Lithium phytate, preparation method therefor, and use thereof in positive electrode material

Abstract

Provided in the present disclosure are lithium phytate, a preparation method therefor, and the use thereof in a positive electrode material. The preparation method comprises the following steps: mixing a phytic acid solution with a lithium source for reaction, adjusting the pH value, and drying same to obtain lithium phytate. Provided in the present disclosure is the lithium phytate preparation method, which involves a simple process, high operability and mild reaction temperature conditions, and which is relatively environmentally-friendly. Pre-preparation of lithium phytate can prevent material structural damage caused by corrosion due to directly applying phytic acid solutions to positive electrode materials, and also can avoid introduction of other alkali metal cations, thereby eliminating adverse effects on positive electrode materials. In addition, using the prepared lithium phytate as a water washing additive to perform water washing and coating on positive electrode materials can effectively reduce residual alkalis on the surfaces of the positive electrode materials, thereby improving the electrochemical properties of the positive electrode materials.

Description

Lithium phytate, preparation method thereof and application thereof in positive electrode material Technical Field

[0001] The present disclosure belongs to the technical field of battery materials, and particularly relates to lithium phytate, a preparation method thereof, and an application thereof in positive electrode materials. Background Art

[0002] Ternary cathode materials are one of the most promising cathode materials for high-performance lithium-ion batteries used in automotive electrification. To address vehicle range and safety issues, ternary materials need to be improved. High nickel content, high voltage, and single crystallization have become the mainstream development directions for ternary materials. However, as nickel content and applied voltage increase, the material surface becomes more active, increasing the electrochemical and chemical reactions between the ternary material and the electrolyte, reducing storage and gas production performance. Single crystallization results in uneven lithium distribution within the ternary material particles during charge and discharge, reducing the material's release capacity. In the current context, high nickel content has become one of the most effective means of increasing battery energy density. However, high-nickel ternary materials have high residual alkali content and are highly hygroscopic. To reduce residual alkali content and improve stability, a water washing step is often introduced during the preparation process to reduce residual alkali on the material surface.

[0003] Coating is an effective means to improve the surface stability of ternary materials. Commonly used coating methods include dry coating and wet coating. Dry coating often has the problem of uneven coating and often has quality requirements for additives; conventional wet coating does not yet have the prospect of large-scale production. As mentioned above, high nickel ternary materials will use a water washing process to reduce the residual alkali on the surface. However, high nickel materials will undergo Li + / H + The exchange causes the lattice lithium in the material to be released, and as the nickel content increases, the risk of lattice lithium release increases dramatically, the lithium content of the material decreases, and a phase change occurs on the surface, which ultimately leads to the degradation of the material's electrical properties.

[0004] Therefore, how to effectively remove the residual alkali on the surface of the positive electrode material and improve the electrochemical performance of the positive electrode material is a problem existing in the current positive electrode materials.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] In view of the deficiencies in the prior art, the purpose of the present disclosure is to provide a lithium phytate, a preparation method thereof and its application in positive electrode materials. The present disclosure provides a method for preparing lithium phytate with a simple process, strong operability, mild reaction conditions and relative environmental protection. By prefabricating lithium phytate, on the one hand, it is possible to prevent the direct use of phytic acid solution in the positive electrode material to cause corrosion and damage the material structure. On the other hand, it is possible to avoid the introduction of other alkali metal cations and eliminate the adverse effects on the positive electrode material. In addition, the prepared lithium phytate is used as a water washing additive to wash and coat the positive electrode material, which can effectively remove the residual alkali on the surface of the positive electrode material and improve the electrochemical performance of the positive electrode material.

[0008] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0009] In a first aspect, the present disclosure provides a method for preparing lithium phytate, the preparation method comprising the following steps:

[0010] The phytic acid solution and the lithium source are mixed to react, the pH is adjusted, and the lithium phytate is obtained after drying.

[0011] The present disclosure provides a method for preparing lithium phytate with a simple process, strong operability, mild reaction conditions, and relative environmental friendliness. By prefabricating lithium phytate, on the one hand, it is possible to prevent the direct application of phytic acid solution to the positive electrode material, thereby preventing corrosion and damaging the material structure; on the other hand, it is possible to avoid the introduction of other alkali metal cations, thereby eliminating the adverse effects on the positive electrode material. In addition, the prepared lithium phytate is used as a water washing additive to wash and coat the positive electrode material, which can effectively remove residual alkali on the surface of the positive electrode material and improve the electrochemical performance of the positive electrode material.

[0012] In the present disclosure, the purpose of adjusting the pH of the solution after the reaction is to completely convert phytic acid into lithium phytate and to prevent the acid radical ions existing in a small amount from reacting with the ternary cathode material.

[0013] It should be noted that lithium phytate refers to the product obtained by the acid-base neutralization reaction of phytate ions and lithium ions.

[0014] It should be noted that phytic acid solution is also known as inositol hexaphosphate solution, cyclohexane hexaphosphate solution, and its molecular formula is C6H 18 O 24 P6 is an organophosphorus compound extracted from plant seeds. It is easily soluble in water, ethanol and acetone, and has strong acidity and strong chelating ability.

[0015] It should be noted that the present disclosure does not specifically limit the concentration of the phytic acid solution, and the concentration can be adjusted according to actual needs. For example, it can be 50-60wt.%, such as 50wt.%, 52wt.%, 54wt.%, 56wt.%, 58wt.% or 60wt.%.

[0016] In one embodiment, the lithium source includes any one of lithium hydroxide monohydrate, lithium oxide, lithium peroxide, lithium carbonate, lithium phosphate, lithium monohydrogen phosphate, or lithium dihydrogen phosphate, or a combination of at least two thereof.

[0017] In the present disclosure, the above-mentioned lithium-containing compounds are used as lithium sources, which can better react with phytic acid to form an acid-base reaction while avoiding the introduction of other types of anionic groups.

[0018] In one embodiment, the mass ratio of the phytic acid solution to the lithium source is 1:(0.15-0.6), for example, it can be 1:0.15, 1:0.2, 1:0.3, 1:0.4, 1:0.5 or 1:0.6.

[0019] In the present disclosure, if the mass ratio of the phytic acid solution to the lithium source is too large, the phytic acid cannot be completely converted and the pH value of the solution is low; if the mass ratio of the phytic acid solution to the lithium source is too small, the pH value of the solution is high and the lithium phytate contains a large amount of unconverted alkaline compound impurities.

[0020] As an optional technical solution of the present disclosure, the reaction temperature is 20-80°C, for example, 25°C, 40°C or 60°C, and the reaction time is 10-120min, for example, 10min, 30min, 50min, 70min, 90min or 110min.

[0021] In one embodiment, the reaction temperature is 25-40° C. and the reaction time is 20-60 min.

[0022] In the present disclosure, the phytic acid solution and the lithium source react within the above-mentioned optional range, and the phytic acid can be completely converted into lithium phytate through acid-base neutralization reaction, thereby avoiding the introduction of acidic groups to damage the positive electrode material.

[0023] In one embodiment, after the pH is adjusted, the pH of the solution is 6-8, for example, 6, 6.5, 7, 7.5 or 8, and 7 is optional.

[0024] In the present disclosure, limiting the pH of the solution to 6-8 helps ensure that the phytic acid solution is converted into neutral lithium phytate. At the same time, the prepared lithium phytate has high purity and low impurity content.

[0025] As an optional technical solution of the present disclosure, the drying method includes any one of heating evaporation, oven drying or vacuum assisted drying.

[0026] In one embodiment, the drying temperature is 80-150°C, for example, 80°C, 100°C, 110°C, 130°C or 150°C, and the drying time is 12-48h, for example, 12h, 18h, 24h, 30h, 36h, 42h or 48h.

[0027] In the present disclosure, drying at 80-150° C. for 12-48 hours can effectively remove moisture and obtain high-purity lithium phytate.

[0028] In a second aspect, the present disclosure provides lithium phytate, which is prepared using the preparation method described in the first aspect.

[0029] The lithium phytate provided in the present disclosure can be used as a precursor for preparing phosphorus-containing compounds or phosphates. In the present disclosure, it is used as a water washing additive to inhibit the side reactions of the ternary positive electrode material during the water washing process, and at the same time can form a coating layer on the surface of the material to improve the electrical properties of the material.

[0030] In a third aspect, the present disclosure provides a use of the lithium phytate described in the second aspect in a positive electrode material for a lithium ion battery.

[0031] In the present disclosure, lithium phytate is applied to the positive electrode material, and the phytate ions can complex with the metal ions on the surface of the positive electrode material to form a lithium ion conductive layer, thereby achieving a coating effect.

[0032] As an optional technical solution of the present disclosure, the specific steps of applying the lithium phytate in the positive electrode material for lithium ion batteries include:

[0033] (1) mixing the lithium phytate and water to obtain a water wash;

[0034] (2) The water washing liquid, alkali metal hydroxide and positive electrode material are mixed and heat treated to obtain a coated and modified positive electrode material.

[0035] In the present disclosure, lithium phytate is used as a water washing additive to coat and modify the positive electrode material, which can form a lithium phosphate fast ion conductor on the surface of the positive electrode material, construct a physical barrier, and inhibit the side reactions of the positive electrode material in the electrolyte, thereby improving the material's cycle performance; in addition, the residual alkali can be removed during the water washing process, exposing more lithium active sites, thereby increasing the discharge capacity of the material.

[0036] As an optional technical solution of the present invention, the concentration of the water washing solution in step (1) is 5-100 g / L, for example, it can be 5 g / L, 10 g / L, 30 g / L, 50 g / L, 70 g / L or 90 g / L, etc., and can be optionally 20-100 g / L.

[0037] In one embodiment, the concentration of the water washing solution in step (1) is 50-100 g / L.

[0038] In the present disclosure, the use of a water washing solution with a concentration of 50-100 g / L helps to ensure that sufficient lithium phytate is coated on the surface of the positive electrode material.

[0039] In one embodiment, the alkali metal hydroxide in step (2) includes any one of lithium hydroxide, sodium hydroxide or potassium hydroxide, or a combination of at least two thereof.

[0040] In the present disclosure, the above substances are used as alkali metal hydroxides to adjust the pH of the water washing solution and inhibit the Li + / H + exchange, and the possibility of lattice lithium extraction.

[0041] In one embodiment, the concentration of the alkali metal hydroxide in the water washing solution in step (2) is 5-120 g / L, for example, 5 g / L, 10 g / L, 30 g / L, 50 g / L, 70 g / L, 90 g / L or 110 g / L.

[0042] In one embodiment, the concentration of the alkali metal hydroxide in the water washing solution in step (2) is 10-85 g / L.

[0043] In the present disclosure, the concentration of alkali metal hydroxide in the water wash solution is 10-85 g / L, which helps to adjust the pH value of the water wash solution and reduce the pH value of the water wash solution. + concentration, thereby better inhibiting the occurrence of Li + / H + Exchange to improve the electrical performance of the positive electrode material.

[0044] In one embodiment, the positive electrode material in step (2) comprises a high nickel ternary positive electrode material, the chemical formula of which is LiNi x Co y Mn z O2, 0.8≤x<1, 0<y≤0.1, 0<z≤0.1, x+y+z=1.

[0045] In the present disclosure, 0.8≤x<1, for example, it can be 0.8, 0.85, 0.9 or 0.95, etc., 0<y≤0.1, for example, it can be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, etc., 0<z≤0.1, for example, it can be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, etc.

[0046] In the present disclosure, lithium phytate is used as a water washing additive to coat and modify the high nickel ternary cathode material, which can effectively remove the residual lithium on the surface of the high nickel material and inhibit the Li + / H + Exchange, reduce the decrease in lattice lithium and material lithium content, and ultimately improve the electrochemical performance of high-nickel ternary materials.

[0047] In one embodiment, the mass ratio of the water washing solution to the positive electrode material in step (2) is 1:(0.4-2), for example, it can be 1:0.4, 1:0.5, 1:1, 1:1.5 or 1:2, etc., and can be optionally 1:(0.5-1).

[0048] In the present disclosure, if the mass ratio of the water washing liquid to the positive electrode material is too small, that is, the amount of the water washing liquid is too little, the viscosity of the positive electrode material after water washing is high and the slurry is not stirred evenly; if the mass ratio of the water washing liquid to the positive electrode material is too large, that is, the amount of the water washing liquid is too large, the side reactions of the positive electrode material during the water washing process increase, and the risk of lithium detachment from the material lattice increases, thereby causing the electrical performance of the material to deteriorate.

[0049] As an optional technical solution of the present disclosure, the mixing process in step (2) is accompanied by stirring, and the stirring rate is 80-300 rpm, for example, it can be 80 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm.

[0050] In the present disclosure, the stirring rate during the mixing process is 80-300 rpm, which can effectively remove the residual lithium on the surface of the positive electrode material and inhibit the material Li + / H + Exchange, reducing the lattice lithium and material lithium content.

[0051] In one embodiment, the mixing time in step (2) is 0.5-3 min, for example, 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min or 3 min.

[0052] In the present disclosure, the mixing process is also the washing process. If the washing process is too long, the material will + / H + The risk of exchange and lattice lithium extraction increases, and the material deteriorates; if the water washing process is too short, the removal effect of residual lithium on the surface of the ternary positive electrode material is poor, and the mixing is uneven, and the lithium phytate coating effect is poor.

[0053] In one embodiment, the heat treatment temperature in step (2) is 300-700°C, for example, 300°C, 400°C, 500°C, 600°C or 700°C, and the time is 5-20h, for example, 5h, 10h, 15h or 20h.

[0054] In the present disclosure, heat treatment at 300-700° C. for 5-20 h is beneficial to reducing the moisture content of the positive electrode material, while enhancing the interface contact between lithium phytate and the positive electrode material and enhancing the surface ionic conductivity of the positive electrode material.

[0055] It should be noted that the present disclosure does not limit the equipment for heat treatment. For example, a box furnace or kiln equipment may be used.

[0056] As an optional technical solution of the present disclosure, the specific steps of applying the lithium phytate in the positive electrode material for lithium ion batteries include:

[0057] (I) mixing a phytic acid solution and a lithium source in a mass ratio of 1:(0.15-0.6) at 20-80° C. for 10-120 minutes, controlling the pH of the solution to be neutral, and drying at 80-150° C. for 12-48 hours to obtain lithium phytate;

[0058] (II) dissolving the lithium phytate in water to obtain a water wash solution with a concentration of 5-100 g / L;

[0059] (III) adding an alkali metal hydroxide to the water wash solution so that the concentration of the alkali metal hydroxide in the water wash solution is 5-120 g / L, then adding a high nickel ternary positive electrode material, stirring and mixing at 80-300 rpm for 0.5-3 minutes, performing solid-liquid separation after the end, and then drying at 110-150° C. for 8-24 hours to remove moisture, and finally heat treating in an oxygen atmosphere, air atmosphere, or nitrogen atmosphere at a temperature of 300-700° C. for 5-20 hours. After the heat treatment, cooling and sieving are performed to obtain a coated modified positive electrode material;

[0060] The mass ratio of the water washing solution to the positive electrode material is 1:(0.4-2), and the mesh number of the sieve is 100-400 meshes.

[0061] In the present disclosure, the drying temperature is 110-150°C, for example, it can be 110°C, 120°C, 130°C, 140°C or 150°C, etc., the time is 8-24h, for example, it can be 8h, 10h, 15h, 20h or 24h, etc., and the mesh size of the sieve is 100-400 mesh, for example, it can be 100 mesh, 200 mesh, 300 mesh or 400 mesh, etc.

[0062] The present invention applies the prepared lithium phytate to the modification process of high nickel ternary cathode materials, which can not only reduce H + concentration, inhibiting the Li + / H +Exchange, and the phytate ions can complex with the metal ions on the surface of the high-nickel ternary positive electrode material to form a lithium ion conductive layer, achieving the effect of water washing coating.

[0063] The numerical range described in the present disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present disclosure no longer exhaustively lists the specific point values ​​included in the range.

[0064] Compared with the prior art, the present disclosure has the following beneficial effects:

[0065] (1) The preparation method of lithium phytate provided by the present disclosure has a simple process, strong operability, mild reaction conditions, and is relatively environmentally friendly. The present disclosure gives priority to the preparation of lithium phytate. On the one hand, this is to prevent the direct use of phytic acid solution, which may cause corrosion of the positive electrode material and damage the material structure; on the other hand, it avoids the introduction of other alkali metal cations to eliminate their adverse effects on the positive electrode material.

[0066] (2) The lithium phytate prepared in the present disclosure can be used as a water washing additive in the modification process of the positive electrode material. On the one hand, it supplements the alkali metal hydroxide and reduces the H + concentration, thereby inhibiting the Li + / H + Exchange, on the other hand, phytate ions can complex with metal ions on the surface of the positive electrode material to form a lithium ion conductive layer, achieving the effect of water washing coating.

[0067] (3) The present disclosure uses lithium phytate as a water washing additive to form a lithium phosphate fast ion conductor on the surface of the positive electrode material, constructing a physical barrier that can inhibit the side reactions of the positive electrode material in the electrolyte, thereby improving the material's cycle performance; in addition, the water washing process can remove residual alkali and expose more lithium active sites, thereby improving the material's discharge capacity.

[0068] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0070] FIG1 is a SEM image of the coated modified positive electrode material prepared in Example 1 of the present disclosure.

[0071] FIG2 is a comparison chart of the cycle performance of the positive electrode materials prepared in Examples 1-3 and Comparative Example 1 in the present disclosure. DETAILED DESCRIPTION

[0072] The technical solution of the present disclosure is further described below through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0073] Example 1

[0074] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0075] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 100:44.8 at 25°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0076] Wherein, the lithium source is lithium hydroxide monohydrate.

[0077] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0078] (1) Dissolve 50 g of lithium phytate in 1 L of deionized water to obtain a water wash solution with a concentration of 50 g / L;

[0079] (2) Add 21g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 21g / L, stir and dissolve completely, then add 2kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 350 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0080] The alkali metal hydroxide is lithium hydroxide monohydrate, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh size of the sieve is 300 meshes.

[0081] FIG1 shows an SEM image of the coated and modified positive electrode material prepared in this embodiment. As can be seen from the image, there is a small amount of coating on the surface of the high-nickel ternary positive electrode material particles.

[0082] Example 2

[0083] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0084] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 100:44.8 at 40°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0085] Wherein, the lithium source is lithium hydroxide monohydrate.

[0086] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0087] (1) Dissolve 50 g of lithium phytate in 0.5 L of deionized water to obtain a water wash solution with a concentration of 100 g / L;

[0088] (2) Add 42g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 84g / L, stir and dissolve completely, then add 1kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 350 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0089] The alkali metal hydroxide is lithium hydroxide monohydrate, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh size of the sieve is 300 meshes.

[0090] Example 3

[0091] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0092] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 100:44.8 at 40°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0093] Wherein, the lithium source is lithium hydroxide monohydrate.

[0094] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0095] (1) Dissolve 50 g of lithium phytate in 1 L of deionized water to obtain a water wash solution with a concentration of 50 g / L;

[0096] (2) Add 40g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 40g / L, stir and dissolve completely, then add 2kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 500 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0097] The alkali metal hydroxide is sodium hydroxide, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh number of the sieve is 300 meshes.

[0098] Example 4

[0099] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0100] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 200:90 at 40°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0101] Wherein, the lithium source is lithium hydroxide monohydrate.

[0102] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0103] (1) Dissolve 100 g of lithium phytate in 1 L of deionized water to obtain a water wash solution with a concentration of 100 g / L;

[0104] (2) Add 42g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 42g / L, stir and dissolve completely, then add 2kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 350 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0105] The alkali metal hydroxide is lithium hydroxide monohydrate, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh size of the sieve is 300 meshes.

[0106] Example 5

[0107] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0108] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 200:90 at 40°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0109] Wherein, the lithium source is lithium hydroxide monohydrate.

[0110] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0111] (1) Dissolve 100 g of lithium phytate in 1 L of deionized water to obtain a water wash solution with a concentration of 100 g / L;

[0112] (2) Add 21g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 21g / L, stir and dissolve completely, then add 2kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 350 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0113] The alkali metal hydroxide is lithium hydroxide monohydrate, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh size of the sieve is 300 meshes.

[0114] Example 6

[0115] This embodiment provides a method for preparing lithium phytate, which comprises the following steps:

[0116] A phytic acid solution with a concentration of 58.6 wt.% and a lithium source were mixed at a mass ratio of 100:44.8 at 40°C for 20 minutes, the pH of the solution was controlled to 7, and then the solution was heated in an oil bath at 120°C for 20 hours to evaporate the water. The mixture was ground and passed through a 200-mesh sieve to obtain lithium phytate.

[0117] Wherein, the lithium source is lithium hydroxide monohydrate.

[0118] This embodiment also provides a method for modifying a positive electrode material using the lithium phytate, the method comprising the following steps:

[0119] (1) Dissolve 50 g of lithium phytate in 1 L of deionized water to obtain a water wash solution with a concentration of 50 g / L;

[0120] (2) Add 10.5g of alkali metal hydroxide to the water washing solution to make the concentration of alkali metal hydroxide in the water washing solution 10.5g / L, stir and dissolve completely, then add 2kg of high nickel ternary positive electrode material LiNi 0.96 Co 0.03 Mn 0.01 O2, stirred and mixed at 100 rpm for 0.5 min, and then centrifuged to collect the solid, and then vacuum dried at 100 ° C for 6 h to remove moisture, and finally heat treated in a box furnace in an oxygen atmosphere for 6 h at a temperature of 350 ° C. After the heat treatment, the temperature was cooled and sieved to obtain a coated modified positive electrode material;

[0121] The alkali metal hydroxide is lithium hydroxide monohydrate, the mass ratio of the water washing solution to the positive electrode material is 1:0.5, and the mesh size of the sieve is 300 meshes.

[0122] Example 7

[0123] The difference between this embodiment and embodiment 1 is that the mass ratio of the phytic acid solution to the lithium source is 100:10.

[0124] The rest of the preparation methods and parameters remained the same as in Example 1.

[0125] Example 8

[0126] The difference between this embodiment and embodiment 1 is that the mass ratio of the phytic acid solution to the lithium source is 100:67.2.

[0127] The rest of the preparation methods and parameters remained the same as in Example 1.

[0128] Example 9

[0129] The difference between this embodiment and embodiment 1 is that the mass ratio of the water washing solution to the positive electrode material is 1:0.3.

[0130] The rest of the preparation methods and parameters remained the same as in Example 1.

[0131] Example 10

[0132] The difference between this embodiment and embodiment 1 is that the mass ratio of the water washing solution to the positive electrode material is 1:3.

[0133] The rest of the preparation methods and parameters remained the same as in Example 1.

[0134] Example 11

[0135] The difference between this embodiment and embodiment 1 is that no alkali metal hydroxide is added in step (2).

[0136] The rest of the preparation methods and parameters remained the same as in Example 1.

[0137] Comparative Example 1

[0138] The difference between this comparative example and Example 1 is that lithium phytate is not prepared, so that the washing liquid in step (1) contains only deionized water.

[0139] The rest of the preparation methods and parameters remained the same as in Example 1.

[0140] Figure 2 shows a comparison of the cycle performance of the positive electrode materials prepared in Examples 1-3 and Comparative Example 1. It can be seen from the figure that after 80 cycles, the capacity retention rates of Examples 1, 2, 3 and Comparative Example 1 are 85.8%, 83.1%, 84.0% and 77.3%, respectively, indicating that the introduction of lithium phytate as a water washing additive can effectively improve the cycle stability of the ternary positive electrode material.

[0141] Comparative Example 2

[0142] The difference between this comparative example and Example 1 is that lithium phytate is not prepared and alkali metal hydroxide is not added in step (2).

[0143] The rest of the preparation methods and parameters remained the same as in Example 1.

[0144] Performance Testing

[0145] The positive electrode materials prepared in the above examples and comparative examples were made into button batteries in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The specific steps included:

[0146] i. The positive electrode material, the conductive agent (i.e., Super P), and the binder (i.e., PVDF) were mixed uniformly in a mass ratio of 94:3:3, and then N-methylpyrrolidone solvent was added and stirred to form a slurry, which was then coated. After drying at 110°C for 2 hours, the sheet was punched and dried again in a vacuum oven at 105°C for 4 hours to obtain the positive electrode sheet;

[0147] ii. The positive and negative electrode sheets, separators, and electrolytes are assembled to obtain button cells, wherein the negative electrode sheet is a lithium metal sheet, the separator is a glass fiber, and the electrolyte is LiPF6 dissolved in a 1:1 volume ratio of ethylene carbonate and diethyl carbonate mixed solvent.

[0148] After the assembled button cells were left to rest for 3 hours, they were tested for their first cycle using a BlueDian battery testing system. The test conditions were: 25°C, 0.1C, and initial efficiency were measured. 1C = 210 mAh / g. Cycling performance was tested using a fully charged button cell, replacing the lithium metal anode with a carbon material. After one cycle at 0.1C, the battery's cycling stability was tested again at 1C. After 80 cycles, the capacity retention was calculated. Furthermore, the content of residual lithium compounds was measured using an acid-base titration method.

[0149] The above test results are shown in Table 1.

[0150] Table 1

[0151] analyze:

[0152] As can be seen from the above table, the lithium phytate prepared in the present invention can be used as a water washing additive in the modification process of the positive electrode material. The addition of alkali metal hydroxide can reduce the decrease in Li2CO3, which is conducive to improving the first-cycle capacity, first-cycle efficiency and cycle performance of the battery. The addition of lithium phytate has little effect on the capacity.

[0153] It can be seen from the data results of Example 1 and Examples 7-8 that if the mass ratio of the phytic acid solution to the lithium source is too large, the prepared lithium phytate contains more unconverted phosphate groups, which will consume the alkali metal hydroxide in the subsequent water washing, resulting in more lithium carbonate consumption in the subsequent water washing, a lower first-cycle capacity, and cycle attenuation; if the mass ratio of the phytic acid solution to the lithium source is too small, the lithium phytate contains more unreacted lithium source, which increases the alkalinity of the water washing solution, increases the residual alkaline impurities in the ternary positive electrode material, and also attenuates the cycle performance.

[0154] From the data results of Example 1 and Example 9-10, it can be seen that if the mass ratio of the water washing liquid to the positive electrode material is too small, the viscosity will be high during the water washing process, and the water washing liquid and the ternary positive electrode material will be unevenly mixed, resulting in poor residual alkali washing effect of the material, high residual lithium in the material, low first cycle capacity, and reduced cycle retention rate; if the mass ratio of the water washing liquid to the positive electrode material is too large, the material will undergo Li + / H + The risk of exchange and lattice lithium extraction increases, and the material structure is damaged, resulting in a low total residual lithium in the material, a significantly reduced charge and discharge capacity, and a faster cycle decay.

[0155] From the data results of Example 1 and Example 11, it can be seen that if no alkali metal hydroxide is added, the alkalinity of the water wash solution is relatively low. + The concentration is high, the material produces Li + / H + The risk of exchange side reactions increases, resulting in lower residual lithium and first-cycle capacity of the material, but the material has a lithium phytate-derived coating layer on the surface, and the degree of cycle attenuation is relatively mild.

[0156] It can be seen from the data results of Example 1 and Comparative Example 1 that if lithium phytate is not prepared, so that the washing liquid in step (1) contains only deionized water, only a finished product of the washed high-nickel ternary positive electrode material is obtained, which is not conducive to suppressing the side reaction between the ternary positive electrode material and water during the washing process, affecting the material performance, and significantly reducing the cycle performance.

[0157] It can be seen from the data results of Example 1 and Comparative Example 2 that if lithium phytate is not prepared and alkali metal hydroxide is not added in step (2), only a finished product of a water-washed high-nickel ternary positive electrode material is obtained, which is not conducive to the structural stability of the ternary positive electrode material, the layered structure of the material surface is destroyed, the residual alkali and the first-cycle capacity are reduced, and the cycle performance is significantly reduced.

Claims

1. A method for preparing lithium phytate, comprising the following steps: The phytic acid solution and the lithium source are mixed to react, the pH is adjusted, and the lithium phytate is obtained after drying.

2. The preparation method according to claim 1, wherein The mass ratio of the phytic acid solution to the lithium source is 1:(0.15-0.6).

3. The preparation method according to claim 1 or 2, wherein The reaction temperature is 25-40°C and the reaction time is 20-60 minutes.

4. The preparation method according to any one of claims 1 to 3, wherein: After the pH adjustment, the pH of the solution is 6-8.

5. The preparation method according to any one of claims 1 to 3, wherein: After the pH adjustment, the pH of the solution was 7.

6. The preparation method according to any one of claims 1 to 5, wherein: The drying temperature is 80-150° C., and the drying time is 12-48 hours.

7. Lithium phytate prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the lithium phytate as claimed in claim 7 in a positive electrode material for lithium ion batteries.

9. The use according to claim 8, wherein: The specific steps of the application include: (1) mixing the lithium phytate and water to obtain a water wash; (2) The water washing liquid, alkali metal hydroxide and positive electrode material are mixed and heat treated to obtain a coated and modified positive electrode material.

10. The use according to claim 9, wherein: The concentration of the water washing solution in step (1) is 50-100 g / L; The alkali metal hydroxide in step (2) includes any one of lithium hydroxide, sodium hydroxide or potassium hydroxide, or a combination of at least two thereof; The concentration of the alkali metal hydroxide in the water washing liquid in step (2) is 10-85 g / L; The positive electrode material in step (2) includes a high-nickel ternary positive electrode material, the chemical formula of which is LiNi x Co y Mn z O2, 0.8≤x<1, 0<y≤0.1, 0<z≤0.1, x+y+z=1; The mass ratio of the water washing solution to the positive electrode material in step (2) is 1:(0.4-2).

11. The use according to claim 9 or 10, wherein: The mixing process in step (2) is accompanied by stirring, and the stirring rate is 80-300 rpm; The mixing time in step (2) is 0.5-3 min; The heat treatment temperature in step (2) is 300-700° C. and the time is 5-20 hours.

12. The use according to any one of claims 9 to 11, wherein: The specific steps of applying the lithium phytate in the positive electrode material for lithium ion batteries include: (I) mixing a phytic acid solution and a lithium source at a mass ratio of 1:(0.15-0.6) at 20-80° C. for 10-120 min, controlling the pH of the solution to be neutral, and drying at 80-150° C. for 12-48 h to obtain lithium phytate; (II) dissolving the lithium phytate in water to obtain a water wash solution with a concentration of 5-100 g / L; (III) adding an alkali metal hydroxide to the water washing liquid so that the concentration of the alkali metal hydroxide in the water washing liquid is 5-120 g / L, then adding a high nickel ternary positive electrode material, stirring and mixing at 80-300 rpm for 0.5-3 min, performing solid-liquid separation after completion, and then drying at 110-150° C. for 8-24 h to remove moisture, and finally performing a heat treatment in an oxygen atmosphere, air atmosphere or nitrogen atmosphere for 5-20 h at a temperature of 300-700° C., cooling and sieving after the heat treatment to obtain a coated modified positive electrode material; The mass ratio of the water washing solution to the positive electrode material is 1:(0.4-2), and the mesh size of the sieve is 100-400 meshes.

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