CN114784271A - Regenerated lithium iron phosphate positive electrode material, preparation method and application - Google Patents
Regenerated lithium iron phosphate positive electrode material, preparation method and application Download PDFInfo
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- H01M4/00—Electrodes
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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Abstract
The invention discloses a regenerated lithium iron phosphate positive electrode material, a preparation method and application thereof, wherein the preparation method comprises the following steps: crushing a lithium iron phosphate positive plate to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive plate is not more than 50 mm; drying the crushed lithium iron phosphate positive plate, adding a cracking auxiliary material into the dried lithium iron phosphate positive plate, putting the dried lithium iron phosphate positive plate into a cracking furnace for anaerobic cracking, separating an aluminum sheet and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities to obtain a lithium iron phosphate composite material, namely the regenerated lithium iron phosphate positive material. The invention adopts an anaerobic cracking technology, retains the carbon coating layer, has simple and efficient process, low energy consumption, low operation cost and better environmental protection, and the regenerated lithium iron phosphate anode material has various performance indexes comparable with that of a commercial lithium iron phosphate anode material, and has the highest first discharge specific capacity of 154mAh/g and the highest first discharge efficiency of 93 percent.
Description
Technical Field
The invention relates to the field of lithium iron phosphate anode materials, in particular to a regenerated lithium iron phosphate anode material, a preparation method and application.
Background
With the improvement of the cost of raw materials of lithium batteries and the continuous update of battery structure optimization technology, compared with ternary lithium batteries with high cost and low safety, the lithium iron phosphate battery is gradually favored by the automobile and energy storage market due to the advantages of lower cost, good thermal stability, high structural stability and the like compared with ternary lithium batteries. In the future, more and more waste lithium iron phosphate batteries and unqualified products in the production process are generated at the production end and the use end, and the high-efficiency recovery of lithium iron phosphate battery materials is trending from the perspective of resource utilization.
A great number of reports have been made on the recovery treatment and recycling of lithium iron phosphate batteries, and the processes can be largely divided into wet process and dry process.
The wet process is mainly used for recovering or purifying high-value elements or raw materials of the lithium iron phosphate battery, such as lithium elements and iron phosphate. However, the problems of waste liquid generation, expensive reagent use and the like are inevitably involved in the process, so that the environmental protection problem, the enterprise material cost increase and the like are caused, and meanwhile, the higher treatment cost brings higher survival pressure to the enterprise due to the lower content of high-valence metal elements in the lithium iron phosphate. The dry process route mainly comprises the following steps: discharging the battery, finely disassembling, crushing, sintering and impurity removing, component regulation and control and particle size control, sintering and repairing in inert atmosphere and the like. For example, patent publication No. CN112658000A provides a method for recycling leftover materials of positive plates of lithium iron phosphate batteries, which includes coarse crushing of positive plates, and subsequent inert atmosphere calcination, fine crushing, primary impurity removal, secondary sintering, jet milling, secondary impurity removal and other processes, thereby finally obtaining lithium iron phosphate products. But the process is complicated, the high-temperature sintering for multiple times brings huge energy consumption and cost increase, and the crushing for multiple times leads to the increase of impurity introduction and the increase of impurity removal cost, so that the commercial value of repairing and recycling the lithium iron phosphate is reduced; the patent of publication No. CN113036253A provides a method for regenerating lithium iron phosphate by selective oxidation-reduction, which comprises the steps of regulating and controlling oxidizing atmosphere through mixed gas of water vapor and carbon dioxide to perform primary sintering on a lithium iron phosphate pole piece, then separating, and finally regulating and controlling the composition of the lithium iron phosphate pole piece under high-temperature inert atmosphere to obtain a lithium iron phosphate product. The patent process is simplified, but in the primary oxidizing atmosphere sintering process, the carbon coating layer on the surface of the lithium iron phosphate is damaged, and simultaneously, ferrous iron in the lithium iron phosphate is partially oxidized into ferric iron, and is difficult to reduce in the subsequent sintering process, so that the difficulty of component regulation and control is increased.
Based on the above problems, there is a need to design a scheme for simplifying the process, retaining the carbon coating layer of lithium iron phosphate to the maximum extent, and realizing regeneration of lithium iron phosphate.
Disclosure of Invention
The invention aims to provide a regenerated lithium iron phosphate positive electrode material which is simplified in process, can reserve a lithium iron phosphate carbon coating layer to the greatest extent and realizes regeneration of lithium iron phosphate, a preparation method and an application scheme. The specific scheme is as follows:
on one hand, the invention provides a preparation method of a regenerated lithium iron phosphate cathode material, which comprises the following steps:
s1: crushing a lithium iron phosphate positive plate to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive plate is not more than 50mm, and the lithium iron phosphate positive plate to be regenerated is a lithium iron phosphate positive plate leftover and/or a defective lithium iron phosphate positive plate in a battery factory;
s2: drying the crushed lithium iron phosphate positive plate, wherein the water content of the dried lithium iron phosphate positive plate is less than 1%;
s3: adding a cracking auxiliary material into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is less than or equal to 0.2%, cracking for 0.5-2h at the cracking temperature of 400 plus materials and 600 ℃, and controlling the retention time of gas generated by cracking to be less than 10s in the cracking furnace to obtain a mixture comprising an aluminum sheet, the cracking auxiliary material and lithium iron phosphate powder;
s4: separating an aluminum sheet, a cracking auxiliary material and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite material;
s5: and (3) scattering the lithium iron phosphate composite material until D99 is less than or equal to 15um to obtain the final regenerated lithium iron phosphate anode material.
As a preferable scheme of the preparation method of the regenerated lithium iron phosphate cathode material, in step S3, the cracking auxiliary material includes one or more of calcium oxide, potassium oxide, and sodium oxide;
in step S1, the particle size of the crushed lithium iron phosphate positive electrode sheet is not greater than 30 mm.
As a preferred scheme of the preparation method of the regenerated lithium iron phosphate cathode material, the particle size of the cracking auxiliary material is larger than 100 meshes, and the Mohs hardness is larger than 6.0.
As a preferable scheme of the preparation method of the regenerated lithium iron phosphate positive electrode material, in step S2, the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1: (25-50).
As a preferable scheme of the preparation method of the regenerated lithium iron phosphate positive electrode material, in step S3, the water content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%;
the residence time of the gas generated by cracking in the cracking furnace is controlled to be less than 3 s.
As a preferable scheme of the preparation method of the regenerated lithium iron phosphate cathode material, in step S3, the cracking furnace includes a roller kiln, a rotary kiln, and a tube furnace.
As a preferable scheme of the preparation method of the regenerated lithium iron phosphate cathode material, in step S4, impurities in the lithium iron phosphate powder are removed to mainly remove aluminum, copper and iron.
As a preferred scheme of the preparation method of the regenerated lithium iron phosphate cathode material, impurity removal modes of lithium iron phosphate powder impurities include color separation, magnetic separation, gravity separation and flotation.
On the other hand, the invention also provides a regenerated lithium iron phosphate cathode material which is prepared according to the preparation method of the regenerated lithium iron phosphate cathode material, and the regenerated lithium iron phosphate cathode material comprises carbon-coated lithium iron phosphate and conductive agent carbon, wherein the carbon-coated lithium iron phosphate is a lithium iron phosphate surface coated with a carbon coating layer.
In another aspect, the invention further provides an application of the regenerated lithium iron phosphate positive electrode material in the preparation of a lithium iron phosphate battery, wherein the prepared regenerated lithium iron phosphate positive electrode material is independently used for the preparation of the lithium iron phosphate battery; or
The prepared regenerated lithium iron phosphate positive electrode material is compounded with a commercial lithium iron phosphate positive electrode material or a repaired and regenerated lithium iron phosphate positive electrode material for preparing a lithium iron phosphate battery, the repaired and regenerated lithium iron phosphate positive electrode material is a lithium iron phosphate positive electrode material which can be reused for preparing the lithium iron phosphate battery after being repaired and regenerated by any chemical or physical method for lithium iron phosphate positive plate leftovers and/or waste lithium iron phosphate positive electrode materials, and the commercial lithium iron phosphate positive electrode material is a lithium iron phosphate positive electrode material purchased from the market.
Compared with the prior art, the invention has at least one or more of the following beneficial effects:
1. the method avoids the reaction of water, oxygen and cracking gas (such as fluorine-containing substances) with lithium iron phosphate and/or carbon in the lithium iron phosphate positive plate by simultaneously controlling the water content, the oxygen content and the residence time of the cracking gas in the cracking furnace, and the control conditions of the water content, the oxygen content and the residence time of the cracking gas in the cracking furnace are mutually matched, cooperated and absent. The adopted anaerobic cracking technology can well reserve the carbon coating layer on the surface of the lithium iron phosphate particles. In addition, although PVDF (polyvinylidene fluoride) can be removed by conventional sintering or baking, iron in the lithium iron phosphate positive plate can be oxidized; in the traditional sintering or roasting process, the carbon coating layer on the surface of the lithium iron phosphate can be removed while the carbon of the conductive agent and the residual carbon of PVDF are removed, so that the repair difficulty of the subsequent process is increased; the method effectively reserves the conductive agent carbon and the carbon coating layer through one-step anaerobic cracking, reduces the addition of subsequent carbon sources, and can directly manufacture the battery without secondary carbon coating and conductive agent supplement of the obtained regenerated lithium iron phosphate cathode material, thereby saving the cost and simplifying the process flow;
2. and introducing cracking auxiliary materials to completely crack the PVDF into carbon instead of fluorine-containing biphenyl substances. After pyrolysis of PVDF, hydrogen fluoride, vinylidene fluoride monomer and fluorine substituted benzene substances (biphenyl) can be generated; among the substances, hydrogen fluoride, vinylidene fluoride monomer and fluorine substituted benzene can be removed in a gas form, but fluorine substituted substances in cracking residues are not easy to remove completely and can be adhered to lithium iron phosphate powder, so that the first charge-discharge capacity is influenced, particle adhesion is caused, and the purity of the electrolyte is influenced; in general, the cracking process needs to ensure complete decomposition of PVDF, and the residual carbon is used as a supplemental carbon coating layer of the lithium iron phosphate material, so as to realize direct regeneration of the lithium iron phosphate material. In order to achieve the purpose, cracking auxiliary materials are required to be introduced to ensure that the PVDF is completely cracked into carbon instead of fluorine-containing biphenyl substances under the process conditions.
3. The lithium iron phosphate anode plate is cracked in one step, the regeneration effect of the lithium iron phosphate anode plate is achieved, residual electrolyte on the surface of the lithium iron phosphate anode plate can be removed, PVDF can be removed, the cohesiveness of the PVDF is invalid, lithium iron phosphate powder is separated from the surface of an aluminum sheet, and compared with the traditional two-step sintering, the energy is saved by more than one time;
4. according to the invention, through pretreatment crushing, the size of the lithium iron phosphate anode plate entering the cracking furnace is enlarged to 50mm, so that the introduction of aluminum impurities in the pretreatment process can be effectively reduced, and the content of the aluminum impurities can be reduced to below 500ppm after cracking;
5. the regenerated lithium iron phosphate anode material obtained by the invention effectively reduces the addition of a conductive agent at the battery manufacturing end, and simultaneously, each performance index of the regenerated lithium iron phosphate anode material is comparable to that of a commercial lithium iron phosphate anode material, the first discharge specific capacity is as high as 154mAh/g, and the first discharge efficiency is as high as 93%;
6. the method has the advantages of simple and efficient process, low energy consumption, lower operation cost compared with the traditional lithium iron phosphate regeneration mode, and better environmental protection.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a process flow chart of a preparation method of a regenerated lithium iron phosphate cathode material according to the patent;
fig. 2 is a TEM test chart of the regenerated lithium iron phosphate positive electrode material of example 1 of the present patent;
fig. 3 is a first charge-discharge curve diagram of the regenerated lithium iron phosphate positive electrode material of patent example 1.
Wherein, the 1-carbon coating layer.
Detailed Description
The embodiments of the present invention will be described in detail below, and the technical solutions in the embodiments of the present invention will be clearly and completely described. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Oxygen-free in this application means that the oxygen content approaches infinity to 0(< 0.5%).
In order to solve the defects and shortcomings of the prior art, the invention provides a regenerated lithium iron phosphate positive electrode material, a preparation method and application. The regenerated lithium iron phosphate anode material prepared by the method does not need to be subjected to carbon coating and conductive agent supplement again, and can be directly used for battery manufacture.
In order to achieve the purpose, the invention adopts the following technical scheme:
firstly, adding a cracking auxiliary material into a lithium iron phosphate positive plate to be regenerated, cracking the lithium iron phosphate positive plate in an oxygen-free atmosphere, and removing residual electrolyte, PVDF and other impurities on the surface of the lithium iron phosphate positive plate to loosen the lithium iron phosphate positive plate and facilitate separation; and then removing impurities such as aluminum, copper, iron and the like in the lithium iron phosphate through processes such as sorting and the like, and controlling the introduction of other impurities, so that the purity of the lithium iron phosphate in the lithium iron phosphate powder is maximized. The process method has the characteristics of high efficiency, low cost and good environmental protection, and can efficiently recycle the lithium iron phosphate positive plate to be regenerated.
The technical scheme mainly aims at recycling the leftovers of the lithium iron phosphate positive plate and the defective lithium iron phosphate positive plate in a battery factory to obtain the regenerated lithium iron phosphate positive material, and is shown as a flow chart of a preparation method shown in figure 1, and the technical scheme comprises the following steps:
s1: crushing a lithium iron phosphate positive plate to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive plate is not more than 50mm, and the lithium iron phosphate positive plate to be regenerated is a lithium iron phosphate positive plate leftover and/or a defective lithium iron phosphate positive plate in a battery factory;
s2: drying the crushed lithium iron phosphate positive plate, wherein the water content of the dried lithium iron phosphate positive plate is less than 1%; preferably, the water content of the dried lithium iron phosphate positive plate is less than 0.5%, wherein the water content of the dried lithium iron phosphate positive plate is detected by an online testing instrument;
s3: adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is less than or equal to 0.2%, cracking for 0.5-2h at the cracking temperature of 400-600 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking in the cracking furnace to be less than 10s to obtain a mixture comprising an aluminum sheet, the cracking auxiliary material and lithium iron phosphate powder; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace; preferably, the residence time of the gas generated by cracking in a cracking furnace is controlled to be less than 3s, and the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tube furnace and the like; the cracking auxiliary materials comprise one or more of calcium oxide, potassium oxide and sodium oxide, and the granularity of the cracking auxiliary materials is preferably larger than 100 meshes, the Mohs hardness is larger than 6.0, so that the cracking auxiliary materials are convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as the supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding the cracking auxiliary material, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100ppm, and if the cracking auxiliary material is not added, the residual quantity of fluorine in the lithium iron phosphate powder can reach 1000ppm generally;
s4: separating an aluminum sheet, a cracking auxiliary material and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite material; removing impurities from the lithium iron phosphate powder, mainly removing impurities such as aluminum, copper, iron and the like, wherein the impurity removal mode comprises but is not limited to color separation, magnetic separation, gravity separation, flotation and the like; the lithium iron phosphate composite material comprises carbon-coated lithium iron phosphate and conductive agent carbon, wherein the carbon-coated lithium iron phosphate is formed by coating a carbon coating layer on the surface of lithium iron phosphate;
s5: and (4) scattering the lithium iron phosphate composite material obtained in the step (S4) until the D99 is less than or equal to 15um, so as to obtain the regenerated lithium iron phosphate cathode material, wherein the D99 is less than or equal to 15um, which means that the particle size of at least 99% of the lithium iron phosphate composite material by weight is less than or equal to 15 micrometers. In an example, the lithium iron phosphate composite is broken up to industry standard by grinding, i.e., the particle size is 15 microns or less.
The prepared regenerated lithium iron phosphate positive electrode material is mainly applied to the preparation of lithium iron phosphate batteries, and is independently used for the preparation of the lithium iron phosphate batteries: or
The regenerated lithium iron phosphate anode material is compounded with a commercial lithium iron phosphate anode material or a repaired and regenerated lithium iron phosphate anode material for preparing a lithium iron phosphate battery, the repaired and regenerated lithium iron phosphate anode material is a lithium iron phosphate anode material which can be reused for preparing the lithium iron phosphate battery after being repaired and regenerated by any chemical or physical method for lithium iron phosphate anode plate leftovers and/or waste lithium iron phosphate anode materials, and the commercial lithium iron phosphate anode material is a lithium iron phosphate anode material purchased from the market.
On the other hand, the invention also provides a regenerated lithium iron phosphate cathode material which is prepared according to the preparation method of the regenerated lithium iron phosphate cathode material, and the regenerated lithium iron phosphate cathode material comprises carbon-coated lithium iron phosphate and conductive agent carbon.
Example 1
The embodiment provides a preparation method of a regenerated lithium iron phosphate anode material, which specifically comprises the following steps:
1. the method comprises the following steps of taking leftovers of the lithium iron phosphate positive plate as a raw material, crushing the leftovers of the lithium iron phosphate positive plate until the particle size is not more than 50mm, and reducing the introduction of impurities such as aluminum powder in the crushing process due to a large crushing size of the leftovers of the lithium iron phosphate positive plate;
2. drying the crushed lithium iron phosphate positive plate to ensure that the water content of the dried lithium iron phosphate positive plate is less than 0.5%; the water content of the dried lithium iron phosphate positive plate is detected by an online testing instrument;
3. adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, cracking for 1h at the cracking temperature of 500 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking to be less than 3s in the cracking furnace to obtain a mixture, wherein the mixture comprises lithium iron phosphate powder, the cracking auxiliary material and an aluminum sheet; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace, and the furnace body type of the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tubular furnace and the like; the cracking auxiliary material comprises one or more of calcium oxide, potassium oxide and sodium oxide, preferably, the granularity of the cracking auxiliary material is more than 100 meshes, and the Mohs hardness is more than 6.0, so that the cracking auxiliary material is convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding cracking auxiliary materials, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100 ppm;
4. performing vibration screening on the mixture to separate lithium iron phosphate powder, aluminum sheets and cracking auxiliary materials, adding vibration screening balls into a vibration screening device, wherein the vibration screening balls are made of rubber, the vibration screening time is 10min, and the mesh number of a screen is 20-325 meshes;
5. after separation is finished, removing impurities from the collected lithium iron phosphate powder to obtain a lithium iron phosphate composite material, wherein the impurities removal from the lithium iron phosphate powder mainly removes impurities such as aluminum, copper and iron, and the like, and the impurity removal modes include but are not limited to color separation, magnetic separation, gravity separation, flotation and the like;
6. and (3) scattering the lithium iron phosphate composite material obtained in the step (5) until D99 is less than or equal to 15um, so as to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 is less than or equal to 15um, which means that the particle size of at least 99% of the lithium iron phosphate composite material is less than or equal to 15 micrometers. In the example, the lithium iron phosphate composite material is broken up to the industry standard by grinding, i.e., the particle size is 15 micrometers or less. As shown in fig. 2, the regenerated lithium iron phosphate positive electrode material has the advantages that the regenerated lithium iron phosphate positive electrode material does not need to be carbon-coated again, and the conductive agent carbon is retained, so that the regenerated lithium iron phosphate positive electrode material can be directly subjected to slurry mixing for manufacturing a lithium iron phosphate battery.
The performance of the prepared regenerated lithium iron phosphate anode material is detected, and the regenerated lithium iron phosphate anode material is firstly prepared into a button cell, and the method comprises the following steps:
1. preparing the regenerated lithium iron phosphate anode material obtained by the method and polyvinylidene fluoride (PVDF) according to the mass ratio of 90:10, firstly dissolving the PVDF in a proper amount of N-methylpyrrolidone (NMP), magnetically stirring for 1h until the solution is transparent, then adding the regenerated lithium iron phosphate anode material into the solution, stirring for 8h for standby application, and taking down the material adhered to the wall and mixing the material into the slurry in the material mixing process;
2. then coating the evenly mixed slurry on a smooth aluminum sheet, putting the coated aluminum sheet into a vacuum drying oven at 80 ℃ for drying for 12h, cutting the dried aluminum sheet into a wafer with the diameter of 14mm, and tabletting under the pressure of 2MPa to be used as a positive pole piece of the button cell;
3. assembling the button cell in a glove box filled with dry argon, taking a metal lithium sheet as a cathode, adopting Celgard 2400 as a diaphragm and using LiPF with 1.0mol/L electrolyte6EC + DMC + EMC, where LiPF6The volume ratio of the/EC, the DMC and the EMC is 1:1:1, assembling the battery into a button cell, standing for 12 hours and testing; wherein LiPF6Lithium hexafluorophosphate, ethylene carbonate as EC, dimethyl carbonate as DMC and ethyl methyl carbonate as EMC.
And (3) carrying out related charge and discharge tests on the prepared button cell:
and charging the button cell to 3.75V at a constant current of 0.2C, then discharging to 2.7V at a constant current of 0.2C, circularly charging and discharging, and calculating the gram capacity of the active substance in the positive electrode of the button cell.
The result of a Transmission Electron Microscope (TEM) test on the regenerated lithium iron phosphate cathode material obtained in this embodiment is shown in fig. 2, and as can be seen from fig. 2, the surface of the regenerated lithium iron phosphate cathode material particle obtained in this embodiment has a carbon coating layer, which indicates that the carbon coating layer on the lithium iron phosphate surface layer can be retained to the greatest extent by the method provided in this embodiment.
Fig. 3 is a first charge-discharge curve diagram of the regenerated lithium iron phosphate positive electrode material according to the embodiment, and it can be obtained from fig. 3 that the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 154mAh/g, and the first discharge efficiency can reach 93%.
Example 2
The embodiment provides a preparation method of a regenerated lithium iron phosphate anode material, which specifically comprises the following steps:
1. the method comprises the following steps of taking leftovers of the lithium iron phosphate positive plate as a raw material, crushing the leftovers of the lithium iron phosphate positive plate until the particle size is not more than 50mm, and reducing the introduction of impurities such as aluminum powder in the crushing process due to a large crushing size of the leftovers of the lithium iron phosphate positive plate;
2. drying the crushed lithium iron phosphate positive plate to ensure that the water content of the dried lithium iron phosphate positive plate is less than 0.5%; the water content of the dried lithium iron phosphate positive plate is detected by an online testing instrument;
3. adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, cracking for 2h at the cracking temperature of 400 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking to be less than 3s in the cracking furnace to obtain a mixture, wherein the mixture comprises lithium iron phosphate powder, the cracking auxiliary material and an aluminum sheet; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace, and the furnace body type of the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tubular furnace and the like; the cracking auxiliary materials comprise one or more of calcium oxide, potassium oxide and sodium oxide, and the granularity of the cracking auxiliary materials is preferably larger than 100 meshes, the Mohs hardness is larger than 6.0, so that the cracking auxiliary materials are convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding cracking auxiliary materials, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100 ppm;
4. performing vibration screening on the mixture to separate lithium iron phosphate powder, aluminum sheets and cracking auxiliary materials, adding vibration screening balls into a vibration screening device, wherein the vibration screening balls are made of rubber, the vibration screening time is 10min, and the mesh number of a screen is 20-325 meshes;
5. after separation is finished, removing impurities from the collected lithium iron phosphate powder to obtain a lithium iron phosphate composite material, wherein the impurities removal from the lithium iron phosphate powder mainly removes impurities such as aluminum, copper and iron, the impurities removal mode comprises but is not limited to color selection, magnetic selection, reselection, flotation and the like, and the lithium iron phosphate composite material comprises carbon-coated lithium iron phosphate and conductive agent carbon;
6. and (4) scattering the lithium iron phosphate composite material obtained in the step (5) until D99 is less than or equal to 15 micrometers, so as to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 is less than or equal to 15 micrometers, and the particle size of at least 99% of the lithium iron phosphate composite material is less than or equal to 15 micrometers. In an example, the lithium iron phosphate composite is broken up to industry standard by grinding, i.e., the particle size is 15 microns or less.
The obtained regenerated lithium iron phosphate positive electrode material is prepared into a button cell according to the method for preparing the button cell in the embodiment 1, and the prepared button cell is subjected to related charge and discharge tests:
the button cell is charged to 3.75V by 0.2C constant current, then discharged to 2.7V by 0.2C constant current, and circularly charged and discharged, the gram capacity of active substances in the positive electrode of the button cell is calculated, and the specific discharge capacity of the regenerated lithium iron phosphate positive electrode material for the first time can reach 142mAh/g and the first discharge efficiency can reach 88 percent.
Example 3
The embodiment provides a preparation method of a regenerated lithium iron phosphate anode material, which specifically comprises the following steps:
1. the method comprises the following steps of crushing the leftovers of the lithium iron phosphate positive plate to be not more than 50mm by taking the leftovers of the lithium iron phosphate positive plate as a raw material, wherein the crushed size of the leftovers of the lithium iron phosphate positive plate is large, so that the introduction of impurities such as aluminum powder in the crushing process is reduced;
2. drying the crushed lithium iron phosphate positive plate to ensure that the water content of the dried lithium iron phosphate positive plate is less than 0.5%; the water content of the dried lithium iron phosphate positive plate is obtained by detecting through an online testing instrument;
3. adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, cracking for 0.5h at the cracking temperature of 600 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking to be less than 10s in the cracking furnace to obtain a mixture, wherein the mixture comprises lithium iron phosphate powder, the cracking auxiliary material and an aluminum sheet; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace, and the furnace body type of the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tubular furnace and the like; the cracking auxiliary materials comprise one or more of calcium oxide, potassium oxide and sodium oxide, and the granularity of the cracking auxiliary materials is preferably larger than 100 meshes, the Mohs hardness is larger than 6.0, so that the cracking auxiliary materials are convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding cracking auxiliary materials, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100 ppm;
4. performing vibration screening on the mixture to separate lithium iron phosphate powder, aluminum sheets and cracking auxiliary materials, adding vibration screening balls into a vibration screening device, wherein the vibration screening balls are made of rubber, the vibration screening time is 10min, and the mesh number of a screen is 20-325 meshes;
5. after separation is finished, removing impurities from the collected lithium iron phosphate powder to obtain a lithium iron phosphate composite material, wherein the impurities removal from the lithium iron phosphate powder mainly removes impurities such as aluminum, copper and iron, the impurities removal mode comprises but is not limited to color selection, magnetic selection, reselection, flotation and the like, and the lithium iron phosphate composite material comprises carbon-coated lithium iron phosphate and conductive agent carbon;
6. and (4) scattering the lithium iron phosphate composite material obtained in the step (5) until D99 is less than or equal to 15 micrometers, so as to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 is less than or equal to 15 micrometers, and the particle size of at least 99% of the lithium iron phosphate composite material is less than or equal to 15 micrometers. In an example, the lithium iron phosphate composite is broken up to industry standard by grinding, i.e., the particle size is 15 microns or less.
The obtained regenerated lithium iron phosphate positive electrode material is prepared into a button cell according to the method for preparing the button cell in the embodiment 1, and the prepared button cell is subjected to related charge and discharge tests:
the button cell is charged to 3.75V by 0.2C constant current, then discharged to 2.7V by 0.2C constant current, and circularly charged and discharged, the gram capacity of active substances in the positive electrode of the button cell is calculated, and the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 147mAh/g and the first discharge efficiency can reach 91 percent.
Example 4
The embodiment provides a preparation method of a regenerated lithium iron phosphate cathode material, which specifically comprises the following steps:
1. taking leftovers of a lithium iron phosphate positive plate as a raw material, and crushing the leftovers of the lithium iron phosphate positive plate until the particle size is not more than 30 mm;
2. drying the crushed lithium iron phosphate positive plate to ensure that the water content of the dried lithium iron phosphate positive plate is less than 1%; the water content of the dried lithium iron phosphate positive plate is detected by an online testing instrument;
3. adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, cracking for 1h at the cracking temperature of 600 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking to be less than 3s in the cracking furnace to obtain a mixture, wherein the mixture comprises lithium iron phosphate powder, the cracking auxiliary material and an aluminum sheet; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace, and the furnace body type of the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tubular furnace and the like; the cracking auxiliary materials comprise one or more of calcium oxide, potassium oxide and sodium oxide, and the granularity of the cracking auxiliary materials is preferably larger than 100 meshes, the Mohs hardness is larger than 6.0, so that the cracking auxiliary materials are convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as the supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding cracking auxiliary materials, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100 ppm;
4. performing vibration screening on the mixture to separate lithium iron phosphate powder, aluminum sheets and cracking auxiliary materials, adding a vibration screening pellet into a vibration screening device, wherein the vibration screening pellet is made of rubber, the vibration screening time is 10min, and the mesh number of a screen is 20-325 meshes;
5. after separation is finished, removing impurities from the collected lithium iron phosphate powder to obtain a lithium iron phosphate composite material, wherein the impurities of the lithium iron phosphate powder mainly remove impurities such as aluminum, copper and iron, and the like, and the impurities removing mode comprises but is not limited to color separation, magnetic separation, gravity separation, flotation and the like, and the lithium iron phosphate composite material comprises carbon-coated lithium iron phosphate and conductive agent carbon;
6. and (4) scattering the lithium iron phosphate composite material obtained in the step (5) until D99 is less than or equal to 15 micrometers, so as to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 is less than or equal to 15 micrometers, and the particle size of at least 99% of the lithium iron phosphate composite material is less than or equal to 15 micrometers. In the example, the lithium iron phosphate composite material is broken up to the industry standard by grinding, i.e., the particle size is 15 micrometers or less.
The obtained regenerated lithium iron phosphate positive electrode material is prepared into a button cell according to the method for preparing the button cell in the embodiment 1, and the prepared button cell is subjected to related charge and discharge tests:
the button cell is charged to 3.75V by 0.2C constant current, then discharged to 2.7V by 0.2C constant current, and circularly charged and discharged, the gram capacity of active substances in the positive electrode of the button cell is calculated, and the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 146mAh/g and the first discharge efficiency can reach 92 percent through testing.
Example 5
The embodiment provides a preparation method of a regenerated lithium iron phosphate anode material, which specifically comprises the following steps:
1. taking leftovers of a lithium iron phosphate positive plate as a raw material, and crushing the leftovers of the lithium iron phosphate positive plate to a particle size of not more than 30 mm;
2. drying the crushed lithium iron phosphate positive plate to ensure that the water content of the dried lithium iron phosphate positive plate is less than 1%; the water content of the dried lithium iron phosphate positive plate is obtained by detecting through an online testing instrument;
3. adding a cracking auxiliary material with the granularity of more than 100 meshes and the Mohs hardness of more than 6.0 into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the cracking furnace is less than 0.2%, cracking for 1h at the cracking temperature of 400 ℃, and controlling the retention time of gas (namely cracking gas) generated by cracking to be less than 10s in the cracking furnace to obtain a mixture, wherein the mixture comprises lithium iron phosphate powder, the cracking auxiliary material and an aluminum sheet; the retention time of the cracking gas is controlled by controlling the gas flow of the cracking furnace, and the furnace body type of the cracking furnace comprises but is not limited to a roller kiln, a rotary kiln, a tubular furnace and the like; the cracking auxiliary material comprises one or more of calcium oxide, potassium oxide and sodium oxide, preferably, the granularity of the cracking auxiliary material is more than 100 meshes, and the Mohs hardness is more than 6.0, so that the cracking auxiliary material is convenient to separate after pyrolysis; the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive plate is 1: (25-50). And adding a cracking auxiliary material to ensure that PVDF in the lithium iron phosphate positive plate to be regenerated is completely cracked into solid carbon and gaseous fluoride, so that the influence of residual fluoride on the subsequent application of the lithium iron phosphate positive plate is avoided, and meanwhile, the solid carbon formed by cracking carbon is used as the supplement of a carbon coating layer of the lithium iron phosphate positive plate. After adding cracking auxiliary materials, detecting that the residual quantity of fluorine in the lithium iron phosphate powder after anaerobic cracking is less than 100 ppm;
4. performing vibration screening on the mixture to separate lithium iron phosphate powder, aluminum sheets and cracking auxiliary materials, adding a vibration screening pellet into a vibration screening device, wherein the vibration screening pellet is made of rubber, the vibration screening time is 10min, and the mesh number of a screen is 20-325 meshes;
5. after separation is finished, removing impurities from the collected lithium iron phosphate powder to obtain a lithium iron phosphate composite material, wherein the impurities of the lithium iron phosphate powder mainly remove impurities such as aluminum, copper and iron, and the like, and the impurities removing mode comprises but is not limited to color separation, magnetic separation, gravity separation, flotation and the like, and the lithium iron phosphate composite material comprises carbon-coated lithium iron phosphate and conductive agent carbon;
6. and (3) scattering the lithium iron phosphate composite material obtained in the step (5) until D99 is less than or equal to 15um, so as to obtain a regenerated lithium iron phosphate positive electrode material, wherein D99 is less than or equal to 15um, which means that the particle size of at least 99% of the lithium iron phosphate composite material is less than or equal to 15 micrometers. In the example, the lithium iron phosphate composite material is broken up to the industry standard by grinding, i.e., the particle size is 15 micrometers or less.
The obtained regenerated lithium iron phosphate positive electrode material is prepared into a button cell according to the method for preparing the button cell in the embodiment 1, and the prepared button cell is subjected to related charge and discharge tests:
the button cell is charged to 3.75V by 0.2C constant current, then discharged to 2.7V by 0.2C constant current, and circularly charged and discharged, the gram capacity of active substances in the positive electrode of the button cell is calculated, and the first discharge specific capacity of the regenerated lithium iron phosphate positive electrode material can reach 138mAh/g and the first discharge efficiency can reach 85% through testing.
The beneficial effects of the invention are:
1. the method avoids the reaction of water, oxygen and cracking gas (such as fluorine-containing substances) with lithium iron phosphate and/or carbon in the lithium iron phosphate positive plate by simultaneously controlling the water content, the oxygen content and the residence time of the cracking gas in the cracking furnace, and the control conditions of the water content, the oxygen content and the residence time of the cracking gas in the cracking furnace are mutually matched, cooperated and absent. The adopted anaerobic cracking technology can well reserve the carbon coating layer on the surface of the lithium iron phosphate particles. In addition, although PVDF (polyvinylidene fluoride) can be removed by conventional sintering or baking, iron in the lithium iron phosphate positive plate can be oxidized; in the traditional sintering or roasting process, the carbon coating layer on the surface of the lithium iron phosphate can be removed while the conductive agent carbon and the residual carbon of PVDF are removed, so that the repair difficulty of the subsequent process is increased; the method effectively reserves the conductive agent carbon and the carbon coating layer through one-step anaerobic cracking, reduces the addition of subsequent carbon sources, and can directly manufacture the battery without secondary carbon coating and conductive agent supplement of the obtained regenerated lithium iron phosphate cathode material, thereby saving the cost and simplifying the process flow;
2. and introducing cracking auxiliary materials to completely crack the PVDF into carbon instead of fluorine-containing biphenyl substances. After pyrolysis of PVDF, hydrogen fluoride, vinylidene fluoride monomer and fluorine substituted benzene substances (biphenyl) can be generated; among the substances, hydrogen fluoride, vinylidene fluoride monomer and fluorine substituted benzene can be removed in a gas form, but fluorine substituted substances in cracking residues are not easy to remove and can be adhered to lithium iron phosphate powder, so that the first charge-discharge capacity is influenced, particle adhesion is caused, and the purity of the electrolyte is influenced; in general, the cracking process needs to ensure complete decomposition of PVDF, and the residual carbon is used as a supplemental carbon coating layer of the lithium iron phosphate material, so as to realize direct regeneration of the lithium iron phosphate material. In order to achieve the purpose, cracking auxiliary materials are required to be introduced to ensure that the PVDF is completely cracked into carbon instead of fluorine-containing biphenyl substances under the process conditions.
3. The lithium iron phosphate anode plate is cracked in one step, the regeneration effect of the lithium iron phosphate anode plate is achieved, residual electrolyte on the surface of the lithium iron phosphate anode plate can be removed, PVDF can be removed, the cohesiveness of the PVDF is invalid, lithium iron phosphate powder is separated from the surface of an aluminum sheet, and compared with the traditional two-step sintering, the energy is saved by more than one time;
4. according to the invention, through pretreatment crushing, the size of the lithium iron phosphate positive plate entering the cracking furnace is enlarged to 50mm, so that the introduction of aluminum impurities in the pretreatment process can be effectively reduced, and the content of the aluminum impurities can be reduced to below 500ppm after cracking;
5. the regenerated lithium iron phosphate anode material obtained by the invention effectively reduces the addition of a conductive agent at the battery manufacturing end, and simultaneously, each performance index of the regenerated lithium iron phosphate anode material is comparable to that of a commercial lithium iron phosphate anode material, the first discharge specific capacity is as high as 154mAh/g, and the first discharge efficiency is as high as 93%;
6. the method has the advantages of simple and efficient process, low energy consumption, lower operation cost compared with the traditional lithium iron phosphate regeneration mode, and better environmental protection.
Although embodiments of the present invention have been shown and described, it should be understood that the above embodiments are illustrative and not restrictive, and that any modifications, equivalents, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A preparation method of a regenerated lithium iron phosphate anode material is characterized by comprising the following steps:
s1: crushing a lithium iron phosphate positive plate to be regenerated, wherein the particle size of the crushed lithium iron phosphate positive plate is not more than 50mm, and the lithium iron phosphate positive plate to be regenerated is a lithium iron phosphate positive plate leftover and/or a defective lithium iron phosphate positive plate in a battery factory;
s2: drying the crushed lithium iron phosphate positive plate, wherein the water content of the dried lithium iron phosphate positive plate is less than 1%;
s3: adding a cracking auxiliary material into the dried lithium iron phosphate positive plate, then putting the dried lithium iron phosphate positive plate added with the cracking auxiliary material into a cracking furnace for anaerobic cracking, wherein the oxygen content in the anaerobic cracking atmosphere is less than or equal to 0.2%, cracking for 0.5-2h at the cracking temperature of 400 plus-sand-salt 600 ℃, and controlling the retention time of gas generated by cracking in the cracking furnace to be less than 10s to obtain a mixture comprising an aluminum sheet, the cracking auxiliary material and lithium iron phosphate powder;
s4: separating an aluminum sheet, a cracking auxiliary material and lithium iron phosphate powder in the mixture, collecting the lithium iron phosphate powder, and removing impurities from the lithium iron phosphate powder to obtain a lithium iron phosphate composite material;
s5: and (3) scattering the lithium iron phosphate composite material until D99 is less than or equal to 15um to obtain the regenerated lithium iron phosphate anode material.
2. The method for preparing the regenerated lithium iron phosphate cathode material of claim 1, wherein in step S3, the cracking auxiliary material comprises one or more of calcium oxide, potassium oxide and sodium oxide.
3. The preparation method of the regenerated lithium iron phosphate cathode material according to claim 2, wherein the cracking auxiliary material has a particle size larger than 100 meshes and a Mohs hardness larger than 6.0.
4. The method for preparing a regenerated lithium iron phosphate cathode material according to claim 1, wherein in step S3, the retention time of the gas generated by cracking in the cracking furnace is controlled to be less than 3S;
in step S2, the moisture content of the dried lithium iron phosphate positive electrode sheet is less than 0.5%.
5. The preparation method of the regenerated lithium iron phosphate positive electrode material according to any one of claims 1 to 3, wherein the mass ratio of the cracking auxiliary material to the dried lithium iron phosphate positive electrode sheet is 1: (25-50).
6. The method for preparing a regenerative lithium iron phosphate positive electrode material as claimed in claim 1, wherein in step S3, the cracking furnace comprises a roller kiln, a rotary kiln and a tube furnace;
in step S4, impurities in the lithium iron phosphate powder are removed to mainly remove aluminum, copper and iron.
7. The preparation method of the regenerated lithium iron phosphate positive electrode material according to claim 1 or 6, wherein the impurity removal manner of the lithium iron phosphate powder material includes color separation, magnetic separation, gravity separation and flotation.
8. The method for preparing a regenerated lithium iron phosphate positive electrode material according to claim 1, wherein in step S1, the particle size of the crushed lithium iron phosphate positive electrode sheet is not greater than 30 mm.
9. The regenerated lithium iron phosphate positive electrode material is characterized in that the regenerated lithium iron phosphate positive electrode material prepared by the preparation method of the regenerated lithium iron phosphate positive electrode material according to any one of claims 1 to 8 comprises carbon-coated lithium iron phosphate and conductive agent carbon.
10. The application of the regenerated lithium iron phosphate positive electrode material in the preparation of the lithium iron phosphate battery is characterized in that the regenerated lithium iron phosphate positive electrode material according to claim 9 is independently used for the preparation of the lithium iron phosphate battery; or
The regenerated lithium iron phosphate positive electrode material according to claim 9 is used for preparing a lithium iron phosphate battery by being compounded with a commercial lithium iron phosphate positive electrode material or a repaired and regenerated lithium iron phosphate positive electrode material.
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