Modified positive electrode lithium supplementing additive, preparation method and application thereof

Abstract

The application provides a modified positive electrode lithium supplementing additive and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials, and can solve the problems of a complicated preparation process and high energy consumption of a method for improving the conductivity and air stability of a lithium supplementing agent. The modified positive electrode lithium supplementing additive comprises a metal element doped lithium-rich lithium ferrite core and a carbon-sulfur composite coating layer coated on the outer surface of the metal element doped lithium-rich lithium ferrite core, wherein the thickness of the carbon-sulfur composite coating layer is 1-20 nm, the sulfur and carbon are uniformly distributed in the carbon-sulfur composite coating layer, the sulfur content is 0.01-0.5 wt%, and the carbon content is 0.1-5 wt%. The modified positive electrode lithium supplementing additive has the advantages of a simple preparation method, low-temperature preparation, low energy consumption, wide universality, and can be applied to the preparation of a positive electrode of a lithium ion battery, and can improve the initial efficiency and overall electrochemical performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a modified positive electrode lithium supplement additive as well as a preparation method and application thereof. BACKGROUND

[0002] With the continuous development of lithium ion battery technology, the performance development under the existing commercial lithium ion battery system (positive electrode-graphite-liquid electrolyte) has almost reached the limit, and the improvement of energy density is still the top priority in the future battery development. As known, in the first cycle process of lithium ion battery, the formation of negative electrode SEI film will consume about 7-10% of active lithium, which means that Li + is partially consumed irreversibly, and the loss of lithium will lead to the decrease of battery capacity, the decrease of coulombic efficiency and the deterioration of cycle performance. When high specific capacity negative electrode materials such as silicon, tin alloy, silicon oxide, tin oxide and amorphous carbon negative electrode are used, the negative electrode material, especially the silicon-based negative electrode material, will further consume Li + , and the consumption of positive electrode lithium source will be further intensified, resulting in the first low coulombic efficiency.

[0003] In order to further improve the energy density of lithium ion battery, supplementing active lithium is an effective means to solve this problem. At present, the existing lithium supplement methods are positive electrode lithium supplement and negative electrode lithium supplement. The negative electrode lithium supplement involves the use of lithium powder, lithium foil and other active metals, which are too active to be stored for a long time, thereby increasing the operation difficulty and production risk. The positive electrode lithium supplement is simple and easy to operate, a small amount of positive electrode lithium supplement agent can be added in the homogenization process of positive electrode sheet preparation, lithium supplement can be realized in the formation stage, the lithium supplement process is safe and has good compatibility with the existing battery manufacturing process, so it has broad commercial application prospects. At present, there are various types of positive electrode lithium supplement agents, among which Li5FeO4 is considered to be the best lithium supplement agent due to its high specific capacity (theoretical 867 mAh / g) and suitable delithiation voltage (3.5-4.7 V). However, Li5FeO4 has poor conductivity and air stability, a small amount of water in the air at room temperature will produce lithium compound impurities, leading to the decrease of material performance and the increase of polarization; and the material preparation cost is high and difficult, which increases the large-scale industrial production and application.

[0004] However, the existing methods for improving the conductivity and air stability of lithium supplement agent are carbon coating or polymer coating, which need to mix the lithium supplement material with the coating source and then sinter at high temperature, or use organic gas to catalyze cracking at high temperature to achieve carbonization or polymerization effect, and the preparation process is complicated and energy-consuming. SUMMARY

[0005] The present application aims at the technical problems of complicated preparation process and high energy consumption of the existing method for improving the conductivity and air stability of the lithium supplement agent, and provides a modified positive electrode lithium supplement additive with simple preparation method, low energy consumption, improved battery initial efficiency and overall electrochemical performance, which improves the ion conductivity by doping metal elements to the lithium-rich lithium ferrite core, and improves the interface instability and low electronic conductivity by introducing a sulfur-carbon composite coating layer on the outer surface of the lithium-rich lithium ferrite core.

[0006] In order to achieve the above-mentioned purpose, the present application provides a modified positive electrode lithium supplement additive, which adopts the technical scheme of: the modified positive electrode lithium supplement additive comprises a lithium-rich lithium ferrite core doped with metal elements and a carbon-sulfur composite coating layer coated on the outer surface of the lithium-rich lithium ferrite core doped with metal elements, wherein the thickness of the carbon-sulfur composite coating layer is 1-20 nm, the sulfur and carbon in the carbon-sulfur composite coating layer are uniformly distributed, and the content of sulfur is 0.01-0.5wt%, and the content of carbon is 0.1-5wt%.

[0007] Preferably, the molecular formula of the modified positive electrode lithium supplement additive is Li5Fe 1-x O4M x @S / C, wherein M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu and Al, and x=0.01-0.49.

[0008] The present application further provides a preparation method of the modified positive electrode lithium supplement additive, which comprises the following steps:

[0009] Step one: uniformly mix a mixed solution of a lithium source, an iron source, a doped metal source and water by ball milling to obtain a slurry;

[0010] Step two: spray dry the slurry to obtain a precursor powder;

[0011] Step three: calcine the precursor powder in an inert gas atmosphere for a certain time, and cool it in the furnace to obtain a doped lithium-rich lithium ferrite;

[0012] Step four: add an organic solvent to the doped lithium-rich lithium ferrite, sulfur and amorphous carbon, vacuum ball mill, dry the powder by a closed spray dryer, recover the solvent, and heat under vacuum for a certain time to obtain the modified positive electrode lithium supplement additive.

[0013] Preferably, the molar ratio of the elements in the lithium source and the iron source in step one is Li:Fe=(4.4-7.0):1.

[0014] Preferably, the lithium source in step one is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4 and CH3COOLi; the iron source is at least one of Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3·9H2O, FeCl3 and FeSO4; and the doping metal source is an oxide, hydroxide or inorganic salt containing at least one metal element of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Ti and Al.

[0015] Preferably, the sulfur in step four is at least one of soluble sulfur and insoluble sulfur; the amorphous carbon is at least one of Super P, acetylene black, Ketjen black, graphene, carbon nanotube, fullerene and carbon-coated aerogel; and the organic solvent is at least one of ethanol, acetonitrile, SC2, carbon tetrachloride, tetrahydrofuran, DMF, DMAC and NMP.

[0016] Preferably, the ball milling speed in step one is 200-600 rpm, and the ball milling time is 1-6 h; the spray drying temperature in step two is 140-200℃; and the calcination temperature in step three is 600-900℃, and the calcination time is 1-40 h.

[0017] Preferably, the vacuum ball milling speed in step four is 100-400 rpm, the ball milling time is 2-10 h, the holding temperature under vacuum is 120-300℃, and the holding time is 1-10 h.

[0018] The modified positive electrode lithium supplement additive of the present application is used for preparing a lithium ion battery.

[0019] Preferably, the modified positive electrode lithium supplement additive is used for preparing a positive electrode of a lithium ion battery, and the amount of the modified positive electrode lithium supplement additive in the positive electrode material of the lithium ion battery is 0.5-5% of the mass ratio of the positive electrode active material.

[0020] Compared with the prior art, the present application has the following advantages and positive effects:

[0021] (1) The lithium-rich lithium iron phosphate core of the modified positive electrode lithium supplement additive of the present application can increase the crystal lattice defects by doping metal elements, which is beneficial to improve the Li +The diffusion rate of lithium ions and the internal conductivity of the particles are improved, thereby improving the ion conductivity of the lithium supplement material itself; the outer surface of the core is coated with a sulfur-carbon composite coating layer, and the sulfur and carbon in the sulfur-carbon composite coating layer are uniformly distributed to form a uniform and dense coating layer; the carbon can improve the electronic conductivity of the material surface, and the elemental sulfur has hydrophobicity, which can improve the sensitivity of the material to moisture in the air; through the synergistic effect of the two, the interface stability and conductivity are improved; and the sulfur element introduced in the application can participate in the formation of an SEI film after battery cycling, thereby improving the stability of the electrode material and electrolyte, and further improving the battery cycling performance.

[0022] (2) The modified positive electrode lithium supplement additive of the application has the advantages of simple preparation method, low-temperature preparation, low energy consumption, wide universality, effective utilization of lithium contained in the core lithium supplement material, use of lithium ions as a sacrificial agent to release all lithium ions at one time during the first charging process, supplement of irreversible lithium ions consumed by the formation of an SEI film on the negative electrode, maintenance of the abundance of lithium ions in the battery system, and improvement of the first efficiency and overall electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure diagram of the modified positive electrode lithium supplement additive provided by the embodiments of the application is shown in the figure;

[0024] 1, metal element doped lithium-rich lithium ferrite core, 2, carbon-sulfur composite coating layer. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0026] The modified positive electrode lithium supplement additive of the application comprises a metal element doped lithium-rich lithium ferrite core and a carbon-sulfur composite coating layer coated on the outer surface of the metal element doped lithium-rich lithium ferrite core. The thickness of the carbon-sulfur composite coating layer is 1-20 nm, the sulfur and carbon in the carbon-sulfur composite coating layer are uniformly distributed, the sulfur content is 0.01-0.5 wt% of the modified positive electrode lithium supplement additive, and the carbon content is 0.1-5 wt% of the modified positive electrode lithium supplement additive. The lithium-rich lithium ferrite is modified by doping metal elements and coating technology, and the obtained modified positive electrode lithium supplement additive has improved conductivity and interface stability through the synergistic effect of the two. Benefiting from the lithium-rich lithium ferrite substrate, the modified positive electrode lithium supplement additive has a specific capacity of more than 650 mAh / g, and due to the dense coating of the carbon-sulfur composite material, the modified positive electrode lithium supplement additive has good conductivity and air stability, and the lithium supplement performance and processing performance are both highly improved.

[0027] The modified positive electrode lithium supplement additive has a core-shell structure, the core is a metal element doped lithium-rich lithium ferrite, the shell is a thin film prepared from sulfur / carbon composite material, and the molecular formula is Li5Fe 1-x O4M x @S / C, wherein M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Al, and x=0.01-0.49.

[0028] The preparation method of the modified positive electrode lithium supplement additive comprises the following steps:

[0029] Step one: a mixed solution of a lithium source, an iron source, a doped metal source and water is uniformly mixed by ball milling to obtain a slurry, wherein the molar ratio of elements in the lithium source and the iron source is Li:Fe=(4.4-7.0):1, preferably (5.0-6.0):1, and the molar ratio of metal elements in the doped metal source to Fe elements in the iron source is x:(1-x), x=0.01-0.49;

[0030] Step two: the above slurry is spray dried to obtain a precursor powder, and the spray drying temperature is 140-200 DEG C;

[0031] Step three: the above precursor powder is calcined in an inert gas atmosphere for a certain time, the calcination temperature is 600-900 DEG C, the calcination time is 1-40 h, and the furnace is cooled to obtain the doped lithium-rich lithium ferrite Li5Fe 1-x O4M x ;

[0032] Step four: the above lithium-rich lithium ferrite Li5Fe 1-x O4M x is mixed with sulfur and amorphous carbon with an organic solvent, vacuum ball milling is performed, closed spray drying machine is used for powder drying and solvent recovery, and the modified positive electrode lithium supplement additive Li5Fe 1-x O4M x @S / C is obtained under vacuum condition for a certain time.

[0033] In the above-mentioned preparation method of the present application, in step one, the lithium source is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4 and CH3COOLi; the iron source is at least one of Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3·9H2O, FeCl3 and FeSO4; the doping metal source is an oxide, hydroxide or inorganic salt containing at least one metal element of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Ti and Al, preferably MnCO3 and Co(NO3)2·6H2O. The purpose of adding water in step one is to dissolve and disperse the raw materials and have low viscosity, so as to enter the spray dryer, and the amount of water is preferably 2-20 times the mass of the solid substance.

[0034] In some embodiments of the present application, in step one, the ball milling speed is 200-600 rpm, and the ball milling time is 1-6 h.

[0035] In step four, the sulfur is at least one of soluble sulfur and insoluble sulfur; the amorphous carbon is at least one of Super P, acetylene black, Ketjen black, graphene, carbon nanotube, fullerene and carbon-coated aerogel; and the organic solvent is at least one of ethanol, acetonitrile, SC2, carbon tetrachloride, tetrahydrofuran, DMF, DMAC and NMP. The amount of sulfur and amorphous carbon is determined according to the proportion of sulfur and carbon in the modified positive electrode lithium supplement additive, and the amount of organic solvent is enough to ensure that the components can be dispersed without agglomeration.

[0036] In some embodiments of the present application, in step four, the vacuum ball milling speed is 100-400 rpm, the ball milling time is 2-10 h, the holding temperature under vacuum condition is 120-300℃, and the holding time is 1-10 h.

[0037] The modified positive electrode lithium supplement agent of the present application is applied to the preparation of lithium ion batteries, preferably to the preparation of the positive electrode of lithium ion batteries, and more preferably to the preparation of soft-packaged batteries.

[0038] The specific capacity test method of the modified positive electrode lithium supplement agent of the present application comprises the following steps:

[0039] The modified positive electrode lithium supplement agent is used as the positive active material to prepare a coin-type half battery for the first charge-discharge test, wherein the supplement agent: SP: PVDF = 8:1:1, the negative electrode is a Li sheet, the voltage range is 2.0-5.0 V, and the current is 0.01-2 C.

[0040] The test method of the modified positive electrode lithium supplement agent for the preparation of lithium ion batteries comprises the following steps:

[0041] The modified positive electrode lithium supplement is mixed with the positive electrode active material to prepare a positive electrode sheet, wherein the amount of the modified positive electrode lithium supplement is 0.5-5% of the mass ratio of the positive electrode active material, the positive electrode active material is at least one of LiCoO2, LiFePO4, and a nickel-cobalt-manganese ternary material, and preferably LiCoO2; and the negative electrode active material is at least one of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon, and silicon-oxygen, and preferably silicon-oxygen negative electrode.

[0042] In order to more clearly and specifically introduce the modified positive electrode lithium supplement, the preparation method and application thereof provided by the embodiments of the present application, the following will be described in combination with specific embodiments.

[0043] Embodiment 1

[0044] The preparation method of the modified positive electrode lithium supplement in Embodiment 1 comprises the following steps:

[0045] Step one: LiNO3 and Fe(NO3)3·9H2O are weighed according to a molar ratio of 6:1, dissolved in deionized water, and 0.1% of MnCO3 by mass fraction is added to the above solution, which is then transferred to a ball mill tank, ball-milled at 600 rpm for 2 h until the solution becomes a uniform slurry;

[0046] Step two: the obtained slurry is spray-dried to obtain a precursor powder;

[0047] Step three: the obtained precursor powder is heated at 800°C in an argon atmosphere for 10 h, and then cooled in the furnace to obtain a doped lithium-rich lithium ferrite product;

[0048] Step four: the above doped lithium-rich lithium ferrite product, 0.1% of sulfur, and 1% of CNT are added to ethanol for liquid-phase dispersion, vacuum ball-milled at 200 rpm for 6 h, and then vacuum-dried to obtain a mixed powder material, which is then transferred to an atmosphere furnace for vacuum sintering, heated at 200°C for 6 h, and then cooled in the furnace to obtain a doubly modified positive electrode lithium supplement.

[0049] Embodiment 2

[0050] In the preparation method of the modified positive electrode lithium supplement in Embodiment 2, the doping raw material in Step one is replaced by 0.2% of Co(NO3)2·6H2O, and the other steps are consistent with Embodiment 1.

[0051] Embodiment 3

[0052] In the preparation method of the modified positive electrode lithium supplement in Embodiment 3, the Li source in Step one is replaced by lithium carbonate, and the Fe source is replaced by Fe2O3, lithium carbonate and Fe2O3 are weighed according to a molar ratio of Li:Fe of 5.5:1, the vacuum sintering condition in Step four is 900°C for 8 h, and the other steps are consistent with Embodiment 1.

[0053] Embodiment 4

[0054] In step one of the preparation method of the modified positive electrode lithium supplement additive of Example 4, the Li source is replaced with CH3COOLi, and the Fe source is replaced with FeC2O4, and CH3COOLi and FeC2O4 are weighed according to a molar ratio of Li:Fe of 5.0:1,

[0055] The other conditions are consistent with those of Example 1.

[0056] Example 5

[0057] In step one of the preparation method of the modified positive electrode lithium supplement additive of Example 5, the mass fraction of MnCO3 is replaced with 0.5%, and the other conditions are consistent with those of Example 1.

[0058] Example 6

[0059] In step four of the preparation method of the modified positive electrode lithium supplement additive of Example 6, the organic solvent is replaced with tetrahydrofuran, and the other conditions are consistent with those of Example 1.

[0060] Example 7

[0061] In step four of the preparation method of the modified positive electrode lithium supplement additive of Example 7, the coated mixed carbon source is replaced with 0.5% thin-layer graphene (≤10 layers), and the other conditions are consistent with those of Example 1.

[0062] Example 8

[0063] In step four of the preparation method of the modified positive electrode lithium supplement additive of Example 8, the mass fraction of sulfur is replaced with 0.05%, the coated mixed carbon source is replaced with 2% Super-P, and the other conditions are consistent with those of Example 1.

[0064] Comparative Example 1

[0065] Step one: LiNO3 and Fe(NO3)3·9H2O are weighed according to a molar ratio of 6:1, dissolved in deionized water, and then transferred to a ball mill tank after stirring uniformly, and ball milling is performed at 600 rpm for 2 h until the solution becomes a uniform slurry;

[0066] Step two: the obtained slurry is subjected to spray drying to obtain a precursor powder;

[0067] Step three: the obtained precursor powder is heated at 800°C for 10 h in an argon atmosphere, and then cooled in the furnace to obtain a lithium-rich lithium iron phosphate product.

[0068] Comparative Example 2

[0069] Step one: LiNO3 and Fe(NO3)3·9H2O were weighed according to the molar ratio of 6:1, dissolved in deionized water, and 0.1% MnCO3 was added to the above solution. After stirring uniformly, it was transferred to a ball mill tank and ball milled at 600 rpm for 2 h until the solution became a uniform slurry;

[0070] Step two: the obtained slurry was spray dried to obtain a precursor powder;

[0071] Step three: the obtained precursor powder was heated at 800°C for 10 h in an argon atmosphere, and then cooled in the furnace to obtain a doped lithium-rich lithium iron oxide Li5Fe 0.95 Mn 0.05 O4.

[0072] Comparative Example 3

[0073] Step one: LiNO3 and Fe(NO3)3·9H2O were weighed according to the molar ratio of 6:1, dissolved in deionized water, and 0.1% MnCO3 was added to the above solution. After stirring uniformly, it was transferred to a ball mill tank and ball milled at 600 rpm for 2 h until the solution became a uniform slurry;

[0074] Step two: the obtained slurry was spray dried to obtain a precursor powder;

[0075] Step three: the obtained precursor powder was heated at 800°C for 10 h in an argon atmosphere, and then cooled in the furnace to obtain a doped lithium-rich lithium iron oxide Li5Fe

[0076] Step four: the above lithium-rich lithium iron oxide product was added to ethanol with 0.1% sulfur and 1% CNT for liquid dispersion, vacuum ball milled at 200 rpm for 6 h, and then vacuum dried to obtain a mixed powder material. Then it was transferred to an atmosphere furnace for vacuum sintering, heated at 200°C for 6 h, and then cooled in the furnace to obtain a lithium-rich lithium iron oxide Li5FeO4@S / C coated only.

[0077] Performance test

[0078] Air stability evaluation

[0079] The lithium supplement products obtained in Examples 1-8 and Comparative Examples 1-3 were used as positive electrode materials to prepare button cells. The lithium supplement products, SP, and PVDF were weighed according to the ratio of 8:1:1, added to a stirring tank, and mixed with an appropriate amount of NMP to form a slurry. The slurry was coated, dried, and rolled to obtain a positive electrode sheet. Then the positive electrode sheet was assembled with a Li sheet to form a lithium ion battery, and charge-discharge tests were performed. The test current was 0.05C, and the voltage was 2.5-4.5V. In addition, the lithium supplement products in Examples 1-8 and Comparative Examples 1-3 were exposed to an air atmosphere with a humidity of 40% for 24 h, and then the same charge-discharge test was performed, and the results are shown in Table 1:

[0080] Table 1 first charge-discharge specific capacity of the positive electrode lithium supplementing agent of examples 1-8 and comparative examples 1-3

[0081]

[0082]

[0083] From the above, comparative example 1 is not doped and not coated, comparative example 2 is not coated, and comparative example 3 is not doped. In the voltage range of 2.5-4.5V, under the condition of 0.05C rate charging, examples 1-8 all show high charge specific capacity, and after exposure to air with a humidity of 40% for 24h, the capacity attenuation is <30mAh / g, which is significantly better than the uncoated group of comparative example 2; as can be seen from example 1 and comparative example 3, doping metal elements can significantly improve the charge-discharge specific capacity. In summary, the product of the present application fully utilizes the synergistic advantages of doping and coating, and the air stability and material electrochemical performance are significantly improved.

[0084] Full battery performance evaluation

[0085] The positive electrode lithium supplementing agent products prepared from example 1 and comparative example 1 were added to soft pack batteries, and three groups of parallel samples were taken for cycle test, wherein the positive electrode was commercial LiCoO2, the negative electrode was commercial silicon monoxide, the battery capacity was 5.0Ah, the cut-off voltage was 2.8V-4.4V, and after 0.5C / 1C cycle for 200 cycles, the capacity retention rate data were as follows in table 2:

[0086] Table 2 battery cycle performance of soft pack batteries added with the positive electrode lithium supplementing agent of example 1 and comparative example 1

[0087]

[0088] From the above, the modified positive electrode lithium supplementing agent prepared by the technical scheme of the present application can effectively improve the stability of the battery, which is mainly due to the introduction of trace elemental sulfur. Sulfur forms polysulfides when subjected to high temperature treatment. When in contact with the electrolyte, these polysulfides chemically react with the carbonate solvents (such as EC) in the electrolyte to generate substances with PEO-like structure (-O-(CH2CH2O) n -CH2CH2S x Li), which can cover the electrode surface as SEI film components, reduce the side reaction between the electrode and the electrolyte, and thus improve the long cycle performance of the battery.

[0089] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A modified cathode lithium supplement additive, characterized in that, The device comprises a lithium iron ferrite core doped with a metal element and a carbon-sulfur composite coating layer covering the outer surface of the lithium iron ferrite core doped with the metal element. The metal element is at least one selected from Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, and Al. The thickness of the carbon-sulfur composite coating layer is 1-20 nm. The carbon-sulfur composite coating layer is a composite coating layer of elemental sulfur and carbon materials. The elemental sulfur and carbon materials are uniformly distributed in the carbon-sulfur composite coating layer. The modified cathode lithium supplement additive contains 0.01-0.5 wt% sulfur and 0.1-5 wt% carbon. The carbon material is at least one selected from Super P, acetylene black, Ketjen black, graphene, carbon nanotubes, fullerene, and carbon-coated aerogel.

2. The modified cathode lithium supplementation additive according to claim 1, characterized in that, The modified cathode lithium supplement additive has the molecular formula Li5Fe 1-x O4M x @S / C, where M is at least one of Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, and Al, and x = 0.01-0.

49.

3. The method for preparing the modified cathode lithium supplementation additive according to claim 1 or 2, characterized in that, Includes the following steps: Step 1: The mixed solution of lithium source, iron source, doped metal source and water is ball-milled to obtain a slurry; Step 2: The slurry is spray-dried to obtain precursor powder; Step 3: Calcine the precursor powder in an inert gas atmosphere for a certain time, and then cool it in the furnace to obtain doped lithium iron ferrite. Step 4: Add organic solvent to the doped lithium iron ferrite, sulfur, and carbon materials, perform vacuum ball milling, dry the powder and recover the solvent using a closed spray dryer, and keep it at a certain temperature under vacuum for a certain period of time to obtain the modified positive electrode lithium supplementation additive.

4. The preparation method of the modified cathode lithium supplementation additive according to claim 3, characterized in that, The molar ratio of the elements in the lithium source and the iron source in step one is Li:Fe = (4.4-7.0):

1.

5. The preparation method of the modified cathode lithium supplementation additive according to claim 3, characterized in that, The lithium source mentioned in step one is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4, and CH3COOLi; the iron source is at least one of Fe2O3, Fe3O4, FeC2O4, Fe(NO3)3•9H2O, FeCl3, and FeSO4; and the doped metal source is an oxide, hydroxide, or inorganic salt containing at least one metal element from Mn, Co, Ni, Ca, Mg, Zr, Ni, Cu, Ti, and Al.

6. The method for preparing the modified cathode lithium supplementation additive according to claim 3, characterized in that, In step four, the sulfur is at least one of soluble and insoluble sulfur; the carbon material is at least one of Super P, acetylene black, Ketchen black, graphene, carbon nanotubes, fullerene, and carbon-coated aerogel; and the organic solvent is at least one of ethanol, acetonitrile, SC2, carbon tetrachloride, tetrahydrofuran, DMF, DMAC, and NMP.

7. The method for preparing the modified cathode lithium supplementation additive according to claim 3, characterized in that, In step one, the ball milling speed is 200-600 rpm and the ball milling time is 1-6 h; in step two, the spray drying temperature is 140-200℃; in step three, the calcination temperature is 600-900℃ and the calcination time is 1-40 h.

8. The method for preparing the modified cathode lithium supplementation additive according to claim 3, characterized in that, In step four, the vacuum ball milling speed is 100-400 rpm, the ball milling time is 2-10 h, the heat preservation temperature under vacuum is 120-300℃, and the heat preservation time is 1-10 h.

9. The application of the modified cathode lithium supplementation additive according to claim 1 or 2, characterized in that, The modified positive electrode lithium supplementation additive is used to prepare lithium-ion batteries.

10. The application of the modified cathode lithium supplementation additive according to claim 9, characterized in that, The modified positive electrode lithium supplementation additive is used to prepare the positive electrode of a lithium-ion battery. The amount of the modified positive electrode lithium supplementation additive in the positive electrode material of the lithium-ion battery is 0.5-5% of the mass ratio of the positive electrode active material.

Images