A solid phase repair method for fluorine-containing lithium iron phosphate

Abstract

The present application relates to a kind of solid phase repair method of fluorine-containing lithium iron phosphate, it relates to lithium ion battery recycling technical field, the method includes: step S1, with lithium source, carbon source and composite modifier by mixing the waste lithium iron phosphate-based powder containing trace fluorine impurities;Wherein, the composite modifier includes at least two combinations in nano-aluminum oxide, titanate and boric acid;Step S2, the mixture of step S1 is carried out in reducing atmosphere and is sintered in stages, by the composite modifier in situ capture fluoride ion during sintering process and interface modification and lattice repair are carried out to lithium iron phosphate particle.Effective removal of residual fluorine (F) impurities in waste lithium iron phosphate powder, realizes the lithium supplement efficiency of waste lithium iron phosphate powder is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling technology, and in particular to a solid-phase remediation method for fluorinated lithium iron phosphate. Background Technology

[0002] With the explosive growth of lithium iron phosphate (LFP) batteries in electric vehicles and energy storage, the green recycling of spent lithium iron phosphate has become a focus of industry attention. Compared with traditional wet recycling (acid leaching-chemical precipitation-resynthesis), solid-phase direct remediation technology is considered the optimal path to achieve closed-loop recycling of lithium batteries due to its significant advantages such as shorter process, lower energy consumption, less chemical reagent consumption, and lower carbon emission intensity.

[0003] In existing industrial practices of direct remediation, residual fluorine (F) impurities in waste lithium iron phosphate powder are the core bottleneck limiting the performance of recycled materials. 1. Sources and hazards of fluorine: Even after initial washing, trace amounts of lithium fluoride (LiF) or electrolyte decomposition products inevitably remain on the surface and in the pores of the cathode powder. During the high-temperature sintering repair stage, these residual fluorides can easily react with the replenished lithium source, reducing the lithium replenishment efficiency. At the same time, the released hydrogen fluoride (HF) gas not only corrodes the sintering equipment but also damages the carbon coating layer on the surface of the lithium iron phosphate particles.

[0004] 2. Deterioration of interface performance: The presence of fluorine impurities will cause the formation of a lithium-phobic and high-resistivity inorganic layer on the surface of recycled particles, which will severely hinder the diffusion kinetics of lithium ions, resulting in the rate performance and long-cycle stability of recycled materials being far lower than those of virgin materials.

[0005] 3. Limitations of traditional methods: Simply adding excessive lithium or extending the sintering time cannot completely eliminate the interference of fluorine on lattice repair, and may instead lead to over-sintering of particles or a significant increase in energy consumption. Summary of the Invention

[0006] This invention provides a solid-phase remediation method for fluorinated lithium iron phosphate to solve the problem of residual fluorine (F) impurities in waste lithium iron phosphate powder reacting with the replenished lithium source, thereby reducing the lithium replenishment efficiency.

[0007] On one hand, the present invention provides a solid-phase remediation method for lithium iron phosphate containing fluorine, the method comprising: Step S1: Mix waste lithium iron phosphate powder containing trace amounts of fluorine impurities with a lithium source, a carbon source, and a composite modifier; wherein the composite modifier includes at least two combinations of nano-sized alumina, titanate, and boric acid. Step S2: The mixture from step S1 is sintered in segments under a reducing atmosphere. During the sintering process, the composite modifier captures fluoride ions in situ and performs interface modification and lattice repair on the lithium iron phosphate particles.

[0008] A further technical solution is that the composite modifier contains at least two of the following: a fluorine-capturing component, an interfacial coupling component, and a sintering fluxing component.

[0009] A further technical solution is that the fluorine capturing component is selected from metal oxides; the interface coupling component is selected from titanate coupling agents; and the sintering fluxing component is selected from boron compounds.

[0010] A further technical solution is that the amount of the composite modifier added is 0.3% to 1.5% of the mass of lithium iron phosphate powder.

[0011] The further technical solution is that, based on the mass of lithium iron phosphate powder, the amount of each component added is as follows: Fluorine capture component: 0.1%–0.5%; Interfacial coupling components: 0.05%–0.6%; Sintering fluxing component: 0.1%~0.4%.

[0012] A further technical solution is that the segmented sintering includes at least a low-temperature segment, a medium-temperature segment, and a high-temperature segment performed sequentially.

[0013] A further technical solution is that the low-temperature range is 200℃~450℃, which is used for the fluorine capturing component to react with fluoride ions to generate stable fluorides and achieve particle surface coating; the medium-temperature range is 550℃~650℃, which is used to reduce the solid-phase reaction energy barrier and promote lithium ion insertion into the lattice; and the high-temperature range is 700℃~750℃, which is used for the interface coupling component to guide the carbon source to form a dense and uniform conductive carbon layer.

[0014] A further technical solution is that the reducing atmosphere is nitrogen, argon, or a nitrogen-hydrogen mixture.

[0015] A further technical solution is that the lithium source is at least one of lithium carbonate, lithium hydroxide, or lithium oxalate.

[0016] On the other hand, the present invention also provides a lithium iron phosphate cathode material prepared by the solid-phase repair method of fluorinated lithium iron phosphate as described in any of the above embodiments.

[0017] The technical solutions provided in the embodiments of the present invention have the following advantages compared with the prior art: By continuously applying in-situ fluorine fixation, interfacial synergy, energy barrier modulation, and glass phase enhancement to the trace amounts of residual fluorine on the surface and pores of cathode powder, the problem of performance degradation caused by residual fluorine is not only solved, but also a qualitative leap in the conductivity and electrochemical lifetime of regenerated lithium iron phosphate materials is achieved, providing a brand-new technical route for the high-value direct repair of waste lithium batteries. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic flowchart of a solid-phase repair method for fluorinated lithium iron phosphate provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Figure 1 This is a schematic flowchart illustrating a solid-phase repair method for fluorinated lithium iron phosphate provided in an embodiment of the present invention. The solid-phase repair method for fluorinated lithium iron phosphate includes the following steps S1-S2.

[0023] S1, mixing waste lithium iron phosphate powder containing trace amounts of fluorine impurities with a lithium source, a carbon source, and a composite modifier; wherein the composite modifier includes at least two combinations of nano-sized alumina, titanate ester, and boric acid.

[0024] S2, the mixture from step S1 is sintered in stages under a reducing atmosphere, and the composite modifier captures fluoride ions in situ during the sintering process and performs interface modification and lattice repair on the lithium iron phosphate particles.

[0025] In a specific embodiment, waste lithium iron phosphate powder containing trace amounts of fluorine is used as the remediation target. Fluorine capture and interface modification are achieved through lithium source replenishment of the lattice lithium deficiency, carbon source reconstruction of the conductive network, and composite modifiers. Segmented sintering allows each component to function step-by-step, avoiding side reactions and improving the uniformity and integrity of the remediation. The composite modifier uses at least two of nano-alumina, titanate, and boric acid to achieve synergistic effects of fluorine fixation, interface coupling, and fluxing diffusion, ensuring a significant improvement in the performance of the recycled material.

[0026] In one embodiment, the composite modifier comprises at least two of a fluorine-capturing component, an interfacial coupling component, and a sintering fluxing component.

[0027] In a specific embodiment, the fluorine trapping component preferentially reacts with fluoride ions to achieve solid fluorine passivation; the interface coupling component improves the compatibility between the carbon source and lithium iron phosphate particles, reconstructing a uniform carbon layer; and the sintering fluxing component lowers the solid-phase reaction energy barrier, promoting lithium ion insertion into the lattice.

[0028] In one embodiment, the fluorine trapping component is selected from metal oxides; the interfacial coupling component is selected from titanate coupling agents; and the sintering fluxing component is selected from boron compounds.

[0029] In specific embodiments, metal oxides (preferably nano-alumina) have a high specific surface area and can react rapidly to generate stable fluorides in the early stage of fluoride ion escape; titanate coupling agents have both organic and inorganic affinity, which improves the uniformity and density of carbon coating; boron compounds (preferably boric acid) can form a micro-molten salt phase at low temperature, which promotes lithium diffusion and constructs a high ion transport interface layer.

[0030] In one embodiment, the amount of the composite modifier added is 0.3% to 1.5% of the mass of lithium iron phosphate powder.

[0031] In a specific embodiment, the composite modifier is added in trace amounts, with the total addition controlled at 0.3%~1.5%. This ensures sufficient fluorine fixation and interface modification without introducing excessive impurity phases, thus avoiding impact on the main structure and electrochemical performance of lithium iron phosphate. Too low an addition amount results in insufficient fluorine fixation and repair; too high an addition amount may lead to the formation of impurity phases, reducing specific capacity.

[0032] In one embodiment, the amount of each component added, based on the mass of lithium iron phosphate powder, is as follows: Fluorine trapping component: 0.1%–0.5%; sufficient to trap residual fluorine and form a stable AlF3 coating layer; Interfacial coupling components: 0.05%–0.6%; effectively improves interfacial compatibility and forms complete carbon coating; Sintering fluxing component: 0.1%–0.4%; lowers the reaction energy barrier, promotes lithium intercalation, and constructs a boron-based fast ion transport layer.

[0033] In one embodiment, the segmented sintering includes at least a low-temperature segment, a medium-temperature segment, and a high-temperature segment performed sequentially.

[0034] In one embodiment, the low-temperature range is 200°C to 450°C, used for the reaction of fluorine-capturing components with fluoride ions to generate stable fluorides and achieve particle surface coating; the medium-temperature range is 550°C to 650°C, used to reduce the solid-phase reaction energy barrier and promote lithium-ion insertion into the lattice; and the high-temperature range is 700°C to 750°C, used for the interface coupling components to guide the carbon source to form a dense and uniform conductive carbon layer.

[0035] In a specific embodiment, multi-stage temperature-controlled sintering is employed, allowing the composite modifier, lithium source, and carbon source to act in stages within temperature ranges. This avoids problems such as insufficient reaction, localized overheating, carbon layer oxidation, and increased fluorine interference caused by a single high temperature. At least three temperature zones can respectively achieve solid fluorine coating, lithium diffusion embedding, and carbon layer reconstruction.

[0036] In one embodiment, the reducing atmosphere is nitrogen, argon, or a nitrogen-hydrogen mixture.

[0037] In a specific embodiment, the sintering process is carried out under an inert or weakly reducing atmosphere to prevent carbon source oxidation and avoid Fe from forming in lithium iron phosphate. 2+ It is oxidized into a heterogeneous phase, ensuring the stability of the material's structure and electrochemical performance. Commonly used atmospheres include high-purity nitrogen, argon, and nitrogen-hydrogen mixtures (with stronger reducing properties).

[0038] In one embodiment, the lithium source is at least one of lithium carbonate, lithium hydroxide, or lithium oxalate.

[0039] In a specific embodiment, a commonly used, easily dispersed, and thermally stable lithium compound is selected, which can effectively release Li+ during the sintering process to replenish the missing lithium in the waste lithium iron phosphate lattice, thereby achieving lattice reconstruction and capacity recovery.

[0040] The embodiments of the present invention can achieve the following advantages: By continuously applying in-situ fluorine fixation, interfacial synergy, energy barrier modulation, and glass phase enhancement to the trace amounts of residual fluorine on the surface and pores of cathode powder, the problem of performance degradation caused by residual fluorine is not only solved, but also a qualitative leap in the conductivity and electrochemical lifetime of regenerated lithium iron phosphate materials is achieved, providing a brand-new technical route for the high-value direct repair of waste lithium batteries.

[0041] The following are comparative examples and experimental embodiments: Comparative Example 1: Take 10 grams of surface-defluorinated lithium iron phosphate electrode powder, add 10% glucose and 5% lithium carbonate, heat to 720℃ and sinter for 4 hours under nitrogen atmosphere, and perform 0.1C and 5C coin cell specific capacity tests, 1C 100-cycle capacity retention rate test, and charge transfer resistance test.

[0042] Comparative Example 2: Based on Comparative Example 1, 0.3% nano-alumina was added, and the mixture was sintered at 720℃ for 4 hours under a nitrogen atmosphere. The coin cell specific capacity was tested at 0.1C and 5C, the capacity retention rate was tested after 100 cycles at 1C, and the charge transfer resistance was tested.

[0043] Example 1: Based on Comparative Example 2, 0.2% tetrabutyl titanate and 0.3% boric acid were added, and the mixture was sintered at 720°C for 4 hours under a nitrogen atmosphere. The coin cell specific capacity was tested at 0.1C and 5C, the capacity retention rate was tested after 100 cycles at 1C, and the charge transfer resistance was tested.

[0044] Example 2: Based on Example 1, the sample was sintered at 400°C for 2 hours under a nitrogen atmosphere, then sintered at 720°C for 4 hours. The sample was then subjected to 0.1C and 5C coin cell specific capacity tests, 1C 100-cycle capacity retention rate tests, and charge transfer resistance tests.

[0045] Example 3: Based on Example 1, the sample was sintered at 600°C for 4 hours under a nitrogen atmosphere, then sintered at 720°C for another 4 hours. The sample was then subjected to 0.1C and 5C coin cell specific capacity tests, 1C 100-cycle capacity retention rate tests, and charge transfer resistance tests.

[0046] Example 4: Based on Example 1, the temperature was raised to 400°C and sintered for 2 hours under a nitrogen atmosphere, then raised to 600°C and sintered for 4 hours, and finally raised to 720°C and sintered for 4 hours. The 0.1C and 5C coin cell specific capacity tests, the 1C 100-cycle capacity retention rate test, and the charge transfer resistance test were performed.

[0047] To further illustrate the effects of the present invention, the specific capacitance, capacity retention rate, and charge transfer resistance of Examples 1-4 and Comparative Examples 1-2 were tested. The test results are shown in Table 1.

[0048] 1. Specific capacity and capacity retention test Charge at a constant current of 0.1C to 3.7V, then charge at a constant voltage of 3.7V until the current drops to 0.02C; let stand for 5 minutes; discharge at 0.1C to 2.0V and let stand for 5 minutes. Charge at a constant current of 1C to 3.7V, then charge at a constant voltage of 3.7V until the current drops to 0.02C; let stand for 5 minutes; discharge at 1C to 2.0V and let stand for 5 minutes. Repeat the above process 100 times.

[0049] 2. Charge transfer resistance test The charge transfer resistance was measured using an electrochemical workstation before and after 100 cycles at 1C, and the values ​​were R0 and R1, respectively. ct 1 and R ct 2.

[0050]

[0051] Table 1 Data from Comparative Examples 1 and 2 show that the specific capacity significantly improved after the addition of nano-alumina, indicating that residual fluorine was captured by alumina to form a stable compound, which is beneficial for lattice repair. The charge transfer resistance decreased after 100 cycles, and the capacity retention was significantly improved. In Example 1, the addition of tetrabutyl titanate and boric acid, followed by sintering, formed a dense carbon coating layer, which improved electronic conductivity and further increased the specific capacity.

[0052] In Example 2, sintering at a low temperature promoted the reaction between residual fluorine and nano-alumina, significantly improving cycle stability.

[0053] In Example 3, after sintering at a medium temperature, boric acid formed a micro-molten salt phase, which promoted the diffusion of lithium ions into the crystal lattice, and the charge transfer resistance was significantly reduced after 100 cycles.

[0054] Example 4 involves sintering at three temperature stages, which effectively captures trace amounts of fluorine to form a stable aluminum fluoride coating on the particle surface, improving 1C cycle performance; a boron-based interface layer with excellent lithium-ion transport characteristics is formed, promoting rapid diffusion of lithium ions into the lattice and significantly improving 5C rate performance; tetrabutyl titanate induces the carbon source to form a dense and uniform conductive carbon layer, improving electronic conductivity and significantly increasing specific capacity.

[0055] This invention also provides a lithium iron phosphate cathode material prepared by the solid-phase repair method of fluorinated lithium iron phosphate as described in any of the above embodiments.

[0056] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Since these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations.

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A solid-phase remediation method for fluorinated lithium iron phosphate, characterized in that, The method includes: Step S1: Mix waste lithium iron phosphate powder containing trace amounts of fluorine impurities with a lithium source, a carbon source, and a composite modifier; wherein, the composite modifier contains a fluorine-capturing component, and the composite modifier also contains at least one of an interfacial coupling component and a sintering fluxing component; the fluorine-capturing component is selected from metal oxides; the interfacial coupling component is selected from titanate coupling agents; the sintering fluxing component is selected from boron compounds; the metal oxide is nano-sized alumina; the titanate coupling agent is tetrabutyl titanate; and the boron compound is boric acid; Step S2: The mixture from Step S1 is sintered in stages under a reducing atmosphere. During the sintering process, the composite modifier captures fluoride ions in situ and modifies the interface and repairs the lattice of the lithium iron phosphate particles. The staged sintering includes at least a low-temperature stage, a medium-temperature stage, and a high-temperature stage performed sequentially. The low-temperature stage is 200℃ to 450℃, used for the fluoride capturing component to react with fluoride ions to generate stable fluorides and achieve particle surface coating. The medium-temperature stage is 550℃ to 650℃, used to reduce the solid-state reaction energy barrier and promote lithium-ion insertion into the lattice. The high-temperature stage is 700℃ to 750℃, used for the interface coupling component to guide the carbon source to form a dense and uniform conductive carbon layer.

2. The method according to claim 1, characterized in that, The amount of the composite modifier added is 0.3% to 1.5% of the mass of lithium iron phosphate powder.

3. The method according to claim 1, characterized in that, The amount of each component added, based on the mass of lithium iron phosphate powder, is as follows: Fluorine capture component: 0.1%–0.5%; Interfacial coupling components: 0.05%–0.6%; Sintering fluxing component: 0.1%~0.4%.

4. The method according to claim 1, characterized in that, The reducing atmosphere is a nitrogen-hydrogen mixture.

5. The method according to claim 1, characterized in that, The lithium source is at least one of lithium carbonate, lithium hydroxide, or lithium oxalate.

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