Lithium iron phosphate positive electrode material precursor, preparation method and device thereof and application thereof

Abstract

The application discloses a lithium iron phosphate positive electrode material precursor, a preparation method and device thereof and application thereof. The lithium iron phosphate positive electrode material precursor is prepared through two-step oxidation and heat preservation, and the end point of the two-step oxidation is monitored through ferrous ion concentration, which is beneficial to the removal of impurities in the lithium iron phosphate positive electrode material precursor, and raw materials from nickel iron ore can be used, so that the lithium iron phosphate positive electrode material precursor has the advantages of wide raw material sources, sufficient reaction and high product purity.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and more specifically, to lithium iron phosphate cathode material precursors, their preparation methods, apparatus, and applications. Background Technology

[0002] With the growing attention given to the research and industrialization of new energy vehicles, lithium iron phosphate has become one of the mainstream cathode materials for new energy vehicle batteries.

[0003] Currently, there are three main methods for preparing lithium iron phosphate: ① Ferrous oxalate method and ferrous acetate method: This method was the first proposed process for preparing lithium iron phosphate and is currently the main process used in large-scale industrial production. However, it is difficult, the product has low compaction density, and the cost is high, so it has been gradually phased out. ② Iron oxide red method: The Fe2O3 raw material used in this method has relatively strict requirements, and the form and amount of divalent iron oxides may vary depending on the preparation process. ③ Ferric phosphate method and ferrous phosphate method: This is the current mainstream process route, but it requires that the iron-phosphorus molar ratio and the number of water of crystallization in the ferrous phosphate raw material be constant to ensure the accuracy of the formulation. It has now become the mainstream process route.

[0004] The precursor of lithium iron phosphate is iron phosphate. To date, the main methods for synthesizing iron phosphate include co-precipitation, hydrothermal, ultrasonic chemical, sol-gel, fluorine system, surfactant template, and biotemplate methods. The existing processes and equipment for preparing lithium iron phosphate cathode material precursors have the following problems: 1. The available raw materials are relatively limited, failing to meet the synthesis requirements of various raw materials such as nickel-iron systems, and thus hindering the production of lower-cost iron phosphate; 2. Incomplete reaction of raw materials results in numerous impurities and low product purity; monitoring indicators are not sensitive enough, leading to significant errors and affecting production stability.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium iron phosphate cathode material precursor, its preparation method, apparatus and application. The preparation method has high controllability and low requirements for raw materials. The prepared lithium iron phosphate cathode material precursor has a low impurity content, which is beneficial to obtaining a high-quality lithium iron phosphate cathode material precursor.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a lithium iron phosphate cathode material precursor, comprising:

[0009] Primary oxidation involves reacting a phosphorus-containing solution containing ferrous ions and phosphate with a first oxidant to obtain a first ferric phosphate slurry. The ferrous content in the first ferric phosphate slurry is 12-14 g / L, the concentration of ferrous ions in the phosphorus-containing solution is greater than 30 g / L, and the iron-phosphorus molar ratio in the phosphorus-containing solution is 0.9-1.0.

[0010] An induction reaction is carried out by adding an inducer that promotes the formation of FePO4 crystals to the first iron phosphate slurry to obtain a second iron phosphate slurry.

[0011] Secondary oxidation involves adding a second oxidant to the second ferric phosphate slurry to react and obtain a third ferric phosphate slurry, wherein the concentration of ferrous ions in the third ferric phosphate slurry is 1 g / L-2 g / L.

[0012] After aging and solid-liquid separation, the third iron phosphate slurry is calcined to obtain the lithium iron phosphate cathode material precursor.

[0013] In an optional embodiment, the iron-phosphorus molar ratio of the phosphorus-containing solution is 0.96-0.98, and the ferrous ion concentration in the phosphorus-containing solution is 40 g / L-70 g / L.

[0014] Preferably, the temperature of the primary oxidation step is 45℃-55℃;

[0015] Preferably, the first oxidant is hydrogen peroxide.

[0016] In an optional embodiment, the inducing agent is hexadecyltrimethylammonium bromide;

[0017] Preferably, the amount of the inducing agent is 1.5wt%-2.5wt% of the first ferric phosphate slurry;

[0018] Preferably, the induction reaction is carried out at a temperature of 65℃-75℃ for 2.5h-3.5h.

[0019] In an optional embodiment, the temperature of the secondary oxidation step is 90℃-100℃, and the time is 3.5h-4.5h;

[0020] Preferably, the second oxidant is hydrogen peroxide.

[0021] In an optional embodiment, the aging step is performed at a temperature of 70°C-95°C for 8-10 hours.

[0022] In an optional embodiment, the calcination temperature is 550℃-600℃ and the time is 2.5-3.5h.

[0023] Secondly, the present invention provides an apparatus for the preparation method of lithium iron phosphate cathode material precursor according to any one of the foregoing embodiments, comprising: a phosphorus-containing liquid tank, a multi-stage reaction tank and an aging and heat preservation tank connected in series, wherein the multi-stage reaction tank is provided with an inducer dosing tube and an oxidant dosing tube for adding a first oxidant and a second oxidant, and a dosing control probe for measuring the concentration of ferrous ions is also provided in the multi-stage reaction tank, wherein the dosing control probe is connected to a dosing controller capable of controlling the liquid flow rate in the oxidant dosing tube via a dosing control signal line.

[0024] In an optional embodiment, the aging and heat preservation tank is connected in series via a discharge pipe to a filter press for pressing the slurry, a drying device for drying the filter cake obtained by pressing, and a rotary kiln for calcining the dried material.

[0025] Thirdly, the present invention provides a lithium iron phosphate cathode material precursor, which is prepared by the preparation method of lithium iron phosphate cathode material precursor described in any one of the foregoing embodiments.

[0026] Fourthly, the present invention provides a lithium iron phosphate cathode material, which is obtained by sintering a lithium iron phosphate cathode material precursor as described in the foregoing embodiments with a lithium source.

[0027] Fifthly, the present invention provides a lithium-ion battery comprising the lithium iron phosphate cathode material described in the foregoing embodiments.

[0028] The present invention has the following beneficial effects:

[0029] This invention facilitates the removal of impurities from lithium iron phosphate cathode material precursors through two-step oxidation and heat preservation, and by monitoring the endpoint of the two-step oxidation through ferrous iron concentration. Furthermore, it can utilize raw materials derived from nickel-iron ore, achieving the advantages of wide availability of raw materials, complete reaction, and high product purity. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the preparation method of the lithium iron phosphate cathode material precursor in Example 1 of the present invention;

[0032] Figure 2 This is a schematic diagram of the device for the lithium iron phosphate cathode material precursor used in Embodiment 1 of the present invention;

[0033] Figure 3 This is a SEM image of the lithium iron phosphate cathode material precursor prepared in Example 1;

[0034] Figure 4 This is a SEM image of the lithium iron phosphate cathode material precursor prepared in Example 2.

[0035] In the diagram: 1.1 - Feed pipe for phosphate-prepared solution; 1.2 - Tank for phosphate-prepared solution; 1.3 - Pump for phosphate-prepared solution; 2.1 - Steam pipe; 2.1.1 - Steam heating coil; 2.2 - Hydrogen peroxide dosing pump; 2.3 - Dosing controller; 2.3.1 - Dosing control probe; 2.3.2 - Dosing control signal line; 2.4 - Inducer dosing pump; 2.6 - Multistage reaction tank; 2.7 - Aging and heat preservation tank; 2.8 - Filter press; 2.9 - Flash evaporation device; 2.10 - Rotary kiln; 2.11 - Finished product. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0037] This invention provides a method for preparing a lithium iron phosphate cathode material precursor, comprising:

[0038] Primary oxidation involves reacting a phosphorus-containing solution containing ferrous ions and phosphate with a first oxidant to obtain a first ferric phosphate slurry. The ferrous content in the first ferric phosphate slurry is 12-14 g / L, the concentration of ferrous ions in the phosphorus-containing solution is greater than 30 g / L, and the iron-phosphorus molar ratio in the phosphorus-containing solution is 0.9-1.0.

[0039] An induction reaction is carried out by adding an inducer that promotes the formation of FePO4 crystals to the first iron phosphate slurry to obtain a second iron phosphate slurry.

[0040] Secondary oxidation involves adding a second oxidant to the second ferric phosphate slurry to react and obtain a third ferric phosphate slurry, wherein the concentration of ferrous ions in the third ferric phosphate slurry is 1 g / L-2 g / L.

[0041] After aging and solid-liquid separation, the third iron phosphate slurry is calcined to obtain the lithium iron phosphate cathode material precursor.

[0042] The content of impurities in the precursor of lithium iron phosphate cathode material has a significant impact on the lithium iron phosphate cathode material itself. The leachate obtained by acid leaching of nickel iron ore contains a large amount of nickel and sulfur elements, which are easily trapped in the precursor of lithium iron phosphate cathode material, thus making it difficult to obtain high-quality lithium iron phosphate cathode material.

[0043] In this embodiment of the invention, during the initial oxidation, a first oxidant is used to oxidize most of the ferrous ions in the reaction solution to ferric iron, resulting in a first ferric phosphate slurry. The first ferric phosphate slurry is acidic, which is unfavorable for the precipitation of ferric phosphate. Therefore, after the primary reaction, an inducing agent is added to the reaction solution to induce the precipitation of ferric phosphate under acidic conditions, resulting in a second ferric phosphate slurry with a higher concentration of ferric phosphate crystals. Simultaneously, while ferric phosphate crystals precipitate, a large number of unoxidized ferrous ions remain in the reaction system. The ferric iron in the ferric phosphate crystals undergoes a displacement reaction with the free ferrous ions in the reaction system. The movement of iron ions enlarges the channels in the ferric phosphate crystals, which facilitates the removal of impurities such as Ni and S trapped in the ferric phosphate precipitate. Therefore, the purity of the ferric phosphate crystals in the third ferric phosphate slurry is greater than that in the second ferric phosphate slurry, which helps reduce the impurity content in the lithium iron phosphate cathode material precursor product.

[0044] In addition, a secondary oxidation process was carried out after the induction reaction to oxidize the remaining ferrous ions in the second ferric phosphate slurry. It should be noted that during the secondary oxidation, not all ferrous ions were oxidized, and some ferrous ions remained, resulting in a ferrous ion concentration of 1g / L-2g / L in the third ferric phosphate slurry. This allows ferrous ions to undergo a displacement reaction with ferric ions in the subsequent aging process, promoting the removal of impurities.

[0045] It should be noted that since the pH of the solution after phosphorus preparation is approximately 0.5, which is relatively acidic, the pH fluctuation is small as the reaction proceeds, resulting in low monitoring accuracy. In this application, the reaction progress is monitored by the concentration of ferrous ions, which is more accurate than pH measurement. Furthermore, the utilization rate of the oxidant is relatively higher in the initial reaction step. Therefore, while ensuring that impurity removal meets requirements, the ferrous ion content in the first ferric phosphate slurry should be as low as possible. Increasing the ferrous ion concentration in the third ferric phosphate slurry within a certain range is beneficial for impurity removal, but excessively high concentrations are detrimental to improving the ferrous ion conversion rate.

[0046] After aging, the slurry undergoes solid-liquid separation, primarily to remove free water trapped in the iron phosphate. However, since the iron phosphate crystals also contain bound water, calcination is necessary to remove the bound water and obtain the lithium iron phosphate cathode material precursor. Furthermore, during calcination, impurities such as sulfur escape, and the escape of impurities and bound water creates numerous channels, which helps increase the specific surface area of ​​the lithium iron phosphate cathode material precursor.

[0047] In some embodiments, the iron-phosphorus molar ratio of the phosphorus-containing solution is 0.96-0.98;

[0048] Normally, the iron-phosphorus molar ratio in the phosphorus-containing solution used in the preparation of lithium iron phosphate cathode material precursors is about 0.9. In the embodiments of the present invention, the iron-phosphorus molar ratio in the phosphorus-containing solution can be increased to 0.96-0.98, which is beneficial to improving the utilization rate of phosphorus.

[0049] In some embodiments, the concentration of ferrous ions in the phosphorus-containing solution is 40 g / L to 70 g / L.

[0050] Typically, the concentration of ferrous ions in the phosphorus-containing solution used in the preparation of lithium iron phosphate cathode material precursors is 40 g / L-50 g / L. If the phosphorus-containing solution is concentrated to increase the concentration of ferrous ions, the concentration of impurities in the solution will also increase proportionally, leading to an increase in the impurity content trapped in the iron phosphate crystals and a decrease in the quality of the final lithium iron phosphate cathode material precursor. In this application, through a two-stage oxidation-induced and aging process, the impurities trapped in the iron phosphate crystals are significantly reduced. Therefore, the preparation method described in this application can obtain high-quality lithium iron phosphate cathode material precursors even using a concentrated phosphorus-containing solution with a higher concentration of ferrous ions. Increasing the concentration of ferrous ions in the phosphorus-containing solution in this invention is beneficial for increasing production capacity and reducing energy consumption.

[0051] In some embodiments, the temperature of the primary oxidation step is 45°C-55°C, which is conducive to the oxidation reaction and improves the utilization rate of the first oxidant.

[0052] In some embodiments, the first oxidant is hydrogen peroxide, which can oxidize ferrous ions to ferric ions without introducing impurities.

[0053] In some embodiments, the inducing agent is hexadecyltrimethylammonium bromide, which can effectively promote the precipitation of ferric phosphate under acidic conditions.

[0054] In some embodiments, the amount of the inducer is 1.5wt%-2.5wt% of the first ferric phosphate slurry. Controlling the amount of the inducer helps to promote the precipitation of ferric phosphate while avoiding the influence of inducer residue on the final product.

[0055] In some embodiments, the induction reaction is carried out at a temperature of 65°C-75°C for 2.5-3.5 hours. In this embodiment, the primary oxidation reaction releases heat, causing the temperature of the reaction system to rise; at the same time, in order to control the precipitation rate of iron phosphate crystals to avoid excessive impurity inclusions, the temperature of the induction reaction should not be too high.

[0056] In some embodiments, the temperature of the secondary oxidation step is 90℃-100℃, and the time is 3.5h-4.5h. In the embodiments of this application, the secondary oxidation step releases heat, causing the temperature of the reaction solution to rise. Therefore, the temperature of the secondary oxidation step is higher than the temperature of the induction reaction. At the same time, holding at this temperature for 3.5h-4.5h is beneficial for the iron phosphate crystals to transform from amorphous crystals to crystalline crystals.

[0057] In some embodiments, the second oxidant is hydrogen peroxide, which can oxidize ferrous ions to ferric ions without introducing impurities.

[0058] In some embodiments, the aging step is performed at a temperature of 70°C-95°C for 8-10 hours. This temperature is conducive to the further growth and improvement of iron phosphate crystals.

[0059] In some embodiments, the calcination temperature is 550℃-600℃, and the time is 2.5-3.5h. This temperature is beneficial for the removal of bound water and impurities, while also ensuring that the lithium iron phosphate cathode material precursor has a suitable specific surface area.

[0060] Another embodiment of the present invention provides an apparatus for the preparation method of lithium iron phosphate cathode material precursor according to any one of the foregoing embodiments, comprising: a phosphorus-mixing liquid tank 1.2, a multi-stage reaction tank 2.6, and an aging and heat preservation tank 2.7 connected in series. The multi-stage reaction tank 2.6 is provided with an inducer dosing pipe and an oxidant dosing pipe for adding a first oxidant and a second oxidant. The multi-stage reaction tank 2.6 is also provided with a dosing control probe 2.3.1 for measuring the concentration of ferrous ions. The dosing control probe 2.3.1 is connected to a dosing controller 2.3 capable of controlling the liquid flow rate in the oxidant dosing pipe via a dosing control signal line 2.3.2.

[0061] In this embodiment, the concentration of ferrous ions in the reaction solution is measured by a dosing control probe 2.3.1, and the concentration is fed back to the dosing controller 2.3 in real time so that the dosing controller 2.3 can control the amount of the first or second oxidant added. Determining the amount of oxidant added by detecting the ferrous ion concentration is a highly automated process with high accuracy and low human error, which helps improve production efficiency and product stability.

[0062] In some embodiments, the aging and heat preservation tank includes, in series via a discharge pipe, a filter press 2.8 for pressing and filtering the slurry, a drying device for drying the filter cake obtained by pressing and filtering, and a rotary kiln 2.10 for calcining the dried material.

[0063] Specifically, the workflow of the lithium iron phosphate cathode material precursor production apparatus in this embodiment of the invention is as follows:

[0064] A. Primary Reaction: The phosphate-prepared solution enters the phosphate-prepared solution tank 1.2 through the phosphate-prepared solution feed pipe 1.1, and then enters the multi-stage reaction tank 2.6 through the phosphate-prepared solution pump 1.3. Steam enters the steam heating coil 2.1.1 through the steam pipe 2.1 to heat the phosphate-prepared solution in the multi-stage reaction tank 2.6. Stirring is started. When the liquid temperature reaches the specified temperature, the dosing controller 2.3 preliminarily calculates the first hydrogen peroxide addition based on the monitored ferrous content, starts the hydrogen peroxide dosing pump 2.2, and adds hydrogen peroxide into the multi-stage reaction tank 2.6 for oxidation reaction until the ferrous content in the first ferric phosphate slurry is 12-14 g / L. If the amount of hydrogen peroxide added is insufficient, the dosing controller 2.3 can control the hydrogen peroxide dosing pump 2.2 to add more hydrogen peroxide. To avoid large temperature fluctuations in the multi-stage reaction tank 2.6 caused by the addition of hydrogen peroxide, a steam pipe 2.1 can be installed outside the oxidant dosing pipe to preheat the oxidant.

[0065] B. Induction reaction: By increasing the steam volume of the steam heating coil 2.1.1, the temperature of the liquid after the first oxidation is increased to the specified temperature for the induction reaction. Then, the inducing agent dosing pump 2.4 is started by the dosing controller 2.3. After quantitative dosing of the inducing agent, the temperature is kept at a preset time to achieve the precipitation of ferric phosphate and promote the removal of Ni and S impurities, thereby improving the purity of ferric phosphate in the slurry.

[0066] C. Secondary oxidation reaction: After the induction reaction is completed, the ferrous concentration is detected by the dosing controller 2.3, and the amount of hydrogen peroxide added by the hydrogen peroxide dosing pump 2.2 is calculated and adjusted according to the ferrous concentration feedback signal. The steam volume of the steam heating coil 2.1.1 is increased to raise the temperature to the secondary oxidation temperature and then kept at that temperature. During this process, hydrogen peroxide is added a second time in a quantitative manner to achieve the formation of ferric phosphate precipitate by ferrous phosphate and phosphoric acid under the oxidation of hydrogen peroxide, thereby improving the utilization rate of ferrous phosphate and the purity of the ferric phosphate precipitate.

[0067] D. The ferric phosphate slurry produced after the reaction in the multi-stage reaction tank 2.6 is pumped to the aging and heat preservation tank 2.7, where the aging reaction is completed, further promoting the crystallization of ferric phosphate. The formed ferric phosphate slurry is pumped into the filter press 2.8 for filtration and washing. After impurities are removed, the ferric phosphate filter cake is conveyed by belt to the flash evaporator 2.9 for crushing and drying into ferric phosphate powder. Subsequently, the ferric phosphate powder enters the rotary kiln 2.10 for calcination, dehydration, and desulfurization to produce qualified ferric phosphate products.

[0068] In this invention, the input end of the dosing controller 2.3 is connected to the dosing control probe 2.3.1 via a dosing control signal line 2.3.2, and the output end is connected to the hydrogen peroxide dosing pump 2.2 and the inducer dosing pump 2.4 via the dosing control signal line 2.3.2. The dosing control probe 2.3.1 detects the temperature and ferrous concentration. After the temperature reaches the target, the dosing controller 2.3 calculates the hydrogen peroxide dosage using its built-in dosing calculation program based on the feedback ferrous concentration signal. The flow rate adjustment knob of the hydrogen peroxide dosing pump 2.2 is then adjusted according to the calculated dosage to achieve automatic dosing control. Similarly, the dosing controller 2.3 calculates the inducer dosage using its built-in dosing calculation program based on the feedback total iron concentration signal. The flow rate adjustment knob of the inducer dosing pump 2.4 is then adjusted according to the calculated dosage to achieve automatic dosing control.

[0069] Another embodiment of the present invention provides a lithium iron phosphate cathode material precursor, which is prepared by the preparation method of lithium iron phosphate cathode material precursor described in any one of the foregoing embodiments.

[0070] Another embodiment of the present invention provides a lithium iron phosphate cathode material, which is obtained by sintering a lithium iron phosphate cathode material precursor as described in the foregoing embodiments with a lithium source.

[0071] The present invention provides a positive electrode sheet, comprising the positive electrode material described in the foregoing embodiments.

[0072] In the positive electrode sheet of the present invention, the positive electrode film layer typically comprises the aforementioned positive electrode material, as well as optionally a binder and optionally a conductive agent, and is typically formed by coating a positive electrode slurry and then drying and cold pressing it. The positive electrode slurry is typically formed by dispersing the aforementioned positive electrode material, optionally a conductive agent, and optionally a binder in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP).

[0073] In some optional embodiments, the positive electrode film may contain 70 wt% to 97 wt% of positive electrode material, based on the total weight of the positive electrode film. Optionally, the weight percentage of the positive electrode material in the positive electrode film is 85% to 97%, 90% to 97%, or 95% to 97%. By adjusting the proportion of positive electrode material in the positive electrode film, the energy density and cycle life of the lithium-ion battery can be further improved.

[0074] In some embodiments, the binder for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and modified polymers thereof.

[0075] Conductive agents can improve the electronic conductivity of the positive electrode film. In some optional embodiments, the positive electrode film may contain 2 wt% to 20 wt% of conductive agent based on the total weight of the positive electrode film. Optionally, the conductive agent may account for 2% to 10% or 2% to 5% of the weight of the positive electrode film.

[0076] In some embodiments, the conductive agent of the positive electrode film may include one or more of superconducting carbon, carbon black (such as SuperP, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] It should be noted that the composition or parameters of each positive electrode film layer given in this invention refer to the composition or parameter range of the single-sided film layer of the positive electrode current collector. When the positive electrode film layer is disposed on two opposite surfaces of the positive electrode current collector, if the composition or parameters of the positive electrode film layer on either surface satisfy this invention, it is considered to fall within the protection scope of this invention.

[0078] The present invention provides a lithium-ion battery, including the positive electrode sheet described in the foregoing embodiments, and further including a negative electrode sheet, an electrolyte and a separator.

[0079] [Negative electrode plate]

[0080] The negative electrode sheet of the present invention includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0081] As an example, the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is laminated on either or both of the two opposite surfaces of the negative electrode current collector.

[0082] The negative electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In some embodiments, the negative electrode current collector can be made of copper foil.

[0083] In the negative electrode sheet of this invention, the negative electrode film layer typically comprises a negative electrode active material, and optionally a binder, optionally a conductive agent, and other optional additives. It is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode and positive electrode materials, and optionally a conductive agent, optionally a binder, and optionally additives, in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0084] In some embodiments, the negative electrode active material may include one or more of artificial graphite, natural graphite, silicon-based materials, and tin-based materials. Optionally, the negative electrode active material includes one or more of artificial graphite and natural graphite. Optionally, the negative electrode active material includes artificial graphite.

[0085] In some embodiments, the conductive agent may include one or more of superconducting carbon, carbon black (e.g., SuperP, acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the adhesive may include one or more of styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0087] In some embodiments, other optional additives include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0088] [Electrolytes]

[0089] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This invention does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from electrolyte solutions. The electrolyte solution includes an electrolyte salt and a solvent.

[0090] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate 2 (LiPO2F), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0091] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0092] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0093] [Isolation membrane]

[0094] A separator is disposed between the positive and negative electrode plates, serving as a separator. The lithium-ion battery of this invention does not have particular limitations on the type of separator; any known porous separator used in lithium-ion batteries can be selected. For example, the separator can be selected from glass fiber film, non-woven fabric film, polyethylene film, polypropylene film, polyvinylidene fluoride film, and one or more multilayer composite films comprising one or more of these materials.

[0095] Positive electrode, negative electrode, and separator can be stacked or wound to form an electrode assembly, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then placed in an outer package, filled with electrolyte, and sealed to obtain a lithium-ion battery.

[0096] The outer packaging of a lithium-ion battery is used to encapsulate the electrode assembly and electrolyte. In some embodiments, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging of a lithium-ion battery can also be a pouch, such as a pouch. The material of the pouch can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0097] This invention does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.

[0098] In some embodiments, lithium-ion batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0099] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0100] The present invention provides an electrical device, including the lithium-ion battery described in the foregoing embodiments.

[0101] This invention also provides an electrical device, comprising at least one of the lithium-ion battery, battery module, or battery pack described in this invention. The lithium-ion battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. The device can select the lithium-ion battery, battery module, or battery pack according to its usage requirements.

[0102] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0103] Example 1

[0104] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor, with specific steps as follows: Figure 1 As shown, use as Figure 2 The device shown, the specific steps include:

[0105] Primary reaction: Fe is selected 2+ Concentration 65g / L, Ni 2+ A 400L solution of phosphorus preparation solution with a concentration of 62g / L and an iron-to-phosphorus ratio of 0.965 was pumped from the phosphorus preparation solution tank into a multi-stage reaction tank. The solution was heated to 50°C by a steam heating coil 2.1.1, and then 23.02kg of 27.5% hydrogen peroxide was added by a dosing controller. After the primary reaction was completed, the ferrous iron concentration in the reaction system was 13.2g / L.

[0106] Induction reaction: After the primary reaction is completed, the liquid in the multi-stage reaction tank is heated to 70°C using a steam heating coil 2.1.1. The dosing controller then adds CTAB inducer to promote precipitation via a dosing pump. The amount of CTAB added is 2 wt% of the liquid in the multi-stage reaction tank. After adding CTAB, the reaction solution is kept at 70°C for 3 hours. During this holding period, the amorphous ferric phosphate precipitate is converted into orthorhombic ferric phosphate.

[0107] Secondary oxidation: After the induction reaction, the dosing controller automatically monitors the ferrous concentration in the reaction solution and adds 5.7 kg of hydrogen peroxide at a concentration of 27.5% to the reaction solution until the ferrous concentration is 1.51 g / L. The liquid is then heated to 95°C using a heating coil and held at that temperature for 4 hours.

[0108] Aging, pressure filtration, flash evaporation, and rotary kiln calcination: After the liquid in the multi-stage reaction tank is kept at 95℃ for 4 hours, it enters the aging tank and is kept at 9 hours. After aging, it enters the pressure filtration system, where it is filtered and washed to obtain a filter cake. At this point, ICP analysis shows that the Ni content in the filter cake is 90 ppm and the S content is 2000 ppm. The filter cake is then flash-dried and calcined in a rotary kiln at 580℃ for 3 hours to obtain the finished ferric phosphate. ICP analysis of the finished ferric phosphate shows that the Ni content is 120 ppm and the S content is 150 ppm. SEM images of the finished ferric phosphate are shown below. Figure 3 The particles have high sphericity and concentrated particle size distribution.

[0109] Example 2:

[0110] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor, with specific steps as follows: Figure 1 As shown, use as Figure 2 The device shown, the specific steps include:

[0111] Primary reaction: Fe is selected 2+ Concentration 65g / L, Ni 2+ A 400L solution of phosphorus preparation solution with a concentration of 62g / L and an iron-to-phosphorus ratio of 0.963 was pumped from the phosphorus preparation solution tank into a multi-stage reaction tank. The solution was heated to 50°C by a steam heating coil 2.1.1, and then 23.12kg of 27.5% hydrogen peroxide was added by a dosing controller. After the primary reaction was completed, the ferrous iron concentration in the reaction system was 12.8g / L.

[0112] Induction reaction: After the primary reaction is completed, the liquid in the multi-stage reaction tank is heated to 70°C using a steam heating coil 2.1.1. The dosing controller then adds CTAB inducer to promote precipitation via a dosing pump. The amount of CTAB added is 2 wt% of the liquid in the multi-stage reaction tank. After adding CTAB, the reaction solution is kept at 70°C for 3 hours. During this holding period, the amorphous ferric phosphate precipitate is converted into orthorhombic ferric phosphate.

[0113] Secondary oxidation: After the induction reaction, the dosing controller automatically monitors the ferrous concentration in the reaction solution and adds 5 kg of hydrogen peroxide at a concentration of 27.5% until the ferrous concentration in the reaction solution reaches 1.49 g / L. The liquid is then heated to 95°C using a heating coil and held at that temperature for 4 hours.

[0114] Aging, filtration, flash evaporation, and rotary kiln calcination: After the liquid in the multi-stage reaction tank is kept at 95℃ for 4 hours, it enters the aging tank and is kept at 9 hours. After aging, it enters the filtration system, where it is filtered and washed to obtain a filter cake. At this point, ICP analysis shows that the Ni content in the filter cake is 85 ppm and the S content is 2100 ppm. The filter cake is then flash-dried and calcined in a rotary kiln at 580℃ for 3 hours to obtain the finished ferric phosphate. ICP analysis shows that the Ni content is 115 ppm and the S content is 160 ppm. SEM images of the finished ferric phosphate are shown below. Figure 4 The particles have high sphericity and concentrated particle size distribution.

[0115] Example 3

[0116] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Example 1 is that the amount of hydrogen peroxide used in the primary reaction and secondary oxidation steps is adjusted so that the ferrous iron concentration in the reaction system is 12 g / L after the primary reaction is completed and 1.49 g / L after the secondary oxidation is completed.

[0117] Example 4

[0118] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Embodiment 1 is that the amount of hydrogen peroxide used in the primary reaction and secondary oxidation steps is adjusted so that the ferrous iron concentration in the reaction system is 14 g / L after the primary reaction is completed and 1.49 g / L after the secondary oxidation is completed.

[0119] Example 5

[0120] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Embodiment 1 is that the amount of hydrogen peroxide used in the secondary oxidation step is adjusted so that the ferrous iron concentration in the reaction system is 1 g / L after the secondary oxidation is completed.

[0121] Example 6

[0122] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Embodiment 1 is that the amount of hydrogen peroxide used in the secondary oxidation step is adjusted so that the ferrous iron concentration in the reaction system is 2 g / L after the secondary oxidation is completed.

[0123] Example 7

[0124] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Example 1 is that the ferrous ion concentration is 70 g / L, the iron-phosphorus molar ratio is 0.98, and the ferrous ion concentration in the reaction system after the primary reaction and the secondary oxidation are the same as in Example 1.

[0125] Example 8

[0126] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor, with specific steps as follows: Figure 1 As shown, use as Figure 2 The device shown, the specific steps include:

[0127] Primary reaction: Fe is selected 2+ Concentration 70g / L, Ni 2+A 62 g / L phosphorus solution with an iron-to-phosphorus ratio of 0.96 was prepared. 400 L of the prepared solution was pumped from the prepared solution tank to the multi-stage reaction tank. The temperature was raised to 50°C by a steam heating coil 2.1.1, and then 27.5% hydrogen peroxide was added by the dosing controller. After the primary reaction was completed, the ferrous iron concentration in the reaction system was 12 g / L.

[0128] Induction reaction: After the primary reaction is completed, the liquid in the multi-stage reaction tank is heated to 65°C using a steam heating coil 2.1.1. The dosing controller then adds CTAB inducer to promote precipitation. The amount of CTAB added is 1.5 wt% of the liquid in the multi-stage reaction tank. After adding CTAB, the reaction solution is kept at 65°C for 3.5 hours. During this holding period, the amorphous ferric phosphate precipitate is converted into orthorhombic ferric phosphate.

[0129] Secondary oxidation: After the induction reaction, the dosing controller automatically monitors the ferrous concentration in the reaction solution and adds hydrogen peroxide at a concentration of 27.5% a second time until the ferrous concentration in the reaction solution is 2 g / L. The liquid is then heated to 90°C using a heating coil and held at that temperature for 4.5 hours.

[0130] Aging, filtration, flash evaporation, and rotary kiln calcination: After the liquid in the multi-stage reaction tank is kept at 90℃ for 4.5 hours, it enters the aging tank and is kept at 90℃ for 10 hours. After aging, it enters the filtration system, where it is filtered and washed to obtain a filter cake. The filter cake is then flash-dried and calcined in a rotary kiln at 550℃ for 3.5 hours to obtain the finished product, ferric phosphate.

[0131] Example 9

[0132] This embodiment provides a method for preparing a lithium iron phosphate cathode material precursor, with specific steps as follows: Figure 1 As shown, use as Figure 2 The device shown, the specific steps include:

[0133] Primary reaction: Fe is selected 2+ Concentration 40g / L, Ni 2+ A 62 g / L phosphorus solution with an iron-to-phosphorus ratio of 0.98 was prepared. 400 L of the prepared solution was pumped from the prepared solution tank to the multi-stage reaction tank. The temperature was raised to 50°C by a steam heating coil 2.1.1, and then 27.5% hydrogen peroxide was added by the dosing controller. After the primary reaction was completed, the ferrous iron concentration in the reaction system was 14 g / L.

[0134] Induction reaction: After the primary reaction is completed, the liquid in the multi-stage reaction tank is heated to 75°C using a steam heating coil (2.1.1). The dosing controller then adds CTAB inducer to promote precipitation. The amount of CTAB added is 2.5 wt% of the liquid in the multi-stage reaction tank. After adding CTAB, the reaction solution is kept at 75°C for 2.5 hours. During this holding period, the amorphous ferric phosphate precipitate is converted into orthorhombic ferric phosphate.

[0135] Secondary oxidation: After the induction reaction, the dosing controller automatically monitors the ferrous concentration in the reaction solution and adds hydrogen peroxide at a concentration of 27.5% a second time until the ferrous concentration in the reaction solution is 1 g / L. The liquid is then heated to 100°C using a heating coil and held at that temperature for 3.5 hours.

[0136] Aging, filtration, flash evaporation, and rotary kiln calcination: After the liquid in the multi-stage reaction tank is kept at 100℃ for 3.5 hours, it enters the aging tank and is kept at 100℃ for 8 hours. After aging, it enters the filtration system, where it is filtered and washed to obtain a filter cake. The filter cake is then flash-dried and calcined in a rotary kiln at 600℃ for 2.5 hours to obtain the finished product, ferric phosphate.

[0137] Comparative Example 1

[0138] This comparative example provides a method for preparing a lithium iron phosphate cathode material precursor, including the following steps:

[0139] Primary reaction: The difference from Example 1 is that after the primary reaction is completed, the ferrous iron in the reaction system is completely oxidized to ferric iron.

[0140] Induction reaction: After the primary reaction is completed, the liquid in the multi-stage reaction tank is heated to 70°C using a steam heating coil 2.1.1. The dosing controller then adds CTAB inducer to promote precipitation via a dosing pump. The amount of CTAB added is 2 wt% of the liquid in the multi-stage reaction tank. After adding CTAB, the reaction solution is kept at 70°C for 3 hours. During this holding period, the amorphous ferric phosphate precipitate is converted into orthorhombic ferric phosphate.

[0141] Secondary oxidation: After the induction reaction, the liquid is heated to 95°C and kept at that temperature for 4 hours using a heating coil.

[0142] Aging, filtration, flash evaporation, and rotary kiln calcination: After the liquid in the multi-stage reaction tank is kept at 95℃ for 4 hours, it enters the aging tank and is kept at 9 hours. After aging, it enters the filtration system, where it is filtered and washed to obtain a filter cake. The filter cake is then flash-dried and calcined in a rotary kiln at 580℃ for 3 hours to obtain the finished product, ferric phosphate.

[0143] Comparative Example 2

[0144] This comparative example provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Comparative Example 1 is that the iron concentration in the reaction system after the primary reaction is 1.5 g / L.

[0145] Comparative Example 3

[0146] This comparative example provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Example 1 is that the amount of hydrogen peroxide used in the secondary oxidation step is adjusted so that the ferrous ions in the reaction system are completely converted into ferric ions after the secondary oxidation is completed.

[0147] Comparative Example 4

[0148] This comparative example provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Example 1 is that pH is used instead of ferrous ion concentration to monitor the reaction system. After the primary reaction is completed, the pH of the reaction system is 0.6, and after the secondary oxidation is completed, the pH of the reaction system is 0.52.

[0149] Comparative Example 5

[0150] This comparative example provides a method for preparing a lithium iron phosphate cathode material precursor. The only difference from Example 1 is that the reaction solution after adding CTAB is kept at 70°C for 1 hour.

[0151] The impurity content in the filter cake and lithium iron phosphate cathode material precursor obtained in the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0152]

[0153] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium iron phosphate cathode material precursor, characterized in that, include: Primary oxidation involves reacting a phosphorus-containing solution containing ferrous ions and phosphate with a first oxidant to obtain a first ferric phosphate slurry. The ferrous content in the first ferric phosphate slurry is 12-14 g / L, the concentration of ferrous ions in the phosphorus-containing solution is greater than 30 g / L, and the iron-phosphorus molar ratio in the phosphorus-containing solution is 0.9-1.

0. An induction reaction is carried out by adding an inducer that promotes the formation of FePO4 crystals to the first iron phosphate slurry to obtain a second iron phosphate slurry. Secondary oxidation involves adding a second oxidant to the second ferric phosphate slurry to react and obtain a third ferric phosphate slurry, wherein the concentration of ferrous ions in the third ferric phosphate slurry is 1 g / L-2 g / L. After aging and solid-liquid separation, the third iron phosphate slurry is calcined to obtain the lithium iron phosphate cathode material precursor.

2. The method of claim 1, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: The iron-phosphorus molar ratio of the phosphorus-containing solution is 0.96-0.

98. ​ 3. The method of claim 2, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: The concentration of ferrous ions in the phosphorus-containing solution is 40 g / L-70 g / L. ​ 4. The method of claim 2, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphorous pentoxide to form a mixture; and heating the mixture to a temperature of 600-800 °C for 2-6 hours. The temperature of the primary oxidation step is 45℃-55℃.

5. The method of claim 2, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphorous pentoxide in a solution; and heating the solution to a temperature of 600-800 °C for 2-4 hours. The first oxidant is hydrogen peroxide.

6. The method of claim 1, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source to form a mixture; and heating the mixture to a temperature of 600-800 °C for 1-10 hours. The inducing agent is hexadecyltrimethylammonium bromide.

7. The method for preparing the lithium iron phosphate cathode material precursor according to claim 6, characterized in that, The amount of the inducer is 1.5wt%-2.5wt% of the first ferric phosphate slurry.

8. The method for preparing the lithium iron phosphate cathode material precursor according to claim 6, characterized in that, The induction reaction is carried out at a temperature of 65℃-75℃ for a time of 2.5h-3.5h.

9. The method of claim 1, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source to form a mixture; and heating the mixture to a temperature of 600-800 °C for 1-10 hours in a non-oxidizing atmosphere. The temperature of the secondary oxidation step is 90℃-100℃, and the time is 3.5h-4.5h.

10. The method of claim 9, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing lithium carbonate, iron oxide, and phosphorous pentoxide; and heating the mixture to a temperature of 600-800 °C for 2-8 hours. The second oxidizing agent is hydrogen peroxide.

11. The method of claim 1, wherein the lithium iron phosphate cathode material precursor is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source to form a mixture; and heating the mixture to a temperature of 600-800 °C for 1-10 hours in a non-oxidizing atmosphere. The aging process is carried out at a temperature of 70℃-95℃ for 8-10 hours. And / or, the calcination temperature is 550℃-600℃, and the time is 2.5-3.5h.

12. A device for applying the preparation method of the lithium iron phosphate anode material precursor according to any one of claims 1-11, characterized in that, include: The phosphorus preparation tank (1.2), the multi-stage reaction tank (2.6), and the aging and heat preservation tank (2.7) are connected in series. The multi-stage reaction tank (2.6) is equipped with an inducer dosing pipe and an oxidant dosing pipe for adding the first oxidant and the second oxidant. The multi-stage reaction tank (2.6) is also equipped with a dosing control probe (2.3.1) for measuring the concentration of ferrous ions. The dosing control probe (2.3.1) is connected to a dosing controller (2.3) that can control the liquid flow rate in the oxidant dosing pipe through a dosing control signal line (2.3.2).

13. The apparatus of claim 12, wherein, include: The aging and heat preservation tank is connected in series via a discharge pipe to a filter press (2.8) for pressing the slurry, a drying device for drying the filter cake obtained by pressing, and a rotary kiln (2.10) for calcining the dried material.

14. A lithium iron phosphate cathode material precursor, characterized in that, It is prepared by the method for preparing lithium iron phosphate cathode material precursor according to any one of claims 1-11.

15. A lithium iron phosphate cathode material, characterized in that, It is obtained by sintering the lithium iron phosphate cathode material precursor as described in claim 14 with a lithium source.

16. A lithium-ion battery, characterized by, Including the lithium iron phosphate cathode material as described in claim 15.

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