Preparation process of pre-lithiation agent lithium ferrite Li5FeO4

Abstract

The present invention belongs to the technical field of lithium supplement materials for lithium-ion batteries, and is specifically a preparation process for lithium ferrite Li5FeO4, a pre-lithiation agent. The present invention uses nano iron powder and LiOH flocculent as raw materials to prepare high-purity Li5FeO4 as a pre-lithiation agent, uses commercial SiO as an anode, and commercially available ternary material Li(Ni 0.4 Co 0.3 Mn 0.3 )O2(NCM433), lithium iron phosphate, etc. as cathodes to assemble lithium-ion batteries, solving the problem of irreversible capacity loss of silicon monoxide (SiO). The present invention combines Li5FeO4 with Li(Ni 0.4 Co 0.3 Mn 0.3 )O2(NCM433) cathode materials were mixed, the resulting cathode was then paired with a SiO anode, and the effect of adding Li5FeO4 on the electrochemical performance of the battery was studied.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery lithium supplement materials, and mainly relates to a preparation process of a pre-lithiation agent, specifically a preparation process of the pre-lithiation agent lithium ferrite Li5FeO4. Background Art

[0002] The application of lithium-ion batteries in transportation has driven the development of smaller, lighter, and more powerful batteries, allowing electric vehicles to travel longer without charging. To achieve this, high-capacity electrode materials are needed. Silicon and silicon oxides are the most promising next-generation high-energy lithium-ion anode materials. The electrolyte solution on the surface of the negative electrode material is relatively + / Li has a low potential and is a thermodynamically unstable system. Therefore, during the first lithiation process, the electrolyte solution will decompose irreversibly on the surface of the negative electrode, forming a layer with a thickness of several angstroms. Solid electrolyte membranes ranging from 100 to several hundred angstroms will cause a large amount of active lithium loss in the whole battery system during this process, especially for alloy-type anode materials such as silicon materials, which have a huge first irreversible capacity loss. Studies have shown that by coating silicon materials or constructing artificial SEI films, the first coulombic efficiency can be effectively improved and the loss of active lithium in the positive electrode can be alleviated, but there is still irreversible capacity loss. In addition to the first irreversible capacity loss, the volume expansion of silicon materials will lead to increased instability of the surface SEI film, and the active lithium in the system will continue to be consumed in subsequent cycles. Therefore, in order to improve the problems of the first irreversible capacity loss and subsequent active lithium consumption of silicon-based materials in the whole battery system, the use of a pre-lithiation scheme to compensate the system for lithium is a very promising improvement method.

[0003] In order to solve the problems of low authorization efficiency and irreversible capacity in lithium-ion batteries, pre-lithiation reagents can be added to the anode or cathode. The pre-lithiation reagent provides additional lithium in the first formation cycle to compensate for the lithium loss caused by irreversible reactions. Anode pre-lithiation reagents include stable metallic lithium and lithium silicide, and cathode pre-lithiation reagents include many sacrificial lithium salt additives, such as metal / lithium oxide, metal / LiF, Li2O2, Li6CoO4 and Li5FeO4. The theoretical capacity of Li5FeO4 (LFO) is 867mAh / g. According to the reaction 2Li5FeO4→Fe2O3+5Li2O, 5 Li are released per mole during the first charge reaction. +, which solves the large irreversible capacity loss caused by hard carbon (first cycle coulombic efficiency = 85%), and improves the cycle performance by providing an additional lithium ion source during the cycle. One advantage of the LFO pre-lithiation agent is that it can react with different cathode active materials. In addition, lithium ferrite (Li5FeO4) material has an inverse fluorite structure, and each part of Li5FeO4 material contains five parts of lithium, which makes its theoretical specific capacity as high as 867mAh / g. The working voltage of Li5FeO4 material is moderate and has good irreversibility. After the first charge and discharge, it can generate inert substances and does not participate in the subsequent electrochemical process, making it able to be used to solve the problem of battery reversible capacity and first efficiency reduction caused by the first charge and discharge. However, the impurity content of the product in Li5FeO4 prepared by the existing technology is relatively high, and the material is prone to obtain a mixed material of multiple crystal forms (Li5Fe5O8, LiFeO2, Li5FeO4) during the preparation process, which affects the charge and discharge performance of the material. Therefore, the present invention uses nano iron powder and LiOH flocculent as raw materials to prepare high-purity Li5FeO4 as a pre-lithiation agent, uses commercial SiO as an anode, and commercially available ternary material Li(Ni 0.4 Co 0.3 Mn 0.3 )O2(NCM433) and lithium iron phosphate as cathode to assemble lithium ion battery, which solves the problem of irreversible capacity loss of silicon monoxide (SiO). 0.4 Co 0.3 Mn 0.3 )O2(NCM433) cathode materials were mixed, the resulting cathode was then paired with a SiO anode, and the effect of adding Li5FeO4 on the electrochemical performance of the battery was studied. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art and to achieve the above-mentioned objectives, the present invention provides a preparation process of lithium ferrite Li5FeO4, a pre-lithiation agent, and the specific operating steps are as follows:

[0005] S1. Soak 3-5g of spherical high-purity iron powder in 50ml of ethylene glycol and 80ml of water, ultrasonically vibrate for 40-60min, let it stand for 10-24h, then centrifuge to separate the upper liquid, dry it in an oven at 60-80℃ for 10-15h, grind the dried iron powder with 0.5-1g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) evenly, then place it in a muffle furnace, and calcine it at a high temperature of 300-500℃ in air for 4-6h to obtain nano-spherical Fe2O3.

[0006] S2. Dissolve 10-18 g of LiOH in 50-80 ml of water, add 5-8 g of sodium carboxymethyl cellulose (CMC) to prepare a LiOH colloid, and then freeze-dry it in a freeze dryer at -60°C. Grind the freeze-dried LiOH colloid to obtain LiOH flocs. The purpose of adding CMC in this step is to prepare the LiOH colloid. After freeze-drying, the LiOH colloid becomes a flocculent substance that is loose and porous, which is conducive to the subsequent reaction with the nano-spherical Fe2O3.

[0007] S3. Use a mortar and pestle to thoroughly mix the nano-Fe2O3 prepared in step S1 with the LiOH flocs prepared in step S2 in a molar ratio of 1:5.5 or 1:6. Soak the mixed powder in acetonitrile solution for 10 hours. Then place the mixture in an XH-300UP microwave ultrasonic machine for 15-20 minutes. The microwave power is set to 220-320W. Then, heat the microwave-ultrasound-treated powder at 550-750℃ for 12-18 hours, with the heating rate controlled at 3-5℃min. -1 The mixture is then heated to 850-900°C and held for 35-40 hours. After cooling, Li₅FeO₄ (LFO) powder is obtained. The ultrasonic microwave treatment in this step is used to more evenly disperse and aggregate the nano-Fe₂O₃ on the LiOH flocs, facilitating subsequent calcination to produce high-purity LFO. The resulting LFO powder is stored in an argon-controlled chamber to prevent reaction with moisture and carbon dioxide. The 10-hour acetonitrile soaking in this step before microwave treatment provides a protective coating. During the ultrasonic microwave reaction, the acetonitrile on the surface transforms into a carbon layer, coating the surface of the mixture. During subsequent high-temperature calcination, the carbon then transforms into carbon dioxide and escapes, producing Li₅FeO₄ with a large specific surface area.

[0008] S4. Weigh the positive electrode material and the Li5FeO4 prepared in step S3 in a mass ratio of 10:1 or 15:2 and mix them evenly to form a cathode material containing Li5FeO4.

[0009] S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as the cathode sheet. Commercial SiO: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as the anode sheet. The resulting mixture is then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue-light working instrument. Both the electrode coating and battery assembly in this step must be completed in a dry room to ensure a dry environment for battery production.

[0010] Preferably, in step S1 of the present invention, the amount of spherical high-purity iron powder used is 5 g, and the ultrasonic oscillation time is 50 min.

[0011] Preferably, in step S1 of the present invention, 0.8 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) is selected.

[0012] Preferably, in step S2 of the present invention, 13 g of LiOH is dissolved in 60 ml of water, and 6 g of sodium carboxymethyl cellulose is added thereto.

[0013] Preferably, in step S3 of the present invention, the nano-Fe2O3 prepared in step S1 and the LiOH flocs prepared in step S2 are completely mixed in a molar ratio of 1:6 using a mortar and pestle.

[0014] Preferably, in step S3 of the present invention, the mixture is placed in an XH-300UP and subjected to microwave ultrasound for 18 minutes, with the microwave power set to 280W.

[0015] Preferably, in step S3 of the present invention, the powder treated with microwave ultrasound is heated at 650°C for 15h, with the heating rate controlled at 3°C min -1 , then continue heating to 880℃ and maintain for 35h.

[0016] Preferably, in step S5 of the present invention, the relative humidity of the drying room is ≤ 10%, and the dew point temperature is ≤ -45°C.

[0017] Preferably: the spherical high-purity iron powder of the present invention is purchased from Shijiazhuang Huabang Mineral Products Co., Ltd.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention uses spherical high-purity iron powder as raw material to prepare uniform nano-spherical Fe2O3 particles, and adds polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, which is conducive to obtaining spherical nanoparticles and reducing the generation of impurities during the subsequent reaction with LiOH flocs.

[0020] 2. The purpose of adding CMC in the present invention is to prepare LiOH colloid. After freeze-drying, the LiOH colloid becomes flocculent and loose and porous, which is conducive to the subsequent reaction with nano-spherical Fe2O3.

[0021] 3. The present invention adopts ultrasonic microwave treatment to disperse and aggregate nano-Fe2O3 more evenly on the top of LiOH flocs, which is conducive to the preparation of purer Li5FeO4 (LFO) powder.

[0022] 4. The present invention is simple to operate, suitable for mass production and low in price.

[0023] 5. The present invention belongs to green production and no harmful intermediates are produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the nano-spherical Fe2O3 prepared in Example 1 of the present invention.

[0025] Figure 2 This is the SEM image of the nano-spherical Fe2O3 prepared in Comparative Example 1 of the present invention.

[0026] Figure 3 The SiO anode and Li(Ni 0.4 Co 0.3 Mn 0.3 ) The situation when O2 cathode pairing (Comparative Example 2).

[0027] Figure 4 SiO anode and Li(Ni 0.4 Co 0.3 Mn 0.3 ) The situation when O2 and Li5FeO4 are mixed cathode pairing (Example 2).

[0028] Figure 5 The voltage-mass specific capacity curves of the full batteries prepared for Comparative Example 3 and Example 3 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. The following describes the embodiments of the present invention by specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other.

[0030] Example 1

[0031] S1. Soak 3 g of spherical high-purity iron powder in 50 ml of ethylene glycol and 80 ml of water, ultrasonically vibrate for 40 minutes, let it stand for 10 hours, then centrifuge to separate the upper liquid, dry it in an oven at 60°C for 15 hours, grind the dried iron powder with 0.5 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) evenly, then place it in a muffle furnace, and calcine it at 300°C in air for 4 hours to obtain nano-spherical Fe2O3.

[0032] S2. Dissolve 10 g of LiOH in 50 ml of water, add 5 g of sodium carboxymethyl cellulose (CMC) to prepare a LiOH colloid, and then freeze-dry it in a freeze dryer at -60°C. Grind the freeze-dried LiOH colloid to obtain LiOH flocs. The purpose of adding CMC in this step is to prepare the LiOH colloid. After freeze-drying, the LiOH colloid becomes flocs, which are loose and porous, which is conducive to the subsequent reaction with nano-spherical Fe2O3.

[0033] S3. Use a mortar and pestle to thoroughly mix the nano-Fe2O3 prepared in step S1 with the LiOH flocs prepared in step S2 in a molar ratio of 1:5.5. Soak the mixed powder in acetonitrile solution for 10 hours. Then place the mixture in an XH-300UP microwave ultrasonic machine for 15 minutes. The microwave power is set to 220W. Then, heat the microwave-ultrasound-treated powder at 550℃ for 12 hours, with the heating rate controlled at 3℃min -1 The mixture is then heated to 850°C and held for 35 hours before cooling to obtain Li5FeO4 (LFO) powder. The ultrasonic microwave treatment in this step is used to more evenly disperse and aggregate the nano-Fe2O3 on the LiOH flocs, facilitating subsequent calcination to produce high-purity LFO. The resulting LFO powder is stored in an argon-controlled box to prevent reaction with moisture and carbon dioxide.

[0034] S4, weigh Li(Ni 0.4 Co 0.3 Mn 0.3 )O2: The Li5FeO4 prepared in step S3 is mixed evenly and used as a cathode material containing Li5FeO4.

[0035] S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as the cathode sheet. Commercial SiO: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as the anode sheet. The resulting mixture is then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue-light working instrument. Both the electrode coating and battery assembly in this step must be completed in a dry room to ensure a dry environment for battery production.

[0036] Comparative Example 1: Except that 50 ml of ethylene glycol and 0.5 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) were not added in step S1, the rest were the same as in Example 1.

[0037] Figure 1This is a scanning electron microscope (SEM) image of the nano-spherical Fe2O3 prepared in Example 1 of the present invention. Figure 2 This is an SEM image of the nano-spherical Fe2O3 prepared in Comparative Example 1 of the present invention. It can be seen from the figure that the nano-spherical Fe2O3 prepared in Example 1 is more evenly dispersed and has fewer surface impurities. The nano-spherical Fe2O3 prepared in Comparative Example 1 is more agglomerated. The evenly dispersed nano-spherical Fe2O3 is more conducive to subsequent mixing with LiOH flocs to produce Li5FeO4 pre-lithium agent according to the molar ratio. Severely agglomerated Fe2O3 and LiOH flocs are more likely to generate impurities such as Li5Fe5O8 after reaction.

[0038] Example 2

[0039] S1. Soak 5 g of spherical high-purity iron powder in 50 ml of ethylene glycol and 80 ml of water, ultrasonically vibrate for 60 minutes, let it stand for 24 hours, then centrifuge to separate the upper liquid, dry it in an 80°C oven for 10 hours, grind the dried iron powder with 1 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) evenly, then place it in a muffle furnace, and calcine it at 500°C in air for 6 hours to obtain nano-spherical Fe2O3.

[0040] S2. 18 g of LiOH was dissolved in 80 ml of water, and 8 g of sodium carboxymethyl cellulose (CMC) was added thereto to prepare a LiOH colloid. The mixture was then freeze-dried in a freeze dryer at -60°C, and the freeze-dried LiOH colloid was crushed to obtain a LiOH floc. The purpose of adding CMC in this step is to prepare the LiOH colloid. After freeze-drying, the LiOH colloid becomes a flocculent substance that is loose and porous, which is conducive to the subsequent reaction with the nano-spherical Fe2O3.

[0041] S3. Use a mortar and pestle to thoroughly mix the nano-Fe2O3 prepared in step S1 with the LiOH flocs prepared in step S2 in a molar ratio of 1:6. Soak the mixed powder in acetonitrile solution for 10 hours. Then place the mixture in an XH-300UP microwave ultrasonic machine for 20 minutes. The microwave power is set to 320W. Then, heat the microwave-ultrasound-treated powder at 750℃ for 18 hours, with the heating rate controlled at 5℃min. -1 The mixture is then heated to 900°C and held for 40 hours before cooling to obtain Li₅FeO₄ (LFO) powder. The ultrasonic microwave treatment in this step is used to more evenly disperse and aggregate the nano-Fe₂O₃ on the LiOH flocs, facilitating subsequent calcination to produce high-purity LFO. The resulting LFO powder is stored in an argon-controlled box to prevent reaction with moisture and carbon dioxide.

[0042] S4, weigh Li(Ni 0.4 Co 0.3 Mn 0.3 )O2: The Li5FeO4 prepared in step S3 is mixed evenly and used as a cathode material containing Li5FeO4.

[0043] S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as the cathode sheet. Commercial SiO: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as the anode sheet. The resulting mixture is then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue-light working instrument. Both the electrode coating and battery assembly in this step must be completed in a dry room to ensure a dry environment for battery production.

[0044] Comparative Example 2: Except that the Li5FeO4 prepared in step S3 is not added in step S4, the rest are the same as in Example 2.

[0045] Figure 3 SiO anode and Li(Ni 0.4 Co 0.3 Mn 0.3 )O2 cathode pairing (Comparative Example 2). SiO half-cell and Li(Ni 0.4 Co 0.3 Mn 0.3 )O2 half-cell experimental voltage curve. Due to the difference in coulombic efficiency and initial capacity loss in the first cycle, the Li(Ni 0.4 Co 0.3 Mn 0.3 A considerable portion of the lithium extracted from the )O2 cathode is used for irreversible reactions in the SiO anode. The loss of lithium in the irreversible reaction leads to low lithium utilization in the reversible cycle, thereby reducing the capacity of the battery. Figure 4 SiO anode and Li(Ni 0.4 Co 0.3 Mn 0.3 )O2 and Li5FeO4 mixed cathode pairing (Example 2). Li5FeO4 produces lithium through irreversible reaction in the first charge, effectively providing additional lithium, which is consumed by irreversible reaction at the first charge of SiO2. It can achieve nearly full utilization of the Li(Ni 0.4 Co 0.3 Mn 0.3 )O2 cathode. This proves that the Li5FeO4 prepared by the present invention can be used as a pre-lithiation agent to achieve the role of lithium supplementation.

[0046] Example 3

[0047] S1. Soak 3-5g of spherical high-purity iron powder in 50ml of ethylene glycol and 80ml of water, ultrasonically vibrate for 50min, let it stand for 16h, then centrifuge to separate the upper liquid, dry it in a 70℃ oven for 13h, grind the dried iron powder with 0.8g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) evenly, then place it in a muffle furnace, and calcine it at 400℃ in air for 5h to obtain nano-spherical Fe2O3.

[0048] S2. Dissolve 17 g of LiOH in 60 ml of water, add 7 g of sodium carboxymethyl cellulose (CMC) to prepare a LiOH colloid, and then freeze-dry it in a freeze dryer at -60°C. Grind the freeze-dried LiOH colloid to obtain LiOH flocs. The purpose of adding CMC in this step is to prepare the LiOH colloid. After freeze-drying, the LiOH colloid becomes flocs, which are loose and porous, which is conducive to the subsequent reaction with the nano-spherical Fe2O3.

[0049] S3. Use a mortar and pestle to thoroughly mix the nano-Fe2O3 prepared in step S1 with the LiOH flocs prepared in step S2 in a molar ratio of 1:5.5. Soak the mixed powder in acetonitrile solution for 10 hours. Then place the mixture in an XH-300UP microwave ultrasonic machine for 16 minutes. The microwave power is set to 280W. Then, heat the microwave-ultrasonicated powder at 650℃ for 16 hours with a heating rate of 4℃min -1 The mixture is then heated to 880°C and held for 38 hours before cooling to obtain Li5FeO4 (LFO) powder. The ultrasonic microwave treatment in this step is used to more evenly disperse and aggregate the Fe2O3 nanoparticles on the LiOH flocs, facilitating subsequent calcination to produce high-purity LFO. The resulting LFO powder is stored in an argon-controlled box to prevent reaction with moisture and carbon dioxide.

[0050] S4. Lithium iron phosphate and Li5FeO4 prepared in step S3 are weighed in a mass ratio of 10:1 and mixed evenly to form a cathode material containing Li5FeO4.

[0051] S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as the cathode sheet. Commercial SiO: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as the anode sheet. The resulting mixture is then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue-light working instrument. Both the electrode coating and battery assembly in this step must be completed in a dry room to ensure a dry environment for battery production.

[0052] Comparative Example 3: Except that commercial Li5FeO4 is used in step S4 instead of Li5FeO4 prepared in step S3, the rest are the same as Example 3.

[0053] Figure 5 The voltage-mass specific capacity curves of full batteries prepared for Comparative Example 3 and Example 3 of the present invention are shown. As can be seen from the figure, compared with the full battery prepared in Comparative Example 3, the full battery prepared in Example 3 shows an increased first cycle charge and discharge capacity. The battery capacity of the full battery prepared in Example 3 is high. The addition of commercial Li5FeO4 cannot completely achieve the lithium replenishment effect of Li5FeO4 prepared in the present invention. Example 3 significantly increases the lithium utilization rate of the positive electrode material by 22.5% compared with the positive electrode material of Comparative Example 3, and increases the discharge capacity of the battery by 11.2%, which has a significant beneficial effect on battery lithium replenishment.

[0054] Example 4

[0055] S1. Soak 4.5 g of spherical high-purity iron powder in 50 ml of ethylene glycol and 80 ml of water, ultrasonically vibrate for 50 minutes, let it stand for 18 hours, then centrifuge to separate the upper liquid, dry it in a 70°C oven for 13 hours, grind the dried iron powder with 0.9 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) evenly, then place it in a muffle furnace, and calcine it at 400°C in air for 5 hours to obtain nano-spherical Fe2O3.

[0056] S2. Dissolve 17 g of LiOH in 70 ml of water, add 7 g of sodium carboxymethyl cellulose (CMC) to prepare a LiOH colloid, and then freeze-dry it in a freeze dryer at -60°C. Grind the freeze-dried LiOH colloid to obtain LiOH flocs. The purpose of adding CMC in this step is to prepare the LiOH colloid. After freeze-drying, the LiOH colloid becomes flocs, which are loose and porous, which is conducive to the subsequent reaction with the nano-spherical Fe2O3.

[0057] S3. Use a mortar and pestle to thoroughly mix the nano-Fe2O3 prepared in step S1 with the LiOH flocs prepared in step S2 in a molar ratio of 1:6. Soak the mixed powder in acetonitrile solution for 10 hours. Then place the mixture in an XH-300UP microwave ultrasonic machine for 18 minutes. The microwave power is set to 310W. Then, heat the microwave-ultrasound-treated powder at 720℃ for 16 hours, with the heating rate controlled at 4℃min -1 The mixture is then heated to 890°C and held for 38 hours before cooling to obtain Li5FeO4 (LFO) powder. The ultrasonic microwave treatment in this step is used to more evenly disperse and aggregate the nano-Fe2O3 on the LiOH flocs, facilitating subsequent calcination to produce high-purity LFO. The resulting LFO powder is stored in an argon-controlled box to prevent reaction with moisture and carbon dioxide.

[0058] S4, weigh Li(Ni 0.4 Co 0.3 Mn 0.3 )O2: The Li5FeO4 prepared in step S3 is mixed evenly and used as a cathode material containing Li5FeO4.

[0059] S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as the cathode sheet. Commercial SiO: acetylene black: polytetrafluoroethylene are mixed uniformly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as the anode sheet. The resulting mixture is then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue-light working instrument. Both the electrode coating and battery assembly in this step must be completed in a dry room to ensure a dry environment for battery production.

[0060] In the present invention, the first coulombic efficiency = first discharge specific capacity / first charge specific capacity × 100%. In the half-cell experiment, the higher the first charge specific capacity and the lower the first discharge specific capacity, the better the irreversibility of the material, which is more conducive to solving the problems of battery reversible capacity and first efficiency decline caused by the first charge and discharge.

[0061] Table 1 The first coulombic efficiency of the full battery prepared by the present invention

[0062] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 First effect 98.3±0.8 96.3±0.3 97.4±0.6 98.9±0.7 78.2±0.8 80.3±0.3 88.3±0.7

[0063] Table 1 shows the first coulombic efficiency of the full battery prepared by the present invention. From the overall comparison, it can be seen that the first coulombic efficiency after lithium replenishment using Li5FeO4 prepared by the present invention is close to 100%. The comparison of the first coulombic efficiency of Example 3 and Comparative Example 3 shows that the lithium replenishment effect of commercial Li5FeO4 is not as good as that of Li5FeO4 prepared by the present invention.

[0064] The above-described embodiments merely represent specific implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of protection of the present invention. It should be noted that, for those skilled in the art, any changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention are equivalent replacements and are included within the scope of protection of the present invention.

Claims

1. A process for preparing the pre-lithiation agent lithium ferrite Li5FeO4, characterized in that: The specific steps are as follows: S1. Soak 3-5 g of spherical high-purity iron powder in 50 ml of ethylene glycol and 80 ml of water, ultrasonically shake for 40-60 min, let it rest for 10-24 h, then centrifuge and dry it in an oven at 60-80 °C for 10-15 h. Grind the dried iron powder with 0.5-1 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, then place it in a muffle furnace and calcine it at 300-500 °C in air for 4-6 h to obtain nano-spherical Fe2O3. S2. Dissolve 10-18 g of LiOH in 50-80 ml of water, add 5-8 g of sodium carboxymethyl cellulose to prepare a LiOH colloid, and then freeze-dry it in a freeze dryer at -60°C. Grind the freeze-dried LiOH colloid to obtain LiOH floccules; S3. Use a mortar and pestle to completely mix the nano-Fe2O3 prepared in step S1 and the LiOH flocs prepared in step S2 in a molar ratio of 1:5.5 or 1:

6. Soak the mixed powder in acetonitrile solution for 10 hours. Then, place the mixture in an XH-300UP microwave ultrasonic oven for 15-20 minutes. The microwave power is set to 220-320 W. Then, heat the microwave-ultrasonicated powder at 550-750 °C for 12-18 hours, and control the heating rate at 3-5 °C min -1 Then continue heating to 850-900℃ and keep it for 35-40 hours, then cool it down to obtain Li5FeO4 powder; S4. Weigh the positive electrode material and the Li5FeO4 prepared in step S3 in a mass ratio of 10:1 or 15:2, mix them evenly and use them as the cathode material containing Li5FeO4; S5. The cathode material containing Li5FeO4 prepared in step S4: acetylene black: polytetrafluoroethylene are mixed evenly in a mass ratio of 9:0.5:0.5, and then evenly coated on aluminum foil to serve as a cathode sheet; commercial SiO: acetylene black: polytetrafluoroethylene are mixed evenly in a mass ratio of 8:1:1, and then evenly coated on copper foil to serve as an anode sheet, and then assembled into a CR2032 potassium ion battery, and its performance is tested on a blue electric working instrument; in this step, the coating of the electrode sheet and the assembly of the battery need to be completed in a drying room to ensure the dryness of the battery manufacturing environment.

2. The preparation process of the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 1, characterized in that: In step S1, the amount of spherical high-purity iron powder used is 5 g, and the ultrasonic oscillation time is 50 min.

3. The preparation process of the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 1 or 2, characterized in that: In step S1, 0.8 g of a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer was used.

4. The preparation process of the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 3, characterized in that: In step S2, 13 g of LiOH was dissolved in 60 ml of water, and 6 g of sodium carboxymethyl cellulose was added thereto.

5. The preparation process of the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 4, characterized in that: In step S3, the nano-Fe2O3 prepared in step S1 and the LiOH flocs prepared in step S2 were thoroughly mixed in a molar ratio of 1:6 using a mortar and pestle.

6. The preparation process of the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 5, characterized in that: In step S3, the mixture was placed in an XH-300UP and subjected to microwave ultrasound for 18 min, with the microwave power set to 280 W.

7. The process for preparing the pre-lithiation agent lithium ferrite Li5FeO4 according to claim 1, characterized in that: In step S3, the powder treated with microwave ultrasound was heated at 650 °C for 15 h, with the heating rate controlled at 3 °C min -1 , then continue heating to 880℃ and maintain for 35h.

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