋ｂ））－２ O ２ wherein 0.5≦b≦1, and element M is one or more of Ni, Co, Mn, Mg, Al, Ti, Zr, Nb, La, Sr, and W; the mass ratio of the first active material to the second active material is 50:50 to 90:10; The particle size distribution of the first active material is D Ａｍｉｎ is 0.1 μm to 0.3 μm, D Ａ１０ is 0.3 μm to 0.6 μm, D Ａ５０ is 0.7 μm to 2.5 μm, D Ａ９０ satisfies 3.0 μm to 10 μm, The particle size distribution of the second active material is D Ｂｍｉｎ is 0.2 μm to 0.4 μm, D Ｂ１０ is 1 μm to 3 μm, D Ｂ５０ is 7 μm to 11 μm, D Ｂ９０ satisfies 15 μm to 25 μm, The particle size distribution of the first active material and the second active material is D ｍｉｎ Ratio D Ａｍｉｎ / D Ｂｍｉｎ is 0.25 to 1.5, D １０ Ratio D Ａ１０ / D Ｂ１０ is 0.1 to 0.6, D ５０ Ratio D Ａ５０ / D Ｂ５０ is 0.1 to 0.35, D ９０ Ratio D Ａ９０ / D Ｂ９０ is 0.12 to 0.67, and 0.2≦[(D Ａ９０ -D Ａ１０ ) / D Ａ５０ ] / [(D Ｂ９０ -D Ｂ１０ ) / D Ｂ５０ ]≦13 is satisfied, The particle size distribution is a volume-based particle size distribution.

2. The doping amount of the element M is 2000 ppm to 5000 ppm, The positive electrode active material composition according to claim 1 , wherein the doping amount of the element M is a ratio of the mass of the element M to the total mass of the elements Mn and M.

3. 2. The positive electrode active material composition according to claim 1, wherein a surface of the first active material is covered with a carbon layer, and a mass of the carbon layer is 1% to 3% of a mass of the first active material.

4. A positive electrode sheet comprising the positive electrode active material composition according to claim 1 .

5. The rolling density of the positive electrode sheet is 2.47 g / cm ３ ~2.79 g / cm ３ The positive electrode sheet according to claim 4 ,

6. A lithium ion secondary battery comprising the positive electrode sheet according to claim 4.

7. An electrochemical device comprising the lithium ion secondary battery according to claim 6.

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