Method for preparing ferrous oxalate for battery cathode material lithium iron phosphate by acid method

Abstract

The invention is applicable to the technical field of preparation of ferrous oxalate, and provides a method for preparing ferrous oxalate for a battery cathode material lithium iron phosphate by an acid method, which comprises the following steps: preparing raw materials: preparing a ferrous sulfate salt solution and an oxalic acid solution under an anaerobic condition; reaction precipitation: slowly dropwise adding the oxalic acid solution into the ferrite solution, maintaining the temperature, and stirring for reaction; centrifuging and washing the precipitate: after the reaction is finished, separating the precipitate, and washing with deionized water to obtain a wet filter cake; drying and post-processing: drying the wet filter cake at high temperature, and crushing and sieving the dried product to obtain the ferrous oxalate. The whole process of preparing ferrous oxalate is anaerobic, Fe < 2 + > oxidation can be prevented, uniform mixing can be promoted by controlling the reaction temperature, improving the reaction rate, inhibiting Fe < 2 + > oxidation, controlling the pH, preventing Fe (OH) 2 generation, maintaining ferrous oxalate dissolution balance and controlling the stirring speed, and coarse grains caused by local supersaturation are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of ferrous oxalate, and particularly relates to a method for preparing ferrous oxalate for use in the acid method for preparing lithium iron phosphate as a cathode material for batteries. Background Art

[0002] With the development and progress of new energy vehicle manufacturing technology, its production and sales volume has gradually increased, and the retail penetration rate has also increased year by year, even exceeding that of traditional fuel passenger cars. New energy vehicles use unconventional vehicle fuels as power sources, so the production of the batteries used as power sources is particularly important. Lithium iron phosphate is a cathode material for batteries, and ferrous oxalate can be used as an iron source for the production of lithium iron phosphate, which is beneficial to the formation of a uniform lithium iron phosphate precursor, reduces the introduction of impurities, and improves the electrochemical performance of the material.

[0003] The acid method for preparing ferrous oxalate uses oxalic acid to react with iron salts to produce ferrous oxalate, which is simple, efficient, and low-cost. However, this process also has some problems, such as ferrous ions being easily oxidized and crystallization being difficult to control. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a method for preparing ferrous oxalate for use in the acid method for preparing lithium iron phosphate as a cathode material for batteries, aiming to solve the problems existing in the above background art.

[0005] The embodiments of the present invention are implemented as follows. A method for preparing ferrous oxalate for use in the acid method for preparing lithium iron phosphate as a cathode material for batteries includes the following steps:

[0006] (1) Raw material preparation: Prepare a ferrous salt solution and an oxalic acid solution under an oxygen-free condition;

[0007] (2) Reaction precipitation: Slowly drop the oxalic acid solution into the ferrous salt solution, maintain the temperature, and stir to carry out the reaction;

[0008] (3) Precipitation centrifugation and washing: After the reaction is completed, separate the precipitate and wash it with deionized water to obtain a wet filter cake;

[0009] (4) Drying and post-treatment: High-temperature dry the wet filter cake, and then crush and screen the dried product to obtain the ferrous oxalate.

[0010] Preferably, in step (1), the ferrous salt solution is an aqueous solution of ferrous sulfate with a concentration of 0.5 - 2.0 mol / L.

[0011] Preferably, in step (1), the method for preparing the oxalic acid solution includes: Dissolve oxalic acid in sulfuric acid-free water, and the molar ratio of the oxalic acid solution to the ferrous salt solution is 1:1.

[0012] Preferably, in step (2), the temperature is 80-90 °C, the reaction time is 1-3 h, and the stirring rate is 300-500 rpm.

[0013] Preferably, in step (2), the pH value is controlled to be 1.0-1.5 during the reaction.

[0014] Preferably, in step (3), vacuum filtration or centrifugal separation is used to separate the precipitate.

[0015] Preferably, in step (4), the temperature of the high-temperature drying is 110-120 °C and the time is 3 min.

[0016] The method for preparing ferrous oxalate for the positive electrode material lithium iron phosphate of an acid-processed battery provided by the embodiment of the present invention has the following characteristics:

[0017] Readily available raw materials: Oxalic acid and ferrous sulfate / ferrous chloride are common chemical raw materials with low costs, suitable for industrial production;

[0018] Direct reaction: The one-step precipitation process is simple, with high reaction efficiency and no need for complex intermediate steps;

[0019] Controllable product purity: By adjusting the excess ratio of oxalic acid (5-10%), side reactions can be inhibited, and the purity of FeC 2 O 4 ·2H 2 O can reach over 99.5%;

[0020] Utilization of by-products: H 2 SO 4 in the mother liquor can be concentrated and recycled, reducing the pressure of waste liquid treatment;

[0021] In the method of preparing the ferrous sulfate solution, an anoxic reaction method is adopted to prevent the oxidation of Fe 2+ By controlling the reaction temperature, the reaction rate can be increased, while the oxidation of Fe 2+ is inhibited. By controlling the pH, the formation of Fe(OH) 2 is prevented, and the dissolution equilibrium of ferrous oxalate is maintained. By controlling the stirring speed, the mixing can be promoted to be uniform, avoiding local supersaturation resulting in coarse crystals. Specific embodiments

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0024] Example 1. A method for preparing ferrous oxalate for use in the positive electrode material lithium iron phosphate by the acid method, comprising the following steps:

[0025] (1) Raw material preparation:

[0026] Preparation of ferrous salt solution: Prepare an aqueous solution of ferrous sulfate (FeSO 4 ·7H 2 O) with a concentration of 0.5 mol / L. Add a small amount of dilute sulfuric acid (pH≈1 - 2) during dissolution. The preparation process is carried out under anaerobic conditions to inhibit the oxidation of Fe 2+ ;

[0027] Preparation of oxalic acid solution: Dissolve oxalic acid (H 2 C 2 O 4 ·2H 2 O) in sulfuric acid with a molar ratio of 1:1 to the ferrous salt solution, and set aside;

[0028] (2) Reaction precipitation:

[0029] Mixing reaction: Slowly drip the oxalic acid solution into the ferrous salt solution, maintain the temperature at 80°C, stir mechanically (300 rpm), and the reaction time is 1 h to ensure the completion of the reaction;

[0030] Control conditions: Maintain the pH of the reaction solution at 1.0 - 1.5 (excess oxalic acid can inhibit the formation of Fe(OH) 2 );

[0031] (3) Precipitation separation and washing:

[0032] Filtration / centrifugation: After the reaction, separate the precipitate by vacuum filtration. The mother liquor (containing H 2 SO 4 ) can be recycled or neutralized;

[0033] Washing: Wash the precipitate with deionized water 3 times in sequence to remove residual acid radicals (SO 4 2- ) and free acid. Use the conductivity of the washing liquid <100 μS / cm and the pH close to neutral as the standard to obtain a wet filter cake;

[0034] (4) Drying and post-treatment:

[0035] Low-temperature drying: Place the wet filter cake in a drying oven (120°C) and dry for 3 minutes to avoid the decomposition of ferrous oxalate (decomposition temperature >160°C);

[0036] Crushing and screening: Grind the dried product by ball milling or air flow crushing and pass through a 200-mesh sieve to obtain a uniform light yellow powder.

[0037] Example 2. A method for preparing ferrous oxalate for use in the acid method for preparing cathode material lithium iron phosphate for batteries, comprising the following steps:

[0038] (1) Raw material preparation:

[0039] Prepare ferrous salt solution: Prepare an aqueous solution of ferrous sulfate (FeSO 4 ·7H 2 O) under anaerobic conditions, with a concentration of 1.0 mol / L. Add a small amount of dilute sulfuric acid (pH≈1 - 2) during dissolution to inhibit the oxidation of Fe 2+ ;

[0040] Prepare oxalic acid solution: Dissolve oxalic acid (H 2 C 2 O 4 ·2H 2 O) in sulfuric acid, with a molar ratio to the ferrous salt solution of 1:1, and set aside;

[0041] (2) Reaction and precipitation:

[0042] Mixing reaction: Slowly add the oxalic acid solution to the ferrous salt solution, maintain the temperature at 80°C, stir mechanically (400 rpm), and react for 2 h to ensure the reaction is complete;

[0043] Control conditions: Maintain the pH of the reaction solution at 1.0 - 1.5 (excess oxalic acid can inhibit the formation of Fe(OH) 2 );

[0044] (3) Precipitation separation and washing:

[0045] Filtration / centrifugation: After the reaction, separate the precipitate by centrifugation. The mother liquor (containing H 2 SO 4 or HCl) can be recycled or neutralized;

[0046] Washing: Wash the precipitate with deionized water 3 times in sequence to remove residual acid radicals (SO 4 2- ) and free acid, and use the conductivity of the washing liquid <100 μS / cm and the pH close to neutral as the standard to obtain a wet filter cake;

[0047] (4) Drying and post-treatment:

[0048] Low-temperature drying: Place the wet filter cake in a high-temperature drying oven (120°C) and dry for 3 minutes to avoid the decomposition of ferrous oxalate (decomposition temperature >160°C);

[0049] Crushing and screening: Grind or crush the dried product by ball milling or air flow, and pass through a 200-mesh sieve to obtain a uniform light yellow powder.

[0050] Example 3: A method for preparing ferrous oxalate for use in the acid - method preparation of the cathode material lithium iron phosphate for batteries, comprising the following steps:

[0051] (1) Raw material preparation:

[0052] Prepare ferrous salt solution: Under anaerobic conditions, prepare an aqueous solution of ferrous sulfate (FeSO 4 ·7H 2 O) with a concentration of 1.5 mol / L. When dissolving, add a small amount of dilute sulfuric acid (pH≈1 - 2) or hydrochloric acid (pH≈1 - 2) to inhibit the oxidation of Fe 2+ ;

[0053] Prepare oxalic acid solution: Dissolve oxalic acid (H 2 C 2 O 4 ·2H 2 O) in sulfuric acid, with a molar ratio to the ferrous salt solution of 1:1, and set aside;

[0054] (2) Reaction and precipitation:

[0055] Mixing reaction: Slowly drip the oxalic acid solution into the ferrous salt solution, maintain the temperature at 80 °C, stir mechanically (500 rpm), and react for 3 h to ensure the completion of the reaction;

[0056] Control conditions: Maintain the pH of the reaction solution at 1.0 - 1.5 (excess oxalic acid can inhibit the formation of Fe(OH) 2 );

[0057] (3) Precipitation separation and washing:

[0058] Filtration / centrifugation: After the reaction, separate the precipitate by centrifugation. The mother liquor (containing H 2 SO4) can be recycled or neutralized;

[0059] Washing: Wash the precipitate with deionized water 5 times in sequence to remove residual acid radicals (SO 4 2- ) and free acid, and use the conductivity of the washing liquid < 100 μS / cm and the pH close to neutral as the standard to obtain a wet filter cake;

[0060] (4) Drying and post - treatment:

[0061] Low - temperature drying: Place the wet filter cake in a high - temperature drying oven (130 °C) and dry for 5 minutes to avoid the decomposition of ferrous oxalate (decomposition temperature > 160 °C);

[0062] Crushing and screening: Grind the dried product by ball milling or air flow crushing, and pass through a 200 - mesh sieve to obtain a uniform light - yellow powder.

[0063] Example 4. A method for preparing ferrous oxalate for use in the positive electrode material lithium iron phosphate by an acid method, comprising the following steps:

[0064] (1) Raw material preparation:

[0065] Preparation of ferrous salt solution: Under anaerobic conditions, prepare an aqueous solution of ferrous sulfate (FeSO 4 ·7H 2 O) with a concentration of 2.0 mol / L. When dissolving, add a small amount of dilute sulfuric acid (pH≈1 - 2) or hydrochloric acid (pH≈1 - 2) to inhibit the oxidation of Fe 2+ ;

[0066] Preparation of oxalic acid solution: Dissolve oxalic acid (H 2 C 2 O 4 ·2H 2 O) in deionized water, with a molar ratio of 1:1 to the ferrous salt solution, and set aside;

[0067] (2) Reaction precipitation:

[0068] Mixing reaction: Slowly drip the oxalic acid solution into the ferrous salt solution, maintain the temperature at 85°C, stir mechanically (300 rpm), and react for 3 h to ensure the completion of the reaction;

[0069] Control conditions: Maintain the pH of the reaction solution at 1.0 - 1.5 (excess oxalic acid can inhibit the formation of Fe(OH) 2 );

[0070] (3) Precipitation separation and washing:

[0071] Filtration / centrifugation: After the reaction, separate the precipitate by vacuum filtration. The mother liquor (containing H 2 SO 4 ) can be recycled or neutralized;

[0072] Washing: Wash the precipitate with deionized water 3 times in sequence to remove residual acid radicals (SO 4 2- ) and free acid, with the conductivity of the washing liquid <100 μS / cm and the pH close to neutral as the standard to obtain a wet filter cake;

[0073] (4) Drying and post-treatment:

[0074] Low-temperature drying: Place the wet filter cake in a high-temperature drying oven (110°C) and dry for 3 minutes to avoid the decomposition of ferrous oxalate (decomposition temperature >160°C);

[0075] Crushing and screening: Grind the dried product by ball milling or jet milling and pass through a 200-mesh sieve to obtain a uniform light yellow powder.

[0076] Example 5. A method for preparing ferrous oxalate for use in the positive electrode material lithium iron phosphate by an acid method, comprising the following steps:

[0077] (1) Raw material preparation:

[0078] Preparation of ferrous salt solution: Prepare an aqueous solution of ferrous chloride (FeCl 2 ·4H 2 O) under anaerobic conditions, with a concentration of 1.5 mol / L. Add a small amount of dilute sulfuric acid (pH≈1 - 2) or hydrochloric acid (pH≈1 - 2) during dissolution to inhibit the oxidation of Fe 2+ ;

[0079] Preparation of oxalic acid solution: Dissolve oxalic acid (H 2 C 2 O 4 ·2H 2 O) in sulfuric acid, with a molar ratio to the ferrous salt solution of 1:1, and set aside;

[0080] (2) Reaction precipitation:

[0081] Mixing reaction: Slowly drip the oxalic acid solution into the ferrous salt solution, maintain the temperature at 75 °C, stir mechanically (400 rpm), and react for 1 h to ensure the completion of the reaction;

[0082] Control conditions: Maintain the pH of the reaction solution at 1.0 - 1.5 (excess oxalic acid can inhibit the formation of Fe(OH) 2 );

[0083] (3) Precipitation separation and washing:

[0084] Filtration / centrifugation: After the reaction, separate the precipitate by centrifugation. The mother liquor (containing H 2 SO4) can be recycled or neutralized;

[0085] Washing: Wash the precipitate 5 times successively with deionized water to remove residual acid radicals (SO 4 2- ) and free acid, and use the conductivity of the washing solution <100 μS / cm and pH close to neutral as the standard to obtain a wet filter cake;

[0086] (4) Drying and post-treatment:

[0087] Low-temperature drying: Place the wet filter cake in a high-temperature drying oven (110 °C) and dry for 4 minutes to avoid the decomposition of ferrous oxalate (decomposition temperature >160 °C);

[0088] Crushing and screening: Grind the dried product by ball milling or air flow crushing, and pass through a 200-mesh sieve to obtain a uniform light yellow powder.

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries by acid process, characterized in that: The following steps are involved: (1) Raw material preparation: prepare ferrous sulfate solution and oxalic acid solution under anaerobic conditions; (2) Reaction precipitation: slowly add the oxalic acid solution to the ferrous salt solution, control the pH value, maintain the temperature, and stir to react; (3) Precipitation centrifugation and washing: After the reaction is completed, the precipitate is separated and washed with deionized water to obtain a wet filter cake; (4) Drying and post-treatment: The wet filter cake is dried at high temperature, and the dried product is crushed and sieved to obtain the ferrous oxalate.

2. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 1, characterized in that: In step (1), the ferrous salt solution is an aqueous solution of ferrous sulfate with a concentration of 0.5-2.0 mol / L.

3. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 2, characterized in that: In step (1), the preparation method of the oxalic acid solution comprises: dissolving oxalic acid in dilute sulfuric acid, and the molar ratio of the oxalic acid solution to the ferrous salt solution is 1:

1.

4. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 1, characterized in that: In step (2), the temperature is 80-90° C., the reaction time is 1-3 h, and the stirring rate is 300-500 rpm.

5. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 1, characterized in that: In step (2), the pH value is controlled at 1.0-1.5 during the reaction.

6. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 1, characterized in that: In step (3), the separation of the precipitate is carried out by vacuum filtration or centrifugal separation.

7. The method for preparing ferrous oxalate for lithium iron phosphate as a positive electrode material for batteries according to claim 1, characterized in that: In step (4), the high temperature drying temperature is 110-120°C and the time is 3 minutes.