Composite modified negative electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery materials, and discloses a composite modified negative electrode material and a preparation method and application thereof, the composite modified negative electrode material comprises a Mn2Si (P2O7) 2 nanometer material, nanometer silicon and layered graphite, and the Mn2Si (P2O7) 2 nanometer material, the nanometer silicon and the layered graphite material are uniformly distributed. The composite modified negative electrode material has good structural stability, and silicon element and nano silicon in pyrophosphate silicate in the negative electrode material can form Si-Si covalent bonds, so that the adhesive force of a surface composite layer of the negative electrode material can be greatly improved, polymer of the nano silicon can be inhibited, the volume expansion of a silicon negative electrode can be relieved, and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery materials, relates to anode materials in lithium-ion battery materials, and specifically relates to a composite modified anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium ions have high specific energy, long life, high working voltage, wide operating temperature range, no memory effect, small self-discharge, and are environmentally friendly. Therefore, they are widely used in fields such as new energy vehicles, power grid energy storage, and portable electronic devices. In order to improve the specific energy of lithium-ion batteries, usually starting from two aspects: the internal structure and materials of lithium-ion batteries. The optimization direction of the internal structure is mainly to reduce the weight of non-active substances such as structural parts, copper foils, and aluminum foils, thereby increasing the proportion of active substances and improving the specific energy of lithium-ion batteries. The optimization direction of materials is mainly to develop anode and cathode materials with higher capacities, as well as cathode materials with higher voltages, to improve the capacity and voltage of the battery, thereby achieving the purpose of improving the energy density of the battery.

[0003] At present, the development direction of anode materials is mainly to improve the capacity performance of the materials. For example, the currently relatively mature Si-based materials doped with ammonia-doped graphite materials or doped metal sulfides and other materials can achieve a capacity performance of more than 1000 mAh / g, far higher than graphite materials. However, Si-based materials have a large volume change during the electrochemical process, which easily leads to irreversible phase changes of silicon particles, thereby causing damage to the electrode structure and attenuation of battery performance, affecting the electrochemical performance of the battery. Summary of the Invention

[0004] In view of the defects and deficiencies existing in the prior art, on the first aspect, the present invention provides a composite modified anode material; on the second aspect, the present invention provides a preparation method of a composite modified anode material; on the third aspect, the present invention provides a battery.

[0005] On the first aspect, the present invention provides a composite modified anode material, including Mn2Si(P2O7)2 nanomaterials, nano-silicon, and layered graphite, wherein the Mn2Si(P2O7)2 nanomaterials, nano-silicon, and layered graphite materials are evenly distributed.

[0006] Preferably, the mass ratio of the Mn2Si(P2O7)2 nanomaterials, the nano-silicon, and the layered graphite is 1:1 to 2:0.01 to 0.05.

[0007] On the second aspect, the present invention provides a preparation method of a composite modified anode material, including the following steps: Step 1: Add soluble silicate into concentrated phosphoric acid to react and obtain gel solution A. Then add gel solution A into soluble manganese salt solution to obtain gel solution B. After reacting for a certain time, filter, wash the obtained filter cake with water and alcohol, and dry it. The obtained solid particles are the Mn2Si(P2O7)2 nanomaterials. Step 2: Ball-mill and mix the Mn2Si(P2O7)2 nanomaterials, nano-silicon and layered graphite to obtain the composite modified anode material.

[0008] Preferably, the soluble silicate is any one or more of sodium silicate, potassium silicate and lithium silicate.

[0009] Preferably, the mass concentration of the concentrated phosphoric acid is 75% - 85%.

[0010] Preferably, the soluble manganese salt is any one or more of manganese nitrate, manganese sulfate and manganese acetate.

[0011] Preferably, the molar ratio of silicate ions, manganese ions and phosphate ions in the gel solution B is 1∶2.03 - 3∶4.01 - 4.03.

[0012] Preferably, in Step 1, the reaction time of the soluble silicate and the concentrated phosphoric acid is 5 - 30 min.

[0013] Preferably, in Step 1, after adding the soluble manganese salt into the gel solution A to obtain the gel solution B, the reaction time is 6 - 12 h.

[0014] Preferably, in Step 2, the mass ratio of the Mn2Si(P2O7)2 nanomaterials, the nano-silicon and the layered graphite is 1∶1 - 2∶0.01 - 0.05.

[0015] Preferably, in Step 2, the ball-milling and mixing time is 1 - 6 h, and the ball-milling speed is 200 - 300 r / min.

[0016] In the third aspect, the present invention provides a battery, including the above-mentioned composite modified anode material or the composite modified anode material prepared by the above-mentioned preparation method.

[0017] Compared with the prior art, the present invention has the following obvious beneficial effects: (1) The composite modified anode material provided by the present invention has good structural stability. At the same time, the silicon element in the pyrophosphate silicate in the anode material and the nano-silicon can form Si - Si covalent bonds, which can greatly improve the adhesion of the composite layer on the surface of the anode material and inhibit the aggregation of nano-silicon, thereby alleviating the volume expansion of the silicon anode and improving the cycle performance of the battery.

[0018] (2) The present invention synthesizes the pyrophosphate silicate Mn2Si(P2O7)2 nanomaterial by the liquid-phase co-precipitation method, and then solid-phase mixes it with nanosilicon and layered graphite to obtain the Mn2Si(P2O7)2 / Si@C anode material. The process is simple and controllable, without calcination, with low energy consumption, which is conducive to popularization and commercialization. Description of the Drawings

[0019] Figure 1 SEM image of the composite modified anode material prepared in Example 1; Figure 2 Cycling performance test graphs of the batteries assembled with the anode materials and nanosilicon prepared in Examples 1-3 and Comparative Examples 1-3; Figure 3 SEM image of the electrode sheet prepared from the anode material prepared in Example 1 before participating in battery cycling; Figure 4 SEM image of the electrode sheet prepared from the anode material prepared in Example 1 after participating in 50 cycles of battery cycling; Figure 5 SEM image of the electrode sheet prepared from the anode material prepared in Comparative Example 1 before participating in battery cycling; Figure 6 SEM image of the electrode sheet prepared from the anode material prepared in Comparative Example 1 after participating in 50 cycles of battery cycling. Detailed Embodiments

[0020] The present invention provides the following specific technical solutions.

[0021] In the first aspect, the present invention provides a composite modified anode material, including the Mn2Si(P2O7)2 nanomaterial, nanosilicon and layered graphite, wherein the Mn2Si(P2O7)2 nanomaterial, nanosilicon and layered graphite materials are evenly distributed.

[0022] Silicon as an anode material has significant advantages in lithium-ion batteries. Silicon anodes can store more lithium ions, thereby improving the energy density and battery life of the battery. However, silicon faces some challenges in practical applications. For example, during the charge and discharge process, there will be a huge volume change, which may lead to the destruction of the electrode structure and the attenuation of battery performance. Therefore, although silicon has the advantage of high capacity, its cycle stability is weak, which limits its wide application in battery anode materials. The inventor found through research that by adding pyrophosphate silicate and layered graphite to the anode material, on the one hand, pyrophosphate silicate has good structural stability, which can greatly improve the mechanical properties of the overall anode material. At the same time, after ball milling, it is in close contact with nano-silicon, which can not only effectively inhibit the agglomeration of nano-silicon, but also relieve the volume expansion of the silicon anode through the interaction between particles; on the other hand, layered graphite has good electronic conductivity and lubricity. Adding layered graphite to the anode material can not only effectively increase the conductivity of the anode material, thereby improving the reaction kinetics of the electrode material, but also utilize the lubricity of layered graphite to improve the distribution uniformity of the composite material; on the third hand, nano-silicon and layered graphite cooperate with Mn2Si(P2O7)2 nano-materials to show good compatibility and synergistic effects. Layered graphite, nano-silicon and Mn2Si(P2O7)2 nano-materials can complement each other in the lithium storage mechanism, jointly optimizing the comprehensive performance of the anode material, making it outstanding in terms of electrochemical performance, mechanical performance, etc., and can synergistically optimize the high-rate cycle stability and reversibility of the silicon anode material, making it more suitable for the application requirements of high-performance batteries.

[0023] Preferably, the mass ratio of the Mn2Si(P2O7)2 nano-material, the nano-silicon and the layered graphite is 1:1~2:0.01~0.05.

[0024] On the second hand, the present invention provides a preparation method of a composite modified anode material, comprising the following steps: Step 1, adding soluble silicate to concentrated phosphoric acid to react to obtain gel solution A, then adding gel solution A to soluble manganese salt solution to obtain gel solution B. After reacting for a certain time, filter, wash the obtained filter cake with water and alcohol, and dry it to obtain the solid particles, which are the Mn2Si(P2O7)2 nano-material; Step 2, ball-mill and mix the Mn2Si(P2O7)2 nano-material, nano-silicon and layered graphite to obtain the composite modified anode material.

[0025] The inventor found through research that by synthesizing pyrophosphate silicate Mn2Si(P2O7)2 nano-materials through the liquid-phase co-precipitation method, the components are uniform, the particle size is small and there is no agglomeration phenomenon, and the performance of the product is stable, which is beneficial to subsequent mixing of nano-silicon and layered graphite, and finally the components in the prepared anode material are uniformly dispersed.

[0026] In practical applications, the layered graphite can be a natural graphite material or an artificial graphite material, as long as it is ensured that the used graphite has a layered structure.

[0027] Preferably, the soluble silicate is any one or more of sodium silicate, potassium silicate and lithium silicate.

[0028] Preferably, the mass concentration of the concentrated phosphoric acid is 75% - 85%.

[0029] Preferably, the soluble manganese salt is any one or more of manganese nitrate, manganese sulfate and manganese acetate.

[0030] Preferably, the average particle size of the nano - silicon is 50 - 100 nm.

[0031] Preferably, the thickness of the layered graphite is 0.3 - 0.6 nm.

[0032] Preferably, the molar ratio of silicate ions, manganese ions and phosphate ions in the gel solution B is 1∶2.03 - 3∶4.01 - 4.03.

[0033] In practical applications, the addition ratio of phosphate ions is consistent with the stoichiometric ratio and can be slightly excessive to ensure complete complexation of phosphate ions. If it is excessive too much, it will form manganese phosphate precipitation with manganese ions in the subsequent process, affecting the performance of the product. The above - mentioned ratio is the preferred range, and no other impurity phases are generated within this range, which is beneficial to improving the electrochemical performance of the anode material.

[0034] Preferably, in step 1, the reaction time after adding the soluble manganese salt to the gel solution A to obtain the gel solution B is 6 - 12 h.

[0035] Preferably, in step 2, the mass ratio of the Mn2Si(P2O7)2 nanomaterial, the nano - silicon and the layered graphite is 1∶1 - 2∶0.01 - 0.05.

[0036] Preferably, in step 2, the ball - milling mixing time is 1 - 6 h and the ball - milling rotation speed is 200 - 300 r / min.

[0037] In a third aspect, the present invention provides a battery, including the above - mentioned composite - modified anode material or the composite - modified anode material prepared by the above - mentioned preparation method.

[0038] To make the technical problems, technical solutions and technical advantages to be solved by the present invention clearer, the following will be described in detail with specific examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention.

[0040] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or prepared by existing methods.

[0041] Example 1: A method for preparing a composite modified anode material, comprising the following steps: Step 1: Add 0.1 mol of sodium silicate to 26.33 mL of concentrated phosphoric acid with a mass concentration of 80%, and carry out a composite reaction at room temperature of 25 °C for 10 min to obtain a uniformly dispersed gel solution A. Subsequently, add the gel solution A to 110 mL of a 2 mol / L manganese nitrate solution, filter, wash with water, wash with alcohol, and dry in sequence after reacting at room temperature for 8 h. The obtained solid particles are Mn2Si(P2O7)2 nanomaterials; Step 2: Take 0.3 g of Mn2Si(P2O7)2 nanomaterials, 15 g of nanosilicon, and 10 g of layered graphite and carry out ball milling and mixing for 4 h. The D50 of the nanosilicon is 80 nm, and the composite modified anode material can be prepared.

[0042] Figure 1 SEM image of the composite modified anode material prepared in Example 1, Figure 1 It can be seen that the overall material morphology is spherical-like and the particle size is uniform.

[0043] Comparative Example 1: A method for preparing an anode material, comprising: carrying out ball milling and solid-phase mechanical mixing of 10 g of layered graphite and 15 g of nanosilicon (80 nm) for 4 h, and the Si / C anode material can be prepared.

[0044] Comparative Example 2: A method for preparing a composite modified anode material, comprising the following steps: Step 1: Add 0.1 mol of sodium silicate to 26.33 mL of concentrated phosphoric acid with a mass concentration of 80%, and carry out a composite reaction at room temperature of 25 °C for 10 min to obtain a uniform gel solution A. Subsequently, add the solution A to 100 mL of a 2 mol / L manganese nitrate solution, filter, wash with water, wash with alcohol, and dry in sequence after reacting for 8 h. The obtained solid particles are Mn2Si(P2O7)2 nanomaterials; Step 2: Take 0.3 g of Mn2Si(P2O7)2 nanomaterials and 10 g of layered graphite and carry out ball milling and mixing for 4 h, and the Mn2Si(P2O7)2 / C anode material can be prepared.

[0045] Comparative Example 3: A preparation method of a composite modified anode material, comprising the following steps: Step 1, Add 0.1 mol of sodium silicate to 26.33 mL of concentrated phosphoric acid with a mass concentration of 85%, and carry out a composite reaction at room temperature of 25°C for 10 min to obtain a uniform gel solution A. Subsequently, add solution A to 100 mL of a manganese nitrate solution with a concentration of 2 mol / L, and after reacting for 8 h, filter, wash with water, wash with alcohol, and dry in sequence. The obtained solid particles are Mn2Si(P2O7)2 nanomaterials; Step 2, Take 0.3 g of Mn2Si(P2O7)2 nanomaterials and 15 g of nanosilicon (80 nm) and carry out ball milling and mixing for 4 h to obtain the Mn2Si(P2O7)2 / Si anode material.

[0046] Example 2: A preparation method of a composite modified anode material, comprising the following steps: Step 1, Add 0.1 mol of lithium silicate to 28.03 mL of concentrated phosphoric acid with a mass concentration of 75%, and carry out a composite reaction at room temperature of 25°C for 30 min to obtain a uniform gel solution A. Subsequently, add solution A to 203 mL of a manganese nitrate solution with a concentration of 1 mol / L, and after reacting at room temperature for 6 h, filter, wash with water, wash with alcohol, and dry to obtain Mn2Si(P2O7)2 nanomaterials.

[0047] Step 2, Take 0.1 g of Mn2Si(P2O7)2 nanomaterials, 10 g of nanosilicon, and 10 g of layered graphite and carry out ball milling and mixing for 1 h. The D50 of the nanosilicon is 50 nm to obtain the composite modified anode material.

[0048] Example 3: A preparation method of a composite modified anode material, comprising the following steps: Step 1, Add 0.1 mol of lithium silicate to 24.85 mL of concentrated phosphoric acid with a mass concentration of 85%, carry out a composite reaction at room temperature of 25°C for 5 min to obtain a uniform gel solution A. Subsequently, add solution A to 100 mL of a manganese acetate solution with a concentration of 3 mol / L, and after reacting at room temperature for 12 h, filter, wash with water, wash with alcohol, and dry to obtain Mn2Si(P2O7)2 nanomaterials.

[0049] Step 2, Take 0.5 g of the Mn2Si(P2O7)2 nanomaterials prepared in Step 1, 10 g of nanosilicon, and 20 g of layered graphite and carry out ball milling and mixing for 6 h. The D50 of the nanosilicon is 100 nm to obtain the composite modified anode material.

[0050] The negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were used as active materials, and were mixed with conductive agent acetylene black (AB) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1. Using N-methylpyrrolidone (NMP) as a solvent, the mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 h to obtain a slurry. The slurry was coated on a current collector aluminum foil using an automatic coater, placed flat on tempered glass and transferred to a vacuum drying oven at 85 °C for drying for 4 h. After punching into a pole piece with a diameter of 14 mm, it was dried in a vacuum drying oven at 105 °C for 4 h, and placed in a glove box with a water content and oxygen content both lower than 0.1 ppm and filled with argon atmosphere for 4 h to reduce the moisture adsorbed by the pole piece during the transfer process. Then, it was assembled into a CR2032 type button cell in the glove box. The separator used for this battery was a porous polyethylene film with a diameter of 18 mm and a model of Celgard 2300, and a lithium sheet was used as the counter electrode.

[0051] After the battery assembly was completed and aged for 12 h, subsequent charge-discharge tests were carried out at a rate of 2C in the voltage range of 0.1 - 3.0 V.

[0052] Figure 2 It is a cyclic performance test chart of the batteries assembled with the negative electrode materials prepared in Examples 1 to 3, Comparative Examples 1 to 3 and nanosilicon. From Figure 2 it can be seen that the negative electrode material provided by the present invention synchronously modifies silicon material with pyrophosphate silicate and carbon material, which can effectively improve the cyclic performance of silicon material.

[0053] Figure 3 It is an SEM image of the pole piece prepared from the negative electrode material prepared in Example 1 before participating in battery cycling. From Figure 3 it can be seen that the thickness of the pole piece before participating in cycling is about 8.6 μm. Figure 4 It is an SEM image of the pole piece prepared from the negative electrode material prepared in Example 1 after participating in 50 cycles of battery cycling. From Figure 4 it can be seen that the thickness of the pole piece after participating in cycling is about 9.7 μm.

[0054] Figure 5 It is an SEM image of the pole piece prepared from the negative electrode material prepared in Comparative Example 1 before participating in battery cycling. From Figure 5 it can be seen that the thickness of the pole piece before participating in cycling is about 11.4 μm. Figure 6 It is an SEM image of the pole piece prepared from the negative electrode material prepared in Comparative Example 1 after participating in 50 cycles of battery cycling. From Figure 6 it can be seen that the thickness of the pole piece after participating in cycling is about 17.9 μm.

[0055] Combined with Figures 3 - 6 , it can be proved that the pole piece prepared from the negative electrode material prepared by the present invention has good structural stability, can greatly relieve the volume expansion of the pole piece, and improve the electrochemical performance of the battery.

[0056] The above-described embodiments are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope of the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A composite modified anode material, characterized in that, It includes Mn2Si(P2O7)2 nanomaterials, nanosilicon and layered graphite, wherein the Mn2Si(P2O7)2 nanomaterials, nanosilicon and layered graphite materials are evenly distributed.

2. The composite modified anode material according to claim 1, wherein The mass ratio of the Mn2Si(P2O7)2 nanomaterials, the nanosilicon and the layered graphite is 1:1~2:0.01~0.

05.

3. A preparation method of a composite modified anode material, characterized in that, It includes the following steps: Step 1: Add soluble silicate into concentrated phosphoric acid for reaction to obtain gel solution A, then add gel solution A into soluble manganese salt solution to obtain gel solution B. After reacting for a certain time, filter, wash the obtained filter cake with water, alcohol, and dry it. The obtained solid particles are Mn2Si(P2O7)2 nanomaterials; Step 2: Ball-mill and mix the Mn2Si(P2O7)2 nanomaterials, nanosilicon and layered graphite to obtain the composite-modified anode material.

4. The preparation method of the composite modified anode material according to claim 3, characterized in that, The molar ratio of silicate ions, manganese ions and phosphate ions in the gel solution B is 1∶2.03~3∶4.01~4.

03.

5. The preparation method of the composite modified anode material according to claim 3 or 4, characterized in that, In Step 2, the mass ratio of the Mn2Si(P2O7)2 nanomaterials, the nanosilicon and the layered graphite is 1∶1~2∶0.01~0.

05.

6. The preparation method of the composite modified anode material according to claim 3, characterized in that, The soluble silicate is any one or more of sodium silicate, potassium silicate and lithium silicate; the soluble manganese salt is any one or more of manganese nitrate, manganese sulfate and manganese acetate.

7. The preparation method of the composite modified anode material according to claim 3, characterized in that The mass concentration of the concentrated phosphoric acid is 75%~85%.

8. The preparation method of the composite modified anode material according to claim 3, characterized in that, In Step 1, the reaction time after adding soluble manganese salt to gel solution A to obtain gel solution B is 6~12h.

9. The preparation method of the composite modified anode material according to claim 3 or 8, characterized in that, In Step 2, the ball-milling and mixing time is 1~6h, and the ball-milling speed is 200~300r / min.

10. A battery, characterized in that, It includes the composite-modified anode material described in any one of claims 1~2 or the composite-modified anode material prepared by the preparation method described in any one of claims 3~9.

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