Conductive carbon black modified lithium iron phosphate electrode material and preparation method thereof

Abstract

The invention provides a conductive carbon black modified lithium iron phosphate electrode material and a preparation method thereof. According to the material, a transition metal doped LiFePO4 matrix is adopted, a specific proportion of dual-scale conductive carbon black combination is matched, stable interface bonding is realized through a P-C covalent bond, and a gradient pore structure is constructed. In the preparation process, through key technologies such as sintering process optimization, carbon black surface modification, programmed flow pore-forming and plasma treatment, the material has high electronic conductivity and excellent ion transmission performance; the obtained electrode material has high specific capacity, excellent rate capability and long cycle life, is suitable for a high-power lithium ion battery positive electrode, and solves the problems of insufficient conductivity and poor interface stability of a traditional lithium iron phosphate material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and relates to a conductive carbon black modified lithium iron phosphate electrode material and a preparation method thereof. BACKGROUND

[0002] As a lithium ion battery cathode material, lithium iron phosphate (LiFePO4) is widely used in the field of power batteries due to its high safety, long cycle life, and abundant raw materials. However, this material has two main technical bottlenecks: one is the extremely low intrinsic electronic conductivity (about 10 -8 S / cm), and the other is the slow lithium ion diffusion rate (about 10 -14 cm 2 / s). These characteristics result in poor rate performance of the material, especially under high-rate charging and discharging conditions, with obvious capacity attenuation. Currently, the industry mainly improves the conductivity of the material through carbon coating and the addition of conductive agents, but the conventional carbon coating process often leads to uneven coating, and a too thick carbon layer may hinder lithium ion transmission; simple mechanical mixing of conductive agents is difficult to build a continuous and efficient conductive network. In addition, the existing technology lacks sufficient regulation of the pore structure of the material, affecting the infiltration of the electrolyte and the ion transmission efficiency. These factors jointly restrict the performance of lithium iron phosphate materials in high-power application scenarios.

[0003] CN 112694078A discloses a graphene-coated lithium iron phosphate composite material and a preparation method thereof, the preparation method comprising: coating graphene oxide and lithium iron phosphate by spray drying or evaporation drying to obtain graphene-coated lithium iron phosphate solids, and then heat-treating the graphene-coated lithium iron phosphate solids to obtain the graphene-coated lithium iron phosphate composite material; wherein the ratio of the flake diameter of the graphene oxide to the D50 of the lithium iron phosphate is 0.05-40. Although the composite material improves the conductivity, the cost of graphene is high, and the coating layer is prone to stacking, so the actual rate performance improvement is limited.

[0004] CN107195979A discloses a power storage polymer lithium ion battery, which is packaged by 2-5 internally connected winding cells through an aluminum plastic film; each cell includes a positive electrode sheet, a separator, a negative electrode sheet, an electrolyte, and a tab; the positive electrode sheet is prepared by coating a positive electrode slurry prepared by a pre-sand milling process; the negative electrode sheet is prepared by coating a negative electrode slurry prepared by a pre-sand milling process; each cell includes a positive tab and a negative tab using a carbon nanotube / carbon black composite conductive agent. Although the lithium ion battery constructs a three-dimensional conductive network, it does not solve the problem of interface bonding between LiFePO4 and carbon materials, and interface peeling is prone to occur during the cycle process.

[0005] CN112151743A provides a thick electrode pore-forming method and its product and use, the pore-forming method includes that the slurry with the viscosity of 6000 mPa · s ~ 9000 mPa · s is coated on the surface of the current collector with the surface roughness Ra ≥1 μm, and is dried, to obtain the thick electrode;The pore-forming method partially solves the problems of poor electrolyte wettability and long lithium ion migration path but uneven pore distribution and lack of gradient design, and the lithium ion transmission is still limited at high rate, and the capacity retention rate is insufficient. SUMMARY

[0006] The present application aims to provide a conductive carbon black modified lithium iron phosphate electrode material and a preparation method thereof, which has high electronic conductivity, excellent rate performance and long cycle life. The intrinsic conductivity is improved by specific Li vacancy regulation and transition metal doping, a three-dimensional conductive network is constructed by using nano / micron carbon black grading, and plasma-induced interface bonding technology and CO2 dynamic regulation pore-forming process are combined, so that the material has high compaction density, excellent rate performance and super-long cycle life, etc. Comprehensive advantages, effectively solve the technical problems of poor conductivity and insufficient high rate performance of traditional lithium iron phosphate materials.

[0007] The object of the present application can be achieved by the following technical solutions:

[0008] In a first aspect, the present application provides a conductive carbon black modified lithium iron phosphate electrode material, comprising:

[0009] Li 1-x Fe 1+x PO4 matrix, wherein 0.01≤x≤0.05, and the Fe site is doped with 1-3 at% of Mn 2+ Or Co 2+ ;

[0010] A conductive carbon black composition comprises 60-70 wt% of nano-carbon black and 30-40 wt% of micron-carbon black, the nano-carbon black has a D50≤100 nm and a specific surface area≥800 m 2 / g, and the micron-carbon black has a D50=1-3 μm and a specific surface area≥60 m 2 / g.

[0011] The surface of the Li 1-x Fe 1+x PO4 particles is combined with the conductive carbon black through P-C covalent bond, and the bonding density is≥0.5 / nm 2 .

[0012] The material has a gradient distributed pore structure, the surface layer porosity is 25-30% and the pore size is 50-100 nm, and the core layer porosity is 15-20% and the pore size is 200-300 nm.

[0013] The conductive carbon black-modified lithium iron phosphate electrode material provided by this invention achieves precise control of Li... 1-x Fe 1+x Li vacancies in PO4 (0.01≤x≤0.05) and 1-3 at.% Mn doped at Fe sites. 2+ / Co 2+ Defect energy levels are introduced into the crystal structure; Li vacancies increase lithium-ion diffusion channels, while Mn... 2+ / Co 2+ Fe replacement 2+ Subsequently, its variable valence state provides additional electronic transition pathways, synergistically increasing the intrinsic electronic conductivity of the material to 10. -4 S / cm, lithium-ion diffusion coefficient increased to 10 -12 cm 2 / s.

[0014] Preferably, the Li 1-x Fe 1+x PO4 is prepared by solid-state method or hydrothermal method, wherein the molar ratio of Li:Fe is (0.95-0.99):(1.01-1.05).

[0015] Preferably, the nano carbon black is acetylene black, the micron carbon black is SuperP, and both are surface modified with a silane coupling agent.

[0016] The conductive carbon black-modified lithium iron phosphate electrode material provided by this invention uses acetylene black as nano-carbon black and SuperP as micron-carbon black, and performs surface modification treatment with a silane coupling agent. In terms of material selection, acetylene black, with its nano-sized particle size and high specific surface area, can effectively fill the gaps between active materials and construct dense conductive pathways; while SuperP, as a micron-sized conductive agent, plays a key role in connecting the conductive network. The two are combined in an optimal ratio to form a complementary conductive system. The surface modification treatment uses silane coupling agent KH-550, and uniform coating is achieved through a precisely controlled ball milling process. During the modification process, one end of the silane coupling agent molecule forms a chemical bond with the carbon black surface, and the other end establishes a connection with the active material. This dual bonding effect significantly enhances the interfacial bonding strength. The modified conductive network not only has excellent electronic conductivity but also exhibits good structural stability.

[0017] This technical solution fundamentally solves the problems of poor interfacial contact and easy damage to the conductive network inherent in traditional physical mixing methods through chemical bonding. The modified electrode material maintains high conductivity while significantly improving its interfacial stability and mechanical strength, laying a solid foundation for excellent electrochemical performance. This innovative surface modification method provides a new technical approach for the development of high-performance lithium-ion battery electrode materials.

[0018] In a second aspect, the present application provides a preparation method of the conductive carbon black modified lithium iron phosphate electrode material according to the first aspect, comprising the following steps:

[0019] (1) mixing raw materials in stoichiometric ratio of Li 1-x Fe 1+x PO4, and adding Mn 2+ or Co 2+ salt, sintering at 650-750℃ for 6-8h to obtain doped LiFePO4 powder;

[0020] (2) mixing nano carbon black and micro carbon black in a certain ratio, adding silane coupling agent for ball milling modification treatment for 1.8-2.2h;

[0021] (3) treating the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) in a planetary ball mill at a rotating speed of 480-520rpm for 2.8-3.2h;

[0022] (4) mixing the mixture obtained in step (3) with a composite pore-forming agent, and passing CO2 gas in a programmed temperature process, wherein the CO2 flow rate is 4.5-5.5mL / min at 200-300℃, and the CO2 flow rate is 10-20mL / min at 300-400℃;

[0023] (5) treating the product obtained in step (4) in an argon plasma environment at a power of 230-270W for 25-35min.

[0024] The preparation method of the conductive carbon black modified lithium iron phosphate electrode material provided by the present application uses plasma to induce P-C bonding. When argon plasma is treated, high-energy particles bombard to break the PO43- bonds on the surface of LiFePO4 to form suspended P atoms, which covalently combine with the π electron cloud of carbon sp 2 to form P-C bonds with a bond energy of 326kJ / mol; the bonding density is ≥0.5 / nm 2 , which improves the interface stability by 3 times, and the carbon black shedding rate is <1% during the cycle process.

[0025] Preferably, the Mn 2+ salt in step (1) is manganese acetate, the Co 2+ salt is cobalt nitrate, and the addition amount is 1-3% of the molar amount of Fe.

[0026] Preferably, the silane coupling agent in step (2) is KH-550, and the addition amount is 0.5-1% of the total mass of carbon black.

[0027] Preferably, the composite pore-forming agent in step (4) is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of (2.8-3.2):1, and the total amount of the composite pore-forming agent added is 8-12% of the mass of LiFePO4.

[0028] The application provides a preparation method of the conductive carbon black modified lithium iron phosphate electrode material.

[0029] Preferably, the purity of the CO2 gas in step (4) is ≥99.5%.

[0030] Preferably, the pressure of the argon plasma treatment in step (5) is 50-100 Pa.

[0031] In a third aspect, the application provides a lithium ion battery positive electrode made of the conductive carbon black modified lithium iron phosphate electrode material as described in the first aspect, wherein the compaction density of the positive electrode is ≥2.7 g / cm 3 , the capacity retention rate at a 5C rate is ≥90%, and the capacity retention rate after 3000 cycles is ≥85%.

[0032] The application has the following beneficial effects:

[0033] (1) The conductive carbon black modified lithium iron phosphate electrode material provided by the application has intrinsic electronic conductivity of 10 -4 S / cm and lithium ion diffusion coefficient of 10 -12 cm 2 / s, through Li vacancy regulation and Mn / Co doping synergistic effect.

[0034] (2) The preparation method of the conductive carbon black modified lithium iron phosphate electrode material provided by the application adopts nano / micron carbon black hierarchical construction to build a gradient conductive network, and combines plasma-induced P-C bonding, so that the compaction density of the electrode reaches 2.7 g / cm 3 , and the interface impedance is reduced by 60%.

[0035] (3) The conductive carbon black modified lithium iron phosphate electrode material provided by the application uses CO2 dynamic regulation pore-forming process to form gradient pores, electrolyte immersion time ≤3 s, 5C capacity retention rate ≥90%, and 3000 cycle capacity retention rate ≥85%. DETAILED DESCRIPTION

[0036] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0037] In one specific embodiment, the present invention provides a conductive carbon black modified lithium iron phosphate electrode material, comprising a LiFePO4 matrix, doping elements, and a modified carbon black conductive agent, wherein the surface of the LiFePO4 matrix is ​​coated with a carbon layer, the doping elements are Mn and Co, and the doping amounts of Mn and Co are 1-3% of the molar amount of Fe, respectively; the modified carbon black conductive agent is obtained by mixing nano-carbon black and micron-carbon black in a certain proportion and modifying it with silane coupling agent KH-550, wherein the amount of KH-550 added is 0.5-1% of the total mass of carbon black.

[0038] In another specific embodiment, the present invention provides a method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described above, the method specifically comprising: (1) mixing iron salt, lithium salt, phosphorus source and dopants manganese acetate and cobalt nitrate, wherein Mn 2+ and Co 2+ The addition amount is 1-3% of the Fe molar amount. The precursor is prepared by spray drying and sintered at 600-800℃ for 5-7h under an inert atmosphere to obtain carbon-coated LiFePO4 powder; (2) Nano carbon black and micron carbon black are mixed in proportion, and 0.5-1% of KH-550 silane coupling agent of total carbon black mass is added for ball milling modification treatment for 1.8-2.2h; (3) The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a speed of 480-520rpm for 2.8-3.2h; (4) The mixture obtained in step (3) is mixed with the carbon black obtained in step (2) and then processed in a planetary ball mill at a speed of 480-520rpm for 2.8-3.2h. The compound is mixed with a composite pore-forming agent, wherein the composite pore-forming agent is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of 2.8-3.2:1, and the amount added is 8-12% of the mass of LiFePO4. During the programmed temperature rise process, CO2 gas with a purity ≥99.5% is introduced, wherein the CO2 flow rate is 4.5-5.5 mL / min at 200-300℃ and 10-20 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment of 50-100Pa with a power of 230-270W for 25-35min.

[0039] Example 1

[0040] This embodiment provides a conductive carbon black-modified lithium iron phosphate electrode material, including Li 0.97 Fe 1.03 PO4 matrix with 2 at% Mn doped at Fe sites. 2+. The conductive carbon black composition comprises 65wt% of nano carbon black and 35wt% of micro carbon black, the D50 of the nano carbon black is 80nm and the specific surface area is 850m 2 / g, the D50 of the micro carbon black is 2pm and the specific surface area is 70m 2 / g. Li 0.97 Fe 1.03 PO4 particles are combined with the conductive carbon black through P-C covalent bond on the surface, and the bonding density is 0.6 / nm 2 . The material has a gradient distribution of pore structure, the surface layer porosity is 28% and the pore size is 75nm, and the core layer porosity is 18% and the pore size is 250nm.

[0041] The embodiment also provides a preparation method of the conductive carbon black modified lithium iron phosphate electrode material as described above, comprising the following steps: (1) mixing raw materials according to the stoichiometric ratio of Li 0.97 Fe 1.03 PO4, adding 2at% of manganese acetate, sintering at 700 DEG C for 7h to obtain doped LiFePO4 powder; mixing the nano carbon black and the micro carbon black according to a ratio of 65:35, adding 0.8% of KH-550 silane coupling agent for ball milling modification treatment for 2h; treating the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) in a planetary ball mill at a rotating speed of 500rpm for 3h; mixing the mixture obtained in step (3) with a composite pore forming agent, the composite pore forming agent being a mixture of NH4HCO3 and ammonium oxalate according to a mass ratio of 3:1, and the total addition amount being 10% of the mass of LiFePO4, and introducing CO2 gas with a purity of 99.5% in a programmed temperature process, wherein the CO2 flow is 5mL / min at 200-300 DEG C and the CO2 flow is 15mL / min at 300-400 DEG C; (5) treating the product obtained in step (4) in an argon plasma environment at 75Pa with a power of 250W for 30min.

[0042] Example 2

[0043] The embodiment provides a conductive carbon black modified lithium iron phosphate electrode material, comprising Li 0.99 Fe 1.01 PO4 matrix, wherein 1at% of Co is doped at Fe site 2+ . The conductive carbon black composition comprises 60wt% of nano carbon black and 40wt% of micro carbon black, the D50 of the nano carbon black is 100nm and the specific surface area is 800m 2 / g, the D50 of the micro carbon black is 1pm and the specific surface area is 60m 2 / g. Li 0.99 Fe 1.01 PO4 particles are combined with the conductive carbon black through P-C covalent bond on the surface, and the bonding density is 0.5 / nm2 The material has a gradient distribution of pore structure, the surface layer porosity is 25% and the pore size is 50 nm, and the core layer porosity is 15% and the pore size is 200 nm.

[0044] The embodiment also provides a preparation method of the conductive carbon black modified lithium iron phosphate electrode material. 0.99 Fe 1.01 PO4 stoichiometric ratio of the raw materials, and 1 at% of cobalt nitrate is added, sintering at 650 DEG C for 8 h to obtain the doped LiFePO4 powder; (2) the nano carbon black and the micro carbon black are mixed at a ratio of 60:40, and 0.5% of KH-550 silane coupling agent is added for ball milling modification treatment for 1.8 h; (3) the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a rotating speed of 480 rpm for 2.8 h; (4) the mixture obtained in step (4) is mixed with a composite pore-forming agent, the composite pore-forming agent is a mixture of NH4HCO3 and ammonium oxalate at a mass ratio of 2.8:1, and the total addition amount is 8% of the mass of LiFePO4, and 99.5% pure CO2 gas is introduced in the process of programmed temperature rising, wherein the CO2 flow rate is 4.5 mL / min at 200-300 DEG C, and the CO2 flow rate is 10 mL / min at 300-400 DEG C; (5) the product obtained in step (4) is treated in an argon plasma environment at 50 Pa with a power of 230 W for 25 min.

[0045] Embodiment 3

[0046] The embodiment provides a conductive carbon black modified lithium iron phosphate electrode material, which comprises Li 0.95 Fe 1.05 PO4 matrix, wherein 3 at% of Mn 2+ is doped at the Fe site; the conductive carbon black composition comprises 70 wt% of nano carbon black and 30 wt% of micro carbon black, the D50 of the nano carbon black is 50 nm and the specific surface area is 900 m 2 / g, and the D50 of the micro carbon black is 3 μm and the specific surface area is 80 m 2 / g; the surface of the Li 0.95 Fe 1.05 PO4 particle is combined with the conductive carbon black through P-C covalent bond, and the bonding density is 0.7 / nm 2 . The material has a gradient distribution of pore structure, the surface layer porosity is 30% and the pore size is 100 nm, and the core layer porosity is 20% and the pore size is 300 nm.

[0047] The embodiment also provides a preparation method of the conductive carbon black modified lithium iron phosphate electrode material. 0.95 Fe 1.05PO4 stoichiometric ratio of the raw materials, and adding 3at% manganese acetate, sintering at 750°C for 6h to obtain doped LiFePO4 powder; (2) mixing nano-carbon black and micro-carbon black at a ratio of 70:30, adding 1% KH-550 silane coupling agent for ball milling modification treatment for 2.2h; (3) treating the LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) in a planetary ball mill at a speed of 520rpm for 3.2h; (4) mixing the mixture obtained in step (3) with a composite pore-forming agent, the composite pore-forming agent being a mixture of NH4HCO3 and ammonium oxalate at a mass ratio of 3.2:1, and the total addition amount being 12% of the mass of LiFePO4, and in the process of programmed temperature rise, 99.5% pure CO2 gas is introduced, wherein the CO2 flow rate is 5.5mL / min at 200-300°C and 20mL / min at 300-400°C; (5) treating the product obtained in step (4) in an argon plasma environment at a power of 270W for 35min.

[0048] Example 4

[0049] The difference between this example and Example 1 is only that the Mn 2+ The doping amount is changed to 0.8at%, and the rest of the parameters are exactly the same.

[0050] Example 5

[0051] The difference between this example and Example 1 is only that the conductive carbon black composition is changed to 75wt% nano-carbon black + 25wt% micro-carbon black, and the rest of the parameters are exactly the same.

[0052] Example 6

[0053] The difference between this example and Example 1 is only that the plasma power is changed to 280W, and the rest of the parameters are exactly the same.

[0054] Example 7

[0055] The difference between this example and Example 1 is only that in step (2), the addition amount of KH-550 silane coupling agent is 0.3%, and the rest of the parameters are exactly the same.

[0056] Example 8

[0057] The difference between this example and Example 1 is only that in step (4), the CO2 flow rate control is changed to 3mL / min at 200-300°C and 8mL / min at 300-400°C, and the rest of the parameters are exactly the same.

[0058] Example 9

[0059] The difference between this embodiment and embodiment 1 is only that in step (4), the CO2 flow control is changed to 7 mL / min at 200-300 DEG C and 22 mL / min at 300-400 DEG C, and the rest of the parameters are completely the same.

[0060] Comparative Example 1

[0061] The difference between this comparative example and embodiment 1 is only that the chemical formula of the lithium iron phosphate is Li 0.92 Fe 1.08 PO4, and the rest of the parameters are completely the same.

[0062] Comparative Example 2

[0063] The difference between this comparative example and embodiment 1 is only that there is no Mn 2+ doping in the Fe site, and the rest of the parameters are completely the same.

[0064] Comparative Example 3

[0065] The difference between this comparative example and embodiment 1 is only that in step (4), the CO2 flow control is changed to 5 mL / min throughout the whole process, and the rest of the parameters are completely the same.

[0066] The conductive carbon black modified lithium iron phosphate electrode materials provided by examples 1-9 and comparative examples 1-3 are made into lithium ion battery anodes, and the battery performance is tested, and the results are shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] Through the comparative analysis of the above test data, the following conclusions can be drawn:

[0071] (1) The specific capacity, 5C capacity retention rate, 3000 cycle retention rate, compaction density, electronic conductivity and lithium ion diffusion coefficient and other key performance indicators of examples 1-9 are significantly better than those of comparative examples 1-3, indicating that the present application significantly improves the energy density, rate performance, cycle stability and structural stability of the lithium iron phosphate electrode material by adopting Mn 2+ / Co 2+ doping, double-scale conductive carbon black combination, P-C covalent bond interface combination and gradient pore structure design.

[0072] (2) As can be seen from the comparison between comparative example 1 and example 4, because the Mn 2+The doping amount is reduced to 0.8 at%, although the material cost is slightly reduced, the electronic conduction capacity is weakened, resulting in that the specific capacity and 5C capacity retention are reduced to 153 mAh / g and 88%, respectively, which shows that the preferred 1-3 at% doping range of the application can effectively balance the electrochemical performance and cost.

[0073] (3) As can be seen from Comparative Example 1 and Example 5, since the ratio of nano-carbon black in Example 5 is increased to 75 wt%, although the electronic conductivity is increased to 1.8×10 -3 S / cm, the insufficient micron carbon black leads to that the compaction density is reduced to 2.68 g / cm 3 , and the cycle stability is slightly reduced, which shows that the preferred 60-70 wt% ratio of nano-carbon black in the application can balance the conductivity and electrode processing performance.

[0074] (4) As can be seen from Comparative Example 1 and Example 6, since the plasma power in Example 6 is increased to 280 W, the P-C bonding density may be slightly increased, but the too high power leads to that the surface of the material is partially carbonized, and the lithium ion diffusion coefficient is not significantly improved, which shows that the preferred 230-270 W plasma treatment range of the application can balance the interface optimization and material stability.

[0075] (5) As can be seen from Comparative Example 1 and Example 7, since the addition amount of silane coupling agent KH-550 in Example 7 is reduced to 0.3%, the carbon black dispersibility is poor, the electronic conductivity is reduced to 0.9×10-3 S / cm, and the cycle retention rate is reduced to 82%, which shows that the preferred 0.5-1% addition amount of silane coupling agent in the application is crucial for the uniform construction of the conductive network.

[0076] (6) As can be seen from Comparative Example 1 and Examples 8-9, since the CO2 flow in Example 8 is too low, the gradient pore structure is not fully developed, and the lithium ion diffusion coefficient is reduced to 2.9×10 -14 cm 2 / s; while the CO2 flow in Example 9 is too high, the surface porosity is too large, resulting in that the compaction density is reduced, which shows that the preferred CO2 program flow control strategy of the application can accurately control the pore gradient distribution.

[0077] (7) As can be seen from Comparative Example 1 and Comparative Examples 1-3, Comparative Example 1 deviates from the preferred range due to the stoichiometric ratio of Li 0.92 Fe 1.08 PO4, the lattice defects increase, the specific capacity and lithium ion diffusion coefficient are significantly deteriorated; Comparative Example 2 has no Mn 2+ doping, the electronic conduction and cycle stability are reduced; Comparative Example 3 cancels the CO2 gradient pore forming, the pore distribution is uneven, and the 5C capacity retention is reduced to 82%, which further verifies the synergistic necessity of the technical features of the application.

[0078] The conductive carbon black modified lithium iron phosphate electrode material of the present application significantly improves the electronic conductivity and structural stability of the material by optimizing the stoichiometric ratio of the matrix, introducing transition metal doping and constructing a double-scale conductive carbon black network; at the same time, with the help of P-C covalent bond interface combination and gradient pore structure design, efficient infiltration of electrolyte and rapid transport of lithium ions are realized, so as to maintain high energy density while having excellent rate performance and long cycle life. The technical scheme overcomes the problems of poor conductivity and unstable interface of traditional lithium iron phosphate materials through the synergistic effect of components and process, and provides an ideal electrode material solution for high-power long-life lithium ion batteries.

[0079] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, without departing from the technical solution of the present application. Any simple modification, equivalent change and modification of the above embodiments made in accordance with the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A conductive carbon black-modified lithium iron phosphate electrode material, characterized in that, include: Li 1-x Fe 1+x The matrix is ​​PO4, where 0.01 ≤ x ≤ 0.05, and the Fe sites are doped with 1-3 at% Mn. 2+ or Co 2+ ; A conductive carbon black composition comprising 60-70 wt% nano-carbon black and 30-40 wt% micron-sized carbon black, wherein the nano-carbon black has a D50 ≤ 100 nm and a specific surface area ≥ 800 m². 2 / g, the micron-sized carbon black has a D50 of 1-3μm and a specific surface area ≥60m². 2 / g; The Li 1-x Fe 1+x The PO4 particles are covalently bonded to conductive carbon black via PC, with a bond density ≥ 0.5 bonds / nm. 2 ; The material has a gradient pore structure, with a surface porosity of 25-30% and a pore size of 50-100 nm, and a core porosity of 15-20% and a pore size of 200-300 nm.

2. The electrode material according to claim 1, characterized in that, The Li 1-x Fe 1+x PO4 is prepared by solid-state method or hydrothermal method, wherein the molar ratio of Li:Fe is (0.95-0.99):(1.01-1.05).

3. The electrode material according to claim 1, characterized in that, The nano carbon black is acetylene black, and the micron carbon black is SuperP, both of which have undergone surface modification treatment with a silane coupling agent.

4. A method for preparing the conductive carbon black modified lithium iron phosphate electrode material as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) According to Li 1-x Fe 1+x The raw materials were mixed in stoichiometric proportions with PO4, and Mn was added. 2+ or Co 2+ Salt was sintered at 650-750℃ for 6-8 hours to obtain doped LiFePO4 powder; (2) Mix nano carbon black and micron carbon black in a certain proportion, add silane coupling agent and ball mill for modification for 1.8-2.2h; (3) The LiFePO4 powder obtained in step (1) and the modified carbon black obtained in step (2) are treated in a planetary ball mill at a speed of 480-520 rpm for 2.8-3.2 h; (4) Mix the mixture obtained in step (3) with the composite pore-forming agent, and introduce CO2 gas during the programmed temperature rise process, wherein the CO2 flow rate is 4.5-5.5 mL / min at 200-300℃ and 10-20 mL / min at 300-400℃; (5) The product obtained in step (4) is treated in an argon plasma environment with a power of 230-270W for 25-35 minutes.

5. The preparation method according to claim 4, characterized in that, The Mn mentioned in step (1) 2+ The salt is manganese acetate, and the Co 2+ The salt is cobalt nitrate, and the amount added is 1-3% of the molar amount of Fe.

6. The preparation method according to claim 4, characterized in that, The silane coupling agent mentioned in step (2) is KH-550, and the amount added is 0.5-1% of the total mass of carbon black.

7. The preparation method according to claim 4, characterized in that, The composite pore-forming agent mentioned in step (4) is a mixture of NH4HCO3 and ammonium oxalate in a mass ratio of (2.8-3.2):1, and the total amount of the composite pore-forming agent added is 8-12% of the mass of LiFePO4.

8. The preparation method according to claim 4, characterized in that, The purity of the CO2 gas mentioned in step (4) is ≥99.5%.

9. The preparation method according to claim 4, characterized in that, The pressure of the argon plasma treatment in step (5) is 50-100 Pa.

10. A lithium-ion battery positive electrode, characterized in that, The positive electrode is made using the conductive carbon black modified lithium iron phosphate electrode material according to any one of claims 1-3, wherein the compaction density of the positive electrode is ≥2.7 g / cm³. 3 Capacity retention at 5C rate is ≥90%, and capacity retention after 3000 cycles is ≥85%.

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