A method for preparing an NFS positive electrode material by using a sodium-electric layer oxygen precursor return solution

Abstract

This invention discloses a method for preparing NFS cathode materials using sodium-ion battery cathode material remelting material, relating to the field of sodium-ion battery cathode material recycling technology. The method includes the following steps: adding bottom water to a dissolving vessel, starting stirring, adding the sodium-ion battery cathode material remelting material to the dissolving vessel for slurry preparation, then adding concentrated sulfuric acid for dissolution; dissolving sodium metabisulfite in water and pumping it into the dissolving vessel; and adding reduced iron powder to the dissolving vessel to prepare Fe. 3+ After reduction and reaction, the liquid is filtered, and the filtrate is transferred to the NFM precursor production line. After nickel replacement, the liquid is filtered and the filtrate is transferred to the NFS cathode material production line, while the filter residue is transferred to the dissolution reactor for reuse. This invention combines the recovery of sodium electrode oxygen precursor remelting material with NFM precursor preparation and NFS spray drying process, which systematically improves the remelting yield and reduces nickel loss and hazardous waste treatment.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a method for preparing NFS cathode materials using sodium-ion battery precursor remelting material. Background Technology

[0002] Sodium-ion batteries, as a supplement to lithium-ion batteries and a replacement for lead-acid batteries, have broad application prospects in power batteries and large-scale energy storage. In existing sodium-ion batteries, the performance of the cathode material is one of the key factors determining its electrochemical performance. Currently, there are three main technical routes: transition metal layered oxides, Prussian blue, and polyanionic compounds. Sodium ferrous sulfate (Na₂SO₄) x Fe y (SO4) z (NFS for short) combines a high redox potential (3.80V) and a high theoretical energy density (540Wh / kg). -1 With its advantages such as stable structure, low price, and green environmental protection, sodium-ion battery is considered the most promising cathode material for industrialization.

[0003] Among sodium-ion battery cathode materials, transition metal layered oxides have strong development potential in the low-speed power field due to their excellent product performance and lower price compared to ternary and lithium iron phosphate cathode materials for lithium-ion batteries. With the development of industrialization, the handling of substandard products from material manufacturers also needs to be addressed. Currently, the main resource recycling method for lithium-ion ternary precursors and cathode materials is wet recycling, which includes processes such as reduction acid leaching, extraction, and evaporation crystallization.

[0004] One of the main characteristics of sodium-ion battery materials is their low price. For material manufacturers, using processes like extraction and evaporation crystallization to improve recovery rates during recycling would significantly increase fixed asset and operational costs. Providing waste to traditional resource recycling companies would also drastically increase processing costs, hindering a virtuous cycle. Taking sodium-ion battery layered oxide (NFM) materials as an example, the precursor production process generates defective products (including waste and R&D samples). These defective NFM precursors contain large amounts of nickel; failure to recycle them would result in nickel loss and hazardous waste disposal issues.

[0005] Therefore, finding a process with low production costs that can effectively recover substandard sodium-ion NFM precursors is a problem that needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost method for preparing NFS cathode materials using sodium-ionized oxygen precursor remelting material.

[0007] The technical solution adopted in this invention is:

[0008] A method for preparing NFS cathode materials using sodium-ion battery oxygen precursor remelting material includes the following steps:

[0009] Step S1: Add bottom water to the dissolving tank, start stirring, and put the sodium-ion battery oxygen precursor back solution into the dissolving tank for slurry preparation, so that the precursor material is fully suspended.

[0010] In step S1:

[0011] The sodium-ion layer oxygen precursor remelting material refers to the unqualified NFM precursors (waste, R&D products, etc.) generated during the production process.

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

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

[0014] Step S2: The weight ratio of concentrated sulfuric acid added to the precursor is 1.0–1.5:1. The addition of concentrated sulfuric acid is mainly for the first dissolution step (dissolving most of the nickel and iron, and a small amount of manganese), and at the same time, the heat generated by the dilution of concentrated sulfuric acid is used to raise the temperature of the dissolution vessel to increase the reaction rate. The dissolution time in step S2 is preferably 120–240 minutes.

[0015] Step S3: Dissolve sodium metabisulfite in water and pump it into the dissolving vessel;

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

[0017] Step S4: Add reduced iron powder to the dissolving vessel, control the final pH to 1-2, and then add pure water;

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

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

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

[0021] Step S6: The filter residue obtained in step S5 is put into a nickel replacement tank for further replacement of the free nickel ions.

[0022] The filter residue obtained in step S5 mainly consists of unreacted iron powder and displaced nickel. The nickel replacement tank further replaces the free nickel ions in the filter residue. Preferably, pure water is used for pipeline flushing and residue washing, and the washing water is added to the nickel replacement tank as base water. 98% sulfuric acid is added to adjust the pH in the nickel replacement tank to maintain it at 4.0-4.5 for nickel ion and iron powder replacement for 60 minutes. Particularly preferably, after replacement, the nickel ion content is checked; if it is still present, iron powder is added until the nickel ions are completely replaced.

[0023] Step S7: The replaced solution in the nickel replacement tank is filtered using a plate and frame filter press. The filtrate is transferred to the NFS mixing tank. After the solution is remixed, NFS cathode material is produced. The filter residue is transferred to the dissolution vessel in step S1 for reuse.

[0024] In step S7: The substituted liquid in the nickel displacement tank is pumped into a plate and frame filter press for filtration using a diaphragm pump.

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

[0026] Preferably, the sintered NFS (sodium ferrous sulfate) cathode material is pulverized using an air jet mill.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] (1) This invention combines the recovery of sodium-ion layer oxygen precursor remelting material with NFM precursor preparation and NFS spray drying process, which systematically improves the remelting yield and reduces nickel loss and hazardous waste treatment.

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

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

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the present invention.

[0033] Figure 2 The image shown is a SEM image of the NFM precursor prepared in Example 1 of this invention, magnified 1000×.

[0034] Figure 3 The image shown is a SEM image of the NFM precursor prepared in Example 2 of this invention, magnified 1000×.

[0035] Figure 4 The image shows a SEM image of the NFS precursor prepared in Example 1 of this invention, magnified 500×.

[0036] Figure 5 The image shows a SEM image of the NFS precursor prepared in Example 2 of this invention, magnified 500×.

[0037] Figure 6 The image shown is a SEM image of the NFS precursor prepared in Comparative Example 1 of this invention, magnified 500×.

[0038] Figure 7 The charge-discharge curves of the NFS cathode material prepared in Example 1 of this invention are shown, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C.

[0039] Figure 8 The charge-discharge curves of the NFS cathode material prepared in Example 2 of this invention are shown, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C.

[0040] Figure 9The charge-discharge curves of the NFS cathode material prepared in Comparative Example 1 of this invention are shown, with an operating voltage of 2.0-4.5V vs. Na+ / Na and a current density of 0.05C. Detailed Implementation

[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 field.

[0043] NFM refers to a layered oxide cathode material for sodium-ion batteries, composed of nickel (Ni), iron (Fe), and manganese (Mn) in a specific ratio. Its structural formula is: NaNi x Fe y Mn z O2, depending on the ratio of Ni, Fe, and Mn, can be NFM 111 (x:y:z = 1:1:1), NFM233, NFM424, or other molar ratios.

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

[0045] NFS: refers to sodium-ion battery cathode material, with the structural formula: Na x Fe y (SO4) z Depending on the ratio of Ni, Fe, and (SO4), there are NFS212 (x:y:z = 2:1:2), NFS435, or other molar ratios.

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

[0047] Sodium-ion layer oxygen precursor remelting material: also known as NFM precursor remelting material, refers to unqualified NFM precursors (waste, R&D products, etc.) generated during the production process.

[0048] Liquid-1: refers to the liquid after iron powder reduction in the dissolving vessel.

[0049] Filtrate-1: refers to the filtrate after the liquid in the dissolving vessel has been filtered by a plate and frame filter press.

[0050] Filter residue-1: refers to the filter residue after the liquid in the dissolving vessel has been filtered by a plate and frame filter press.

[0051] Liquid 2: refers to the liquid soluble in the nickel displacement tank.

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

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

[0054] Example 1

[0055] Reference Figure 1 As shown, the present invention provides a method for preparing NFS cathode materials using sodium electrode layer oxygen precursor remelting material, comprising the following steps:

[0056] Weigh 1000 kg of NFM111 precursor remelting material (tested to show: moisture content 1%, nickel content 22.43 wt%), 1155 kg of 98% sulfuric acid, 430 kg of sodium metabisulfite, and 108 kg of iron powder.

[0057] Add 3m to the dissolving vessel 3 Using pure water as the base water, and with stirring started, the weighed NFM111 precursor resolvate was slurried for 60 minutes. Then, weighed 98% sulfuric acid was added to the dissolving vessel for 180 minutes. The previously weighed sodium metabisulfite was dissolved in pure water to prepare a 0.88 mol / L solution, which was then pumped into the dissolving vessel at a flow rate of 200 L / h, with the pH controlled at the dissolution endpoint at 0.5. 108 kg of iron powder was then added to the prepared solution for Fe... 3+ After reduction, once the pH in the dissolving vessel reaches 1.5, add pure water to control the total volume of the liquid in the vessel to 6000L.

[0058] The reduced feed solution-1 is then pumped into a plate and frame filter press for filtration. The filtrate-1 is transferred to a salt solution storage tank, where 98% sulfuric acid is added to adjust the pH to 1.5-2.0. Nitrogen gas (99.99% purity, 20 L / min) is introduced for protection. This feed solution is then transferred to the NFM precursor production line, where the proportions are adjusted to produce a 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 The feed solution in the salt solution temporary storage tank is supplemented with nickel sulfate hexahydrate, manganese sulfate monohydrate, and deionized water according to the element ratio to prepare a salt solution with Ni:Fe:Mn = 1:1:1 and a total metal concentration of 2 mol / L; ② Deionized water and 7.8 wt% ammonia water are added to the reactor to prepare a bottom water with an ammonia concentration of 0.25 mol / L, the temperature is raised to 50℃, the stirring speed is 350 rpm, and N2 is introduced for atmosphere protection; ③ 32 wt% sodium hydroxide solution, 7.8 wt% ammonia water solution, and the prepared 2 mol / L salt solution are pumped into the reactor in proportion to carry out a co-precipitation reaction; ④ The particle size of the slurry in the reactor is detected using a laser particle size analyzer. After the D50 reaches 5.5 μm, the feeding is stopped. The obtained precursor slurry is washed, dried, and sieved with 6 wt% sodium hydroxide solution and deionized water to obtain the NFM111 precursor product.

[0060] The filter residue-1 obtained from the aforementioned plate and frame filter press is placed into a nickel replacement tank. 500L of pure water is used for pipeline flushing and residue washing, and the washing water is added to the nickel replacement tank as bottom water. 98% sulfuric acid is added to adjust the pH in the nickel replacement tank to 4.0-4.5 for nickel ion and iron powder replacement for 60 minutes. The resulting liquid-2 from the nickel replacement tank is sent to a plate and frame filter press for filtration. After component analysis, the resulting filtrate-2 is reconstituted and transferred to the NFS production line. The filter residue-2 is returned to the dissolution tank to participate in the dissolution of the next batch of recycled material to recover nickel.

[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 2.28 g / L). Then, 142 kg of anhydrous sodium sulfate, 5 kg of iron powder, and 260 kg of ferrous sulfate heptahydrate are weighed and added to the aforementioned NFS primary batching tank, with a dissolution time of 60 min. Then, solution-1 is sequentially passed through an iron remover and filter before being transferred to the NFS batching tank. The Gauss strength of the magnetic rod in the iron remover is 12000 GS. The adsorbed iron slag is added to the dissolution kettle for the next batch dissolution. 184 kg of... A 5wt% CNT (carbon nanotube) slurry was added to an NFS (non-carbon nanotube) mixing tank to prepare an NFS precursor slurry to be sprayed. The molar ratio of sodium to iron was 2:1. The NFS precursor slurry was then spray-dried to obtain the NFS precursor. The spray drying parameters were set as follows: inlet temperature 190℃ and outlet temperature 105℃. The NFS precursor was then sintered at 350℃ under a nitrogen atmosphere and held for 6 hours to obtain the NFS cathode material.

[0062] Product characterization and performance:

[0063] (1) Nickel recovery status

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

[0065] Table 1

[0066] 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 3.0 mg / 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 separate remelting is 93.46%. After reusing the filter residue, the overall recovery rate can be increased to 99.67%. The unused iron powder in the process is recovered by plate and frame filter press and can be fed back into the dissolving kettle for dissolution and reduction. The ferrous sulfate solution produced by the dissolved iron powder can be used as the bottom water for NFS feed under the protection of iron powder to supplement ferrous sulfate.

[0068] (2) Preparation of NFM precursor and NFS precursor

[0069] In this embodiment, the prepared NFM precursor and NFS precursor were characterized by SEM images, as shown below. Figure 2 , Figure 4 As shown, from Figure 2 It can be seen that the NFM precursor prepared by this invention has good uniformity and no obvious micronization. From Figure 4 It can be seen that the prepared NFS precursor is a hollow spherical particle, and the material has good brittleness.

[0070] (3) Charge and discharge performance test

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

[0072] Test method:

[0073] LIR2016 coin cells were fabricated using the prepared positive electrode material, with a positive electrode coating ratio of 8:1:1 (positive electrode material: binder: conductive agent). Electrical performance was tested using a Xinwei battery testing cabinet with a test voltage window of 2-4.5V and a charge / discharge rate of 0.05C.

[0074] Test results:

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

[0076] Replacement example:

[0077] The preparation method is the same as in 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 slurry to be sprayed is tested, as shown in Table 2. (Ferric iron was detected using KSCN colorimetric reagent. A 0.1 mol / L solution was prepared, and 10 mL of the sample solution to be tested was added dropwise with KSCN colorimetric reagent.)

[0078] Table 2

[0079] Example 1 5kg Not detected Examples 1-2 1kg Color development Examples 1-3 2kg show Examples 1-4 3kg Slight color development 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 precursor production process of NFS cathode materials, the oxidation prevention function of ferrous sulfate in the wet process is crucial. 2+ To Fe 3+ The conversion will greatly affect the co-precipitation of the product. Experiments have shown that when the amount of iron powder added is 5 kg, that is, when the mass of iron powder added accounts for about 2% of the mass of ferrous sulfate heptahydrate added, better reduction of ferric iron and antioxidant properties of the solution can be achieved.

[0082] Example 2

[0083] Reference Figure 1 As shown, a method for preparing NFS cathode materials using sodium-ion battery oxygen precursor back-solution material includes the following steps:

[0084] Weigh 1000 kg of NFM111 precursor remelting material (tested to show: moisture content 1.2%, nickel content 22.65 wt%), 1201 kg of 98% sulfuric acid, 430 kg of sodium metabisulfite, and 110 kg of iron powder.

[0085] Add 3m to the dissolving vessel 3 Using pure water as the base water, and with stirring started, the weighed NFM precursor resolvate was slurried for 60 minutes. Then, the weighed 98% sulfuric acid was slowly added to the dissolving vessel for 180 minutes. The previously weighed sodium metabisulfite was dissolved in pure water to prepare a 0.88 mol / L solution, which was then pumped into the dissolving vessel at a flow rate of 200 L / h, with the pH controlled at the dissolution endpoint at 0.5. Finally, 110 kg of iron powder was added to the prepared solution for Fe... 3+ After reduction, once the pH in the dissolving vessel reaches 1.5, add pure water to control the total volume of the liquid in the vessel to 6000L.

[0086] The reduced feed solution-1 is then pumped into a plate and frame filter press for filtration. The filtrate-1 is transferred to a salt solution storage tank, where 98% sulfuric acid is added to adjust the pH to 1.5-2.0. Nitrogen gas (99.99% purity, 20 L / min) is introduced for protection. This feed solution is then transferred to the NFM precursor production line, where the proportions are adjusted to produce a 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 The feed solution in the salt solution temporary storage tank is supplemented with nickel sulfate hexahydrate, manganese sulfate monohydrate, and deionized water according to the element ratio to prepare a salt solution with Ni:Fe:Mn = 1:1:1 and a total metal concentration of 2 mol / L; ② Deionized water and 7.8 wt% ammonia water are added to the reactor to prepare a bottom water with an ammonia concentration of 0.25 mol / L, the temperature is raised to 50℃, the stirring speed is 350 rpm, and N2 is introduced for atmosphere protection; ③ 32 wt% sodium hydroxide solution, 7.8 wt% ammonia water solution, and the prepared 2 mol / L salt solution are pumped into the reactor in proportion to carry out a co-precipitation reaction; ④ The particle size of the slurry in the reactor is detected using a laser particle size analyzer. After the D50 reaches 5.5 μm, the feeding is stopped. The obtained precursor slurry is washed, dried, and sieved with 6 wt% sodium hydroxide solution and deionized water to obtain the NFM111 precursor product.

[0088] The filter residue-1 obtained from the aforementioned plate and frame filter press is placed into a nickel replacement tank. 500L of pure water is used for pipeline flushing and residue washing, and the washing water is added to the nickel replacement tank as bottom water. 98% sulfuric acid is added to adjust the pH in the nickel replacement tank to 4.0-4.5 for nickel ion and iron powder replacement for 60 minutes. The resulting liquid-2 from the nickel replacement tank is sent to a plate and frame filter press for filtration. After component analysis, the resulting filtrate-2 is reconstituted and transferred to the NFS production line. The filter residue is returned to the dissolution tank to participate in the dissolution of the next batch of recycled material to recover nickel.

[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 2.43 g / L). Then, 115 kg of anhydrous sodium sulfate, 7 kg of iron powder, and 318 kg of ferrous sulfate heptahydrate are weighed and added to the aforementioned NFS primary batching tank, with a dissolution time of 60 min. Then, Solution-1 is sequentially passed through an iron remover and filter before being transferred to the NFS batching tank. The magnetic rod of the iron remover has a Gaussian strength of 12000 GS. The adsorbed iron slag is added to the dissolution kettle for the next batch dissolution. 184 kg of... A 5wt% CNT (carbon nanotube) slurry was added to an NFS (Neuro-Factory) mixing tank to prepare an NFS precursor slurry to be sprayed. The molar ratio of sodium to iron was 4:3. The NFS precursor slurry was then spray-dried to obtain the NFS precursor. The spray drying parameters were set as follows: inlet temperature 190℃ and outlet temperature 105℃. The NFS precursor was then sintered at 350℃ under a nitrogen atmosphere and held for 6 hours to obtain the NFS cathode material.

[0090] Product characterization and performance:

[0091] (1) Nickel recovery status

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

[0093] Table 3

[0094]

[0095]

[0096] As shown in the table above: the nickel recovery rate obtained by separate remelting is 92.67%. After reusing the filter residue, the overall recovery rate can be increased to 99.59%. The unused iron powder in the process is recovered by plate and frame filter press and can be fed back into the dissolving kettle for dissolution and reduction. The ferrous sulfate solution produced by the dissolved iron powder can be used as the bottom water for NFS feed under the protection of iron powder to supplement ferrous sulfate.

[0097] (2) Preparation of NFM precursor and NFS precursor

[0098] In this embodiment, the prepared NFM precursor and NFS precursor were characterized by SEM images, as shown below. Figure 3 , Figure 5 As shown, from Figure 3 It can be seen that the prepared NFM precursor has good uniformity and no obvious micronization. From Figure 5 It can be seen that the prepared NFS precursor is a hollow spherical particle, and the material has good brittleness.

[0099] (3) Charge and discharge performance test

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

[0101] Test method:

[0102] LIR2016 coin cells were fabricated using the prepared positive electrode material, with a positive electrode coating ratio of 8:1:1 (positive electrode material: binder: conductive agent). Electrical performance was tested using a Xinwei battery testing cabinet with a test voltage window of 2-4.5V and a charge / discharge rate of 0.05C.

[0103] Test results:

[0104] 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 initial charge capacity reaches 94.86mAh / g, the initial discharge capacity reaches 90.19mAh / g, and the initial efficiency reaches 95.08%, indicating good capacity performance. The median voltage reaches 3.73V.

[0105] Comparative Example 1

[0106] This embodiment uses VC reducing agent for NFS preparation process, taking the preparation of NFS212 material as an example (NFS212, i.e., its molecular formula Na). x Fe y (SO4) z In the equation (x:y:z = 2:1:2), the steps include:

[0107] Step 1: Weigh 142 kg of anhydrous sodium sulfate, 16 kg of vitamin C, 275 kg of ferrous sulfate heptahydrate, and 500 L of pure water and add them to the NFS premixing tank to prepare the solution. The dissolution time is set to 60 min. After completion, transfer the solution to the NFS mixing tank. Weigh 184 kg of 5 wt% CNTs carbon nanotube slurry and add it to the NFS mixing tank to prepare the NFS precursor slurry to be sprayed. The molar ratio of sodium to iron in the mixture is 2:1.

[0108] Step 2: Spray dry the NFS precursor obtained above to prepare the NFS precursor; the spray drying parameters are set as follows: inlet temperature 190℃, outlet temperature 105℃.

[0109] Step 3: The NFS precursor obtained above is sintered at 350°C in a nitrogen atmosphere and held for 6 hours to obtain the NFS cathode material.

[0110] Product characteristics:

[0111] The NFS precursor prepared in Comparative Example 1 was characterized by SEM images, such as... Figure 6 As shown, from Figure 6It can be seen that the prepared NFS precursor is a hollow spherical particle, and the material has good brittleness.

[0112] Performance testing:

[0113] The charge-discharge performance of the NFS cathode material prepared in Comparative Example 1 was tested:

[0114] Test method:

[0115] The NFS cathode material prepared in Comparative Example 1 was used to fabricate LIR2016 coin cells, 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.

[0116] Test results:

[0117] 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 initial charge capacity reaches 85.91mAh / g, the initial discharge capacity reaches 82.94mAh / g, and the initial efficiency reaches 96.55%, indicating good capacity performance. The median voltage reaches 3.67V.

[0118] analyze:

[0119] The cost and product performance of Embodiment 1 of the present invention are compared with those of Comparative Example 1, as shown in Table 4.

[0120] Table 4

[0121]

[0122] Analysis: As can be seen from the table above, when both Example 1 and Comparative Example 1 prepared NFS212 cathode materials, the charge and discharge electrical performance of the products obtained were not significantly different. The production process of the present invention has a significant cost advantage over VC when using iron powder.

Claims

1. A method for preparing NFS cathode materials using sodium electrode layer oxygen precursor remelting material, characterized in that, Includes the following steps: Step S1: Add bottom water to the dissolving vessel, start stirring, and put the sodium-ion battery oxygen precursor back solution into the dissolving vessel for pulping. The sodium-ion layer oxygen precursor remelting material refers to the unqualified NFM precursor generated during the production process, and the NFM precursor is NFM111 precursor. Step S2: In the dissolving kettle after pulping, add concentrated sulfuric acid to dissolve the sodium-ion layer oxygen precursor according to the weight of the recycled material added; Step S3: Dissolve sodium metabisulfite in water and pump it into the dissolving vessel; Step S4: Add reduced iron powder to the dissolving vessel, control the final pH to 1-2, and then add pure water; The amount of iron powder added is based on the iron content in the sodium-electric layer oxygen precursor remelting material, and the molar ratio of iron content in the sodium-electric layer oxygen precursor remelting material to iron powder is 2:

1. Step S5: Filter the liquid after the reaction in step S4. Transfer the filtrate to a salt solution storage tank. After testing the composition of the filtrate, add materials and start producing NFM precursor again. The supplementary material is selected from one or more of nickel sulfate, ferrous sulfate, manganese sulfate crystal salt and pure water; Step S6: Put the filter residue obtained in step S5 into the nickel replacement tank to further replace the free nickel ions in the filter residue; Step S7: Filter the nickel replacement solution in the nickel replacement tank, transfer the filtrate to the NFS mixing tank, and produce NFS cathode material after reconfiguring the solution. The filter residue is transferred to the dissolution vessel in step S1 for reuse.

2. The method for preparing NFS cathode material using sodium electrode layer oxygen precursor remelting material according to claim 1, characterized in that: In step S1: the pulping time is 30 to 120 minutes.

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

1.

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

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

5.

6. The method for preparing NFS cathode material using sodium electrode layer oxygen precursor back-solution material according to claim 1, characterized in that: In step S5: the reaction solution from step S4 is transferred to a plate and frame filter press for filtration using a diaphragm pump. The composition of the filtrate is then tested, acid is added to lower the pH of the solution, and nitrogen gas is introduced for protection. The solution is then transferred to the NFM precursor production line, where materials are added to the required ratio as needed, and NFM precursor preparation is carried out. The supplementary material is selected from one or more of nickel sulfate, ferrous sulfate, manganese sulfate crystal salt and pure water.

7. The method for preparing NFS cathode material using sodium electrode layer oxygen precursor remelting material according to claim 6, characterized in that: In step S5: the filtered filtrate is transferred to a salt solution storage tank, 98% sulfuric acid is added to adjust the pH of the solution to 1.5-2.0, and nitrogen gas is introduced for protection, with a purity of 99.99% and a flow rate of 20 L / min. Then, the solution is transferred to the NFM precursor production line.

8. The method for preparing NFS cathode material using sodium electrode layer oxygen precursor back-solution material according to claim 1, characterized in that: In step S6: Add 98% sulfuric acid to adjust the pH of the nickel replacement tank to 4.0-4.5 and carry out nickel ion iron powder replacement for 60 minutes.

9. The method for preparing NFS cathode material using sodium electrode layer oxygen precursor remelting material according to claim 1, characterized in that: In step S7: In the NFS mixing tank, the iron content in the filtrate is first detected, and then materials are added as needed. After the liquid preparation is completed, CNTs are mixed and spray-dried to obtain the NFS precursor. Under a nitrogen atmosphere, the NFS precursor is sintered at 350°C and held for 6 hours to obtain the NFS cathode material. The supplementary material is selected from one or more of sodium sulfate, ferrous sulfate, iron powder, and pure water.

Images