Anode active material for lithium ion battery, lithium ion battery anode and preparation method thereof

Abstract

The application discloses an anode active material for a lithium ion battery, a lithium ion battery anode and a preparation method thereof, and belongs to the field of battery materials and applications. The anode active material comprises graphite, an inorganic coating layer attached to the graphite, and a metal oxide layer attached to the outside of the inorganic coating layer, wherein the inorganic coating layer contains graphene or carbon nanotubes, and the metal oxide layer is at least one oxide of Al, Mg, Zr, Ti, Ag, Ni and Mo. The lithium ion battery anode is formed by coating slurry containing the anode active material on a current collector. The fast-charging graphite prepared by the application has moderate processability, the slurry prepared by the mixing method used has good stability, the pole piece is not prone to powder falling, the surface density of the anode piece is 220 g / m 2 and still has good fast-charging performance.

Description

Technical Field

[0001] This invention relates to the field of battery materials and applications, specifically to an anode active material for lithium-ion batteries, a lithium-ion battery anode, and a method for preparing the same. Background Technology

[0002] As the electric vehicle industry accelerates its development and user acceptance of electric vehicles continues to increase, charging, range, and safety remain the three major factors influencing users' purchase decisions, with charging being the most pressing issue. Electric vehicle users have a strong demand for rapid charging; "fast charging within 5 minutes, as convenient and quick as refueling" has become a common user requirement. High-power fast charging (3C and above) can essentially achieve a charging experience similar to refueling. However, traditional battery cell development often sacrifices energy density to pursue fast charging capabilities. For users with "range anxiety," developing battery cells that balance high energy density and fast charging performance is particularly important. This invention, based on this objective, develops a high-performance anode sheet that achieves 3C and above fast charging capabilities while maintaining an electrode surface density of 220g / m². 2 above.

[0003] A search revealed Chinese patent application number 201210439111.3, published on May 21, 2014, which discloses a fast-charging lithium battery. This battery includes a battery casing and an anode, cathode, and electrolyte disposed within the casing. A porous polymer separator separates the anode and cathode. The battery casing has a sealing cap and corresponding electrode tabs. The cathode is characterized by a structure in which cathode material is provided on both sides of a foil-like support. The cathode material is prepared from lithium-ionized transition metal intercalated active material, nano-sized bentonite, carbon powder, and PVDF. The anode also has a foil-like support in the middle and is made of carbonaceous material. The thickness ratio of the anode to the cathode is 1:1.5 to 1:4. The surface of the lithium-ionized transition metal intercalated active material particles has a conductive carbonized layer. A conductive network is formed within the cathode material layer prepared by the lithium-ion transition metal intercalation active material with a carbonized layer, nano-sized bentonite, carbon powder, and PVDF. The carbonized layer is prepared by adding carbon powder to phenolic resin and carbonizing it at high temperature. In the cathode material, the lithium-ion transition metal intercalation active material, nano-sized bentonite, and carbon powder account for 92-94%, 0.5-1.5%, and 2-3% by weight, respectively, with the balance being PVDF. The nano-sized bentonite particles have a diameter of 20-30 nm and are prepared by a high-speed shearing method. The bentonite particles are coated with graphite material. However, the main function of the cathode active coating layer is to improve the anode migration capability, while the anode coating improves the ion intercalation capability; their effects and manufacturing processes differ.

[0004] Chinese patent application No. 201010170254.X, published on October 27, 2010, discloses an anode active material for lithium-ion batteries and a lithium-ion battery containing the material. The anode active material comprises: a carbon-based anode active material and Li2SiF6. The carbon-based anode active material includes a carbon core material and a carbide layer formed by partially or completely covering the edges of the carbon core material. However, this anode active material is only carbon-coated, which cannot achieve high-rate fast charging performance under high areal density.

[0005] Therefore, there is an urgent need to find an anode active material for lithium-ion batteries, a lithium-ion battery anode, and a method for preparing the same, in order to meet the above requirements. Summary of the Invention

[0006] 1. The problem to be solved

[0007] To address the issue of insufficient energy density in existing lithium-ion batteries with strong fast-charging capabilities, this invention provides an anode active material for lithium-ion batteries. By optimizing the structure and composition of the anode active material, a high specific capacity anode active material is obtained. When applied to anode sheets and combined with a preparation method that achieves excellent dispersion, a high-energy and fast-charging lithium-ion battery anode is obtained.

[0008] 2. Technical Solution

[0009] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0010] An anode active material for lithium-ion batteries includes graphite, an inorganic coating layer attached to the graphite, and a metal oxide layer attached to the outside of the inorganic coating layer. The inorganic coating layer contains graphene or carbon nanotubes, and the metal oxide layer is at least one oxide selected from Al, Mg, Zr, Ti, Ag, Ni, and Mo.

[0011] Furthermore, in the case of a coin cell, at a charging rate of 0.1C, the specific capacity of the anode active material is at least 355 mAh / g.

[0012] Furthermore, the anolyte active material has a D50 of 10–15 μm and a diffusion coefficient of 10. -11 ~10 -13 cm 2 / s.

[0013] Furthermore, the graphite is natural graphite or artificial graphite coated.

[0014] Furthermore, the preparation method of the anolyte is as follows: graphite is mixed with an inorganic coating agent and sintered at high temperature under oxygen-free conditions to form an inorganic coating layer; after the sintered product is cooled, it is mixed with a metal oxide and a binder, and then calcined to form a metal oxide layer, thus obtaining the anolyte. The inorganic coating agent is graphene or carbon nanotubes, and the metal oxide is at least one oxide selected from Al, Mg, Zr, Ti, Ag, Ni, and Mo.

[0015] Furthermore, the sintering temperature for forming the inorganic coating layer is 2000–2500℃, and the sintering time is 1–3 hours.

[0016] Furthermore, the calcination temperature for forming the metal oxide layer is 1200–1500℃, and the calcination time is 0.5–5h.

[0017] A lithium-ion battery anode is prepared by coating an anode slurry containing the aforementioned anode active material onto a current collector to obtain an anode sheet.

[0018] Furthermore, the areal density of the anode sheet is at least 220 g / m². 2 .

[0019] A method for preparing the above-mentioned lithium-ion battery anode includes the following steps:

[0020] (1) Mix the dispersant in the solvent to obtain a gel solution;

[0021] (2) Add conductive paste to the adhesive in step (1), mix evenly to obtain conductive adhesive, and divide the conductive adhesive into two parts, conductive adhesive A and conductive adhesive B, for later use;

[0022] (3) Add solvent, anodic active material and conductive powder to conductive adhesive solution A in multiple portions and stir to form a flocculent conductive mixture;

[0023] (4) Mix the flocculent conductive mixture in step (3) with conductive adhesive B evenly, and add solvent, anti-cracking solvent and binder emulsion. After mixing evenly, discharge the material to obtain anode slurry.

[0024] (5) Coat the anode slurry from step (4) onto the current collector to obtain an anode sheet;

[0025] In the above steps, the solvent is generally water, and the adhesive emulsion is SBR or PAA.

[0026] Further, in step (1), the dispersant is a mixture of carboxymethyl cellulose and polyacrylonitrile with a low degree of substitution (below 1.0), the mixing ratio of carboxymethyl cellulose and polyacrylonitrile is 1.0:(0.1~0.5), the solid content of the mixture is 1.5~2%; the solvent is water, and the conductivity is below 0.01μS / cm.

[0027] Further, in step (2), the conductive slurry is at least one of single-arm carbon nanotubes, graphene, multi-arm carbon nanotubes, carbon nanofibers, and Ketjen black; in step (3), the conductive powder is at least one of single-arm carbon nanotubes, graphene, multi-arm carbon nanotubes, carbon nanofibers, and Ketjen black in powder form. Adding two forms of conductive agent to the anode slurry, especially the addition of conductive powder, is beneficial to the dispersion of the conductive material.

[0028] Furthermore, in step (2), the mass ratio of conductive adhesive A to conductive adhesive B is greater than 1.

[0029] Furthermore, in step (4), the anti-cracking agent is selected with a boiling point higher than that of the solvent water, and the trace amount (less than 500 ppm) of residue after baking does not react with the electrolyte. Preferably, it is one of N-methylpyrrolidone, ethylene glycol, glycerol, butanediol, or diethyl carbonate.

[0030] 3. Beneficial effects

[0031] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0032] (1) The fast-charging graphite produced by this invention has moderate processing performance. It adopts a double-layer coating process. The inorganic coating layer ensures that the graphite has a high solid-phase diffusion coefficient, while the oxide coating layer can effectively reduce the charge transfer resistance and increase the lithium diffusion coefficient, thereby inhibiting the decomposition of the electrolyte on the graphite surface and improving the electrochemical performance of the material. It should be noted that the inventors found that it is impossible to achieve 220 g / m³ using only inorganic coating. 2 It still maintains good high-rate fast charging performance with 4C charging despite its low areal density;

[0033] (2) The slurry mixing method in the invention adopts a dual dispersant method. Low-substituted carboxymethyl cellulose has good fluidity, stable performance and strong compatibility. Polyacrylonitrile (PAN) has strong polar nitrile functional groups, which is beneficial to improve the stability of the electrode sheet structure and the wettability of the electrolyte. When used with an anti-cracking agent, the slurry produced has good stability and high electrode sheet peel strength.

[0034] (3) The anode sheet prepared by this invention has an surface density of 220 g / m². 2 With an active material specific capacity of over 355mAh / g, it still has good fast charging performance and energy density, and the product achieves an average fast charging capability of over 3C.

[0035] (4) The battery anode of the present invention is provided with an anti-cracking agent, the purpose of which is not only to enhance peel strength, but also, in particular, to enhance the peel strength of the electrode sheet with an surface density of 220 g / m². 2Even at these conditions, it still exhibits good adhesion without cracking or material loss; at the same time, it enhances electrochemical performance, and when the residual amount after coating is less than 100ppm, the product still has a long cycle life. Attached Figure Description

[0036] Figure 1 Scanning electron microscope (SEM) images of the anolyte active material were prepared for Example 1.

[0037] Figure 2 This is a flowchart of the method for preparing the lithium-ion battery anode of the present invention;

[0038] Figure 3 These are actual images of the anode sheets obtained in Examples 1, 2, 3 and Comparative Example 1 of this invention after peel strength tests. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, the experimental materials and reagents used in the embodiments are commercially available. Where specific techniques or conditions are not specified in the embodiments, they can be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions.

[0040] Example 1

[0041] This embodiment describes a method for preparing a lithium-ion battery anode, based on... Figure 2 The flowchart shown below illustrates the specific steps as follows:

[0042] (1) Mix dispersant CMC with a certain amount of water to prepare a 1.8% adhesive solution;

[0043] (2) Add 0.01% single-arm carbon nanotube slurry to the above adhesive solution to obtain 1.7% conductive slurry;

[0044] (3) Take 1 / 2 of the conductive paste and add solvent, anodic active material and single-arm carbon nanotube paste in batches, and stir to form a flocculent with 65% solid content.

[0045] (4) Add the remaining conductive slurry to the above dispersed flocculents, mix evenly, add some solvent, crack-preventing butanediol, and binder SBR emulsion, mix evenly, and the slurry solid content is 52% before discharging;

[0046] (5) Apply the above slurry to the current collector, with a coating density of 230 g / m². 2 The anode sheet was then prepared.

[0047] (6) The active material is prepared as follows: graphene or single-arm carbon nanotube slurry is mixed with graphite powder evenly, sintered at 2000℃ for 3 hours, then asphalt binder and alumina are added, and sintered at 1200℃ for 0.5 hours to obtain lightweight granulated secondary particles with a D5013μm and a diffusion coefficient of 10. -11 ~10 -13 cm 2 / s, in the case of a coin cell half-cell, at a charging rate of 0.1C, the specific capacity of the anode active material in this embodiment reaches more than 355mAh / g.

[0048] Figure 1 Scanning electron microscope (SEM) images of the anolyte active material were prepared for Example 1.

[0049] Example 2

[0050] This embodiment describes a method for preparing a lithium-ion battery anode, based on... Figure 2 The flowchart shown below illustrates the specific steps as follows:

[0051] (1) Mix the dispersant CMC with a certain amount of water to prepare a 1.5% adhesive solution;

[0052] (2) Add 0.02% single-arm carbon nanotube slurry to the above adhesive solution to obtain 1.4% conductive slurry;

[0053] (3) Take 60% of the conductive paste and add solvent, anodic active material and single-arm carbon nanotube paste in batches, and stir to form a flocculent material with 60% solid content;

[0054] (4) Add the remaining conductive slurry to the above dispersed flocculents, mix evenly, add some solvent, crack-preventing ethylene glycol, and binder SBR emulsion, mix evenly, and the slurry solid content is 51% before discharging.

[0055] (5) Apply the above slurry to the current collector, with a coating density of 220 g / m². 2 The anode sheet was then prepared.

[0056] (6) The active material is prepared as follows: graphene or single-arm carbon nanotube slurry is stirred evenly with graphite powder, sintered at 2500℃, then resin binder and magnesium oxide are added, and sintered at 1500℃ for 1.5h to obtain lightweight granulated secondary particles with a D50 of 15μm and a diffusion coefficient of 10. -11 ~10 -13 cm 2 / s, in the case of a coin cell half-cell, at a charging rate of 0.1C, the specific capacity of the anode active material in this embodiment reaches more than 355mAh / g.

[0057] Example 3

[0058] This embodiment describes a method for preparing a lithium-ion battery anode, based on... Figure 2 The flowchart shown below illustrates the specific steps as follows:

[0059] (1) Mix dispersant CMC with a certain amount of water to prepare a 2% adhesive solution;

[0060] (2) Add 0.03% single-arm carbon nanotube slurry to the above adhesive solution to obtain 1.7% conductive slurry;

[0061] (3) Take 55% conductive paste and add solvent, anodic active material and single-arm carbon nanotube paste in batches, and stir to form flocculent material with 60% solid content;

[0062] (4) Add the remaining conductive slurry to the above dispersed flocculents, mix evenly, add some solvent, crack-preventing N-methylpyrrolidone, and binder SBR emulsion, mix evenly, and the slurry solid content is 51% before discharging;

[0063] (5) Apply the above slurry to the current collector, with a coating density of 240 g / m². 2 The anode sheet was then prepared.

[0064] (6) The active material is prepared as follows: graphene or single-arm carbon nanotube slurry is mixed with graphite powder and sintered at 2200℃ for 1.5h. Then, asphalt binder and zirconium oxide are added and sintered at 1200℃ for 2h to obtain lightweight granulated secondary particles with a D5014μm and a diffusion coefficient of 10. -11 ~10 -13 cm 2 / s, in the case of a coin cell half-cell, at a charging rate of 0.1C, the specific capacity of the anode active material in this embodiment reaches more than 355mAh / g.

[0065] Comparative Example 1

[0066] In comparison, the preparation method of the lithium-ion battery anode in this comparative example is as follows:

[0067] (1) Mix dispersant CMC with a certain amount of water to prepare a 2% adhesive solution;

[0068] (2) Add the conductive paste, solvent, active material, conductive powder, and SBR binder in batches and mix them to form a paste with a solid content of 51%.

[0069] (3) The active material is prepared by mixing graphene or single-arm carbon nanotube slurry with graphite powder, sintering at 2000℃, adding asphalt binder, and sintering at 1300℃ to obtain light granulated secondary particles D50 13μm.

[0070] Comparative Example 2

[0071] In comparison, the preparation method of the lithium-ion battery anode in this comparative example is as follows:

[0072] (1) Mix the dispersant CMC with a certain amount of water to prepare a 1.3% adhesive solution;

[0073] (2) Add 0.01% single-arm carbon nanotube slurry to the above adhesive solution to obtain 1.7% conductive slurry;

[0074] (3) Take 1 / 2 of the conductive paste and add solvent, active material and conductive powder in batches, and stir to form a flocculent material with a solid content of 65%;

[0075] (4) Add the remaining conductive slurry to the above dispersed flocculents, mix evenly, add some solvent and SBR binder emulsion, mix evenly, and the slurry solid content is 52% before discharging;

[0076] (5) Apply the above slurry to the current collector, with a coating density of 200 g / m². 2 The anode sheet was then prepared.

[0077] (6) The active material is prepared by mixing graphene or single-arm carbon nanotube slurry with graphite powder, sintering at 2000℃, adding asphalt binder, and sintering at 1500℃ to obtain light granulated secondary particles D50 13μm.

[0078] The electrode sheets produced by the above methods in Examples 1 to 3 were normal. The slurry in Comparative Example 1 showed sedimentation. The electrode sheet produced by Comparative Example 2 showed slight cracking. The peel strength of each group of electrode sheets was tested.

[0079] Performance testing

[0080] The anode sheet from Examples 1-3 and Comparative Example 2 was combined with a ternary NCM613 cathode sheet and a low-viscosity lithium-ion electrolyte to form an aluminum-cased 20110140A30Ah laminated battery cell. After the battery cell was manufactured, it was charged at a 3C rate within the 10-80% SOC range. The battery cells from Examples 1-3 took about 14 minutes, while the battery cell from Comparative Example 2 took 42 minutes. Then, it was charged at 1C to 100% SOC, and the fast charging interface was disassembled.

[0081] Table 1 shows the peel strength comparison between Examples 1-3 and Comparative Example 2.

[0082]

[0083] Depend on Figure 3As shown in Table 1, the peel strength of Examples 1-3 differs significantly from that of Comparative Example 2. The peel strength of the electrode sheet not prepared using the method of this invention is below 10 N / m, and significant material loss occurs during processing. The electrode sheet prepared using the method of this invention has a peel strength of 13-16 N / m, meeting processing requirements. To further verify the fast charging effect of this invention on the battery cell, the prepared battery cell was tested for 4C fast charging. Lithium deposition occurred in the middle of the electrode sheet in the comparative example, while Examples 1-3 showed excellent fast charging performance. Furthermore, according to the different proportions of this invention, 200 g / m² can be achieved. 2 The above describes the 3C fast charging capability. It should be noted that the performance test used DC charging in the 10-80% SOC range. If a multi-step charging method is used, the charging power can be increased to over 3C.

[0084] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. An anode active material for lithium-ion batteries, characterized in that: The material comprises graphite, an inorganic coating layer attached to the graphite, and a metal oxide layer attached to the outside of the inorganic coating layer. The inorganic coating layer is graphene or carbon nanotubes, and the metal oxide layer is at least one oxide selected from Al, Mg, Zr, Ti, Ag, Ni, and Mo, with a diffusion coefficient of 10. -11 ~10 -13 cm 2 / s; The preparation method of the anodic active material is as follows: graphite is mixed with an inorganic coating agent and sintered at high temperature under oxygen-free conditions to form an inorganic coating layer; after the sintered product is cooled, it is mixed with metal oxide and binder and calcined to form a metal oxide layer, thereby obtaining the anodic active material, wherein: The sintering temperature for forming the inorganic coating layer is 2000~2500℃, and the sintering time is 1~3h; The calcination temperature for forming the metal oxide layer is 1200~1500℃, and the calcination time is 0.5~2h.

2. The anode active material for lithium-ion batteries according to claim 1, characterized in that: In the case of a coin cell, at a charging rate of 0.1C, the specific capacity of the anode active material is at least 355 mAh / g.

3. The anode active material for lithium-ion batteries according to claim 1, characterized in that: The D50 of the anolyte active material is 10~15 μm.

4. A lithium-ion battery anode, characterized in that: An anode sheet is prepared by coating an anode slurry containing the anode active material as described in any one of claims 1 to 3 onto a current collector.

5. The lithium-ion battery anode according to claim 4, characterized in that: The areal density of the anode sheet is at least 220 g / m². 2 .

6. A method for preparing the lithium-ion battery anode according to claim 5, characterized in that: The steps are as follows: (1) The dispersant is mixed in the solvent to obtain a gel solution; (2) Add conductive paste to the adhesive in step (1), mix evenly to obtain conductive adhesive, and divide the conductive adhesive into two parts, conductive adhesive A and conductive adhesive B, for later use; (3) Add solvent, anolyte, and conductive powder to conductive adhesive solution A in multiple portions and stir to form a flocculent conductive mixture; (4) Mix the flocculent conductive mixture in step (3) with conductive adhesive B evenly, and add solvent, anti-cracking solvent and binder emulsion. After mixing evenly, discharge the material to obtain anode slurry. (5) The anode slurry from step (4) is coated onto the current collector to obtain an anode sheet.

7. The method for preparing a lithium-ion battery anode according to claim 6, characterized in that: In step (1), the dispersant is a mixture of carboxymethyl cellulose and polyacrylonitrile with a degree of substitution of less than 1.0, the mixing ratio of carboxymethyl cellulose and polyacrylonitrile is 1.0:(0.1~0.5), the solid content of the mixture is 1.5~2%; the solvent is water.

8. The method for preparing a lithium-ion battery anode according to claim 6, characterized in that: In step (2), the conductive paste is at least one of single-arm carbon nanotubes, graphene, multi-arm carbon nanotubes, carbon nanofibers, and Ketjen black; in step (3), the conductive powder is at least one of single-arm carbon nanotubes, graphene, multi-arm carbon nanotubes, carbon nanofibers, and Ketjen black in powder form.

9. The method for preparing a lithium-ion battery anode according to claim 6, characterized in that: In step (2), the mass ratio of conductive adhesive A to conductive adhesive B is greater than 1.

10. The method for preparing a lithium-ion battery anode according to claim 6, characterized in that: In step (4), the anti-cracking solvent is one of N-methylpyrrolidone, ethylene glycol, glycerol, butanediol, or diethyl carbonate.

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