Method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder

Abstract

The invention belongs to the technical field of recovery of retired / waste lithium ion batteries, and particularly discloses a method for preparing a lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder, which comprises the following steps: (1) preparing waste lithium iron phosphate powder; (2) adding a lithium source, a manganese source and a phosphorus source into the mixture, and mixing, so that the element molar ratio of Li to Fe to Mn to P in the mixture is (1.0-1.2): (0.1-0.9): (0.9-0.1): 1; and (3) carrying out hydrothermal treatment or heating solid-phase treatment on the mixture in a protective atmosphere to obtain the lithium iron manganese phosphate positive electrode material. According to the method, the decommissioned / waste lithium iron phosphate positive electrode material is taken as a raw material, the lithium iron manganese phosphate positive electrode material is obtained through regeneration under the condition that a decommissioned lithium iron phosphate olivine crystal structure is not damaged, all components in the lithium iron phosphate waste material are utilized to the maximum extent, and the process is low in energy consumption, simple in flow and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling retired / wasted lithium-ion batteries, and more specifically, relates to a method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder. Background Art

[0002] With the widespread application of electric vehicles, mobile communications, energy storage power stations and renewable energy, the demand for batteries is growing year by year. Recycling and reuse are considered an important part of sustainable development in this field. Among them, the recycling and reuse of lithium-ion batteries is an important research direction.

[0003] In the context of lithium iron phosphate battery recycling, lithium manganese iron phosphate batteries have a higher working potential (Li + / Li, 4.0V), high energy density and long cycle life have attracted much attention. At present, there are several main ways to regenerate lithium iron phosphate waste powder into lithium manganese iron phosphate. One is to oxidize and remove impurities and then mix the materials in proportion, and then obtain the lithium iron manganese phosphate positive electrode material through a high-temperature calcination process. The invention with application number CN202310235408.6 is named "A method for preparing lithium iron manganese phosphate positive electrode material from waste lithium iron phosphate powder", and a method for recycling after oxidative calcination using waste lithium iron phosphate powder is disclosed. This method involves two-step high-temperature treatment, high energy consumption, and complicated steps; the invention with application number CN202410280450.4 is named "A method for preparing lithium iron manganese phosphate positive electrode material from waste lithium iron phosphate", and it is disclosed that after oxidative calcination of waste lithium iron phosphate, manganese source, phosphorus source and carbon source are simultaneously supplemented for sintering treatment. This method additionally introduces a carbon source as a reducing agent (the introduction of the reducing agent can avoid the change of valence state of iron element during oxidative calcination) and coats the product to form a carbon coating layer, and the performance of the prepared lithium iron manganese phosphate positive electrode material needs to be improved. In addition, oxidative calcination of lithium iron phosphate will destroy its olivine crystal structure, cause structural phase separation, and even completely convert it into non-olivine crystal structure substances such as Li3Fe2(PO4)3 and iron phosphate, making it more difficult to synthesize lithium manganese iron phosphate with an olivine crystal structure; secondly, after oxidation, the elements are leached out of the solution to obtain the corresponding salt, and the product is obtained by adding materials in proportion and then calcining at high temperature. The invention with application number CN202111342244.4 is named "A method for recovering lithium iron phosphate waste powder to prepare lithium manganese iron phosphate", and a method for preparing lithium manganese iron phosphate by obtaining a precursor raw material through acid leaching is disclosed. This method uses an acid leaching process to convert lithium iron phosphate into iron phosphate, which will produce more waste liquid and increase the environmental protection treatment cost in the production process. In addition, there are also patents that propose to sinter a mixture of retired lithium iron phosphate with precursors such as lithium iron manganese phosphate and lithium manganese phosphate. The invention name of application number CN202311856954.8 is "A method for preparing lithium iron manganese phosphate by a solid phase method from recycled lithium iron phosphate". It discloses a method for sintering a lithium iron manganese phosphate precursor using iron phosphate as an iron source and a phosphorus source and a second carbon source, and then mixing the precursor with retired lithium iron phosphate and a first carbon source and sintering it a second time. The precursor sintering of this method is close to the synthesis of new materials. Retired lithium iron phosphate is not used as the main raw material. Instead, iron phosphate that is not directly obtained from retired batteries is used as a lithium source and a phosphorus source for the synthesis of precursor materials. In addition, the two carbon coating treatments may also make the transmission of manganese and iron ions difficult, increasing the difficulty and cost of regeneration. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder, wherein the overall process design is improved, and retired / abandoned lithium iron phosphate positive electrode material is used as raw material, and the lithium iron manganese phosphate positive electrode material is regenerated without destroying the retired lithium iron phosphate olivine crystal structure. The method of the present invention uses lithium iron phosphate waste powder as the main raw material for regeneration, and auxiliary addition of lithium source, phosphorus source, and manganese source, directly batching and mixing, and then recycling, so as to maximize the utilization of each component in the lithium iron phosphate waste material. This process has low energy consumption, simple process and low cost. The method of the present invention has high atomic utilization efficiency, simplified process flow, convenient operation steps and excellent environmental compatibility.

[0005] To achieve the above object, according to one aspect of the present invention, a method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder is provided, characterized in that it comprises the following steps:

[0006] (1) dismantling retired and / or discarded lithium iron phosphate batteries, stripping active materials, and crushing to obtain waste lithium iron phosphate powder;

[0007] (2) Determine the proportions of Li, Fe, and P in the waste lithium iron phosphate powder obtained in step (1); then, based on the Fe element contained in the waste lithium iron phosphate powder, without introducing other Fe sources, add a lithium source, a manganese source, and a phosphorus source to the waste lithium iron phosphate powder to obtain a mixture, so that the molar ratio of Li:Fe:Mn:P in the mixture is (1.0-1.2):(0.1-0.9):(0.9-0.1):1;

[0008] (3) The mixture obtained in step (2) is treated by hydrothermal method or solid phase heating under protective atmosphere to obtain lithium manganese iron phosphate positive electrode material.

[0009] As a further preferred embodiment of the present invention, in step (3), the hydrothermal treatment is specifically a hydrothermal reaction at a temperature of 200-300° C. for 10-15 hours.

[0010] As a further preferred embodiment of the present invention, in step (3), the heating solid phase treatment adopts a two-stage sintering, wherein the first stage sintering is carried out at a temperature of 300-500°C for 1-24h, and the second stage sintering is carried out at a temperature of 600-750°C for 2-24h.

[0011] As a further preferred embodiment of the present invention, in step (3), the protective atmosphere is selected from nitrogen and argon.

[0012] As a further preferred embodiment of the present invention, in step (2), the lithium source is selected from lithium carbonate, lithium oxalate, lithium hydroxide, and lithium acetate;

[0013] The manganese source is selected from manganese oxide, manganese carbonate, manganese sulfate, and manganese acetate;

[0014] The phosphorus source is selected from ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0015] As a further preferred embodiment of the present invention, the method further comprises the steps of:

[0016] (4) The lithium iron manganese phosphate positive electrode material obtained in step (3) is subjected to carbon coating treatment to obtain a carbon-coated lithium iron manganese phosphate positive electrode material.

[0017] As a further preferred embodiment of the present invention, the carbon coating treatment is to mix the lithium manganese iron phosphate positive electrode material obtained in step (3) with a carbon source and then calcine under a protective atmosphere.

[0018] As a further preferred embodiment of the present invention, in step (4), the carbon source is sucrose or glucose, and the amount used is 5wt% to 25wt% of the lithium manganese iron phosphate positive electrode material;

[0019] The calcination is specifically carried out at a temperature of 200-400° C. for 2-4 hours, followed by treatment at a temperature of 300-500° C. for 2-4 hours.

[0020] As a further preferred embodiment of the present invention, in step (1), the crushing is performed so that the particle size D50 of the waste lithium iron phosphate powder is less than 20 μm; preferably, the crushing is performed so that the particle size D50 of the waste lithium iron phosphate powder is less than 5 μm.

[0021] As a further preferred embodiment of the present invention, in step (2), the mixing is specifically performed by ball milling;

[0022] Preferably, the ball milling mixing is wet ball milling mixing, using ethanol as a dispersant, the mixing speed is 200-500 rpm, and the mixing time is 2-12 hours.

[0023] Through the above technical scheme conceived by the present invention, compared with the prior art, the present invention provides a method for effectively converting waste lithium iron phosphate powder into lithium iron manganese phosphate positive electrode material for the recycling problem of lithium iron phosphate, directly using retired / abandoned lithium iron phosphate positive electrode material to prepare lithium iron manganese phosphate positive electrode material, using lithium iron phosphate waste with olivine crystal structure as a framework (using the Fe element contained in the waste lithium iron phosphate powder as the only Fe source, without introducing other iron sources), regenerating lithium iron manganese phosphate, the process does not destroy the olivine crystal structure, and can achieve the upgrading and recycling of battery positive electrode materials from lithium iron phosphate to iron manganese phosphate. In addition, unlike the direct regeneration of retired lithium iron phosphate materials into lithium iron phosphate with reduced performance and unable to meet the performance requirements of existing materials, the present invention realizes upgrading and recycling by regenerating retired lithium iron phosphate materials into lithium iron manganese phosphate materials, and the regenerated lithium iron manganese phosphate materials can meet the needs of the existing commercial level.

[0024] Specifically, the method of the present invention can achieve the following beneficial effects:

[0025] (1) Raw material utilization efficiency: The present invention uses retired lithium iron phosphate electrode material as the main raw material, and auxiliary lithium source, manganese source, and phosphorus source are added, and retired lithium iron phosphate is used as the only iron source; the conductive carbon in the retired lithium iron phosphate material can be used as an auxiliary carbon source, and no additional carbon source can be added, so as to maximize the utilization of each component of the retired lithium iron phosphate material and achieve a better material utilization rate. The present invention expects that the regenerated lithium iron manganese phosphate material belongs to the olivine crystal structure, and the iron phosphate crystal structure formed by degradation in the retired lithium iron phosphate maintains the olivine structure. If other iron sources are introduced (such as the common iron phosphate, ferrous oxalate, and ferrous acetate in other patents are not olivine crystal structures, and commercial lithium iron phosphate is also a monoclinic system), different crystal structures lead to more energy consumption in the process of synthesizing lithium iron manganese phosphate, resulting in the synthesis of easy generation of heterogeneous products, which will make the performance of the regenerated product unsatisfactory; therefore, the method of the present invention uses retired lithium iron phosphate as the only iron source, so that it can better play the advantage of the iron phosphate crystal structure in the retired lithium iron phosphate as the olivine structure.

[0026] (2) Process simplification: The present invention has a simple process flow. After the raw materials are mixed, a hydrothermal method or a heating solid phase treatment under a protective atmosphere (especially a one-step two-stage sintering treatment) is used. There is no intermediate synthesis process, which can shorten the production cycle and reduce production costs and energy consumption.

[0027] During the regeneration process, the present invention uses retired lithium iron phosphate that still maintains an olivine crystal structure as the main raw material, does not destroy its crystal structure, and uses the raw material crystal structure as a template to achieve lithium iron manganese phosphate crystal growth. Compared with lithium iron phosphate with destroyed olivine crystal structure after commercial iron phosphate, leached iron phosphate, or high-temperature oxidation calcination treatment, the non-structural reconstruction process presented by the method is conducive to the growth of lithium iron manganese phosphate crystals with the same olivine structure, and the electrochemical properties of the regenerated lithium iron manganese phosphate material can meet the level of commercial lithium iron manganese phosphate.

[0028] The method of the present invention adopts retired lithium iron phosphate materials. Different from directly regenerating retired lithium iron phosphate materials into lithium iron phosphate with degraded performance and unable to meet the performance requirements of existing materials, the present invention realizes upgraded recycling by regenerating retired lithium iron phosphate materials into lithium iron manganese phosphate materials. The regenerated lithium iron manganese phosphate materials can meet the requirements of existing commercial levels.

[0029] (3) Environmental performance: By adopting environmentally friendly reaction conditions and materials, during the sintering process, residual substances such as PVDF and conductive carbon black are used as auxiliary carbon sources and dopants in the inert gas atmosphere to participate in the process of converting lithium iron phosphate into lithium manganese iron phosphate. Therefore, no additional impurity removal treatment is required, which reduces environmental pollution and conforms to the concept of green chemistry.

[0030] (4) Economic benefits: This method uses low-priced and widely available retired lithium iron phosphate as the main raw material, which has a low raw material cost and provides an economical and effective way to recycle waste lithium iron phosphate battery materials, thereby increasing the reuse value of industrial waste.

[0031] In summary, the present invention uses waste lithium iron phosphate positive electrode materials as the main raw materials, and adopts a one-step hydrothermal method or a one-step sintering process after mixing, which not only optimizes the disposal process of waste lithium iron phosphate positive electrode materials, but also provides a new method for producing high-performance lithium iron manganese phosphate positive electrode materials, which is beneficial to promoting waste resource utilization and sustainable development of battery materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The SEM (scanning electron microscope) images of the prepared lithium manganese iron phosphate positive electrode material 1 at different magnifications. The scale in the figure represents 1 μm.

[0033] Figure 2 This is the XRD (X-ray diffraction) spectrum of the prepared lithium manganese iron phosphate positive electrode material 1.

[0034] Figure 3 The charge and discharge curve of the prepared lithium manganese iron phosphate positive electrode material 1 at a current density of 0.1C.

[0035] Figure 4This is a cycle performance diagram of the prepared lithium manganese iron phosphate positive electrode material 1 at a current density of 0.5C.

[0036] Figure 5 This is a rate performance diagram of the prepared lithium manganese iron phosphate positive electrode material 1.

[0037] Figure 6 This is the charge / discharge specific energy diagram of the prepared lithium manganese iron phosphate positive electrode material 1 at a current density of 0.1C.

[0038] Figure 7 The SEM (scanning electron microscope) images of the prepared lithium manganese iron phosphate positive electrode material 2 at different magnifications. The scale in the figure represents 1 μm.

[0039] Figure 8 This is the XRD (X-ray diffraction) spectrum of the prepared lithium manganese iron phosphate positive electrode material 2.

[0040] Fig. 9 The charge and discharge curve of the prepared lithium manganese iron phosphate positive electrode material 2 at a current density of 0.1C.

[0041] Fig.10 This is a diagram of the cycling performance of the prepared lithium manganese iron phosphate positive electrode material 2 at a current density of 0.5C.

[0042] Fig.11 This is a rate performance diagram of the prepared lithium manganese iron phosphate positive electrode material 2.

[0043] Fig.12 This is the charge / discharge specific energy diagram of the prepared lithium manganese iron phosphate positive electrode material 2 at a current density of 0.1C.

[0044] Fig.13 The SEM (scanning electron microscope) images of the prepared lithium manganese iron phosphate positive electrode material 3 at different magnifications. The scale in the figure represents 1 μm.

[0045] Fig.14 This is the XRD (X-ray diffraction) spectrum of the prepared lithium manganese iron phosphate positive electrode material 3.

[0046] Fig.15 The charge and discharge curve of the prepared lithium manganese iron phosphate positive electrode material 3 at a current density of 0.1C.

[0047] Fig.16 This is a cycle performance diagram of the prepared lithium manganese iron phosphate positive electrode material 3 at a current density of 0.5C.

[0048] Fig.17 This is a rate performance diagram of the prepared lithium manganese iron phosphate positive electrode material 3.

[0049] Fig.18 This is the charge / discharge specific energy diagram of the prepared lithium manganese iron phosphate positive electrode material 3 at a current density of 0.1C. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] The SOH (i.e., state of health) of the used batteries used in the following examples is measured by using a battery testing system, an electrochemical workstation, etc. to measure the actual capacity and conduct an SOH estimation test (SOH is approximately equal to the ratio of the actual capacity to the theoretical capacity). SOH indicates the health of the battery, that is, the percentage of the current performance of the battery relative to the performance of a new battery. SOH is used to evaluate the aging degree and remaining service life of the battery. It is generally believed in the industry that when the SOH drops to 80%, the battery can be retired or disposed of.

[0052] The waste lithium iron phosphate powder obtained by disassembling and crushing in the embodiments below can be determined by inductively coupled plasma emission spectrometry (ICP-AES) to determine the proportion of Li, Fe, and P elements therein. The crushing operation used in the embodiments below, like the conventional operation in the prior art, is to crush the waste lithium iron phosphate powder to a particle size D50 <5μm (of course, it can also be crushed to a particle size D50 <20μm). The mixing operation used in the embodiments below is to use ethanol as a dispersant for wet ball milling, the ball milling speed is 350rpm, and the ball milling time is 6h (of course, the ball milling speed of the wet ball milling can also be other speeds of 200-500rpm, and the ball milling time can be other time lengths of 2-12h; of course, in addition to ball milling, other mixing operations known in the prior art can also be used).

[0053] The following are specific embodiments:

[0054] Embodiment 1

[0055] (1) Dismantle the waste batteries with SOH=90%, peel off the active materials, crush them, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0056] (2) The powder obtained in step (1) is mixed with lithium hydroxide, manganous oxide and diammonium hydrogen phosphate, and the molar ratio of the elements in the mixed powder is Li:Fe:Mn:P=1.05:0.6:0.4:1.

[0057] (3) The mixture obtained in step (2) is placed in a hydrothermal reactor and treated at 300° C. for 10 h. After filtering and drying, a lithium manganese iron phosphate positive electrode material is obtained, which is recorded as lithium manganese iron phosphate positive electrode material 1.

[0058] Embodiment 2

[0059] (1) Dismantle the SOH=10% waste battery, peel off the active material, crush it, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0060] (2) The powder obtained in step (1) is mixed with lithium hydroxide, manganese acetate tetrahydrate and diammonium hydrogen phosphate, and the molar ratio of each element in the mixed powder is Li:Fe:Mn:P=1.05:0.7:0.3:1.

[0061] (3) The mixture obtained in step (2) was sintered under argon protection at 500° C. for 3 hours and then at 750° C. for 6 hours to obtain a lithium iron manganese phosphate positive electrode material, which was recorded as lithium iron manganese phosphate positive electrode material 2.

[0062] Embodiment 3

[0063] (1) Dismantle the SOH=70% waste battery, peel off the active material, crush it, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0064] (2) The powder obtained in step (1) is mixed with lithium hydroxide, manganous oxide and ammonium dihydrogen phosphate, and the molar ratio of the elements in the mixed powder is Li:Fe:Mn:P=1.05:0.66:0.34:1.

[0065] (3) The mixture obtained in step (2) was sintered under nitrogen protection at 450° C. for 4 hours and then at 700° C. for 8 hours to obtain a lithium iron manganese phosphate positive electrode material, which was recorded as lithium iron manganese phosphate positive electrode material 3.

[0066] Embodiment 4

[0067] (1) Dismantle the SOH=10% waste battery, peel off the active material, crush it, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0068] (2) The powder obtained in step (1) is mixed with lithium acetate, manganese acetate and diammonium hydrogen phosphate, and the molar ratio of each element in the mixed powder is Li:Fe:Mn:P=1.05:0.5:0.5:1.

[0069] (3) The mixture obtained in step (2) is placed in a hydrothermal kettle and treated at 200° C. for 15 h. After filtering and drying, a lithium iron manganese phosphate positive electrode material is obtained, which is recorded as lithium iron manganese phosphate positive electrode material 4.

[0070] Embodiment 5

[0071] (1) Dismantle the SOH=60% waste battery, peel off the active material, crush it, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0072] (2) The powder obtained in step (1) is mixed with lithium carbonate, manganous oxide and ammonium dihydrogen phosphate, and the molar ratio of each element in the mixed powder is Li:Fe:Mn:P=1.03:0.9:0.1:1.

[0073] (3) The mixture obtained in step (2) was sintered under Ar gas protection at 450° C. for 4 hours and then at 700° C. for 12 hours to obtain a lithium manganese iron phosphate positive electrode material, which was recorded as lithium manganese iron phosphate positive electrode material 5.

[0074] Embodiment 6

[0075] (1) Dismantle the waste batteries with SOH=60%, peel off the active materials, crush them, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0076] (2) The powder obtained in step (1) is mixed with lithium hydroxide, manganese sulfate and diammonium hydrogen phosphate, and the molar ratio of the elements in the mixed powder is Li:Fe:Mn:P=1.0:0.8:0.2:1.

[0077] (3) The mixture obtained in step (2) was sintered under Ar gas protection at 500° C. for 3 hours and then at 750° C. for 10 hours to obtain a lithium iron manganese phosphate positive electrode material, which was recorded as lithium iron manganese phosphate positive electrode material 6.

[0078] Embodiment 7

[0079] (1) Dismantle the waste batteries with SOH=90%, peel off the active materials, crush them, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0080] (2) The powder obtained in step (1) is mixed with lithium acetate, manganese acetate and diammonium hydrogen phosphate, and the molar ratio of each element in the mixed powder is Li:Fe:Mn:P=1.15:0.6:0.4:1.

[0081] (3) The mixture obtained in step (2) is placed in a hydrothermal kettle and treated at 300° C. for 12 h. After filtering and drying, a lithium manganese iron phosphate positive electrode material is obtained, which is recorded as lithium manganese iron phosphate positive electrode material 7.

[0082] Embodiment 8

[0083] (1) Dismantle the waste batteries with SOH=90%, peel off the active materials, crush them, obtain the waste lithium iron phosphate powder, and determine the proportion of Li, Fe, and P elements therein.

[0084] (2) The powder obtained in step (1) is mixed with lithium hydroxide, manganous oxide and ammonium dihydrogen phosphate, and the molar ratio of each element in the mixed powder is Li:Fe:Mn:P=1.0:0.9:0.1:1.

[0085] (3) The mixture obtained in step (2) was sintered under Ar gas protection at 450° C. for 4 hours and then at 700° C. for 8 hours to obtain a lithium manganese iron phosphate positive electrode material, which was recorded as lithium manganese iron phosphate positive electrode material 8.

[0086] Embodiment 9

[0087] The lithium iron manganese phosphate positive electrode material 1 was carbon-coated, mixed with 10% wt sucrose, and calcined in an argon atmosphere: 200° C. for 2 h, 700° C. for 3 h, to obtain a lithium iron manganese phosphate positive electrode material, recorded as lithium iron manganese phosphate positive electrode material 9.

[0088] Embodiment 10

[0089] The lithium iron manganese phosphate positive electrode material 2 was carbon-coated, mixed with 5% wt sucrose, and calcined in an argon atmosphere: 250° C. for 2 h, 650° C. for 4 h, to obtain a lithium iron manganese phosphate positive electrode material, recorded as lithium iron manganese phosphate positive electrode material 10.

[0090] Embodiment 11

[0091] The lithium iron manganese phosphate positive electrode material 3 was carbon-coated, mixed with 15% wt sucrose, and calcined in a nitrogen atmosphere: 200° C. for 2 h, 700° C. for 3 h, to obtain a lithium iron manganese phosphate positive electrode material, which was recorded as lithium iron manganese phosphate positive electrode material 11.

[0092] Comparative Example 1

[0093] Lithium iron manganese phosphate positive electrode material was prepared from waste lithium iron phosphate according to the method disclosed in Chinese patent application CN118405678A. The difference from Example 3 is that in step (1), the positive electrode sheet is crushed and placed in a calcining furnace for the first sintering in an air atmosphere. The sintering system is: 3°C / min to 500°C, kept warm for 3h, and the ventilation volume is 20L / min.

[0094] Comparative Example 2

[0095] Commercial iron phosphate dihydrate was used to prepare lithium iron phosphate positive electrode material, which was different from Example 3 only in that iron phosphate dihydrate was used in the raw material instead of waste lithium iron phosphate.

[0096] The lithium manganese iron phosphate positive electrode material samples prepared in Examples 1 to 11 and the samples regenerated in Comparative Examples 1 to 2 were assembled into lithium half-cells and heated at 0.1C (1C = 150 mAh g -1 ) conditions, the electrochemical performance is shown in Table 1.

[0097] Table 1: Summary of electrochemical properties of lithium manganese iron phosphate positive electrode materials 1 to 11 prepared in Examples 1 to 11

[0098]

[0099]

[0100] Take Examples 1, 2, and 3 as examples:

[0101] Depend on Figure 1 , Figure 7 , Fig.13 By comparison, it can be seen that the particle size distribution of lithium manganese iron phosphate materials regenerated by different methods is relatively uniform. Figure 2 The particle size is relatively small. And the agglomeration phenomenon is obvious, which limits its electrochemical performance. In addition, the SOH of the raw material retired lithium iron phosphate mainly affects the proportion of trace impurities (mainly iron phosphate phase) produced by the lithium iron phosphate cycle, as well as the lithium deficiency of the waste lithium iron phosphate obtained by disassembly and crushing, and has little impact on the subsequent process.

[0102] Depend on Figure 2 , Figure 8 , Fig.14 From the comparison, it can be seen that the lithium manganese iron phosphate materials regenerated by different methods all correspond to olivine-type Li(Mn, Fe)PO4 (JCPDS13-0336) and show good crystallinity. Even if the manganese source and lithium source are changed, the lithium manganese iron phosphate material can still be directly regenerated from waste lithium iron phosphate.

[0103] Depend on Figure 3 , Fig. 9 , Fig.15 By comparison, it can be seen that the solid phase regeneration method corresponding to Example 3 has better effect, and Example 2 may have relatively low performance due to severe agglomeration phenomenon.

[0104] Depend on Figure 4 , Fig.10 , Fig.16 From the comparison, it can be seen that the lithium manganese iron phosphate materials regenerated by different methods have good long-cycle performance.

[0105] Depend on Figure 5 , Fig.11 , Fig.17 By comparison, it can be seen that Example 3 has a particularly obvious advantage at low rate cycles (166 mAh / g); but at 0.5C and higher rates, Example 2 is closer to Example 3. The inventors analyzed that it is because the manganese source / lithium source containing organic acid radicals is heated in an inert atmosphere, and part of the carbon elements of the organic acid radicals will be converted into a carbon layer coated on the particle surface, but due to the uneven coating of the solid phase mixture, the uneven interface is caused. Although the manganese source / lithium source in Example 3 has no inorganic acid radicals, the regeneration process is conducive to forming a relatively clean and uniform interface. In contrast, its low rate performance is worse than that of Example 3, but the increase in rate is accompanied by a higher electronic conduction rate. The carbon layer described in Example 2 plays a partial role, so it is close to Example 3.

[0106] Depend on Figure 6 , Fig.12 , Fig.18 The comparison also proves the superiority of the effect of Example 3.

[0107] As can be seen from Table 1, Examples 1-8 of the present invention prove that the regenerated lithium manganese iron phosphate material still has excellent performance without the additional introduction of a carbon source; Examples 9-11 introduce a carbon source, which is a further carbon coating treatment, and the performance can be further improved.

[0108] In addition, the regeneration performance of Example 3 is significantly better than that of Comparative Example 1. The inventors believe that the regeneration process is more difficult due to the introduction of other impurities during the air sintering process of Comparative Example 1. The calcination of Example 3 adopts an inert atmosphere without introducing air / oxygen. The olivine crystal structure is not oxidized into impurities such as lithium iron phosphate and iron oxide by high-temperature treatment in an oxygen-deficient environment corresponding to an inert atmosphere.

[0109] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing lithium iron manganese phosphate positive electrode material from lithium iron phosphate waste powder, characterized in that: The following steps are involved: (1) dismantling retired and / or discarded lithium iron phosphate batteries, stripping active materials, and crushing to obtain waste lithium iron phosphate powder; (2) Determine the proportions of Li, Fe, and P in the waste lithium iron phosphate powder obtained in step (1); then, based on the Fe element contained in the waste lithium iron phosphate powder, without introducing other Fe sources, add a lithium source, a manganese source, and a phosphorus source to the waste lithium iron phosphate powder to obtain a mixture, so that the molar ratio of Li:Fe:Mn:P in the mixture is (1.0-1.2):(0.1-0.9):(0.9-0.1):1; (3) The mixture obtained in step (2) is treated by hydrothermal method or solid phase heating under protective atmosphere to obtain lithium manganese iron phosphate positive electrode material.

2. The method according to claim 1, characterized in that: In step (3), the hydrothermal treatment is specifically a hydrothermal reaction at a temperature of 200-300° C. for 10-15 hours.

3. The method according to claim 1, characterized in that: In step (3), the heating solid phase treatment adopts two-stage sintering, wherein the first stage sintering is carried out at a temperature of 300-500°C for 1-24h, and the second stage sintering is carried out at a temperature of 600-750°C for 2-24h.

4. The method according to claim 1, characterized in that: In step (3), the protective atmosphere is selected from nitrogen and argon.

5. The method according to claim 1, characterized in that: In step (2), the lithium source is selected from lithium carbonate, lithium oxalate, lithium hydroxide, and lithium acetate; The manganese source is selected from manganese oxide, manganese carbonate, manganese sulfate, and manganese acetate; The phosphorus source is selected from ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

6. The method according to claim 1, characterized in that: The method further comprises the steps of: (4) The lithium iron manganese phosphate positive electrode material obtained in step (3) is subjected to carbon coating treatment to obtain a carbon-coated lithium iron manganese phosphate positive electrode material.

7. The method according to claim 6, characterized in that The carbon coating treatment is to mix the lithium manganese iron phosphate positive electrode material obtained in step (3) with a carbon source and then calcine it under a protective atmosphere.

8. The method according to claim 7, characterized in that: In step (4), the carbon source is sucrose or glucose, and the amount used is 5wt% to 25wt% of the lithium manganese iron phosphate positive electrode material; The calcination is specifically carried out at a temperature of 200-400° C. for 2-4 hours, followed by treatment at a temperature of 300-500° C. for 2-4 hours.

9. The method according to claim 1, characterized in that: In step (1), the crushing is performed so that the particle size D50 of the waste lithium iron phosphate powder is less than 20 μm; preferably, the crushing is performed so that the particle size D50 of the waste lithium iron phosphate powder is less than 5 μm.

10. The method according to claim 1, characterized in that: In step (2), the mixing is specifically performed by ball milling; Preferably, the ball milling mixing is wet ball milling mixing, using ethanol as a dispersant, the mixing speed is 200-500 rpm, and the mixing time is 2-12 hours.

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