A lithium ferrite lithium supplement prepared by a step-by-step lithium addition method and a preparation method thereof

Abstract

The invention discloses a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method and a preparation method thereof. Firstly, all iron sources, part of lithium sources and additives are mixed and sintered to prepare a precursor, and then the precursor and the remaining lithium source are mixed to prepare a finished product, thereby reducing the amount of lithium source used in the second step of sintering and reducing the amount of lithium liquid phase melt under a high temperature state, so that all elements are evenly distributed, and the material has excellent performance. When preparing the precursor, air atmosphere sintering can be used, and lithium carbonate can also be used as a lithium source without introducing additional impurities; wherein air atmosphere sintering can reduce costs, and the iron source is not limited, and low-valent iron compounds can be used; lithium carbonate as a lithium source has great advantages in terms of process and cost.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, power, and energy storage fields due to their advantages such as high energy density, good cycle performance, high operating voltage, and no memory effect. They are currently one of the most promising energy sources.

[0003] However, during the first charge and discharge process of lithium-ion batteries, a SEI film will form on the negative electrode surface. This process will consume a large amount of lithium ions, which means that part of the lithium ions released from the positive electrode material will be irreversibly consumed, reducing the battery's initial coulombic efficiency and reversible capacity. In graphite negative electrode lithium batteries, the first charge will consume about 10% of the lithium source. In alloy or silicon negative electrode lithium batteries, lithium consumption is higher than 10%.

[0004] To improve this problem, the following methods are currently used: pre-lithiation of negative electrode materials, pre-lithiation of positive electrode materials, and pre-lithiation of pole pieces. Among them, the pre-lithiation process of positive electrode materials is relatively simple and has low cost, and is a preferred method for industrialization. The pre-lithiation of positive electrode materials mainly involves adding lithium supplements to positive electrode materials. The theoretical capacity of lithium ferrite materials exceeds 800mAh / g, and the operating voltage window is consistent with that of conventional lithium-ion batteries. In addition, they basically do not participate in the electrochemical process in the later stage. They are a lithium supplement for positive electrode materials with broad prospects.

[0005] However, the chemical formula of lithium ferrite contains a lot of lithium. The conventional preparation method is to add all the lithium sources in one step and then mix and sinter, which causes the following problems: ① The mass of the lithium source is usually much larger than that of the iron source, which is easy to mix unevenly, resulting in local lithium excess. ② The huge lithium content causes a large amount of lithium liquid phase melt to form when the mixture is sintered in the kiln, causing uneven distribution of materials with large specific gravity differences (iron sources or additives). Summary of the invention

[0006] In view of the fact that the chemical formula of lithium ferrite in the prior art contains a lot of lithium, the conventional preparation method is to add all lithium sources in one step and then mix and sinter, which leads to uneven mixing and causes local lithium excess, and the huge lithium content causes the mixture to form a large amount of lithium liquid melt when sintered in a kiln, resulting in uneven distribution of materials (iron sources or additives) with large specific gravity differences. The present invention provides a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method and a preparation method thereof, as well as a lithium ferrite precursor of the lithium supplement and a preparation method thereof, and lithium ferrite prepared using the precursor and a preparation method thereof.

[0007] The purpose of the present invention is to provide a step-by-step lithium addition method for preparing lithium ferrite, first preparing a lithium-containing precursor, and then using the precursor to prepare lithium ferrite, in order to solve the problem caused by the need to use a large amount of lithium source during the preparation process.

[0008] The technical solution of the present invention is as follows:

[0009] The preparation method comprises the following steps:

[0010] Precursor preparation: The iron source, lithium source and additive are mixed and the mixture is sintered to obtain a precursor; the lithium source, iron source and additive have a molar ratio of Li: Mixing, where M is the added metal element;

[0011] Precursor coating: the precursor and the coating material are mixed and sintered to obtain a coated precursor;

[0012] Finished product preparation: the coated precursor and the lithium source are mixed and sintered to obtain a lithium ferrite lithium supplement;

[0013] Lithium ferrite chemical formula: Li x Fe y M (1-y) O z , where M is the additive metal element, 4.9≤x≤5.3, 0.8≤y≤1, z=0.5×(x+3).

[0014] The purpose of the present invention is achieved through the following technical solutions:

[0015] A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method comprises the following steps:

[0016] S1. Precursor preparation: Lithium source, iron source and additives are mixed in molar ratio. Performing a mixing process, wherein M is an added metal element, and sintering and crushing the mixture to obtain a precursor;

[0017] The lithium source is selected from one of lithium carbonate, lithium nitrate, lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium oxalate and lithium oxide;

[0018] The iron source is selected from one of ferrous oxide, ferric oxide, ferric hydroxide, ferrous hydroxide, ferric oxalate and ferric nitrate;

[0019] The additives are various metal element compounds that are desired to be doped, and the doped metal elements are Co, W, Ca, Al, Mg, Zn, Sb, rare earth elements, etc.;

[0020] S2, precursor coating: the precursor obtained in the previous step and the carbon source are mixed and sintered to obtain a carbon-coated precursor; wherein the mass ratio of carbon in the precursor and the carbon source is , the carbon source is selected from glucose, sucrose, etc.;

[0021] S3, finished product preparation: the coated precursor obtained in the previous step is mixed with a lithium source and then sintered, and the sintered product is crushed and sieved to obtain a lithium ferrite lithium supplement. The chemical formula of lithium ferrite is Li x Fe y M (1-y) O z , where M is the additive metal element, 4.9≤x≤5.3, 0.8≤y≤1, z=0.5×(x+3);

[0022] The lithium source and the precursor are in a molar ratio mix;

[0023] The sintering described in S3, wherein the sintering temperature is The sintering time is , the sintering atmosphere is a mixture of reducing atmosphere and inert gas;

[0024] The obtained lithium ferrite lithium supplement has the following performance indicators: the first charging capacity is greater than 690 mAh / g, and the first discharging capacity is less than 14 mAh / g.

[0025] Furthermore, the mixing described in steps S1, S2, and S3 is dry mixing, which can be processed by a ball mill mixer, a high-speed mixer, or the like.

[0026] Further, the mixture described in step S1 is sintered to obtain a precursor, wherein the sintering temperature is The sintering time is , the sintering atmosphere is air; the sintering in step S2, wherein the sintering temperature is The sintering time is The sintering atmosphere is an inert atmosphere, which can be an inert gas such as nitrogen, argon, etc. Considering the cost, nitrogen is preferred.

[0027] Furthermore, the additives described in step S1, the selected compounds must meet the following conditions: no additional impurities are introduced; the particle size is close to or smaller than the particle size of the raw material.

[0028] Furthermore, the mass ratio of the precursor and the carbon in the carbon source described in step S2 is preferably 100:10.

[0029] Furthermore, in the sintering described in step S3, the sintering atmosphere is a reducing atmosphere. To ensure that the carbon of the precursor lithium is not oxidized, a reducing atmosphere is used, including hydrogen and hydrocarbon gases, etc. To ensure safety and reduce costs, a mixture of reducing gas and inert gas is used.

[0030] The present invention also relates to a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method, which is obtained by using the above-mentioned preparation method of a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method, wherein the chemical formula of the lithium ferrite is Li x Fe y M (1-y) O z , M is an additive metal element, 4.9≤x≤5.3, 0.8≤y≤1, z=0.5×(x+3); the lithium ferrite lithium supplement has high crystallinity, high purity, no impurities, high first charge capacity, small discharge capacity, and has the following performance indicators: first charge capacity>690 mAh / g, first discharge capacity<14 mAh / g.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The preparation method of a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method described in the present invention comprises the following steps: firstly, all the iron source, part of the lithium source and an additive are mixed and sintered to prepare a precursor, and then the precursor and the remaining lithium source are mixed to prepare a finished product, thereby reducing the amount of lithium source used in the second step of sintering, reducing the amount of lithium liquid phase melt under high temperature, making all elements evenly distributed, and having excellent material properties. When preparing the precursor, air atmosphere sintering can be used, and lithium carbonate can also be used as a lithium source without introducing additional impurities; wherein air atmosphere sintering can reduce costs, and the iron source is not limited, and low-valent iron compounds can be used; lithium carbonate as a lithium source has great benefits in terms of process and cost.

[0033] 2. The lithium ferrite lithium supplement prepared by the step-by-step lithium addition method described in the present invention adds doping elements to the precursor. Because the precursor is sintered in an air atmosphere, the types of doping elements that can be selected are increased, and low-cost compounds can be selected. In addition, the amount of lithium source used in the precursor is not large, and the uneven distribution of the additives will not be caused by the huge difference in the amount of the main raw material and the amount of the additives.

[0034] 3. The lithium ferrite lithium supplement prepared by the step-by-step lithium addition method described in the present invention comprises carbon coating the precursor, and sintering the carbon-coated precursor and the lithium source, so that the carbon can be evenly distributed inside the lithium ferrite, thereby improving the conductivity of the lithium ferrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0036] Figure 1 This is a SEM image of a precursor in a method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method according to Example 1 of the present invention;

[0037] Figure 2The XRD diagram of the finished product obtained by the preparation method of lithium ferrite lithium supplement prepared by a step-by-step lithium addition method in Example 1 of the present invention;

[0038] Figure 3 The XRD diagram of the finished product obtained by the preparation method of lithium ferrite lithium supplement prepared by a step-by-step lithium addition method in Example 2 of the present invention;

[0039] Figure 4 The XRD diagram of the finished product obtained by the preparation method of lithium ferrite lithium supplement prepared by a step-by-step lithium addition method in Example 3 of the present invention;

[0040] Figure 5 The XRD diagram of the finished product obtained by the preparation method of lithium ferrite lithium supplement prepared by a step-by-step lithium addition method in Example 4 of the present invention;

[0041] Figure 6 This is the XRD pattern of the finished product prepared in Comparative Example 1. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Embodiment 1:

[0044] A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method comprises the following steps:

[0045] S1. Preparation of precursor: lithium source, iron source, additives, molar ratio Li: (Fe + W) = 1.2: 1 (Fe is 0.99, W is 0.01), weigh 93.72g of lithium carbonate, 167.51g of ferric oxide, 4.88g of tungsten oxide, mix well and sinter.

[0046] The sintering temperature is 800°C, the sintering time is 1 hour, the sintering atmosphere is air, and the material is taken out after cooling to room temperature, and then crushed to obtain a precursor;

[0047] S2, precursor coating: the precursor obtained in the above step and the carbon source are mixed evenly and then sintered, wherein the sintering temperature is 200°C, the sintering time is 3h, the sintering atmosphere is nitrogen, and the mixture is cooled to room temperature and taken out to obtain a carbon-coated precursor; wherein the mass ratio of carbon in the precursor and the carbon source is 200g:50g, and the carbon source is selected from glucose;

[0048] S3. Preparation of finished product: According to the molar ratio of Li:Fe=3.9:1, 203.41g of the carbon-coated precursor obtained in the previous step and 577.01g of lithium nitrate are mixed and sintered at a sintering temperature of 700°C and a sintering time of 10h in a reducing atmosphere (3% hydrogen + 97% nitrogen). After cooling to room temperature, the mixture is taken out and then crushed and sieved to obtain a lithium ferrite lithium supplement.

[0049] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0050] The first charge capacity is 697mAh / g, and the discharge capacity is 9mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0051] Figure 1 is a SEM image of the precursor in step S1, and the precursor is a single crystal particle with uniform particle size;

[0052] Figure 2 This is the XRD diagram of the lithium ferrite supplement. From the diagram, it can be seen that the prepared lithium ferrite supplement is consistent with the diffraction peak of the PDF card.

[0053] Embodiment 2:

[0054] A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method comprises the following steps:

[0055] S1. Preparation of precursor: lithium source, iron source, additive, molar ratio Li: (Fe + Ca) = 1.15: 1 (Fe is 0.95, Ca is 0.05), weigh 89.81g of lithium carbonate, 155.78g of ferroferric oxide, 2.95g of calcium oxide, mix them evenly and sinter them, wherein the sintering temperature is 700°C, the sintering time is 2h, the sintering atmosphere is air, cool to room temperature, take out, and then crush the materials to obtain the precursor;

[0056] S2, precursor coating: the precursor obtained in the above step and the carbon source are mixed evenly and then sintered, wherein the sintering temperature is 300°C, the sintering time is 2h, the sintering atmosphere is nitrogen, and the mixture is cooled to room temperature and taken out to obtain a carbon-coated precursor; wherein the mass ratio of carbon in the precursor and the carbon source is 200g:50g, and the carbon source is selected from glucose;

[0057] S3, finished product preparation: according to the molar ratio of Li:Fe=4.0:1, 203.41g of the carbon-coated precursor obtained in the previous step and 128.25g of lithium oxide are mixed and sintered, wherein the sintering temperature is 800°C, the sintering time is 4h, and the sintering atmosphere is a reducing atmosphere (3% hydrogen + 97% nitrogen). After cooling to room temperature, the mixture is taken out, and then crushed and sieved to obtain a lithium ferrite lithium supplement;

[0058] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0059] The first charge capacity is 694mAh / g, and the discharge capacity is 10mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0060] Figure 3 This is the XRD diagram of the lithium ferrite supplement. From the diagram, it can be seen that the prepared lithium ferrite supplement is consistent with the diffraction peak of the PDF card.

[0061] Embodiment 3:

[0062] A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method comprises the following steps:

[0063] S1. Preparation of precursor: lithium source and iron source, weigh 97.94g lithium hydroxide and 226.58g iron hydroxide at a molar ratio of Li:Fe=1.1:1, mix well and sinter, wherein the sintering temperature is 600°C, the sintering time is 3h, the sintering atmosphere is air, cool to room temperature, take out, and then crush the material to obtain a precursor;

[0064] S2, precursor coating: the precursor obtained in the above step and the carbon source are mixed evenly and then sintered, wherein the sintering temperature is 400°C, the sintering time is 1 hour, the sintering atmosphere is nitrogen, and the mixture is cooled to room temperature and taken out to obtain a carbon-coated precursor; wherein the mass ratio of carbon in the precursor and the carbon source is 200g:50g, and the carbon source is selected from glucose;

[0065] S3, finished product preparation: according to the molar ratio of Li:Fe=4.1:1, 203.41g of the carbon-coated precursor obtained in the previous step and 369.03g of lithium hydroxide are mixed and sintered, wherein the sintering temperature is 800°C, the sintering time is 6h, the sintering atmosphere is a reducing atmosphere (5% hydrogen + 95% nitrogen), cooled to room temperature, taken out, and then crushed and sieved to obtain a lithium ferrite lithium supplement;

[0066] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0067] The first charge capacity is 709mAh / g, and the discharge capacity is 13.4mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0068] Figure 4 This is the XRD diagram of the lithium ferrite supplement. From the diagram, it can be seen that the prepared lithium ferrite supplement is consistent with the diffraction peak of the PDF card.

[0069] Embodiment 4:

[0070] A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method comprises the following steps:

[0071] S1. Preparation of precursor: lithium source, iron source, additive, molar ratio Li: (Fe + Co) = 1: 1 (Fe is 0.98, Co is 0.02), weigh 145.75g of lithium nitrate, 186.59g of ferrous hydroxide, 3.15g of cobalt monoxide, mix well and sinter, wherein the sintering temperature is 500°C, the sintering time is 4h, the sintering atmosphere is air, cool to room temperature, take out, and then crush the materials to obtain the precursor;

[0072] S2, precursor coating: the precursor obtained in the above step and the carbon source are mixed evenly and then sintered, wherein the sintering temperature is 400°C, the sintering time is 1 hour, the sintering atmosphere is nitrogen, and the mixture is cooled to room temperature and taken out to obtain a carbon-coated precursor; wherein the mass ratio of carbon in the precursor and the carbon source is 200g:50g, and the carbon source is selected from glucose;

[0073] S3, finished product preparation: according to the molar ratio of Li:Fe=4.2:1, 203.41g of the carbon-coated precursor obtained in the previous step and 378.03g of lithium hydroxide were mixed and sintered, wherein the sintering temperature was 900°C, the sintering time was 6h, and the sintering atmosphere was a reducing atmosphere (5% hydrogen + 95% nitrogen). After cooling to room temperature, the mixture was taken out, and then crushed and sieved to obtain a lithium ferrite lithium supplement;

[0074] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0075] The first charge capacity is 746mAh / g, and the discharge capacity is 12mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0076] Figure 5 This is the XRD diagram of the lithium ferrite supplement. From the diagram, it can be seen that the prepared lithium ferrite supplement is consistent with the diffraction peak of the PDF card.

[0077] Comparative Example 1:

[0078] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses a one-time lithium addition method, while Example 1 uses a step-by-step lithium addition method.

[0079] Weigh 472.54g of lithium hydroxide and 171.76g of ferric oxide at a molar ratio of Li:Fe=5.2:1, mix them, heat them to 900°C in a mixed reducing gas (5% hydrogen + 95% nitrogen), keep them warm for 6 hours, cool them to room temperature, take them out, and then crush and sieve them to obtain a lithium ferrite lithium supplement;

[0080] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0081] The first charge capacity is 201mAh / g, and the discharge capacity is 12.1mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0082] Figure 6 This is the XRD diagram of the lithium ferrite lithium supplement. From the diagram, it can be seen that the lithium ferrite lithium supplement has impurity peaks and low purity.

[0083] Comparative Example 2:

[0084] The difference between Comparative Example 1 and Example 2 is that Comparative Example 2 uses a one-time lithium addition method, while Example 2 uses a step-by-step lithium addition method.

[0085] Weigh 170.03g of lithium oxide and 182.17g of ferric oxide at a molar ratio of Li:Fe=5.0:1, mix them, heat them to 800°C in a mixed reducing gas (3% hydrogen + 97% nitrogen), keep them warm for 4 hours, cool them to room temperature, take them out, and then crush and sieve them to obtain a lithium ferrite lithium supplement;

[0086] The obtained lithium ferrite lithium supplement has the following performance indicators:

[0087] The first charge capacity is 97mAh / g, and the discharge capacity is 12.6mAh / g. For details on the power-off test method, please refer to the lithium supplement capacity test steps in the subsequent experimental example.

[0088] Experimental example:

[0089] Lithium Supplement Capacity Test:

[0090] The lithium supplement prepared in the embodiment and the comparative example was made into a button half-battery to test the capacity, and the specific steps were as follows:

[0091] Weigh NMP: lithium supplement: carbon black: PVDF in a mass ratio of 25:8:1:1, mix well and apply on aluminum foil, dry in a vacuum oven and cut into discs, and assemble with metal lithium negative electrode, separator and electrolyte into CR2032 button half-cell;

[0092] Battery test conditions: 0.1C charge and discharge, voltage .

[0093] Results and Discussion:

[0094] The following are the capacity test results of the embodiments and comparative examples:

[0095] Table 1: Capacity test results of examples and comparative examples

[0096]

[0097] 1. By comparing Examples 1-4 with Comparative Example 1, it can be seen that the capacity results show that the preparation method of the lithium ferrite lithium supplement prepared by the step-by-step lithium addition method of the present invention adopts the step-by-step lithium addition method, and the prepared lithium ferrite lithium supplement has no impurity peak, high purity, and correspondingly high capacity, the first charge capacity>690mAh / g, 694-746mAh / g, the first charge capacity can reach up to 746mAh / g, and the first discharge capacity<14mAh / g, 9.0-13.4mAh / g. Comparative Example 1 adopts the one-time lithium addition method, and the prepared lithium ferrite lithium supplement has many impurities, the sample purity is low, and the corresponding capacity is also low, 97-201mAh / g, and the lowest is only 97mAh / g.

[0098] 2. In addition, the four embodiments of the present invention adopt different lithium sources and iron sources, and the prepared lithium ferrite lithium supplements can achieve a relatively high initial charging capacity, all of which are greater than 690 mAh / g, indicating that the preparation method of the lithium ferrite lithium supplement prepared by the step-by-step lithium addition method described in the present invention has great process flexibility, can adapt to different production lines, and is easy to industrialize.

[0099] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a lithium ferrite lithium supplement prepared by a step-by-step lithium addition method, characterized in that: The following steps are involved: S1. Precursor preparation: lithium source, iron source and additive are mixed at a molar ratio of Li: (Fe + M) = (1.0-1.2): 1, wherein M is the added metal element, and the mixture is sintered and crushed to obtain a precursor, wherein the sintering temperature is 500-800°C, the sintering time is 1-4h, and the sintering atmosphere is air; The lithium source is selected from one of lithium carbonate, lithium nitrate, lithium hydroxide monohydrate, anhydrous lithium hydroxide, lithium oxalate and lithium oxide; The iron source is selected from one of ferrous oxide, ferric oxide, ferric hydroxide, ferrous hydroxide, ferric oxalate and ferric nitrate; The additive is a doped metal element compound, and the doped metal element is Co, W, Ca, Al, Mg, Zn, Sb, or a rare earth element; S2, precursor coating: the precursor obtained in the previous step and the carbon source are mixed and sintered at a sintering temperature of 200-400°C for 1-3 hours in an inert atmosphere to obtain a carbon-coated precursor; wherein the mass ratio of the carbon in the precursor and the carbon source is 100:(5-20), and the carbon source is selected from glucose and sucrose; S3, finished product preparation: the coated precursor obtained in the above step is mixed with a lithium source and then sintered, and the sintered product is crushed and sieved to obtain a lithium ferrite lithium supplement, wherein the chemical formula of lithium ferrite is Li x Fe y M (1-y) O z , M is the additive metal element, 4.9≤x≤5.3, 0.8≤y≤1, z=0.5×(x+3); The lithium source and the precursor are mixed in a molar ratio of Li:Fe=(3.8-4.2):1; The sintering described in S3, wherein the sintering temperature is 700-900°C, the sintering time is 4-10 hours, and the sintering atmosphere is a mixture of reducing atmosphere and inert gas; The obtained lithium ferrite lithium supplement has the following performance indicators: the first charge capacity is greater than 690 mAh / g, and the first discharge capacity is less than 14 mAh / g.

2. The method for preparing a lithium ferrite lithium supplement prepared by a stepwise lithium addition method according to claim 1, characterized in that: The mixing described in steps S1, S2 and S3 is dry mixing, which is processed by a ball mill mixer or a high-speed mixer.

3. The method for preparing a lithium ferrite lithium supplement prepared by a stepwise lithium addition method according to claim 1, characterized in that: The mass ratio of the precursor and the carbon in the carbon source described in step S2 is 100:

10.

4. A lithium ferrite lithium supplement prepared by a step-by-step lithium addition method, characterized in that: The preparation method of the lithium ferrite lithium supplement prepared by the step-by-step lithium addition method according to any one of claims 1 to 3 is obtained, wherein the chemical formula of the lithium ferrite is Li x Fe y M (1-y) O z , M is an additive metal element, 4.9≤x≤5.3, 0.8≤y≤1, z=0.5×(x+3); the lithium ferrite lithium supplement has high crystallinity, high purity, no impurities, high first charge capacity, small discharge capacity, and has the following performance indicators: first charge capacity>690mAh / g, first discharge capacity<14 mAh / g.

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