Method for preparing NFS positive electrode material by adopting sodium electrode layer oxygen precursor re-dissolution material

Abstract

The invention discloses a method for preparing an NFS positive electrode material by using a sodium electrode layer oxygen precursor re-dissolving material, and relates to the technical field of sodium ion battery positive electrode material recovery, and the method comprises the following steps: adding bottom water into a dissolving kettle, starting stirring, adding the sodium electrode layer oxygen precursor re-dissolving material into the dissolving kettle for pulping, and then adding concentrated sulfuric acid for dissolving; adding water to dissolve sodium pyrosulfite, and pumping the dissolved sodium pyrosulfite into the dissolving kettle; adding reduced iron powder into the dissolving kettle to reduce Fe < 3 + >, filtering the material liquid after the reaction is finished, and transferring the filtered filtrate into an NFM precursor production line; replacing filter residues with nickel, filtering feed liquid, transferring filtrate into an NFS positive electrode material production line, and transferring the filter residues into a dissolving kettle for recycling; according to the method, the recovery of the sodium electrode layer oxygen precursor re-dissolution material is combined with the NFM precursor preparation and NFS spray drying process, so that the re-dissolution yield is systematically improved, and the nickel loss and hazardous waste treatment are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method for preparing an NFS positive electrode material by using a sodium electrolyte layer oxygen precursor re-dissolved material. Background Art

[0002] As a supplement to lithium-ion batteries and a replacement for lead-acid batteries, sodium-ion batteries have broad application prospects in the fields of power batteries and large-scale energy storage. In existing sodium-ion batteries, the performance of the positive electrode material is one of the key factors that determine its electrochemical performance. Currently, there are three main technical routes: transition metal layered oxides, Prussian blue, and polyanions. Sodium ferrous sulfate (Na x Fe y (SO4) z , referred to as NFS) has both high redox potential (3.80V), high theoretical energy density (540Whkg -1 ), stable structure, low price, green and pollution-free, etc., and is considered to be the most likely positive electrode material for the industrialization of sodium-ion batteries.

[0003] Among sodium-ion battery cathode materials, transition metal layered oxides offer significant potential for development in the low-speed powertrain sector, owing to their superior performance and lower price compared to ternary and lithium iron phosphate cathode materials for lithium-ion batteries. With the development of this industry, the handling of substandard materials by material manufacturers is becoming increasingly important. Currently, the primary resource recycling method for lithium-ion battery ternary precursors and cathode materials is wet recovery, which involves processes such as reduction acid leaching, extraction, and evaporative crystallization.

[0004] One of the key characteristics of sodium-ion battery materials is their low price. However, if material manufacturers employ extraction, evaporation, and crystallization processes to increase recycling rates, this significantly increases fixed asset and production operating costs. Providing waste materials to traditional resource recycling manufacturers also significantly increases processing costs, hindering a virtuous cycle. For example, the precursor production process for sodium-ion layered oxide materials (NFMs) often produces defective products (including scrap and R&D products). These NFM precursors contain significant amounts of nickel. If not recycled, this leads to nickel loss and hazardous waste disposal issues.

[0005] Therefore, it is a problem that needs to be solved in this field to explore a process that has low production cost and can effectively recycle unqualified sodium layer oxide NFM precursors. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing NFS positive electrode materials by using sodium layer oxygen precursor re-dissolved materials with low production cost.

[0007] The technical solution adopted by the present invention is:

[0008] A method for preparing NFS positive electrode material by using sodium layer oxygen precursor re-dissolved material comprises the following steps:

[0009] Step S1: adding bottom water to the dissolving kettle, starting stirring, and adding the sodium layer oxygen precursor back-dissolved material into the dissolving kettle for slurrying, so that the precursor material is fully suspended;

[0010] In step S1:

[0011] The sodium layer oxygen precursor re-dissolved material refers to the unqualified NFM precursor (waste materials, R&D products, etc.) produced during the production process.

[0012] The pulping time is 30 to 120 minutes, preferably 60 minutes.

[0013] Step S2: In the dissolving kettle after slurry preparation, add concentrated sulfuric acid according to the weight of the precursor to dissolve;

[0014] Step S2: The weight ratio of concentrated sulfuric acid to precursor is 1.0-1.5:1. The addition of concentrated sulfuric acid primarily performs the first dissolution step (dissolving the majority of the nickel and iron, with a small amount of manganese). The heat generated by the concentrated sulfuric acid dilution simultaneously raises the temperature of the dissolution vessel, increasing the reaction rate. The dissolution time in Step S2 is preferably 120-240 minutes.

[0015] Step S3: dissolving sodium metabisulfite in water and pumping the solution into a dissolving kettle;

[0016] In step S3, the addition of sodium metabisulfite is mainly for reduction leaching of high-valent manganese oxides and hydroxides. Preferably, the concentration of the sodium metabisulfite solution is controlled at 0.5 to 1 mol / L, the flow rate of the solution into the dissolution kettle is controlled at 180 to 200 L / h, and the endpoint pH is controlled at 0.4 to 0.5.

[0017] Step S4: adding reduced iron powder to the dissolution kettle, controlling the end point pH to be 1-2, and then adding pure water;

[0018] In step S4: the addition of iron powder is mainly for Fe 3+ Preferably, the amount of iron powder added is calculated based on the iron content in the precursor, and preferably the molar ratio of the iron content in the precursor to the iron powder is 2:1.

[0019] Step S5: The liquid after the reaction in step S4 is filtered using a plate and frame filter press, and the filtered filtrate is transferred to a salt solution temporary storage tank. After the composition of the filtrate is tested, relevant materials are added as needed to re-produce the NFM precursor;

[0020] In step S5: the liquid after the reaction in step S4 is transferred to a plate and frame filter press using a diaphragm pump for filtration. After testing the nickel, iron and manganese element ratio, total metal concentration and trivalent iron content, acid is added to lower the solution pH, and nitrogen is introduced for protection. The solution is then transferred to the NFM precursor production line. Materials (the materials are selected from one or more of nickel sulfate, ferrous sulfate, manganese sulfate crystal salt and pure water) are added as needed to the required ratio before NFM precursor preparation. Further: the filtered filtrate is transferred to a salt solution temporary storage tank, 98% sulfuric acid is added to adjust the pH of the liquid to 1.5-2.0, and nitrogen is introduced for protection, wherein the nitrogen purity is 99.99% and the flow rate is 20L / min. Then, the liquid is transferred to the NFM precursor production line.

[0021] Step S6: putting the filter residue obtained by filtration in step S5 into a nickel replacement tank to further replace the free nickel ions therein;

[0022] The filter residue obtained by filtration in step S5 mainly includes unreacted iron powder and replaced nickel, and the free nickel ions in the filter residue are further replaced by a nickel replacement tank. Preferably, pure water is used for pipe flushing and slag washing, and the washing water is put into the nickel replacement tank as bottom water; 98% sulfuric acid is added, and the pH in the nickel replacement tank is regulated to maintain at 4.0-4.5, and nickel ion iron powder replacement is carried out for 60 minutes. Particularly preferably, after the replacement is completed, the nickel ion content is detected. If it is still present, iron powder is added until the nickel ion is completely replaced.

[0023] Step S7: The liquid after replacement in the nickel replacement tank is filtered using a plate and frame filter press, and the filtrate is transferred to the NFS batching tank. After the liquid is reconfigured, the NFS positive electrode material is produced, and the filter residue is transferred to the dissolution kettle in step S1 for reuse.

[0024] In step S7: the slurry after replacement in the nickel replacement tank is pumped into a plate and frame filter press using a diaphragm pump for filtration.

[0025] In the NFS batching tank, the iron content in the filtrate is first tested, and then relevant materials are added as needed to prepare the liquid (the added materials are selected from one or more of sodium sulfate, ferrous sulfate, iron powder, and pure water). After the liquid is prepared, CNTs are mixed and spray-dried to obtain an NFS precursor; under a nitrogen atmosphere, the NFS precursor is sintered at 350°C and kept warm for 6 hours to obtain the NFS (sodium ferrous sulfate) positive electrode material.

[0026] Preferably, the sintered NFS (sodium ferrous sulfate) positive electrode material is pulverized using a jet mill.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention combines the recovery of sodium oxide precursor re-dissolved material with the preparation of NFM precursor and NFS spray drying process, which systematically improves the re-dissolved yield and reduces nickel loss and hazardous waste treatment.

[0029] (2) The present invention uses iron powder as a protective agent for the NFS liquid, which reduces the use of reducing agents such as VC, reduces the BOM cost of NFS production (reduces the use of VC), is conducive to achieving scale and may reduce the impact of the introduction of organic matter on subsequent material synthesis.

[0030] (3) The present invention can realize the recycling of sodium electrode layer oxygen precursor re-dissolved material with low cost and high nickel recovery rate, and simultaneously carry out the preparation of ① NFM precursor; ② NFS positive electrode material.

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a process flow chart of the present invention.

[0033] Figure 2 This is the SEM image of the NFM precursor prepared in Example 1 of the present invention, with a magnification of 1000×.

[0034] Figure 3 This is the SEM image of the NFM precursor prepared in Example 2 of the present invention, with a magnification of 1000×.

[0035] Figure 4 This is the SEM image of the NFS precursor prepared in Example 1 of the present invention, with a magnification of 500×.

[0036] Figure 5 This is the SEM image of the NFS precursor prepared in Example 2 of the present invention, with a magnification of 500×.

[0037] Figure 6 This is the SEM image of the NFS precursor prepared in Comparative Example 1 of the present invention, with a magnification of 500×.

[0038] Figure 7 This is the charge and discharge curve of the NFS positive electrode material prepared in Example 1 of the present invention, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C.

[0039] Figure 8 This is the charge and discharge curve of the NFS positive electrode material prepared in Example 2 of the present invention, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C.

[0040] Figure 9This is the charge and discharge curve of the NFS positive electrode material prepared in Comparative Example 1 of the present invention, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to specific embodiments.

[0042] In the embodiments of the present invention, the products and equipment involved, unless otherwise specified, are existing technologies or commercially available products in the art.

[0043] NFM: refers to a sodium ion battery layered oxide positive electrode material composed of nickel (Ni), iron (Fe), and manganese (Mn) in a certain proportion. The structural formula is: NaNi x Fe y Mn z O2, depending on the ratio of Ni, Fe, and Mn, has NFM 111 (x:y:z=1:1:1), NFM233, NFM424, or other molar content ratios.

[0044] NFM precursor: refers to the unsintered material of NFM, the structural formula is: Ni x Fe y Mn z (OH)2, depending on the ratio of Ni, Fe, and Mn, there is NFM 111 precursor (x:y:z=1:1:1) or other molar content ratios.

[0045] NFS: refers to the positive electrode material of sodium ion battery, the structural formula is: Na x Fe y (SO4) z According to the different ratios of Ni, Fe, and (SO4), there are NFS212 (x:y:z=2:1:2), NFS435 or other molar content ratios.

[0046] NFS precursor: refers to the unsintered material of NFS. Depending on the configuration ratio, there are NFS212 precursor (x:y:z=2:1:2), NFS435 precursor or other molar content ratios.

[0047] Sodium electrode layer oxygen precursor re-melt material: that is, NFM precursor re-melt material, refers to the unqualified NFM precursor (waste materials, R&D products, etc.) produced during the production process.

[0048] Feed liquid-1: refers to the feed liquid after iron powder is added to the dissolving kettle for reduction.

[0049] Filtrate-1: refers to the filtrate after the liquid in the dissolving kettle is filtered through a plate and frame filter press.

[0050] Filter residue-1: refers to the filter residue after the liquid in the dissolving kettle is filtered through a plate and frame filter press.

[0051] Feed liquid-2: refers to the feed liquid dissolved in the nickel displacement tank.

[0052] Filtrate-2: refers to the filtrate after the liquid in the nickel displacement tank is filtered through a plate and frame filter press.

[0053] Filter residue-2: refers to the filter residue after the liquid in the nickel displacement tank is filtered through a plate and frame filter press.

[0054] Example 1

[0055] Reference Figure 1 As shown, the present invention is a method for preparing NFS positive electrode material by using sodium layer oxygen precursor re-dissolved material, the steps are as follows:

[0056] Weigh 1000 kg of NFM111 precursor re-dissolved material (the re-dissolved material was tested to have a moisture content of 1% and a nickel content of 22.43 wt %), 1155 kg of 98% sulfuric acid, 430 kg of sodium metabisulfite, and 108 kg of iron powder.

[0057] Add 3m 3 Pure water is used as the base water, stirring is started, and the weighed NFM111 precursor is returned to the dissolution material for 60 minutes; then the weighed 98% sulfuric acid is added to the dissolution kettle for 180 minutes; the weighed sodium metabisulfite is dissolved in pure water to form a 0.88 mol / L solution, which is pumped into the dissolution kettle at a flow rate of 200 L / h and the pH at the dissolution end point is controlled at 0.5. 108 kg of iron powder is added to the above prepared solution for Fe 3+ Reduction, after the pH in the dissolution kettle reaches 1.5, add pure water to control the total volume of the liquid in the kettle to 6000L.

[0058] The reduced liquid-1 is then pumped into a plate-and-frame filter press for filtration. The filtered filtrate-1 is transferred to a salt solution temporary storage tank, 98% sulfuric acid is added to adjust the pH of the liquid to 1.5-2.0, and nitrogen is introduced for protection, wherein the nitrogen purity is 99.99% and the flow rate is 20 L / min; then, the liquid is transferred to the NFM precursor production line, and the new NFM111 precursor (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2).

[0059] The NFM precursor production line process is as follows: ① For the liquid in the salt solution storage tank, nickel sulfate hexahydrate, manganese sulfate monohydrate, and deionized water are added according to the element ratio test to prepare a salt solution of Ni:Fe:Mn=1:1:1, and the total metal concentration is 2 mol / L; ② Deionized water and 7.8wt% ammonia water are added to the reactor to prepare bottom water with an ammonia concentration of 0.25 mol / L, the temperature is raised to 50°C, the stirring speed is 350rpm, and N2 is introduced for atmosphere protection; ③ 32wt% sodium hydroxide solution, 7.8wt% ammonia solution, and the above-configured 2 mol / L salt solution are pumped into the reactor in proportion for co-precipitation reaction; ④ The slurry particle size in the reactor is detected using a laser particle size analyzer, and the feeding is stopped when D50 reaches 5.5μm. The obtained precursor slurry is washed, dried, and sieved with 6wt% sodium hydroxide solution and deionized water to obtain the NFM111 precursor product.

[0060] The filter residue-1 after filtration by the plate and frame filter press is placed in a nickel exchange tank. 500L of pure water is used to flush the pipes and wash the residue. The rinse water is then added to the nickel exchange tank as bottom water. 98% sulfuric acid is added to adjust the pH in the nickel exchange tank to maintain at 4.0-4.5, and nickel ion iron powder is replaced for 60 minutes. The feed liquid-2 obtained from the nickel exchange tank is sent to a plate and frame filter press for filtration. After the obtained filtrate-2 is tested for its composition, the feed liquid is reconfigured and transferred to the NFS production line. The filter residue-2 is then returned to the dissolution kettle to participate in the dissolution of the next batch of re-dissolved material to recover the nickel element.

[0061] The NFS production line process is as follows: Filtrate-2 is transferred to the NFS primary batching tank, and the iron content in the filtrate is tested (iron content is 2.28g / L). Then, 142kg of anhydrous sodium sulfate, 5kg of iron powder, and 260kg of ferrous sulfate heptahydrate are weighed and added to the above-mentioned NFS primary batching tank, and the dissolution time is configured to be 60min; then, solution-1 is sequentially passed through a deironing device and a filter and transferred to the NFS batching tank. The deironing device magnetic bar has a Gaussian strength of 12000GS, and the adsorbed iron slag is added to the dissolution kettle to participate in the dissolution of the next batch; 184kg of 5wt% CNTs carbon nanotube slurry was put into an NFS batching tank to prepare an NFS precursor slurry to be sprayed, and the molar ratio of sodium to iron was 2:1. The above-mentioned NFS precursor slurry to be sprayed was spray-dried to prepare an NFS precursor. The spray drying parameters were set as an inlet temperature of 190°C and an outlet temperature of 105°C; the above-mentioned NFS precursor was sintered at 350°C under a nitrogen atmosphere and kept warm for 6 hours to obtain an NFS positive electrode material.

[0062] Product characterization and performance:

[0063] (1) Nickel recovery

[0064] The nickel content and recovery of different materials in this embodiment were detected and counted, as shown in Table 1:

[0065] Table 1

[0066] name Material mass / volume Nickel content Equivalent nickel metal content Nickel recycling ratio Precursor 1000kg 22.43wt% 224.30kg 0.00％ Filtrate-1 <![CDATA[6m 3 ]]> 34.94g / L 209.63kg 93.46％ Filter residue-1 76.40kg 17.58wt% 13.43kg 0.00％ Filtrate-2 500L 3.0mg / L 1.50g 0.00％ Filter residue-2 77.57kg 17.96wt% 13.93kg 6.21％ .

[0067] As shown in the table above: the nickel recovery rate obtained by re-dissolution alone is 93.46%. After reusing the filter residue, the overall yield can be increased to 99.67%. The iron powder not used in the process is recovered by plate and frame filter pressing and can be returned to the dissolution kettle for dissolution and reduction. The ferrous sulfate solution produced by the dissolved iron powder can be used as NFS ingredient bottom water under the protection of iron powder to supplement ferrous sulfate.

[0068] (2) Prepared NFM precursor and NFS precursor

[0069] In this embodiment, the prepared NFM precursor and NFS precursor were characterized by SEM images, as shown in FIG. Figure 2 、 Figure 4 As shown, from Figure 2 It can be seen that the NFM precursor prepared by the present invention has good uniformity and no obvious micro-powder phenomenon. Figure 4 It can be seen that the prepared NFS precursor is hollow spherical particles and the material is relatively fragile.

[0070] (3) Charge and discharge performance test

[0071] The charge and discharge performance of the NFS cathode material prepared in Example 1 was tested:

[0072] Test method:

[0073] The prepared cathode material was used to fabricate LIR2016 button-type batteries, with a cathode coating ratio of 8:1:1 (cathode material: binder: conductive agent). Electrical performance was tested using a Xinwei battery test cabinet, with a test voltage window of 2-4.5V and a charge / discharge rate of 0.05C.

[0074] Test results:

[0075] The test results are as follows Figure 7 As shown, from Figure 7 It can be seen that the charge and discharge curves of the prepared NFS positive electrode material are normal. At a rate of 0.05C, the first charge capacity reaches 85.96mAh / g, the first discharge capacity reaches 82.29mAh / g, the first efficiency reaches 95.73%, the capacity performance is good, and the median voltage reaches 3.69V.

[0076] Replacement example:

[0077] The preparation method is the same as that of Example 1, except that the amount of iron powder added in the NFS production line process is adjusted, and its effect on the ferric iron content of the spraying material is tested, as shown in Table 2. (The ferric iron detection uses KSCN color developer, a 0.1 mol / L solution is prepared, 10 mL of the sample solution to be tested is taken, and KSCN color developer is added dropwise)

[0078] Table 2

[0079] Serial number Iron powder addition amount Detection of trivalent iron in spraying material Example 1 5kg Not detected Example 1-2 1kg Color rendering Examples 1-3 2kg show Examples 1-4 3kg Slightly colored Examples 1-5 4kg Not detected Examples 1-6 6kg Not detected Examples 1-7 7kg Not detected Examples 1-8 8kg Not detected .

[0080] analyze:

[0081] In the production and preparation process of NFS cathode material precursor, the anti-oxidation work of ferrous sulfate in the wet process is very important. 2+ Fe 3+ The conversion will greatly affect the co-precipitation of the product. Through experiments, it was found that when the amount of iron powder added was 5 kg, that is, the mass of iron powder added accounted for about 2% of the mass of ferrous sulfate heptahydrate added, better trivalent iron reduction and solution antioxidant properties could be achieved.

[0082] Example 2

[0083] Reference Figure 1 As shown, a method for preparing NFS positive electrode material by using sodium layer oxygen precursor re-dissolved material, the steps are as follows:

[0084] Weigh 1000 kg of NFM111 precursor re-dissolved material (the re-dissolved material was tested to have a moisture content of 1.2% and a nickel content of 22.65 wt %), 1201 kg of 98% sulfuric acid, 430 kg of sodium metabisulfite, and 110 kg of iron powder.

[0085] Add 3m 3 Pure water was used as the bottom water, stirring was started, and the weighed NFM precursor was returned to the dissolution material for slurrying for 60 minutes; then the weighed 98% sulfuric acid was slowly added to the dissolution kettle for 180 minutes; the above-mentioned weighed sodium metabisulfite was dissolved in pure water to form a 0.88 mol / L solution, which was pumped into the dissolution kettle at a flow rate of 200 L / h and the pH at the dissolution end point was controlled at 0.5; 110 kg of iron powder was added to the above-prepared solution for Fe 3+ Reduction, after the pH in the dissolution kettle reaches 1.5, add pure water to control the total volume of the liquid in the kettle to 6000L.

[0086] The reduced liquid-1 is then pumped into a plate-and-frame filter press for filtration. The filtered filtrate-1 is transferred to a salt solution temporary storage tank, 98% sulfuric acid is added to adjust the pH of the liquid to 1.5-2.0, and nitrogen is introduced for protection, wherein the nitrogen purity is 99.99% and the flow rate is 20 L / min; then, the liquid is transferred to the NFM precursor production line, and the new NFM111 precursor (Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2).

[0087] The NFM precursor production line process is as follows: ① For the liquid in the salt solution storage tank, nickel sulfate hexahydrate, manganese sulfate monohydrate, and deionized water are added according to the element ratio test to prepare a salt solution of Ni:Fe:Mn=1:1:1, and the total metal concentration is 2 mol / L; ② Deionized water and 7.8wt% ammonia water are added to the reactor to prepare bottom water with an ammonia concentration of 0.25 mol / L, the temperature is raised to 50°C, the stirring speed is 350rpm, and N2 is introduced for atmosphere protection; ③ 32wt% sodium hydroxide solution, 7.8wt% ammonia solution, and the above-configured 2 mol / L salt solution are pumped into the reactor in proportion for co-precipitation reaction; ④ The slurry particle size in the reactor is detected using a laser particle size analyzer, and the feeding is stopped when D50 reaches 5.5μm. The obtained precursor slurry is washed, dried, and sieved with 6wt% sodium hydroxide solution and deionized water to obtain the NFM111 precursor product.

[0088] The filter residue-1 after filtration by the plate and frame filter press is placed in a nickel exchange tank. 500L of pure water is used to flush the pipes and wash the residue. The rinse water is then added to the nickel exchange tank as bottom water. 98% sulfuric acid is added to adjust the pH in the nickel exchange tank to maintain at 4.0-4.5, and nickel ion iron powder is replaced for 60 minutes. The feed liquid-2 obtained from the nickel exchange tank is sent to a plate and frame filter press for filtration. After the obtained filtrate-2 is tested for its composition, the feed liquid is reconfigured and transferred to the NFS production line. The filter residue is returned to the dissolution kettle and participates in the dissolution of the next batch of re-dissolved material to recover the nickel element.

[0089] The NFS production line process is as follows: Filtrate-2 is transferred to the NFS primary batching tank, and the iron content in the filtrate is tested (iron content is 2.43g / L). Then, 115kg of anhydrous sodium sulfate, 7kg of iron powder, and 318kg of ferrous sulfate heptahydrate are weighed and added to the above-mentioned NFS primary batching tank, and the dissolution time is configured to be 60min; then, solution-1 is sequentially passed through a deironing device and a filter and transferred to the NFS batching tank. The magnetic rod of the deironing device has a Gaussian strength of 12000GS, and the adsorbed iron slag is added to the dissolution kettle to participate in the dissolution of the next batch; 184kg of 5wt% CNTs carbon nanotube slurry was put into an NFS batching tank to prepare an NFS precursor slurry to be sprayed, and the molar ratio of sodium to iron was 4:3. The above-mentioned NFS precursor slurry to be sprayed was spray-dried to prepare an NFS precursor. The spray drying parameters were set as an inlet temperature of 190°C and an outlet temperature of 105°C; the above-mentioned NFS precursor was sintered at 350°C under a nitrogen atmosphere and kept warm for 6 hours to obtain an NFS positive electrode material.

[0090] Product characterization and performance:

[0091] (1) Nickel recovery

[0092] The nickel content and recovery of different materials in this embodiment were detected and counted, as shown in Table 3:

[0093] Table 3

[0094]

[0095]

[0096] As shown in the table above: the nickel recovery rate obtained by re-dissolution alone is 92.67%. After reusing the filter residue, the overall yield can be increased to 99.59%. The iron powder not used in the process is recovered by plate and frame filter pressing and can be returned to the dissolution kettle for dissolution and reduction. The ferrous sulfate solution produced by the dissolved iron powder can be used as NFS ingredient bottom water under the protection of iron powder to supplement ferrous sulfate.

[0097] (2) Prepared NFM precursor and NFS precursor

[0098] In this embodiment, the prepared NFM precursor and NFS precursor were characterized by SEM images, as shown in FIG. Figure 3 、 Figure 5 As shown, from Figure 3 It can be seen that the prepared NFM precursor has good uniformity and no obvious micro-powder phenomenon. Figure 5 It can be seen that the prepared NFS precursor is hollow spherical particles and the material is relatively fragile.

[0099] (3) Charge and discharge performance test

[0100] The charge and discharge performance of the NFS cathode material prepared in Example 2 was tested:

[0101] Test method:

[0102] The prepared cathode material was used to fabricate LIR2016 button-type batteries, with a cathode coating ratio of 8:1:1 (cathode material: binder: conductive agent). Electrical performance was tested using a Xinwei battery test cabinet, with a test voltage window of 2-4.5V and a charge / discharge rate of 0.05C.

[0103] Test results:

[0104] The test results are as follows Figure 8 As shown, from Figure 8 It can be seen that the charge and discharge curves of the material are normal. At a rate of 0.05C, the first charge capacity reaches 94.86mAh / g, the first discharge capacity reaches 90.19mAh / g, the first efficiency reaches 95.08%, the capacity performance is good, and the median voltage reaches 3.73V.

[0105] Comparative Example 1

[0106] This embodiment adopts VC reducing agent to carry out NFS preparation process, taking the preparation of NFS212 material as an example (NFS212, i.e. its molecular formula Na x Fe y (SO4) z , x:y:z=2:1:2), comprising the following steps:

[0107] Step 1: Weigh 142kg of anhydrous sodium sulfate, 16kg of VC, 275kg of ferrous sulfate heptahydrate, and 500L of pure water into the NFS pre-batch tank to prepare the slurry. The dissolution time is 60 minutes, and then the solution is transferred to the NFS batch tank. Weigh 184kg of 5wt% CNTs carbon nanotube slurry and put it into the NFS batch tank to prepare the NFS precursor slurry to be sprayed. The molar ratio of sodium to iron is 2:1.

[0108] Step 2: spray drying the NFS precursor slurry to be sprayed to prepare the NFS precursor; the spray drying parameters are set at an inlet temperature of 190°C and an outlet temperature of 105°C;

[0109] Step 3: Sinter the NFS precursor obtained above at 350°C under a nitrogen atmosphere and keep it warm for 6 hours to obtain the NFS positive electrode material.

[0110] Product Characterization:

[0111] The NFS precursor prepared in Comparative Example 1 was characterized by SEM images. Figure 6 As shown, from Figure 6It can be seen that the prepared NFS precursor is hollow spherical particles and the material is relatively fragile.

[0112] Performance testing:

[0113] The NFS cathode material prepared in Comparative Example 1 was subjected to charge and discharge performance tests:

[0114] Test method:

[0115] LIR2016 button cells were fabricated using the NFS cathode material prepared in Comparative Example 1. The cathode coating ratio was 8:1:1 (cathode material: binder: conductive agent). Electrical performance tests were conducted using a Xinwei battery test cabinet with a test voltage window of 2-4.5V and a charge / discharge rate of 0.05C.

[0116] Test results:

[0117] The test results are as follows Figure 9 As shown, from Figure 9 It can be seen that the charge and discharge curves of the material are normal. At a rate of 0.05C, the first charge capacity reaches 85.91mAh / g, the first discharge capacity reaches 82.94mAh / g, the first efficiency reaches 96.55%, the capacity performance is good, and the median voltage reaches 3.67V.

[0118] analyze:

[0119] The costs and product performances of Example 1 of the present invention and Comparative Example 1 are compared, as shown in Table 4.

[0120] Table 4

[0121]

[0122] Analysis: It can be seen from the above table that when both Example 1 and Comparative Example 1 prepare NFS212 positive electrode materials, the charge and discharge performance of the obtained products are not much different. The production process of the present invention has obvious advantages in cost compared with VC using iron powder.

Claims

1. A method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material, characterized in that: The steps include: Step S1: adding bottom water to the dissolving kettle, starting stirring, and putting the sodium layer oxygen precursor back into the dissolving kettle for slurrying; Step S2: In the dissolving kettle after slurry preparation, add concentrated sulfuric acid according to the weight of the precursor to dissolve; Step S3: dissolving sodium metabisulfite in water and pumping the solution into a dissolving kettle; Step S4: adding reduced iron powder to the dissolution kettle, controlling the end point pH to be 1-2, and then adding pure water; Step S5: filtering the liquid after the reaction in step S4, transferring the filtered filtrate to a salt solution temporary storage tank, testing the composition of the filtrate, and adding relevant materials to re-produce the NFM precursor; Step S6: putting the filter residue obtained by filtration in step S5 into a nickel replacement tank to further replace the free nickel ions therein; Step S7: Filter the liquid after replacement in the nickel replacement tank, transfer the filtrate to the NFS batching tank, and produce NFS positive electrode material after re-configuration of the liquid. The filter residue is transferred to the dissolution kettle of step S1 for reuse.

2. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S1: the sodium layer oxygen precursor re-dissolved material refers to the unqualified NFM precursor produced during the production process, and the slurrying time is 30 to 120 minutes.

3. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: Step S2: The weight ratio of the added amount of concentrated sulfuric acid to the precursor is 1.0-1.5:

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4. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: The dissolution time in step S2 is 120 to 240 minutes.

5. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S3, the concentration of the sodium metabisulfite solution is controlled at 0.5 to 1 mol / L, the flow rate of the solution pumped into the dissolution kettle is controlled at 180 to 200 L / h, and the endpoint pH is controlled at 0.4 to 0.

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6. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S4: the amount of iron powder added is calculated based on the iron content in the precursor, and the molar ratio of the iron content in the precursor to the iron powder is 2:

1.

7. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S4: In step S5: The feed liquid after the reaction in step S4 is transferred to a plate and frame filter press using a diaphragm pump for filtration, and then the composition of the filtrate is detected, acid is added to lower the pH of the solution, and nitrogen is introduced for protection, and then transferred to the NFM precursor production line. After adding materials as needed to the required ratio, the NFM precursor is prepared.

8. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 7, characterized in that: In step S4: the filtered filtrate is transferred to a salt solution temporary storage tank, 98% sulfuric acid is added to adjust the pH of the liquid to 1.5-2.0, and nitrogen is introduced for protection, wherein the nitrogen purity is 99.99% and the flow rate is 20L / min. Then, the liquid is transferred to the NFM precursor production line.

9. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S6: 98% sulfuric acid is added, the pH in the nickel replacement tank is regulated to be maintained at 4.0-4.5, and nickel ion iron powder replacement is performed for 60 minutes.

10. The method for preparing NFS cathode material by using sodium layer oxygen precursor re-dissolved material according to claim 1, characterized in that: In step S7: In the NFS batching tank, the iron content in the filtrate is first detected, and then relevant materials are added as needed. After the material liquid is prepared, the CNTs are mixed and spray-dried to obtain an NFS precursor; under a nitrogen atmosphere, the NFS precursor is sintered at 350°C and kept warm for 6 hours to obtain the NFS positive electrode material.

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