Method for preparing high-compaction phosphate lithium battery positive electrode material by acid dissolution method

Abstract

The present invention provides a method for preparing a high-compaction phosphate lithium battery positive electrode material by an acid dissolution method. In a pretreatment stage of a preparation process, an acid dissolution step is added. An iron source and a manganese source are partially dissolved using a mixed acid, which reduces the solid content of a slurry, and can shorten the time of a subsequent sand grinding step or further increase the solid content of a sand grinding slurry, thereby improving production efficiency and reducing energy consumption. In addition, during acid dissolution treatment, the original pure solid iron source and manganese source are transformed into a mixed system of solid particles of iron source / manganese source and ionic iron source / manganese source. The advantage of this reaction system is that different reaction processes are directly performed with raw materials in different states during a sintering process to form a product having mixed large and small particles, which ultimately improves the compaction density and volume energy density of the phosphate positive electrode material.

Description

Method for preparing high-density phosphate lithium battery positive electrode material by acid dissolution Technical Field

[0001] The invention relates to a method for preparing a high-density phosphate lithium battery positive electrode material by an acid dissolution method, belonging to the field of lithium battery positive electrode material preparation. Background Art

[0002] Lithium-ion batteries, with their high energy density, long life, lack of memory effect, and high operating voltage, have become the primary development direction for portable energy storage and power batteries. Cathode materials are a key factor in determining the cost, safety, and electrochemical performance of lithium-ion batteries. Lithium iron phosphate / lithium manganese iron phosphate, both olivine-type lithium transition metal phosphates, have become one of the mainstream lithium battery cathode materials due to their low cost, environmental friendliness, abundant raw material reserves, high safety, and stable operating voltage.

[0003] While the stable crystal structure of lithium iron phosphate / lithium manganese iron phosphate materials improves safety, they also suffer from low electronic conductivity and lithium ion mobility, which seriously affect their electrochemical performance, namely, mass energy density. Through extensive research, researchers have significantly improved the mass energy density of phosphate cathode materials through methods such as nano-scaling, carbon coating, and element doping.

[0004] As electric vehicles have higher requirements for driving range, the energy density of phosphate cathode materials has been challenged again. When the mass energy density is close to the theoretical value, further improving the volume energy density has become the focus of research. The important indicator for measuring volume energy density is the powder compaction density. The current compaction density of commercial phosphate cathode materials is much lower than the theoretical density (about 3.6g / cm 3 ), among which the compaction density of lithium iron phosphate is mostly 2.35-2.6g / cm 3 The compaction density of lithium manganese iron phosphate is mostly 2.2-2.38g / cm 3 Therefore, there is huge room for improvement in the compaction density of phosphate positive electrode materials.

[0005] Existing technologies mainly achieve high compaction of phosphate cathode materials through the following means: First, by controlling the particle size of sand milling, the product crystal size is different, thereby achieving high compaction. This solution is cumbersome to operate, and the compaction of the two sizes of particles is low, often less than 2.6g / cm 3 , such as patents CN202111046942.X and CN202010117579.5. Second, by selecting iron phosphate raw materials with high and low iron-phosphorus ratios, the product can be mixed with large and small particles and compacted tightly, such as patent CN201811397958.3. This solution has extremely high requirements for the selection of the iron-phosphorus ratio of iron phosphate, making it difficult to commercialize.

[0006] Summary of the Invention

[0007] In response to the above-mentioned problems existing in the prior art, the present invention provides a method for preparing a high-density phosphate lithium battery positive electrode material by an acid dissolution method. This method utilizes the property that the iron source and manganese source partially dissolve in mixed acid, and fully mixes and reacts the iron source and manganese source with the mixed acid to form a reaction system of solid particulate iron source / manganese source and ionic iron source / manganese source. During the sintering process, the solid particulate iron source / manganese source generates a large-particle phosphate positive electrode material through a solid-phase reaction. The soluble ionic iron source / manganese source first decomposes into nano-scale iron-manganese oxides during the sintering process, and then undergoes a solid-phase reaction to generate a small-particle phosphate positive electrode material. Ultimately, the compaction density of the phosphate positive electrode material is increased by mixing large and small particles, thereby improving the volume energy density.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a high-density phosphate lithium battery positive electrode material by an acid dissolution method, comprising the following steps:

[0010] 1) Mixing the iron source, manganese source, mixed acid and solvent to form a slurry, and mixing them by stirring and grinding to allow them to react fully;

[0011] A lithium source, a carbon source, and a dopant are added to the slurry, and the solid particles in the slurry are ground to nanometer level by sand milling, and then spray-dried to obtain a precursor;

[0012] 2) The precursor is calcined in a nitrogen atmosphere and then crushed to obtain a high-density lithium phosphate battery positive electrode material.

[0013] In step 1) of the present invention, the iron source is selected from ferric phosphate and / or ferric phosphate dihydrate, wherein the iron-to-phosphorus ratio is 0.955-1:1, preferably 0.965-0.975:1;

[0014] The manganese source is selected from any one of manganese carbonate, trimanganese tetraoxide, manganese dioxide, manganese oxalate, and manganese hydrogen phosphate, or a combination of at least two thereof, preferably any one of manganese carbonate, trimanganese tetraoxide, and manganese hydrogen phosphate, or a combination of at least two thereof;

[0015] The mixed acid is selected from a combination of at least two of phosphoric acid, oxalic acid, citric acid, hydrochloric acid, sulfuric acid, and nitric acid, preferably, the molar proportion of oxalic acid in the mixed acid is ≥10% and ≤90%;

[0016] The lithium source is selected from lithium carbonate and / or lithium hydroxide;

[0017] The carbon source is selected from any one or a combination of at least two of glucose, sucrose, starch, polyethylene glycol, polyvinyl alcohol, and polyacrylic acid, preferably any one or a combination of at least two of glucose, sucrose, and polyethylene glycol;

[0018] The dopant is selected from any one or a combination of at least two of titanium oxide, niobium oxide, magnesium oxide, titanium tetrachloride, titanium sulfate, isopropyl titanate, and isobutyl titanate, preferably any one or a combination of at least two of titanium oxide, niobium oxide, and magnesium oxide;

[0019] In step 1) of the present invention, the molar ratio of the iron source to the manganese source, the mixed acid, the lithium source, and the dopant is 100: 0-400: 10-250: 50-510: 0.5-7.5. The amount of the carbon source added is 5-15 wt% of the total weight of the solid material (referring to the total weight of the iron source, the manganese source, the lithium source, and the dopant);

[0020] The solvent is selected from water, ethanol or methanol; the amount of the solvent is such that the solid content of the slurry before sanding is 30-50 wt%, preferably 35-45 wt%.

[0021] In step 1) of the present invention, the stirring speed of the stirring mill is 100-200 rpm; the stirring time is 30-120 min;

[0022] The particle size of the slurry after sand grinding is controlled at D50 = 200-900nm, preferably 400-700nm;

[0023] The particle size of the precursor is controlled at D50=15-80 μm, preferably 30-60 μm.

[0024] In step 2) of the present invention, the nitrogen atmosphere has a nitrogen purity of ≥99.9995% and a pressure of 20-50 Pa. The calcination temperature is 750-800° C. and the holding time is 8-12 hours.

[0025] The high-density phosphate cathode material prepared by the present invention has a particle size range of D10 = 0.3-0.5 μm, D50 = 1-5 μm, and D90 ≤ 5 μm; for high-density lithium iron phosphate, the powder compaction density is ≥ 2.60 g / cm 3 , the gram capacity of button battery is ≥156mAh / g (0.1C, 25℃); for high-density lithium manganese iron phosphate, the powder compaction density is ≥2.40g / cm 3 , the gram capacity of the button battery is ≥148mAh / g (0.1C, 25℃).

[0026] The method described in the present invention adds an acid dissolution step before the conventional sand milling process in the pre-treatment stage of the preparation of the phosphate positive electrode material, and the iron source and manganese source are fully mixed and reacted with the mixed acid through a stirred mill. This step utilizes the characteristic that the iron source and manganese source are partially dissolved in the mixed acid to form a mixed system of solid particle iron source / manganese source and ionic iron source / manganese source. The advantage of this reaction system is that during the sintering process, raw materials in different states undergo different reaction processes, thereby forming a product with a mixture of large and small particles. Specifically, the solid particle iron source / manganese source directly generates large-particle phosphate positive electrode material through solid-phase reaction during the sintering process, while the soluble ionic iron source / manganese source first decomposes into nano-scale iron-manganese oxide during the sintering process, and then undergoes solid-phase reaction to generate small-particle phosphate positive electrode material. Ultimately, a phosphate positive electrode material with a mixture of large and small particles is formed, which improves the compaction density and volume energy density.

[0027] Compared with the existing technology, the technical solution of the present invention has the following beneficial effects:

[0028] The present invention adds an acid dissolution step to the pretreatment stage of the phosphate cathode material preparation process. This step uses mixed acid to partially dissolve the iron and manganese sources, reducing the solid content of the slurry. This can shorten the subsequent sand milling process or further increase the solid content of the sand milled slurry, thereby improving production efficiency and reducing energy consumption. Furthermore, after the acid dissolution treatment, the original pure solid iron and manganese sources are transformed into a mixed system of solid particulate iron / manganese sources and ionic iron / manganese sources. This reaction system has the advantage of directly utilizing different reaction processes in different raw materials during the sintering process to form a product with a mixture of large and small particles, ultimately improving the compacted density and volumetric energy density of the phosphate cathode material.

[0029] Compared with physical blending or selecting different types of iron phosphate raw materials, this method has the characteristics of simple operation and high adaptability of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the process of preparing high-density phosphate positive electrode materials by acid dissolution. DETAILED DESCRIPTION

[0031] The present invention is now described below in conjunction with specific embodiments. It should be noted that the embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the contents of the present invention are also protected by the present invention.

[0032] The sources of the reagents and raw materials used in the examples and comparative examples of the present invention are as follows. Unless otherwise specified, the remaining reagents and raw materials are all common commercially available products:

[0033] The test methods used in the examples and comparative examples of the present invention are as follows:

[0034] Particle size distribution: tested using Malvern MS3000.

[0035] Compaction density: tested using Sansi tester UTM7305.

[0036] Gram capacity (mass energy density) of button cells: button cells were prepared and tested using a Xinwei tester with a voltage range of 2.0V-3.75V.

[0037] Example 1

[0038] Preparation of high-density phosphate lithium battery cathode materials by acid dissolution method:

[0039] 1) Ferric phosphate (100 mol), manganese carbonate (150 mol), mixed acid (150 mol phosphoric acid, 20 mol oxalic acid, 30 mol nitric acid) and water were mixed to form a slurry with a solid content of 40%. The slurry was mixed and fully reacted in a stirred mill at a speed of 200 rpm for 80 min.

[0040] 2) 128 mol of lithium carbonate, 5 mol of titanium dioxide, and 8% glucose (total solid content) were added to the above slurry, followed by water addition and mixing to prepare a slurry with a solid content of 40 wt%. The slurry was sand-milled to a particle size of 500 nm. The sand-milled slurry was dried using a spray dryer to obtain a precursor with a particle size of 40 μm.

[0041] 3) The precursor is transferred to a kiln in a nitrogen atmosphere (≥99.995%) and calcined at a furnace pressure of 30 Pa, a calcination temperature of 790° C., and a calcination time of 12 h to form a lithium manganese iron phosphate material through a solid phase reaction, which is then pulverized to obtain high-density lithium manganese iron phosphate.

[0042] The particle size of lithium manganese iron phosphate product is D10=0.41μm, D50=1.38μm, D90=3.32μm.

[0043] The powder compaction density of lithium manganese iron phosphate product is 2.41g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 156mAh / g (0.1C, 25℃).

[0044] Example 2

[0045] Preparation of high-density phosphate lithium battery cathode materials by acid dissolution method:

[0046] 1) Ferric phosphate (100 mol), mixed acid (20 mol oxalic acid, 30 mol nitric acid) and water were mixed to form a slurry with a solid content of 40%. The slurry was mixed and fully reacted in a stirred mill at a speed of 200 rpm for 80 min.

[0047] 2) 51 mol of lithium carbonate, 5 mol of titanium dioxide, and 8% glucose (total solid content) were added to the above slurry, followed by water addition and mixing to prepare a slurry with a solid content of 40 wt%. The slurry was sand-milled to a particle size of 500 nm. The sand-milled slurry was dried using a spray dryer to obtain a precursor with a particle size of 40 μm.

[0048] 3) The precursor is transferred to a kiln in a nitrogen atmosphere (≥99.995%) and calcined at a furnace pressure of 30 Pa, a calcination temperature of 790° C., and a calcination time of 12 h to form a lithium iron phosphate material through a solid-phase reaction, which is then pulverized to obtain high-density lithium iron phosphate.

[0049] The particle size of lithium iron phosphate product is D10=0.39μm, D50=1.32μm, D90=4.59μm.

[0050] The powder compaction density of lithium iron phosphate products is 2.68g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 160mAh / g (0.1C, 25℃).

[0051] Example 3

[0052] Preparation of high-density phosphate lithium battery cathode materials by acid dissolution method:

[0053] 1) Ferric phosphate (100 mol), mixed acid (20 mol oxalic acid, 30 mol nitric acid) and water were mixed to form a slurry with a solid content of 38%. The slurry was mixed and fully reacted in a stirred mill at a speed of 150 rpm for 120 min.

[0054] 2) 52 mol of lithium carbonate, 4 mol of titanium dioxide, and 10% by weight of glucose (total solid content) were added to the above slurry, followed by water addition and mixing to prepare a slurry with a solid content of 38 wt%. The slurry was sand-milled to a D50 of 400 nm. The sand-milled slurry was dried using a spray dryer to obtain a precursor with a particle size of D50 of 35 μm.

[0055] 3) The precursor is transferred to a kiln in a nitrogen atmosphere (≥99.995%) and calcined at a furnace pressure of 30 Pa, a calcination temperature of 780° C., and a calcination time of 12 h to form a lithium iron phosphate material through a solid-phase reaction, which is then pulverized to obtain high-density lithium iron phosphate.

[0056] The particle size of lithium iron phosphate product is D10=0.37μm, D50=1.11μm, D90=3.96μm.

[0057] The powder compaction density of lithium iron phosphate products is 2.62g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 161mAh / g (0.1C, 25℃).

[0058] Comparative Example 1

[0059] The method of Example 1 is referred to, except that the operation of step 1) is different: the iron phosphate and manganese carbonate in step 1) are directly added to step 2), and then processed to obtain lithium manganese iron phosphate product.

[0060] The particle size of lithium manganese iron phosphate product is D10=0.31μm, D50=1.13μm, D90=4.89μm.

[0061] The powder compaction density of lithium manganese iron phosphate product is 2.25g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 145mAh / g (0.1C, 25℃).

[0062] Comparative Example 2

[0063] The method of Example 1 was referred to, except that the molar amount of the mixed acid in step 1) was increased proportionally to 1.5 times, namely 225 mol of phosphoric acid, 30 mol of oxalic acid, and 45 mol of nitric acid, and then treated to obtain the lithium manganese iron phosphate product.

[0064] The particle size of lithium manganese iron phosphate product is D10=0.38μm, D50=1.44μm, D90=5.63μm.

[0065] The powder compaction density of lithium manganese iron phosphate product is 2.35g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 121mAh / g (0.1C, 25℃).

[0066] Comparative Example 3

[0067] Refer to the method of Example 2, except that the mixed acid in step 1) is replaced with 50 mol oxalic acid.

[0068] The final performance of the lithium iron phosphate product is as follows:

[0069] The particle size of lithium iron phosphate product is D10=0.35μm, D50=1.02μm, D90=3.99μm.

[0070] The powder compaction density of lithium iron phosphate products is 2.45g / cm3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 159mAh / g (0.1C, 25℃).

[0071] Comparative Example 4

[0072] The method was carried out in accordance with Example 2, except that the mixed acid in step 1) was replaced with 50 mol phosphoric acid.

[0073] The final performance of the lithium iron phosphate product is as follows:

[0074] The particle size of lithium iron phosphate product is D10=0.64μm, D50=1.92μm, D90=7.23μm.

[0075] The powder compaction density of lithium iron phosphate products is 2.75g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 138mAh / g (0.1C, 25℃).

[0076] Comparative Example 5

[0077] The method was carried out in accordance with Example 2, except that the mixed acid in step 1) was replaced with 3 mol of oxalic acid and 47 mol of nitric acid.

[0078] The final performance of the lithium iron phosphate product is as follows:

[0079] The particle size of lithium iron phosphate product is D10=0.36μm, D50=1.34μm, D90=4.13μm.

[0080] The powder compaction density of lithium iron phosphate products is 2.50g / cm 3 The gram capacity (mass energy density) of the button battery at 0.1C discharge is 160mAh / g (0.1C, 25℃).

Claims

1. A method for preparing a high-density phosphate lithium battery positive electrode material by acid dissolution, characterized in that the steps include: 1) Mixing an iron source, a manganese source, a mixed acid and a solvent to form a slurry, and mixing them evenly by stirring and grinding to allow them to react fully; Adding lithium source, carbon source and dopant into the slurry, grinding the solid particles in the slurry to nanometer level by sand milling, and then spray drying to obtain a precursor; 2) The precursor is calcined in a nitrogen atmosphere and then crushed to obtain a high-density lithium phosphate battery positive electrode material.

2. The method according to claim 1, characterized in that In step 1), the molar ratio of the iron source to the manganese source, the mixed acid, the lithium source, and the dopant is 100:0-400:10-250:50-510:0.5-7.

5.

3. The method according to claim 1 or 2, characterized in that: In step 1), the iron source is selected from ferric phosphate and / or ferric phosphate dihydrate, wherein the iron-to-phosphorus ratio is 0.955-1:1; and / or The manganese source is selected from at least one of manganese carbonate, manganese tetraoxide, manganese dioxide, manganese oxalate and manganese hydrogen phosphate; and / or The lithium source is selected from lithium carbonate and / or lithium hydroxide; and / or The dopant is selected from at least one of titanium oxide, niobium oxide, magnesium oxide, titanium tetrachloride, titanium sulfate, isopropyl titanate, and isobutyl titanate.

4. The method according to any one of claims 1 to 3, characterized in that: In step 1), the mixed acid is selected from a combination of at least two of phosphoric acid, oxalic acid, citric acid, hydrochloric acid, sulfuric acid, and nitric acid. Preferably, the molar ratio of oxalic acid in the mixed acid is ≥10% and ≤90%.

5. The method according to any one of claims 1 to 4, characterized in that: In step 1), the carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, polyvinyl alcohol, and polyacrylic acid; Preferably, the amount of carbon source added is 5-15 wt % of the total weight of the solid material.

6. The method according to any one of claims 1 to 5, characterized in that: In step 1), the solvent is selected from at least one of water, ethanol or methanol; Preferably, the amount of the solvent used is such that the solid content of the slurry is 30-50 wt %.

7. The method according to any one of claims 1 to 6, characterized in that: In step 1), the stirring speed of the stirring mill is 100-200 rpm, and the stirring time is 30-120 min; The particle size of the slurry after sand grinding is controlled at D50 = 200-900nm, preferably 400-700nm; The particle size of the precursor is controlled at D50=15-80 μm, preferably 30-60 μm.

8. The method according to any one of claims 1 to 7, characterized in that: In step 2), the nitrogen atmosphere has a nitrogen purity of ≥99.9995% and a pressure of 20-50Pa.

9. The method according to any one of claims 1 to 8, characterized in that: In step 2), the calcination temperature is 750-800° C. and the time is 8-12 hours.

10. A high-density phosphate cathode material prepared according to the method of any one of claims 1 to 9, characterized in that: The particle size range is D10=0.3-0.5μm, D50=1-5μm, D90≤5μm.

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