CN105514344B - The method that lithium ion battery cathode surface is modified is realized by electrophoretic deposition graphene - Google Patents

Abstract

The invention provides a method for modifying the surface of lithium-ion battery cathode by electrophoretic deposition of graphene. The modification method is to add graphene stable dispersion liquid into the battery, and use the coated lithium-ion battery cathode as the electrophoresis The negative electrode, the inert metal sheet is used as the electrophoretic positive electrode, the electrodes are kept at a certain distance, and the graphene is deposited on the surface of the lithium-ion battery cathode under an appropriate deposition voltage and deposition time, that is, a graphene-surface-modified lithium-ion battery cathode is obtained. The invention can effectively increase the initial specific capacity of the electrode and improve cycle performance. The method has simple process and low production cost.

Description

A Method for Surface Modification of Lithium-ion Battery Cathode by Electrophoretic Deposition of Graphene

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a method for realizing the surface modification of lithium ion battery cathodes by electrophoretic deposition of graphene.

Background technique

Lithium-ion batteries have been widely used in notebook computers, mobile phones, wearable devices, electric vehicles and other fields due to their advantages such as high cell voltage, large specific energy, small self-discharge and no memory effect. However, the capacity of lithium-ion batteries will gradually decay during the charge-discharge cycle, shortening their service life. In order to reduce the cost of use, the cycle performance of lithium-ion batteries needs to be continuously improved.

In order to improve the cycle performance of lithium-ion batteries, the methods often adopted by cathode researchers include surface modification and bulk doping of cathode materials with dissimilar elements. Among them, the surface modification is to deposit heterogeneous materials on the surface of the cathode material by means of solution method (such as sol-gel method and solvent evaporation method) or atomic layer deposition. The use of atomic layer deposition can also achieve uniform deposition on the surface of the entire cathode sheet. Heterogeneous materials. The deposited heterogeneous material has the ability to inhibit the side reaction between the cathode and the electrolyte during the charging process, slow down the decomposition of the electrolyte and form a stable interfacial reaction film at the electrode/electrolyte interface (ie solid-electrolyte interphase layer, SEI film ) function, and also has the function of inhibiting the dissolution of the cathode material by the HF impurities in the electrolyte. Therefore, the surface modification improves the stability of the cathode, which in turn can improve the cycle performance of the full battery. Graphene is a carbon material with a two-dimensional planar structure, which has the advantages of high electrical conductivity and high chemical stability, and is suitable as a coating modification layer material for various cathode materials of lithium-ion batteries. Existing research reports start from the cathode material powder, and use graphene dispersion or graphite oxide dispersion to finally realize the coating of graphene on the surface of the cathode powder material. For example, the cathode material powder is added to the graphite oxide solution, and after the graphite oxide is coated on the surface of the cathode material particles, the graphite oxide is converted into graphene through solution reducing agent reduction or heating deoxidation reduction to obtain graphene-coated Composites of cathode material particles. The composite material is mixed with a binder and a conductive additive and coated on an aluminum foil current collector, and finally a graphene-modified cathode is obtained. However, the void structure of deposited graphene on the surface will reduce the tap density of the composite material, which will lead to a decrease in the volume specific energy of Li-ion batteries.

Contents of the invention

The purpose of the present invention is to solve the defects of the above-mentioned prior art, utilize the electrophoretic deposition technology of graphene solution, deposit graphene on the surface of the cathode that has been coated, realize the graphene modification to the whole pole piece of the cathode, increase the cathode Conductivity can effectively increase the initial specific capacity of the electrode and improve cycle performance. The method has simple process and low production cost.

For reaching above-mentioned object, the present invention adopts following technical scheme:

A method for modifying the surface of a lithium-ion battery cathode by electrophoretic deposition of graphene. The modification method is to add a stable dispersion of graphene into an electric swimming pool, and use the coated lithium-ion battery cathode as an electrophoretic negative electrode, which is inert The metal sheet or graphite sheet is used as the positive electrode of electrophoresis, and the electrodes are kept at a certain distance. Graphene is deposited on the surface of the lithium-ion battery cathode under an appropriate deposition voltage and deposition time, that is, a graphene-surface-modified lithium-ion battery cathode is obtained.

Further, in the above-mentioned method for modifying the cathode surface of a lithium-ion battery by electrophoretic deposition of graphene, the electrode spacing is 1-20 cm, the deposition voltage is 2-1000 V, and the deposition time is 1-600 min.

Further, the method for realizing the surface modification of lithium-ion battery cathode by electrophoretic deposition of graphene as described above is used to prepare lithium-ion battery cathode or the active material is one or more of the following materials:

LiFePO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiFe _x Mn _1-x PO ₄ , where 0<x<1, Li ₂ FeSiO ₄ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ , where 0<x<1, LiNi _1-x Mn _x O ₂ , where 0<x<1, LiCo _{1- x} Mn _x O ₂ , where 0<x<1, LiM _x Mn _2-x O ₄ , where M=Ni, Co, Fe, Cr, Cu, Al, Ti, Zr, Ge and Sn, 0<x<2, LiNi _1-x Al _x O ₂ , where 0< x≤0.6, a combination of one or more of Li ₂ MnSiO ₄ , a combination of one or more of various heterogeneous ion-doped materials for each of the above-mentioned active materials, and a non-graphene surface coating of the above-mentioned active materials A combination of one or more of the modified materials, Li _a Ni _x Co _y M _z O ₂ , wherein M=Mn, Al, Fe, Mg, Cu, Sr, Ga, In, Ge, Zr, Cr, A combination of one or more of La, Ce, Ti, Ca, V, B, Be, Y, Mo, Tb, Ho, Tm, Nb, Sn, Zn, Pr, Si, 0.95≤a≤1.25,0 <x<1.0, 0<y<1.0, 0<z<1.0, x+y+z=1, Li _a Ni _x Co _y M _z O ₂ non-graphene coated modified material, wherein M=Mn, A1, Fe, Mg, Cu, Sr, Ga, In, Ge, Zr, Cr, La, Ce, Ti, Ca, V, B, Be, Y, Mo, Tb, Ho, Tm, Nb, Sn, Zn, A combination of one or more of Pr and Si, 0.95≤a≤1.25, 0<x<1.0, 0<y<1.0, 0<z<1.0, x+y+z=1.

Further, as mentioned above, by electrophoretic deposition of graphene to realize the method for modifying the cathode surface of lithium ion battery, the inert metal sheet is one of Ti sheet, Pd sheet, Au sheet, Pt sheet, Pb sheet, stainless steel sheet .

Further, the method for realizing the surface modification of lithium-ion battery cathode by electrophoretic deposition of graphene as described above, the stable dispersion of graphene is graphene-ethanol dispersion, graphene-isopropanol dispersion, graphene- One of acetone dispersion, graphene-N-methylpyrrolidone, graphene-dioctyl phthalate.

The positive effect of the present invention is as follows:

(1) The graphene deposited on the surface of the cathode induces the formation of a stable SEI film at the electrode/electrolyte interface, which significantly improves the cycle performance of the electrode.

(2) The deposition of graphene on the surface of the electrode enhances the conductivity of the electrode, so that the initial specific capacity of the electrode is improved.

(3) The method of graphene electrophoretic deposition modified cathode is aimed at the modification of the prepared cathode pole piece, which can avoid the problem of reducing the volume specific energy of the lithium ion battery caused by the graphene-coated cathode powder material as much as possible. At the same time, the electrophoretic deposition modification process is simple, the production cost is low, and it is convenient for large-scale application.

Description of drawings

Fig. 1 is the method flowchart that the present invention realizes lithium-ion battery cathode surface modification by electrophoretic deposition graphene;

Fig. 2 is the scanning electron microscope image (SEM) of LiNi _0.5 Mn _1.5 O ₄ cathode before and after graphene surface modification in embodiment 1 of the present invention;

Fig. 3 is a schematic diagram of the initial charge and discharge curves of original LiNi _0.5 Mn _1.5 O ₄ and graphene-modified LiNi _0.5 Mn _1.5 O ₄ in Example 1 of the present invention;

4 is a schematic diagram of cycle performance curves of the original LiNi _0.5 Mn _1.5 O ₄ and graphene-modified LiNi _0.5 Mn _1.5 O ₄ electrodes in Example 1 of the present invention;

Figure 5 shows the change of SEI film resistance R _SEI and electron transfer resistance R _ct of the original LiNi _0.5 Mn _1.5 O ₄ electrode and electrophoretic deposited graphene modified LiNi _0.5 Mn _1.5 O ₄ electrode of the present invention with cycle times.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the following technical solutions in the present invention are clearly and completely described. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As one of the preferred technical solutions, the present invention realizes the concrete steps of cathode surface graphene modification method as follows:

(1) Preparation of graphene-ethanol dispersion

Ultrasonic disperse 0.15g of graphite oxide prepared by Hummers method (ultrasonic power is 427W, ultrasonic time is 1 hour) in 150mL of deionized water to obtain dispersion A, then dissolve 1.35g of p-phenylenediamine in 150mL of dimethylformamide To obtain solution B, mix dispersion A and solution B, heat and reflux at 90°C for 24 hours, centrifuge and wash with acetone three times, and wash once by suction filtration. Then a certain amount of graphene product is ultrasonically dispersed in a certain amount of absolute ethanol solution (ultrasonic power is 100W, ultrasonic time is 30 minutes), to obtain a stable graphene ethanol dispersion with a concentration of 2.5mg/mL.

(2) Preparation of cathode

Take a certain amount of cathode active material, carbon black, PVDF according to the mass ratio of the amount of cathode active material, carbon black, and the addition amount of polyvinylidene fluoride (PVDF) to be 80:10:10, and cathode active material and carbon black Mix and stir for 20 minutes, then add an appropriate amount of N-methylpyrrolidone (NMP), stir for 2 hours, then add the binder PVDF, stir for 12 hours to obtain a uniform slurry, and use a scraper to evenly coat the slurry on A1 The cathode was obtained after drying on the foil at 50°C for 5 hours.

(3) Electrophoretic deposition of graphene modified cathode

The prepared graphene-ethanol dispersion is added in the electrolytic cell, with the prepared negative electrode as the electrophoretic negative pole, the titanium sheet is as the electrophoretic positive pole, the electrode spacing is 2cm, and the graphene is deposited on the deposition voltage of 20V and the deposition time of 2min. After the surface of the cathode is dried at room temperature, a graphene-modified cathode is obtained.

Example 1

(1) Preparation of graphene ethanol dispersion

Ultrasonic disperse 0.15g of graphite oxide prepared by Hummers method (ultrasonic power is 427W, ultrasonic time is 1 hour) in 150mL of deionized water to obtain dispersion A, then dissolve 1.35g of p-phenylenediamine in 150mL of dimethylformamide To obtain solution B, mix dispersion A and solution B, heat at 90°C under reflux for 24 hours, centrifuge and wash with acetone three times, and wash once by suction filtration. Then a certain amount of graphene product was ultrasonically dispersed in a certain amount of absolute ethanol solution (ultrasonic power was 100W, ultrasonic time was 30 minutes), to obtain a stable graphene-ethanol dispersion with a concentration of 2.5mg/mL.

(2) Preparation of LiNi _0.5 Mn _1.5 O ₄ cathode

Weigh a certain amount _{of LiNi 0.5 Mn 1.5 O 4 powder , carbon black} , PVDF, mix LiNi _0.5 Mn _1.5 O ₄ with carbon black and stir for 20min, then add an appropriate amount of N-methylpyrrolidone (NMP), stir for 2h, then add binder PVDF, stir for 12h to obtain a uniform slurry The slurry was uniformly coated on the A1 foil with a scraper, and dried at 50°C for 5 hours to obtain a LiNi _0.5 Mn _1.5 O ₄ cathode.

(3) Preparation of graphene-modified LiNi _0.5 Mn _1.5 O ₄ cathode by electrophoretic deposition

Add the prepared graphene-ethanol dispersion into the electrolytic cell, use the prepared LiNi _0.5 Mn _1.5 O ₄ cathode as the negative electrode for electrophoresis, and the titanium sheet as the positive electrode for electrophoresis, with an electrode distance of 2 cm, at a deposition voltage of 20V and a deposition time of 2 min Graphene was deposited on the surface of the cathode, and after drying at room temperature, the graphene-modified LiNi _0.5 Mn _1.5 O ₄ cathode was obtained.

Example 2

(1) Synthetic graphene isopropanol dispersion

Ultrasonic disperse 0.15g of graphite oxide prepared by Hummers method (ultrasonic power is 427W, ultrasonic time is 1 hour) in 150mL of deionized water to obtain dispersion A, then dissolve 1.35g of p-phenylenediamine in 150mL of dimethylformamide To obtain solution B, mix dispersion A and solution B, heat at 90°C under reflux for 24 hours, centrifuge and wash with acetone three times, and wash once by suction filtration. Then a certain amount of graphene product is ultrasonically dispersed in a certain amount of isopropanol solution (ultrasonic power is 100W, ultrasonic time is 30 minutes), to obtain a stable graphene-isopropanol dispersion with a concentration of 1.5mg/mL.

(2) Preparation of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ cathode

Weigh a certain amount of LiNi _0.5 Mn _1.5 O according to the mass ratio of the amount of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ cathode active material, the amount of carbon black, and the amount of PVDF added is 80:10:10 ₄ powder, carbon black, PVDF, mix Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ with carbon black and stir for 20min, then add appropriate amount of NMP, stir for 2h, then add binder PVDF, stir After 12 hours, a uniform slurry was obtained, and the slurry was uniformly coated on the A1 foil with a scraper, and dried at 50°C for 5 hours to obtain a Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ cathode .

(3) Preparation of graphene-modified Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ cathode by electrophoretic deposition

The prepared graphene-isopropanol dispersion is added in the electrolytic cell, with the prepared Li(Ni _1/3 Co _1/3 Mn _1/3 )O _The electrode is used as the negative electrode for electrophoresis, the stainless steel sheet is used as the positive electrode for electrophoresis, and the electrode Graphene was deposited on the Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ electrode at a deposition voltage of 1000V and a deposition time of 5min at a distance of 20cm, and after drying at room temperature, a graphene-modified Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ electrode.

Example 3

(1) Synthetic graphene acetone dispersion

Ultrasonic disperse 0.15g of graphite oxide prepared by Hummers method (ultrasonic power is 427W, ultrasonic time is 1 hour) in 150mL of deionized water to obtain dispersion A, then dissolve 1.35g of p-phenylenediamine in 150mL of dimethylformamide To obtain solution B, mix dispersion A and solution B, heat at 90°C under reflux for 24 hours, centrifuge and wash with acetone three times, and wash once by suction filtration. Then a certain amount of graphene product is ultrasonically dispersed in a certain amount of acetone (ultrasonic power is 100W, ultrasonic time is 30 minutes), to obtain a concentration of 0.5mg/mL stable graphene-acetone dispersion.

(2) Preparation of LiNi _0.8 Co _0.15 Al _0.05 O ₂ electrode.

A certain amount of LiNi _0.8 Co _0.15 Al _0.05 O ₂ , carbon black, and PVDF were weighed according to the mass ratio of LiNi _0.8 Co _0.15 Al _0.05 O ₂ cathode active material, carbon black, and PVDF being 60:30:10. Mix LiNi _0.8 Co _0.15 Al _{0.0 5} O ₂ with carbon black and stir for 20 minutes, then add an appropriate amount of NMP, stir for 2 hours, then add the binder PVDF, and stir for 12 hours to obtain a uniform slurry, and use a scraper to spread the slurry evenly Covered on Al foil and dried at 50°C for 5h to prepare LiNi _0.8 Co _0.15 Al _{0.0 5} O ₂ electrode.

(3) Electrophoretic deposition of graphene-modified LiNi _0.8 Co _0.15 Al _0.05 O ₂ electrodes.

Add the prepared graphene acetone dispersion into the electrolytic cell, use the prepared LiNi _0.8 Co _0.15 Al _0.05 O ₂ electrode as the negative electrode of electrophoresis, and the Au sheet as the positive electrode of electrophoresis, the electrode spacing is 1 cm, the deposition voltage of 1000V and the Graphene was deposited on the LiNi _0.8 Co _0.15 Al _0.05 O ₂ electrode under the deposition time, and after drying at room temperature, the graphene-modified LiNi _0.8 Co _0.15 Al _0.05 O ₂ electrode was obtained.

Example 4:

(1) The 1st step of preparing graphene dispersion liquid is identical with the (1) step of embodiment 1.

(2) Take a certain amount of LiFePO ₄ powder, carbon black, PVDF according to the mass ratio of the amount of LiFePO ₄ cathode active material, the amount of carbon black and PVDF added to be 80: 10: 10, mix LiFePO ₄ with carbon black and Stir for 20 minutes, then add an appropriate amount of NMP, stir for 2 hours, then add the binder PVDF, and stir for 12 hours to obtain a uniform slurry, use a scraper to evenly coat the slurry on the Al foil, and dry it at 50°C for 5 hours. Obtain LiFePO ₄ cathode.

(3) Add the prepared graphene-ethanol dispersion into the electrolytic cell, use the prepared _LiFePO cathode as the negative electrode for electrophoresis, and the Pt sheet as the positive electrode for electrophoresis, with an electrode spacing of 3cm, at a deposition voltage of 20V and a deposition time of 30min Graphene was deposited on the surface of the cathode, and after drying at room temperature, the graphene-modified LiFePO ₄ cathode was obtained.

Example 5:

(1) The 1st step of preparing graphene dispersion liquid is identical with the (1) step of embodiment 1.

(2) Take a certain amount of _LiCoO2 powder, carbon black and PVDF according to the mass ratio of the amount of _LiCoO2 cathode active material, the amount of carbon black and PVDF added to be 80:10:10, mix _LiFePO4 with carbon black and Stir for 20 minutes, then add an appropriate amount of NMP, stir for 2 hours, then add the binder PVDF, and stir for 12 hours to obtain a uniform slurry, use a scraper to evenly coat the slurry on the Al foil, and dry it at 50°C for 5 hours. A LiCoO ₂ cathode was obtained.

(3) Add the prepared graphene-isopropanol dispersion into the electrolytic cell, use the prepared _LiCoO2 electrode as the negative electrode for electrophoresis, and the graphite sheet as the positive electrode for electrophoresis, with an electrode spacing of 20cm, at a deposition voltage of 5V and a deposition time of 600min Graphene was deposited on the Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ electrode for a certain time, _and after drying at room temperature, the graphene-modified Li(Ni _1/3 Co _1/3 Mn _{1 /3} ) O ₂ electrode.

Fig. 1 is the method flowchart that the present invention realizes lithium-ion battery cathode surface modification by electrophoretic deposition graphene;

Fig. 2 is the scanning electron microscope image (SEM) of LiNi _0.5 Mn _1.5 O ₄ electrodes before and after graphene surface modification in the embodiment of the present invention 1; Can find out by the contrast before and after Fig. 2 graphene surface modification, electrophoretic method can make Graphene is deposited on the electrode surface, and there are discrete and uneven pores on the graphene deposition layer.

Fig. 3 is the initial charge-discharge curve schematic diagram of original LiNi _0.5 Mn _1.5 O ₄ and graphene-modified LiNi _0.5 Mn _1.5 O ₄ electrodes in Example 1 of the present invention; As can be seen from Fig. 3, after surface electrodeposition graphene, LiNi The mass-specific capacity _{of 0.5 Mn1.5O4} is significantly improved.

Figure 4 is a schematic diagram of the cycle performance curves of the original LiNi _0.5 Mn _1.5 O ₄ and graphene-modified LiNi _0.5 Mn _1.5 O ₄ electrodes in Example 1 of the present invention. It can be seen from Figure 4 that after the electrodeposition of graphene on the surface, LiNi _0.5 The Mn _1.5 O ₄ electrode still has a high capacity retention rate after 1000 cycles, and the cycle performance is obviously improved.

Fig. 5 is original LiNi _0.5 Mn _1.5 O ₄ electrode of the present invention and electrophoretic deposition graphene modified LiNi _0.5 Mn _1.5 O ₄ electrode SEI film resistance R _SEI and electron transfer resistance R _ct change with cycle number; By Fig. 5 can It can be seen that both the initial R _SEI and R _ct of the graphene-modified LiNi _0.5 Mn _1.5 O ₄ electrode are smaller than those of the pristine electrode. And with the increase of cycles, the increase of both impedances of the graphene-modified LiNi _0.5 Mn _1.5 O ₄ electrode is significantly smaller than that of the original LiNi _0.5 Mn _1.5 O ₄ electrode. It is shown that the graphene deposited on the surface can reduce the electrode polarization and induce a stable SEI film at the electrode/electrolyte interface.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (5)

1. A method for realizing lithium-ion battery cathode surface modification by electrophoretic deposition of graphene, is characterized in that: described modification method is that graphene stable dispersion is added in the electric swimming pool, with the good lithium-ion battery of coating The cathode is used as the electrophoretic negative electrode, and the inert metal sheet or graphite sheet is used as the electrophoretic positive electrode. The electrodes are kept at a certain distance, and graphene is deposited on the cathode surface of the lithium-ion battery under an appropriate deposition voltage and deposition time, that is, graphene-surface-modified lithium Ion battery cathode. 2. the method for realizing lithium-ion battery cathode surface modification by electrophoretic deposition of graphene as claimed in claim 1, characterized in that: the electrode spacing is 1-20cm, the deposition voltage is 2-1000V, and the deposition time is 1-600min. 3. the method for realizing lithium-ion battery cathode surface modification by electrophoretic deposition of graphene as claimed in claim 1, is characterized in that: the active material that is used to prepare lithium-ion battery cathode is one or more of following materials: LiFePO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiFe _x Mn _1-x PO ₄ , where 0<x<1, Li ₂ FeSiO ₄ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ , where 0<x<1, LiNi _1-x Mn _x O ₂ , where 0<x<1, LiCo _1-x Mn _x O ₂ , where 0<x<1, LiM _x Mn _2-x O ₄ , where M=Ni, Co, Fe, Cr, Cu, Al, Ti, Zr, Ge and Sn, 0<x<2, LiNi _1-x Al _x O ₂ , where 0< x≤0.6, a combination of one or more of Li ₂ MnSiO ₄ , a combination of one or more of various heterogeneous ion-doped materials for each of the above-mentioned active materials, and a non-graphene surface coating of the above-mentioned active materials A combination of one or more of the modified materials, Li _a Ni _x Co _y M _z O ₂ , wherein, M=Mn, Al, Fe, Mg, Cu, Sr, Ga, In, Ge, Zr, Cr, A combination of one or more of La, Ce, Ti, Ca, V, B, Be, Y, Mo, Tb, Ho, Tm, Nb, Sn, Zn, Pr, Si, 0.95≤a≤1.25, 0 <x<1.0, 0<y<1.0, 0<z<1.0, x+y+z=1, Li _a Ni _x Co _y M _z O ₂ non-graphene coated modified material, wherein M=Mn, Al, Fe, Mg, Cu, Sr, Ga, In, Ge, Zr, Cr, La, Ce, Ti, Ca, V, B, Be, Y, Mo, Tb, Ho, Tm, Nb, Sn, Zn, A combination of one or more of Pr and Si, 0.95≤a≤1.25, 0<x<1.0, 0<y<1.0, 0<z<1.0, x+y+z=1. 4. the method for realizing lithium-ion battery cathode surface modification by electrophoretic deposition of graphene as claimed in claim 1, is characterized in that: described inert metal sheet is Ti sheet, Pd sheet, Au sheet, Pt sheet, Pb sheet, One of the stainless steel sheets. 5. the method for realizing lithium-ion battery cathode surface modification by electrophoretic deposition graphene as claimed in claim 1, is characterized in that: described graphene stable dispersion liquid is graphene-ethanol dispersion liquid, graphene-isopropanol One of dispersion liquid, graphene-acetone dispersion liquid, graphene-N-methylpyrrolidone, graphene-dioctyl phthalate.