Modified lithium iron(III) oxide material, preparation method therefor and use thereof

Abstract

A modified lithium iron(III) oxide material, a preparation method therefor and a use thereof. The modified lithium iron(III) oxide material comprises a nickel-doped lithium iron(III) oxide substrate, and a thin layer of an iron-nickel lithium oxide and a carbon coating layer sequentially stacked on a surface of the nickel-doped lithium iron(III) oxide substrate, the thin layer of iron-nickel lithium oxide being generated in situ on the surface of the nickel-doped lithium iron(III) oxide substrate. In the modified lithium iron(III) oxide material, the molar ratio of elemental lithium to elemental iron is 5:(0.9-1.1), the molar ratio of elemental nickel to elemental lithium is (0.01-0.05):5, and the carbon coating amount is 0.5-5wt%. The modified lithium iron(III) oxide material comprises a unique nickel-iron-lithium oxide thin layer, which significantly improves the stability of the lithium iron(III) oxide material, can reduce or inhibit the generation of residual alkali, and has excellent lithium replenishment performance.

Description

A modified lithium ferrite material and its preparation method and application Technical Field

[0001] The present application belongs to the field of lithium-ion battery materials and relates to a modified lithium ferrite material and its preparation method and application. Background Art

[0002] During the first charge and discharge process of lithium-ion batteries, a lithium-containing interface layer (SEI) will be generated on the surface of the negative electrode. This interface has the properties of a solid electrolyte and is crucial to the performance of lithium-ion batteries. The SEI film is insoluble in organic solvents and can exist stably in organic electrolytes. It can effectively prevent the co-embedding of solvent molecules, thereby improving the cycle performance and service life of the electrode. However, the formation of SEI will consume the active lithium in the battery, resulting in a loss of the battery's reversible capacity. At present, the first efficiency of commercial graphite negative electrodes is usually around 90%, while the first efficiency of silicon-based negative electrode materials with higher capacity is even lower, usually around 85% or even lower.

[0003] To compensate for the loss of active lithium during the initial charge and discharge process, the current mainstream technologies include positive electrode lithium replenishment processes and negative electrode lithium replenishment processes. In terms of technological maturity, there are currently many manufacturers engaged in the production of metal Li powder and Li foil-related materials and equipment for lithium replenishment, as well as research on lithium replenishment processes, and their industry maturity is relatively high. However, negative electrode lithium replenishment has high requirements for equipment and environment, and safety is difficult to guarantee. In contrast, the positive electrode lithium replenishment process has good safety and has no impact on existing production processes. Currently, there are relatively few manufacturers and research institutions engaged in research on positive electrode lithium replenishment materials, and the preparation and modification of related lithium replenishment materials and the improvement of lithium replenishment processes still need to be studied.

[0004] As a lithium-rich material, lithium ferrite has a theoretical specific capacity of 867mAh / g and a moderate operating voltage. The inert substances generated after the first charge and discharge do not participate in the subsequent electrochemical process, making it an ideal positive electrode lithium supplement additive.

[0005] CN108878849A discloses a synthesis process for a lithium-rich oxide and a lithium-ion battery containing the lithium-rich oxide. The specific synthesis process of the lithium-rich oxide is as follows: weigh a lithium source and an iron source in an appropriate molar ratio, disperse them in deionized water, and after they are completely dissolved, weigh an appropriate amount of an organic carbon source and add it to the above solution; stir the solution at 80°C until a sol is formed; spray dry the sol to obtain a spherical precursor powder, and then calcine the precursor powder in an inert gas atmosphere for a certain time, and cool it in the furnace to obtain a lithium-rich oxide Li5FeO4 / C with a core-shell structure.

[0006] CN110459748A discloses a method for preparing a carbon-coated lithium ferrite material, which comprises the following steps: (1) mixing an iron source and a lithium source, and sintering them to obtain lithium ferrite, wherein the molar ratio of the lithium source to the iron source is (5-25):1; (2) crushing the lithium ferrite obtained in step (1); and (3) vapor-coating the crushed lithium ferrite in step (2) with a carbon source to obtain a carbon-coated lithium ferrite material.

[0007] The lithium ferrite material described in the above solution has the problems of high residual alkali content or poor stability. Therefore, it is very necessary to develop a lithium ferrite material with low residual alkali content and good stability.

[0008] Summary of the Invention

[0009] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0010] This application provides a modified lithium ferrite material, its preparation method, and its application. In this application, lithium ferrite powder is doped with a nickel source, and mechanical grinding is performed to form a unique thin layer of nickel-iron-lithium oxide on the surface of the lithium ferrite material. This significantly improves the stability of the lithium ferrite material, reduces or inhibits the formation of residual alkali, and exhibits excellent lithium replenishment performance.

[0011] In the first aspect, the present application provides a modified lithium ferrite material, which includes a nickel-doped lithium ferrite matrix and a thin layer of iron-nickel lithium oxide and a carbon coating layer stacked in sequence on the surface of the nickel-doped lithium ferrite matrix, wherein the iron-nickel lithium oxide thin layer is in situ generated on the surface of the nickel-doped lithium ferrite matrix. In the modified lithium ferrite material, the molar ratio of lithium element to iron element is 5:(0.9~1.1) (for example: 5:0.9, 5:0.95, 5:1, 5:1.05 or 5:1.1, etc.), the molar ratio of nickel element to lithium element is (0.01~0.05):5 (for example: 0.01:5, 0.02:5, 0.03:5, 0.04:5 or 0.05:5, etc.), and the carbon coating amount is 0.5~5wt%, for example: 0.5wt%, 1wt%, 2wt%, 3wt% or 5wt%, etc.

[0012] In the modified lithium ferrite material described in the present application, a unique nickel-iron-lithium oxide thin layer is generated on the surface of the lithium ferrite material, which significantly improves the stability of the lithium ferrite material, can reduce or inhibit the generation of residual alkali, and has excellent lithium replenishment performance.

[0013] The amount of nickel added affects the performance of the modified lithium ferrite material. A molar ratio of nickel in the nickel source to lithium in the lithium source of 0.01 to 0.05:5 yields the best modified lithium ferrite material. Too little nickel makes it difficult to achieve a uniform reaction during ball milling, and the improvement is limited. Too much nickel can affect the structure of the main lithium ferrite phase and reduce capacity.

[0014] In the modified lithium ferrite material provided herein, controlling the carbon coating amount to 0.5-5wt% can improve the electrical properties of the modified lithium ferrite material. Preferably, the carbon coating amount is 0.8-3wt%, more preferably 1-3wt%, and even more preferably 1-2.5wt%, to achieve even better electrical properties.

[0015] According to the embodiment provided in the present application, the molar ratio of nickel element to lithium element includes but is not limited to 0.01:5, 0.02:5, 0.03:5, 0.04:5 or 0.05:5, etc.

[0016] Preferably, the nickel element is doped by grinding, more preferably by ball milling. The nickel doping process does not include high-temperature sintering and pulverization operations.

[0017] Preferably, the average thickness of the carbon coating layer is 10 to 500 nm, more preferably 80 to 400 nm, and even more preferably 100 to 300 nm.

[0018] In the present application, the average thickness of the carbon coating layer is tested by performing a powder cross-section SEM test on the modified lithium ferrite material, and then selecting at least 10 points from the SEM cross-section image, calculating their thickness values, removing the maximum and minimum values, and calculating the average value to obtain the average thickness.

[0019] The coating described in the present application is full coating, that is, the carbon material achieves 100% coating of the nickel-doped lithium ferrite matrix.

[0020] In the modified lithium ferrite material provided in the present application, the carbon coating layer is a homogeneous carbon coating layer. The "homogeneous" refers to the SEM test results of the modified lithium ferrite material, and at least 50% of the area of ​​the carbon material outside the matrix has no obvious accumulation or agglomeration phenomenon, so as to obtain better comprehensive performance.

[0021] Preferably, the carbon source forming the carbon coating layer is a gaseous carbon source, including but not limited to any one of ethylene, acetylene, methane, ethane, propylene, propane or butene, or a combination of at least two thereof. Gaseous carbon sources of the same type that can achieve the same or similar effects can also be used in this application.

[0022] According to some embodiments provided in the present application, the residual alkali content of the modified lithium ferrite material is <5%; according to other embodiments provided in the present application, the residual alkali content of the modified lithium ferrite material is <4.5%; according to some embodiments provided in the present application, the residual alkali content of the modified lithium ferrite material is <3.5%.

[0023] The residual alkali includes LiOH and Li2CO3.

[0024] In a second aspect, the present application provides a method for preparing a modified lithium ferrite material, the preparation method comprising the following steps:

[0025] (1) mixing a lithium source and an iron source, and sintering the mixture to obtain a lithium ferrite matrix;

[0026] (2) grinding the lithium ferrite matrix and the nickel source to obtain a nickel-doped lithium ferrite matrix;

[0027] (3) Using a carbon source, the nickel-doped lithium ferrite matrix obtained in step (2) is subjected to vapor-phase carbon coating to obtain the modified lithium ferrite material.

[0028] The present application, by subjecting lithium ferrite powder to a doping reaction with a nickel source, strictly controlling the molar ratio of lithium, iron and nickel elements, and combining appropriate process conditions, can generate a unique nickel-iron lithium oxide thin layer on the surface of the lithium ferrite material, thereby significantly improving the stability of the lithium ferrite material, reducing or inhibiting the generation of residual alkali, and having excellent lithium replenishment performance.

[0029] Preferably, the lithium source in step (1) includes any one of lithium oxide, lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrite, lithium nitrate, lithium oxalate, lithium acetate or lithium phosphate, or a combination of at least two thereof.

[0030] Preferably, the iron source includes any one of ferric chloride, ferrosoferric oxide, ferric oxide, ferric hydroxide, ferric oxyhydroxide, ferric nitrate, ferric acetate, ferric citrate, ferric phosphate, ferrous oxalate, ferric formate or ferric acetate, or a combination of at least two thereof.

[0031] Preferably, the molar ratio of the lithium element in the lithium source to the iron element in the iron source is 5:(0.9-1.1), for example: 5:0.9, 5:0.92, 5:0.95, 5:1 or 5:1.1.

[0032] Preferably, the sintering process in step (1) includes one-step sintering and two-step sintering.

[0033] Preferably, the temperature of the two-step sintering is higher than the temperature of the one-step sintering.

[0034] Preferably, the one-step sintering is sintering at 100-250° C. for 0.5-4 h.

[0035] Preferably, the two-step sintering is sintering at 600-900° C. for 5-20 hours.

[0036] Preferably, the nickel source in step (2) comprises any one of nickelous oxide, nickel trioxide, nickel hydroxide, nickel hydroxide oxide, nickel nitrate, nickel nitrite, nickel carbonate, nickel oxalate or nickel acetate, or a combination of at least two thereof.

[0037] Preferably, the molar ratio of the nickel element in the nickel source to the lithium element in the lithium source is (0.01-0.05):5, for example: 0.01:5, 0.02:5, 0.03:5, 0.04:5 or 0.05:5, etc.

[0038] Preferably, the lithium ferrite matrix is ​​crushed and sieved before the grinding treatment in step (2).

[0039] Preferably, the mesh size of the sieve is 400-500 mesh, for example, 400 mesh, 420 mesh, 450 mesh, 480 mesh or 500 mesh.

[0040] Preferably, the milling process comprises mechanochemical ball milling.

[0041] Preferably, the ball-to-material ratio of the mechanochemical ball milling is (10-45):1, for example: 10:1, 15:1, 20:1, 30:1, 40:1 or 45:1.

[0042] This application utilizes mechanochemical ball milling to react a nickel source with excess lithium on the surface of lithium ferrite particles to produce lithium nickelate. This creates a thin layer of iron-nickel-lithium composite material on the surface of the lithium ferrite particles, forming a superior core-shell structure. Because lithium nickelate is more stable than lithium ferrite, it can effectively reduce the amount of residual alkali generated and improve the overall stability of the modified lithium ferrite material. Lithium nickelate itself also has certain lithium-replenishing properties.

[0043] Compared with the co-blending sintering method, the mechanochemical ball milling method can control the reaction in the surface layer of the powder, and replace the high-temperature sintering method, avoiding the processes such as crushing and screening after sintering.

[0044] Preferably, the carbon source in step (3) comprises any one of ethylene, acetylene, methane, ethane, propylene, propane or butene, or a combination of at least two thereof.

[0045] The present application sets the temperature of gas-phase carbon coating according to the decomposition temperature of different carbon sources. The temperature of gas-phase carbon coating is close to or higher than the decomposition temperature (slightly lower temperature can decompose, but the reaction is not complete), for example, 700-1000°C.

[0046] Preferably, the gas-phase carbon coating in step (3) is carried out in an inert atmosphere.

[0047] Preferably, the inert atmosphere comprises nitrogen and / or argon.

[0048] This application utilizes high-temperature sintering of a carbon source gas to deposit carbon nanoparticles onto the surface of a modified lithium ferrite material in the form of vapor. This allows for a complete coating, improving material stability, reducing residual alkali content, and enhancing conductivity. Compared to conventional carbon powder blend coatings and polymer coatings, the carbon nanoparticles are smaller in size and offer better surface modification and coating effects.

[0049] Furthermore, rotating the chemical vapor deposition chamber at a speed of 0.3 to 15.0 rpm, particularly 0.5 to 10.0 rpm, can achieve better coating results. If the speed is too slow, the modified lithium ferrite material at the bottom layer will not easily come into contact with the carbon source gas; if the speed is too high, the powder may be centrifugally thrown up or compacted into agglomerates, which is not conducive to carbon coating.

[0050] Preferably, the gas phase carbon coating time is 1 to 3 hours.

[0051] In a third aspect, the present application provides a positive electrode plate, which comprises the modified lithium ferrite material as described in the first aspect or the modified lithium ferrite material prepared by the method described in the second aspect.

[0052] In a fourth aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet as described in the third aspect.

[0053] Compared with the related art, this application has the following beneficial effects.

[0054] (1) The modified lithium ferrite material provided in the present application is capable of generating a unique nickel-iron lithium oxide thin layer on the surface of the lithium ferrite material by doping lithium ferrite powder with a nickel source, controlling the molar ratio of lithium, iron and nickel elements, and combining with appropriate process conditions. This significantly improves the stability of the lithium ferrite material, can reduce or inhibit the generation of residual alkali, and has excellent lithium replenishment performance.

[0055] (2) The present application uses mechanical force chemical ball milling to achieve the effect of chemical reaction by mechanical force, avoiding the use of high-temperature sintering and eliminating the need for pulverization after sintering, thereby saving process steps and energy consumption. In addition, the use of mechanical force chemical ball milling can make the nickel source react mainly with the surface or excess lithium element in the surface layer of the lithium ferrite particles. The generated iron-nickel-lithium composite oxide covers the surface of the lithium ferrite particles, which is beneficial to isolate the lithium ferrite from contact with moisture and oxygen in the external environment, reduce side reactions, improve the stability of the lithium ferrite powder, have a protective effect, and help inhibit or reduce the amount of residual alkali generated.

[0056] (3) The modified lithium ferrite material provided in this application uses a gaseous carbon source to form a homogeneous carbon coating layer, which has excellent conductivity and can improve electrochemical performance; in addition, this fully coated homogeneous carbon coating layer can better isolate the air and further improve environmental stability.

[0057] (4) The residual alkali content of the modified lithium ferrite described in this application can reach below 1.56%, the initial coulombic efficiency of the manufactured battery can reach above 85%, the 3C discharge capacity retention rate can reach above 88%, and the capacity retention rate after 500 cycles at 25°C can reach above 99%.

[0058] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG1 is a cross-sectional SEM image of the modified lithium ferrite material described in Example 1 of the present application;

[0060] FIG2 is a SEM image of the modified lithium ferrite material described in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0062] Example 1

[0063] This embodiment provides a modified lithium ferrite material, and a preparation method of the modified lithium ferrite material comprises the following steps:

[0064] (1) Using a mixer, 298.81 g (10 mol, equivalent to 20 mol of lithium element) of lithium oxide and 312.99 g (1.96 mol, equivalent to 3.92 mol of iron element) of ferric oxide were mixed to obtain a mixed powder; in an argon atmosphere, the mixed powder was heated to 100° C. and kept at this temperature for 4.0 h, then heated to 600° C. and kept at this temperature for 20.0 h, and after high-temperature sintering, the mixed powder was naturally cooled to 25° C. to obtain lithium ferrite;

[0065] (2) In an argon atmosphere, lithium ferrite was broken up and crushed using a crusher, and sieved with a 500-mesh sieve; the sieve residue was crushed again, sieved again, and 2.99 g (0.04 mol, equivalent to 0.04 mol of nickel element) of nickelous oxide was added, and mixed using a mixer to obtain a mixed powder of lithium ferrite and nickelous oxide, and then in an argon atmosphere, the mixed powder was mechanochemically ball milled using a ball mill for 5.0 h at a ball-to-material ratio of 30:1 to obtain a nickel-doped lithium ferrite matrix;

[0066] (3) Under an argon atmosphere, 100 g of the nickel-doped lithium ferrite substrate obtained in step (2) was placed in a chemical vapor deposition furnace, the temperature was raised to 700° C., acetylene was then introduced, and the cavity of the chemical vapor deposition furnace was rotated at a speed of 0.5 rpm. The temperature was kept constant for 3.0 h, and then the introduction of the carbon source gas was stopped. The temperature was lowered to 25° C. to obtain the modified lithium ferrite material with a carbon coating amount of 1.4 wt%.

[0067] The cross-sectional SEM image of the modified lithium ferrite material is shown in FIG1 . As can be seen from FIG1 , a coating layer exists on the surface of a single particle of the modified lithium ferrite powder prepared in the present application, and the average thickness of the coating layer is 200 nm.

[0068] Example 2

[0069] This embodiment provides a modified lithium ferrite material, and a preparation method of the modified lithium ferrite material comprises the following steps:

[0070] (1) Using a mixer, 298.81 g (10 mol, equivalent to 20 mol of lithium element) of lithium oxide and 319.38 g (2 mol, equivalent to 4 mol of iron element) of ferric oxide were mixed to obtain a mixed powder; in an argon atmosphere, the mixed powder was heated to 250° C., kept at this temperature for 0.5 h, then heated to 900° C., kept at this temperature for 5.0 h, sintered at high temperature, and then naturally cooled to 25° C. to obtain lithium ferrite;

[0071] (2) In an argon atmosphere, lithium ferrite was broken up and crushed using a crusher, and sieved with a 500-mesh sieve; the sieve residue was crushed again, and 14.94 g (0.2 mol, equivalent to 0.2 mol of nickelous oxide) was added, and mixed using a mixer to obtain a mixed powder of lithium ferrite and nickelous oxide. Then, in an argon atmosphere, the mixed powder was mechanochemically ball milled using a ball mill for 0.5 h at a ball-to-material ratio of 10:1 to obtain a nickel-doped lithium ferrite matrix;

[0072] (3) Under an argon atmosphere, 100 g of the nickel-doped lithium ferrite substrate obtained in step (2) was placed in a chemical vapor deposition furnace, the temperature was raised to 1000° C., and then ethane was filled in. The cavity of the chemical vapor deposition furnace was rotated at a speed of 10.0 rpm, and the temperature was kept constant for 1.0 h. Then, the carbon source gas was stopped and the temperature was lowered to 25° C. to obtain the modified lithium ferrite material.

[0073] The carbon coating amount is 2.01 wt %, and the average thickness of the carbon coating layer is 300 nm.

[0074] Example 3

[0075] The only difference between this embodiment and embodiment 1 is that the lithium source is replaced by 20 mol of lithium hydroxide, the iron source is 4.4 mol of ferric chloride, and the nickel source is 0.2 mol of nickel nitrate. Other conditions and parameters are exactly the same as those in embodiment 1.

[0076] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0077] Example 4

[0078] The only difference between this embodiment and embodiment 1 is that the lithium source is replaced with 10 mol of lithium oxalate, the iron source is 3.6 mol of ferric chloride, and the nickel source is 0.2 mol of nickel hydroxide. Other conditions and parameters are exactly the same as those in embodiment 1.

[0079] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0080] Comparative Example 1

[0081] The only difference between this comparative example and Example 1 is that no nickel source is added, and other conditions and parameters are exactly the same as those in Example 1.

[0082] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0083] Comparative Example 2

[0084] The only difference between this comparative example and Example 1 is that step (3) adopts a solid phase coating process, and the coating carbon source is changed to sucrose for solid phase coating. The other conditions and parameters are exactly the same as those in Example 1.

[0085] The carbon coating amount is 0.87 wt %; the SEM image of the modified lithium ferrite material is shown in FIG2 .

[0086] Comparative Example 3

[0087] The only difference between this comparative example and Example 1 is that the nickel source is directly mixed with the iron source and the lithium source and sintered without mechanochemical ball milling. Other conditions and parameters are exactly the same as those in Example 1.

[0088] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0089] Comparative Example 4

[0090] The only difference between this comparative example and Example 1 is that the mass of the nickelous oxide in step (2) is 2.4 g (0.032 mol, equivalent to 0.032 mol of nickel element), and the other conditions and parameters are exactly the same as those in Example 1.

[0091] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0092] Comparative Example 5

[0093] The only difference between this embodiment and embodiment 1 is that the mass of the nickelous oxide in step (2) is 19.74 g (0.24 mol, equivalent to 0.24 mol of nickel element), and the other conditions and parameters are exactly the same as those in embodiment 1.

[0094] The carbon coating amount is 1.4 wt %, and the average thickness of the carbon coating layer is 200 nm.

[0095] Performance testing:

[0096] 0.3 g of lithium ferrite sample prepared in Example and Comparative Example was added to 100 mL of methanol solvent respectively, and stirred at 800 rpm for 5 min using a 3 cm magnetic stirrer. The filtrate was filtered and tested using a Mettler GS20 automatic titrator to obtain the value of the sum of residual alkali LiOH and Li2CO3.

[0097] (1) LFP, the modified lithium ferrite material obtained in Examples 1-4 and Comparative Examples 1-5, the conductive agent SuperP, carbon nanotubes, and the binder polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 94:2:1.5:0.5:2 to prepare a positive electrode slurry (solid content of 60%). The double-sided surface density was 340 g / cm 2 Coated on the current collector aluminum foil, dried at 70°C, and then cold pressed at 4MPa at room temperature. After trimming, cutting, and slitting, the tabs are welded to make the positive electrode sheet.

[0098] (2) Under an inert protective atmosphere, artificial graphite negative electrode material, conductive agent SuperP and adhesive PVDF were mixed with NMP in a mass ratio of 97.5:1.0:1.5 to prepare a negative electrode slurry (solid content of 50%), which was coated on the current collector copper foil with a thickness of 100 μm. After drying at 100°C, it was cold pressed at 4 MPa at room temperature, and then trimmed, cut and stripped, and the tabs were welded to make the negative electrode sheet;

[0099] (3) Using a PE porous polymer film as a separator, the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets, and wound to obtain a bare cell; the bare cell is placed in an aluminum-plastic shell package and placed under a relative vacuum pressure of -0.95×10 5Pa, dried at 100 ° C to a moisture content of less than 100 ppm. The electrolyte is injected into the dried bare battery cell, wherein the electrolyte consists of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (concentration 1.0M), and the battery is packaged, allowed to stand, formed (0.02C constant current charging for 2h, 0.1C constant current charging for 2h), shaped, and capacity tested (capacity separation) to make a soft-pack lithium-ion battery.

[0100] 1. First Coulombic efficiency test:

[0101] The prepared battery was formed and capacity-scaled using a battery test cabinet. The formation process was to charge at a constant current of 0.05C for 2.0 hours, then at a constant current of 0.15C for 2.5 hours, then at a constant current of 0.33C to 4.2V, and then at a constant voltage charge of 4.2V to a cutoff current of 0.02C. The capacity was then scaled by discharging at 0.33C to 2.5V. The sum of the above charge capacities and the discharge capacity were recorded as the initial charge capacity and the initial discharge capacity, and the initial charge specific capacity, the initial discharge specific capacity, and the initial coulombic efficiency were calculated.

[0102] 2. Normal temperature cycle performance test:

[0103] At 25°C, charge the battery to 3.7V at 0.5C constant current and constant voltage, with a cut-off current of 0.02C, and leave it for 5 minutes. Then discharge it to 2.5V at 1C constant current and leave it for 5 minutes. After 500 cycles of charge and discharge, calculate the capacity retention rate at the 500th cycle. The calculation formula is as follows:

[0104] 500th cycle capacity retention rate (%)=(500th cycle discharge capacity / 1st cycle discharge capacity)×100%.

[0105] The test results are shown in Table 1:

[0106] Table 1

[0107] As can be seen from Table 1, from Examples 1-4, the residual alkali content of the modified lithium ferrite described in the present application can reach less than 1.56%, the first coulombic efficiency of the manufactured battery can reach more than 85%, the 3C discharge capacity retention rate can reach more than 88%, and the capacity retention rate after 500 cycles at 25°C can reach more than 99%.

[0108] By comparing Example 1 and Comparative Example 1, it can be seen that the present application, by doping lithium ferrite powder with a nickel source and controlling the molar ratio of lithium, iron and nickel elements, and combining with appropriate process conditions, can generate a unique nickel-iron lithium oxide thin layer on the surface of the lithium ferrite material, significantly improving the stability of the lithium ferrite material, reducing or inhibiting the generation of residual alkali, and having excellent lithium replenishment performance.

[0109] By comparing Example 1 and Comparative Example 2, it can be seen that the present application can fully and completely coat the modified lithium ferrite material by sintering the carbon source gas at high temperature and depositing carbon nanovapor on the surface of the modified lithium ferrite material, thereby improving the stability of the material, reducing the amount of residual alkali, and improving conductivity. As for solid-phase coating, it can be seen from Figure 2 that the solid-phase coating surface is uneven, with some particles exposed and not covered with a carbon layer, and it is difficult to form a homogeneous carbon coating layer on the coated part.

[0110] A comparison of Example 1 and Comparative Example 3 demonstrates that the present invention utilizes mechanochemical ball milling to react the nickel source with the excess lithium on the surface of the lithium ferrite particles to produce lithium nickelate. This results in a thin layer of iron-nickel-lithium composite material on the surface of the lithium ferrite particles, forming an excellent core-shell structure. Because lithium nickelate is more stable than lithium ferrite, it can effectively reduce the amount of residual alkali generated and improve the overall stability of the modified lithium ferrite material. The lithium nickelate itself also has certain lithium replenishment properties.

[0111] By comparing Example 1 and Comparative Examples 4-5, it can be seen that the amount of nickel added in the modified lithium ferrite material described in the present application will affect the performance of the modified lithium ferrite material. The molar ratio of the nickel element in the nickel source to the lithium element in the lithium source is controlled at (0.01-0.05):5, and the modified lithium ferrite material is better. If the amount of nickel added is too small, it is difficult to react uniformly during the ball milling process, and the improvement effect is limited. If the amount of nickel added is too large, the main phase lithium ferrite structure is affected and the capacity is reduced.

[0112] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A modified lithium ferrite material, comprising a nickel-doped lithium ferrite substrate and a thin layer of iron-nickel lithium oxide and a carbon coating layer sequentially stacked on the surface of the nickel-doped lithium ferrite substrate, wherein the thin layer of iron-nickel lithium oxide is in-situ generated on the surface of the nickel-doped lithium ferrite substrate. In the modified lithium ferrite material, the molar ratio of lithium element to iron element is 5:(0.9-1.1), the molar ratio of nickel element to lithium element is (0.01-0.05):5, and the carbon coating amount is 0.5-5wt%.

2. The modified lithium ferrite material according to claim 1, wherein: The average thickness of the carbon coating layer is 10 to 500 nm.

3. The modified lithium ferrite material according to claim 1, wherein: The carbon source for forming the carbon coating layer is a gaseous carbon source, including any one of ethylene, acetylene, methane, ethane, propylene, propane or butene, or a combination of at least two thereof.

4. The modified lithium ferrite material according to claim 1, wherein: The residual alkali content of the modified lithium ferrite material is less than 5%.

5. A method for preparing a modified lithium ferrite material, comprising the following steps: (1) mixing a lithium source and an iron source, and sintering the mixture to obtain a lithium ferrite matrix; (2) grinding the lithium ferrite matrix and the nickel source to obtain a nickel-doped lithium ferrite matrix; (3) Using a carbon source, the nickel-doped lithium ferrite matrix obtained in step (2) is subjected to vapor phase carbon coating to obtain the modified lithium ferrite material.

6. The preparation method according to claim 5, wherein The lithium source in step (1) comprises any one of lithium oxide, lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrite, lithium nitrate, lithium oxalate, lithium acetate or lithium phosphate, or a combination of at least two thereof; Preferably, the iron source comprises any one of ferric chloride, ferroferric oxide, ferric oxide, ferric hydroxide, ferric oxyhydroxide, ferric nitrate, ferric acetate, ferric citrate, ferric phosphate, ferrous oxalate, ferric formate or ferric acetate, or a combination of at least two thereof; Preferably, the molar ratio of the lithium element in the lithium source to the iron element in the iron source is 5:(0.9-1.1).

7. The preparation method according to claim 5, wherein The sintering process includes one-step sintering and two-step sintering, and the temperature of the two-step sintering is higher than the temperature of the one-step sintering.

8. The preparation method according to claim 5, wherein The nickel source in step (2) comprises any one of nickelous oxide, nickel trioxide, nickel hydroxide, nickel hydroxide, nickel nitrate, nickel nitrite, nickel carbonate, nickel oxalate or nickel acetate, or a combination of at least two thereof; Preferably, the molar ratio of the nickel element in the nickel source to the lithium element in the lithium source is (0.01-0.05):

5.

9. The preparation method according to claim 5, wherein: Before the grinding treatment in step (2), the lithium ferrite matrix is ​​crushed and sieved; Preferably, the milling process comprises mechanochemical ball milling; Preferably, the ball-to-material ratio of the mechanochemical ball milling is (10-45):

1.

10. The preparation method according to claim 5, wherein: The carbon source in step (3) includes any one of ethylene, acetylene, methane, ethane, propylene, propane or butene, or a combination of at least two thereof; Preferably, the gas phase carbon coating is performed in an inert atmosphere.

11. A positive electrode plate, comprising the modified lithium ferrite material according to claims 1-4 or the modified lithium ferrite material obtained by the method according to any one of claims 5-10. 12 . A lithium ion battery comprising the positive electrode sheet according to claim 11 .

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