A lithium ion battery current collector surface treatment method, current collector and lithium ion battery

Abstract

This invention provides a method for surface treatment of current collectors in lithium-ion batteries, a current collector, and a lithium-ion battery. Phosphorus-doped graphene is synthesized electrochemically using phytic acid solution and carbon paper as raw materials. The phosphorus-doped graphene is then coated onto the positive and negative electrode current collectors of the lithium-ion battery. The phosphorus-doped graphene surface on the current collector of this invention is richly bonded with phytic acid molecules. Phytic acid has a unique hexagonal structure; its six "tentacles" link the current collector and the active material together, effectively improving the electrode stability and lifespan of the lithium-ion battery during cycling. The lithium-ion battery made based on the above current collector has the advantages of high safety performance and long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically, relates to a method for surface treatment of a lithium-ion battery current collector, a current collector, and a lithium-ion battery. Background Technology

[0002] In the production of lithium-ion batteries, aluminum foil and copper foil are used as current collectors for battery electrodes. However, the surfaces of metal sheets such as aluminum foil and copper foil are too smooth and flat. When they come into contact with particulate active materials, the contact area is small and the bonding strength is weak, which affects the battery's ohmic impedance, electrode stability, cycle life and other indicators.

[0003] Pre-treating the current collector surface by coating it with specific materials can effectively solve this problem. Carbon materials have a unique porous structure, resulting in a large contact area when in contact with particulate active materials. Therefore, carbon materials, such as graphene, are widely used in the surface treatment of lithium-ion battery current collectors. However, while the introduction of graphene can increase the contact area between the current collector and the active material, the bonding strength between graphene and the active material is still not guaranteed, often resulting in low electrode peel strength.

[0004] Phytic acid-assisted phosphorus-doped graphene has abundant phytic acid molecules bonded to its surface. Phytic acid itself has a special hexagonal structure, and its six "tentacles" allow for close contact between the current collector and the active material, thus solving the above problems. Summary of the Invention

[0005] In view of the above-mentioned technical defects of the prior art, the present invention provides a method for surface treatment of lithium-ion battery current collector, current collector and lithium-ion battery that can enhance the bonding strength between current collector and electrode material.

[0006] To achieve the above objectives, the present invention provides a surface treatment method for lithium-ion battery current collectors as follows:

[0007] 1) Phosphorus-doped graphene is synthesized by electrochemical method using phytic acid solution and carbon paper as raw materials; the mass ratio of phytic acid to carbon paper is 50:1 to 100:1, and too low a phytic acid content will affect the performance of the synthesized phosphorus-doped graphene.

[0008] 2) Coating phosphorus-doped graphene onto the positive and negative current collectors of lithium-ion batteries.

[0009] Preferably, the electrochemical method in step 1) is an electrochemical solution stripping method;

[0010] The electrochemical solution stripping method uses a DC constant voltage source as the stripping power source; the electrochemical solution stripping method uses phytic acid solution as the stripping solution and carbon paper as the electrochemical stripping carbon source;

[0011] Phytic acid has the chemical formula C6H. 18 O 24 P6, the electrochemical solution stripping method uses carbon paper as the carbon source, with the chemical formula C.

[0012] Preferably, the DC constant voltage source voltage is 5 to 12V, for example, it can be 5V, 6V, 7V, 8V, 9V or 12V, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. If the DC constant voltage source voltage is too high, the synthesized graphene material will be oxidized, and if it is too low, the carbon paper electrochemical peeling will not be complete. If the DC constant voltage source action time is too short, the carbon paper electrochemical peeling will not be complete.

[0013] The duration of the DC constant voltage source is 0.2 to 1 hour, for example, it can be 0.2 hours, 0.4 hours, 0.6 hours, 0.8 hours or 1 hour, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the molar concentration of the phytic acid solution is 2 to 8 mol / L, for example, it can be 2 mol / L, 4 mol / L, 6 mol / L or 8 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. If the concentration of the phytic acid solution is too high, it will affect the structural strength of the carbon paper and lead to incomplete electrochemical stripping. If it is too low, it will affect the doping rate of the generated graphene material. If the carbon paper thickness is too high, it will affect the electrochemical stripping reaction. If it is too low, it will affect the concentration of the product.

[0015] The thickness of the carbon paper is 0.1 to 1 mm, for example, it can be 0.1 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm or 1 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the positive electrode current collector material is aluminum foil and the negative electrode current collector material is copper foil.

[0017] Preferably, in step 2), the method for coating the positive and negative electrode current collector surfaces with phosphorus-doped graphene is a flat plate coating method or a brush coating method.

[0018] Preferably, the thickness of the phosphorus-doped graphene coating on the positive and negative electrode current collector surfaces is 50–500 nm, for example, 50 nm, 100 nm, 200 nm, 300 nm, or 500 nm, but not limited to the listed values; other unlisted values ​​within the range are also applicable. Excessive coating thickness affects the battery energy density, while insufficient thickness has limited modification effect on the current collector surface.

[0019] The phosphorus-doped graphene synthesized in this invention has abundant phytic acid molecules bonded to its surface. Phytic acid has a special hexagonal structure, and its six "tentacles" link the current collector and electrode materials together, which can effectively improve the electrode stability and service life of lithium-ion batteries.

[0020] The second invention provides a current collector obtained by the surface treatment method described above, wherein the surface of the current collector is coated with phosphorus-doped graphene.

[0021] Thirdly, the present invention provides a lithium-ion battery, wherein the surface of the electrode material of the lithium-ion battery is the current collector described above, and the phosphorus-doped graphene on the surface of the current collector is located between the electrode material and the current collector.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] In this invention, the phosphorus-doped graphene surface of the lithium-ion battery current collector is bonded with abundant phytic acid molecules. Phytic acid has a special hexagonal structure, and its six "tentacles" link the current collector and the active material together, which can effectively improve the electrode stability and service life of the lithium-ion battery.

[0024] A method for applying phytic acid-assisted phosphorus-doped graphene to the surface treatment of lithium-ion battery current collectors aims to enhance the bonding strength between the current collector and the active material by using phytic acid-assisted phosphorus-doped graphene to coat aluminum and copper foil current collectors of a specific thickness. This method can effectively improve the stability and lifespan of lithium-ion battery electrodes. Attached Figure Description

[0025] Figure 1 a is a schematic diagram of phosphorus-doped graphene generated with phytic acid assistance in the method of the present invention. Figure 1 b is a schematic diagram of the molecular structure of phytic acid;

[0026] Figure 2 This is the X-ray photoelectron spectrum of phosphorus-doped graphene generated with phytic acid assistance in Example 1 of the present invention.

[0027] Figure 3 This is a schematic diagram illustrating the mechanism of action of phytic acid-assisted phosphorus-doped graphene on the surface of a lithium-ion battery current collector in the method of this invention.

[0028] Figure 4 This is a scanning electron microscope image of phosphorus-doped graphene generated with phytic acid assistance in Example 1 of the present invention after being coated onto a lithium-ion battery current collector.

[0029] In all the accompanying drawings, the same reference numerals are used to denote the same structures or parts, wherein: 1-graphene, 2-phytic acid, 3-current collector, 4-electrode material, 5-lithium-ion battery. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] This invention provides a method for surface treatment of phytic acid-assisted phosphorus-doped graphene for lithium-ion battery current collectors, comprising the following steps:

[0032] 1) Phosphorus-doped graphene was synthesized by electrochemical solution exfoliation using phytic acid solution and carbon paper as raw materials (the mass ratio of phytic acid to carbon paper was 50:1 to 100:1). The electrochemical solution exfoliation method used a DC constant voltage source as the exfoliation power source, phytic acid solution as the exfoliation solution, and carbon paper as the electrochemical exfoliation carbon source. The DC constant voltage source voltage was 5 to 12 V, the DC constant voltage source action time was 0.2 to 1 h, the phytic acid solution concentration was 2 to 8 mol / L, and the carbon paper thickness was 0.1 to 1 mm.

[0033] 2) Phytic acid-assisted phosphorus-doped graphene is coated onto the positive and negative electrode current collectors (aluminum and copper foils) of lithium-ion batteries. The phosphorus-doped graphene surface is richly bonded with phytic acid molecules. Phytic acid has a unique hexagonal structure; its six "tentacles" link the current collector and the active material together, effectively improving the electrode stability and lifespan of lithium-ion batteries. The method for coating the current collector surface with phosphorus-doped graphene is either planar coating or brush coating, with a coating thickness of 50–500 nm.

[0034] Figure 1 a is a schematic diagram of phosphorus-doped graphene generated with phytic acid assistance in the method of the present invention. As can be seen from the figure, the surface of graphene 1 of the phosphorus-doped graphene generated with phytic acid assistance is connected with abundant phytic acid 2. Figure 1 b is a schematic diagram of the molecular structure of phytic acid 2. As can be seen from the figure, phytic acid 2 has a special hexagonal structure. These six "tentacles" can connect to graphene 1 on one side and the target substance on the other side. Figure 3 This is a schematic diagram of the mechanism of action of phosphorus-doped graphene generated with phytic acid in the method of the present invention on the surface of lithium-ion battery current collector 3. As can be seen from the figure, the hexagonal phytic acid 2 realizes the connection between graphene 1 and electrode material 4 on lithium-ion battery current collector 3, and strengthens the bonding strength between current collector 3 and electrode material 4.

[0035] To illustrate the method of the present invention in more detail, the following description is provided in conjunction with embodiments:

[0036] Example 1

[0037] 1) Phosphorus-doped graphene was synthesized using phytic acid solution and carbon paper as raw materials (phytic acid to carbon paper mass ratio of 50:1) via an electrochemical solution exfoliation method. The electrochemical solution exfoliation method used a DC constant voltage source as the exfoliation power source, phytic acid solution as the exfoliation solution, a DC constant voltage source voltage of 5V, a DC constant voltage source action time of 0.5h, a phytic acid solution concentration of 5mol / L, and a carbon paper thickness of 0.5mm. Figure 1 As shown, the surface of the generated phosphorus-doped graphene is bonded with abundant phytic acid 2 molecules with a special hexagonal structure.

[0038] Figure 2 The image shown is the X-ray photoelectron spectrum of the phosphorus-doped graphene obtained in Example 1. Figure 2 It can be seen that the generated graphene 1 has a distinct P2p peak in the X-ray photoelectron spectrum, which indicates that phosphorus was successfully doped into graphene 1, further proving that phytic acid 2 molecules were successfully attached to the surface of graphene 1.

[0039] 2) Phytic acid-assisted phosphorus-doped graphene was coated onto the positive and negative current collectors of a lithium-ion battery, with a coating thickness of 200 nm. For example... Figure 3 As shown, the six "tentacles" of phytic acid 2 link the current collector 3 and the electrode material 4 together.

[0040] Figure 4 The image shown is a scanning electron microscope image of phosphorus-doped graphene generated with phytic acid assistance in Example 1 after it has been coated onto the lithium-ion battery current collector 3.

[0041] 3) Using lithium iron phosphate as the active material and lithium foil as the counter electrode, a lithium-ion battery was assembled. The capacity retention of the battery was tested after 300 cycles at a current density of 200 mA / g.

[0042] Example 2

[0043] Except for step 1), where the DC constant voltage source voltage for electrochemical stripping is 8V, the method is the same as in Example 1.

[0044] Example 3

[0045] Except for step 1), where the DC constant voltage source voltage for electrochemical stripping is 12V, the method is the same as in Example 1.

[0046] Example 4

[0047] 1) Phosphorus-doped graphene was synthesized via an electrochemical solution exfoliation method using phytic acid solution 2 and carbon paper as raw materials (phytic acid to carbon paper mass ratio of 70:1). The electrochemical solution exfoliation method employed a DC constant voltage source as the exfoliation power source, phytic acid solution 2 as the exfoliation solution, a DC constant voltage source voltage of 5V, an application time of 0.2h, a phytic acid solution concentration of 2mol / L, and a carbon paper thickness of 0.1mm. Figure 1 As shown, the surface of the generated phosphorus-doped graphene is bonded with abundant phytic acid 2 molecules with a special hexagonal structure.

[0048] 2) Phytic acid-assisted phosphorus-doped graphene was coated onto the positive and negative current collectors of a lithium-ion battery, with a coating thickness of 50 nm. For example... Figure 3 As shown, the six "tentacles" of phytic acid 2 link the current collector 3 and the electrode material 4 together.

[0049] 3) Using lithium iron phosphate as the active material and lithium foil as the counter electrode, a lithium-ion battery was assembled. The capacity retention of the battery was tested after 300 cycles at a current density of 200 mA / g.

[0050] Example 5

[0051] Except for step 1), where the electrochemical stripping DC constant voltage source action time is 0.5 h, the method is the same as in Example 4.

[0052] Example 6

[0053] Except for step 1), where the electrochemical stripping DC constant voltage source action time is 1 hour, the method is the same as in Example 4.

[0054] Example 7

[0055] 1) Phosphorus-doped graphene was synthesized using phytic acid solution and carbon paper as raw materials (phytic acid to carbon paper mass ratio of 60:1) via an electrochemical solution exfoliation method. The electrochemical solution exfoliation method used a DC constant voltage source as the exfoliation power source, phytic acid solution as the exfoliation solution, a DC constant voltage source voltage of 10V, an application time of 1h, a phytic acid solution concentration of 2mol / L, and a carbon paper thickness of 0.5mm. Figure 1 As shown, the surface of the generated phosphorus-doped graphene is bonded with abundant phytic acid 2 molecules with a special hexagonal structure.

[0056] 2) Phytic acid-assisted phosphorus-doped graphene was coated onto the positive and negative current collectors of a lithium-ion battery, with a coating thickness of 200 nm. For example... Figure 3 As shown, the six "tentacles" of phytic acid 2 link the current collector 3 and the electrode material 4 together.

[0057] 3) Using lithium iron phosphate as the active material and lithium foil as the counter electrode, a lithium-ion battery was assembled. The capacity retention of the battery was tested after 300 cycles at a current density of 200 mA / g.

[0058] Example 8

[0059] The method is the same as in Example 7, except that the phytic acid solution concentration is 5 mol / L in step 1).

[0060] Example 9

[0061] Except for the phytic acid solution concentration of 8 mol / L in step 1), the method is the same as in Example 7.

[0062] Example 10

[0063] 1) Phosphorus-doped graphene was synthesized using phytic acid solution and carbon paper as raw materials (phytic acid to carbon paper mass ratio of 100:1) via an electrochemical solution exfoliation method. The electrochemical solution exfoliation method used a DC constant voltage source as the exfoliation power source, phytic acid solution as the exfoliation solution, a DC constant voltage source voltage of 8V, a DC constant voltage source action time of 0.5h, a phytic acid solution concentration of 5mol / L, and a carbon paper thickness of 0.5mm. Figure 1 As shown, the surface of the generated phosphorus-doped graphene is bonded with abundant phytic acid 2 molecules with a special hexagonal structure.

[0064] (2) Phytic acid-assisted phosphorus-doped graphene was coated onto the positive and negative current collectors of a lithium-ion battery, with a coating thickness of 50 nm. For example... Figure 3 As shown, the six "tentacles" of phytic acid 2 link the current collector 3 and the electrode material 4 together.

[0065] 3) Using lithium iron phosphate as the active material and lithium foil as the counter electrode, a lithium-ion battery was assembled. The capacity retention of the battery was tested after 300 cycles at a current density of 200 mA / g.

[0066] Example 11

[0067] Except for step 2), where the phosphorus-doped graphene coating thickness is 200 nm, the method is the same as in Example 10.

[0068] Example 12

[0069] Except for step 2), where the phosphorus-doped graphene coating thickness is 500 nm, the method is the same as in Example 10.

[0070] Example 13

[0071] Except for step 3), where the active material is a 523-based ternary material, the method is the same as in Example 1.

[0072] Example 14

[0073] Except for step 3), where the active material is graphite, the method is the same as in Example 1.

[0074] Comparative Example 1

[0075] The method described herein is identical to that of Example 1, except that the surface treatment of the current collector is not performed.

[0076] Comparative Example 2

[0077] The method is the same as in Example 13, except that the surface treatment of the current collector is not performed.

[0078] Comparative Example 3

[0079] The method described herein is identical to that of Example 14, except that the surface treatment of the current collector is not performed.

[0080] The test results are shown in Table 1:

[0081] Table 1

[0082] Examples / Comparative Examples 300-cycle capacity retention rate / % Example 1 86 Example 2 86 Example 3 87 Example 4 83 Example 5 85 Example 6 85 Example 7 79 Example 8 87 Example 9 89 Example 10 88 Example 11 89 Example 12 82 Example 13 80 Example 14 72 Comparative Example 1 53 Comparative Example 2 49 Comparative Example 3 38

[0083] The following points can be observed from Table 1:

[0084] (1) As can be seen from Examples 1 to 3, the change of the DC constant voltage source voltage in step (1) of the method within 5V to 12V has little effect on the cycle performance of lithium-ion batteries.

[0085] (2) As can be seen from Examples 4 to 6, the variation of the electrochemical stripping DC constant voltage source action time in step (1) of the method within 0.2h to 1h has little effect on the cycle performance of lithium-ion batteries.

[0086] (3) As can be seen from Examples 7 to 9, the concentration of phytic acid solution in step (1) of the method has a significant impact on the cycle performance of lithium-ion batteries. When the concentration is 2 mol / L, the capacity retention rate of lithium-ion batteries after cycling is significantly lower than that of the concentrations of 5 mol / L and 8 mol / L.

[0087] (4) As can be seen from Examples 10-12, the thickness of the phosphorus-doped graphene coating in step (2) of the method has a significant impact on the cycle performance of lithium-ion batteries. When the thickness is 500nm, the capacity retention rate of lithium-ion batteries after cycling is significantly lower than that of the thicknesses of 50nm and 200nm.

[0088] (5) As can be seen from Example 1 and Comparative Example 1, Example 13 and Comparative Example 2, Example 14 and Comparative Example 3, regardless of whether it is lithium iron phosphate, ternary or graphite material, the cycle performance of lithium batteries assembled after being coated with phosphorus-doped graphene is significantly improved.

[0089] In summary, in the method of the present invention, the phosphorus-doped graphene surface of the lithium-ion battery current collector is bonded with abundant phytic acid molecules. Phytic acid has a special hexagonal structure, and its six "tentacles" link the current collector and the active material together, which can effectively improve the electrode stability and service life of the lithium-ion battery for electromagnetic emission.

[0090] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for surface treatment of a lithium-ion battery current collector, characterized in that, The surface treatment method is as follows: 1) Phosphorus-doped graphene is synthesized by electrochemical method using phytic acid solution and carbon paper as raw materials; the mass ratio of phytic acid to carbon paper is 50:1 to 100:1; the electrochemical method is electrochemical solution exfoliation. The electrochemical solution stripping method uses a DC constant voltage source as the stripping power source; the electrochemical solution stripping method uses phytic acid solution as the stripping solution and carbon paper as the electrochemical stripping carbon source; the DC constant voltage source voltage is 5~12V; the DC constant voltage source action time is 0.2h~1h; the phytic acid solution molar concentration is 2~8mol / L; the carbon paper thickness is 0.1~1mm; 2) Phosphorus-doped graphene is coated onto the positive and negative current collectors of a lithium-ion battery. The positive current collector material is aluminum foil and the negative current collector material is copper foil. The thickness of the phosphorus-doped graphene coated on the surface of the positive and negative current collectors is 50~500nm.

2. The surface treatment method for lithium-ion battery current collectors according to claim 1, characterized in that, In step 2), the method for coating the positive and negative electrode current collector surfaces with phosphorus-doped graphene is either a flat plate coating method or a brush coating method.

3. A current collector obtained by the surface treatment method according to any one of claims 1 to 2, wherein the surface of the current collector is coated with phosphorus-doped graphene.

4. A lithium-ion battery, characterized in that, The surface of the electrode material of the lithium-ion battery is the current collector as described in claim 3, and the phosphorus-doped graphene on the surface of the current collector is located between the electrode material and the current collector.

Images