CN106784700B - A kind of multi-layer silicon/graphene composite lithium battery negative electrode material and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of energy materials, and provides a foam nickel collector multilayer silicon/graphene composite lithium battery negative electrode material and a preparation method thereof, which are used to overcome the severe volume effect of the silicon negative electrode in the electrochemical lithium storage process and the difficulty in forming the negative electrode material. The stable surface solid electrolyte membrane and its low intrinsic conductivity lead to the defect of poor electrical cycle performance; the negative electrode material of the multilayer silicon/graphene composite lithium battery of the present invention includes foamed nickel and graphene alternately arranged on the foamed nickel. layer and silicon layer, and the top layer is graphene layer; a multi-layer "graphene/silicon/graphene" sandwich structure is formed, and the high mechanical properties and high electrical conductivity of graphene are used to wrap silicon powder in layers, effectively inhibiting silicon The volume of the powder changes dramatically during the charging and discharging process, which is conducive to the formation of a stable SEI film, and improves the rate characteristics and cycle stability while maintaining the high specific capacity of silicon; at the same time, the preparation method is simple in process, low in cost, and repeatable. it is good.

Description

A kind of multi-layer silicon/graphene composite lithium battery negative electrode material and preparation method thereof

technical field

The invention belongs to the technical field of energy materials, and relates to a lithium battery negative electrode material and a preparation method thereof, in particular to a foam nickel collector multilayer silicon/graphene composite lithium battery negative electrode material and a preparation method thereof.

Background technique

The development of green energy technology and low-carbon economy has put forward higher and higher requirements for the next-generation high-performance lithium-ion batteries. In terms of anode materials, the current commercial lithium-ion batteries mainly use graphite-based carbon anode materials; however, graphite The theoretical specific capacity of the battery is only 372mAh·g ^-1 , and the lithium intercalation potential platform is close to that of metal lithium, and the "lithium precipitation" phenomenon is prone to occur during fast charging or low-temperature charging, which leads to safety hazards; therefore, the development of high-energy power lithium-ion batteries urgently needs to seek High-capacity, long-cycle, safe and reliable new anode materials to replace graphite-like carbon anodes.

Among various anode materials, silicon has attracted the attention of more and more researchers with its obvious advantages and potential. The theoretical lithium storage capacity of silicon is as high as 4200mAh·g ^-1 , which is more than 10 times that of graphite. The lithium storage element has the highest capacity; the voltage platform of silicon is slightly higher than that of graphite, and it is difficult to cause the phenomenon of "lithium precipitation" on the surface during charging, and its safety performance is better than that of graphite anode material; in addition, silicon is the most abundant in the earth's crust. One of the elements, it is widely available, cheap and suitable for industrial production; however, there are still many problems with silicon as the negative electrode of next-generation lithium-ion batteries: First, in the process of electrochemical lithium storage, silicon atoms combine with lithium atoms to obtain Li _4.4 silicon In the alloy phase, the volume expansion change of the material reaches more than 300%, and the mechanical force generated by the huge volume effect will gradually separate the electrode active material and the current collector, and the silicon active phase will also pulverize itself, thereby losing contact with the current collector. Second, silicon itself is a semiconductor material with low intrinsic conductivity, only 6.7·10 ^-4 S·cm ^-1 , and a conductive agent needs to be added to improve the electronic conductivity of the electrode; Third, the decomposition of LiPF ₆ in the existing electrolyte produces a small amount of HF, which causes corrosion to silicon, resulting in the capacity decay of the silicon-based negative electrode, and, due to its severe volume effect, it is difficult for silicon to form a stable surface in the conventional LiPF ₆ electrolyte. For solid electrolyte (SEI) films, along with the destruction of the electrode structure, new SEI films are continuously formed on the newly exposed silicon surface, resulting in a decrease in charge-discharge efficiency and aggravation of capacity fading.

Based on this, overcoming the above defects becomes the research focus of the present invention.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a kind of foam nickel collector multilayer silicon/graphene composite lithium battery negative electrode material and preparation method thereof for the defect of the above-mentioned silicon negative electrode, the multilayer silicon/graphene composite lithium battery negative electrode material adopts multilayer The silicon/graphene alternating structure forms a multi-layer "graphene/silicon/graphene" sandwich structure, and the high mechanical properties and high electrical conductivity of graphene are used to wrap the silicon powder in layers, which can effectively improve the cycle performance of the silicon anode and make it Meets performance standards for commercial lithium-ion batteries.

To achieve the above object, the technical scheme adopted in the present invention is:

A multi-layer silicon/graphene composite lithium battery negative electrode material, comprising nickel foam, graphene layers and silicon layers alternately arranged on the nickel foam, and the topmost layer is a graphene layer; wherein the number of silicon layers is n, 1≤n≤20, the number of graphene layers is n+1.

Further, the preparation method of the above-mentioned multilayer silicon/graphene composite lithium battery negative electrode material comprises the following steps:

Step 1. Press the foam nickel into a disc, and clean it for later use;

Step 2, adding graphene oxide powder into absolute ethanol, ultrasonically dispersing for 30-60min, and preparing a graphene oxide solution of 1-5M;

Step 3, cleaning the nano-silicon, and then adding the nano-silicon into the mixed solution whose volume ratio is absolute ethanol:ethylene glycol=9:1, to prepare a silicon dispersion solution with a concentration of 1-5M;

Step 4, soak the nickel foam into the graphene oxide solution, take it out and dry it in an inert atmosphere at 60-90°C for 10-15 minutes;

Step 5. Infiltrate the nickel foam after the treatment in step 4 into the silicon dispersion solution, take it out and dry it in an inert atmosphere at 60-90°C for 5-10 minutes;

Step 6, repeating steps 4 to 5, to prepare a silicon/graphene composite lithium battery negative electrode material with the number of silicon layers n, 1≤n≤20;

Step 7, using a tablet press to press the silicon/graphene composite negative electrode material prepared in step 6 into a sheet at 8-10Mpa;

Step 8. Put the sheet into a vacuum tube furnace, and reduce graphene oxide in an inert atmosphere at 550-650° C. to obtain a negative electrode material for a foamed nickel collector multilayer silicon/graphene composite lithium battery.

Further, the cleaning process of the nickel foam in the step 1 is as follows: preparing a 4-6M hydrochloric acid solution, adding the nickel foam pressed into a disc into the hydrochloric acid solution, ultrasonically cleaning for 10-20 minutes, and then cleaning with anhydrous ethanol.

The cleaning process of the nano-silicon in the step 3 is as follows: drop HF into a mixed solution with a volume ratio of absolute ethanol:deionized water=1:1 to prepare a 4-6M HF solution; then add the nano-silicon into the HF solution , ultrasonic cleaning for 10-20min, centrifugation or suction filtration.

The heat treatment process of the vacuum tube furnace in the step 8 is as follows: the heating rate is 5°C/min, the temperature is raised to 550-650°C, and the temperature is kept for 2 hours.

The inert gas in the steps 1 to 8 includes all common inert gases, such as nitrogen, argon and the like.

The beneficial effects of the present invention are:

The invention provides a negative electrode material of a foamed nickel collector multilayer silicon/graphene composite lithium battery, which adopts a multilayer silicon/graphene alternating structure to form a multilayer "graphene/silicon/graphene" sandwich structure, and utilizes the graphene The high mechanical properties and high electrical conductivity encapsulate the silicon powder in layers, which can effectively suppress the huge volume change of the silicon powder during the charging and discharging process, which is conducive to the formation of a stable SEI film, and improves the rate characteristics while maintaining the high specific capacity of silicon. Cycling stability; the anode material of the multilayer silicon/graphene composite lithium battery can be charged and discharged for 500 cycles at 3A·g ^-1 current, and still has a cycle retention rate of more than 60%; at 0.2, 0.4, 1, 2, 4 , 8, 16A·g ^-1 step charge-discharge current changes, the corresponding specific capacities are 2190, 1920, 1715, 1520, 1270, 960mAh·g ^-1 respectively; it fully shows that it has high current charge and discharge capacity and good cycle charge The discharge performance can meet the negative electrode application of next-generation lithium-ion batteries. At the same time, the present invention provides a method for preparing the multi-layer silicon/graphene composite lithium battery negative electrode material, the method has the advantages of simple process, low cost and good repeatability; the preparation of the multi-layer silicon/graphene composite lithium battery negative electrode material has the advantages of High current charge and discharge capability and good cycle charge and discharge performance.

Description of drawings

Fig. 1 is the XRD diffraction spectrum of the 5-layer silicon/graphene composite negative electrode material in the embodiment.

Fig. 2 is the Raman spectrum of the 5-layer silicon/graphene composite negative electrode material in the embodiment.

FIG. 3 is a specific capacity diagram for 500 cycles of the 5-layer silicon/graphene composite negative electrode material in the embodiment.

FIG. 4 is a rate cycle specific capacity diagram of the 5-layer silicon/graphene composite negative electrode material in the embodiment.

Detailed ways

The present invention will be specifically described below with reference to the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto.

Example 1

This embodiment provides the preparation of a 5-layer foam nickel collector silicon/graphene composite lithium battery negative electrode material, which includes the following steps:

Step 1. Pretreatment of nickel foam: prepare a 4M hydrochloric acid solution, add the nickel foam pressed into discs into the hydrochloric acid solution, ultrasonically clean for 20 minutes, and then clean with absolute ethanol;

Step 2, adding graphene oxide powder into absolute ethanol, ultrasonically dispersing for 60min, and preparing a 1M graphene oxide solution;

Step 3. Drop HF into a mixed solution with a volume ratio of absolute ethanol:deionized water=1:1 to prepare a 5M HF solution; then add the nano-silicon into the HF solution, ultrasonically clean for 20min, and then centrifuge or filter with suction; The cleaned nano-silicon is added to the mixed solution whose volume ratio is absolute ethanol:ethylene glycol=9:1, and the preparation concentration is 1M silicon dispersion solution;

Step 4. Infiltrate the nickel foam (pull out after being completely immersed in the solution) into the graphene oxide solution, and dry it in an inert atmosphere at 80° C. for 15 minutes after taking it out;

Step 5. Immerse the nickel foam into the silicon solution, take it out, and dry it in an inert atmosphere at 80°C for 10 minutes;

Step 6, repeating steps 4 and 5, to prepare a composite lithium battery negative electrode material with 2 silicon layers, 3 graphene layers, and 5 layers in total;

Step 7, pressing the negative electrode material of the multi-layer silicon/graphene oxide composite lithium battery with nickel foam as the collector electrode into thin sheets with 10Mpa on the tablet press;

Step 8. Put the composite electrode sheet into a vacuum tube furnace, and reduce graphene oxide under an inert atmosphere at 600 ° C to obtain a nickel foam collector multilayer silicon/graphene composite lithium battery negative electrode material; wherein the heating rate of the heat treatment is 5 ℃/min, the temperature was raised to 600℃, and the temperature was kept for 2h.

The structure and electrical properties of the negative electrode material of the 5-layer foam nickel collector silicon/graphene composite lithium battery prepared above were characterized and tested, and the results are as follows:

1. Structural characteristics

As shown in Figure 1, the three strong peaks (110), (220) and (310) in the XRD of the 5-layer silicon/graphene composite negative electrode are consistent with the pattern of silicon; the (002) peak corresponding to graphite at 26° broadens, This is due to the diffraction peak broadening effect caused by the thin number of graphene layers; indicating that silicon and graphene coexist in the composite structure.

As shown in Fig. 2, in the Raman spectrum of the 5-layer silicon/graphene composite anode, a thin and high peak at 513 cm ^-1 corresponds to the silicon nanomaterial; at 1305 cm ^-1 corresponds to the D peak of graphene, which is due to dispersion and defects The resulting peak; the G peak corresponding to graphene at 1590 cm ^-1 , which is the vibration peak of sp ² carbon atoms bonding; the D peak intensity is significantly stronger than the G peak, indicating that graphene oxide has been reduced to graphene.

2. Electrical properties

As shown in Figure 3, the 5-layer silicon/graphene composite anode has good cycling characteristics, and it still has a cycle retention rate of 60% after 500 cycles at a current of 3 A·g ⁻¹ . As shown in Figure 4, the specific capacity diagrams at different current rates, at 0.2, 0.4, 1, 2, 4, 8, and 16 A·g ^-1 current rates, the corresponding specific capacities are 2190, 1920, 1715, and 1520, respectively. , 1270, 960mAh·g ^-1 ; can meet the charge and discharge of large current, with good rate characteristics.

Example 2

3-layer, 7-layer, 9-layer, and 11-layer silicon/graphene composite lithium battery negative electrode materials were prepared by the same process in Example 1, and their structure and electrical properties were characterized and the test results maintained the same characteristics as Example 1.

In short, through the design of material structure, layered graphene encapsulates silicon nanopowders, so that the volume change of silicon during charging and discharging will not affect the cycling effect, thereby forming a stable SEI film; the preparation method is a simple and practical , and the effective preparation method of high-performance silicon composite anode can realize the commercial application of silicon in lithium-ion batteries.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (3)

1. A preparation method of a multilayer silicon/graphene composite lithium battery cathode material comprises foamed nickel, graphene layers and silicon layers, wherein the graphene layers and the silicon layers are sequentially and alternately arranged on the foamed nickel, and the graphene layer is arranged on the topmost layer; wherein the number of the silicon layers is n, n is more than or equal to 1 and less than or equal to 20, and the number of the graphene layers is n + 1; the multilayer silicon/graphene composite lithium battery negative electrode material is 3 A.g^-1The charge and discharge cycle is 500 circles under current, and the cycle retention rate is over 60 percent; the preparation method of the multilayer silicon/graphene composite lithium battery cathode material comprises the following steps:

step 1, pressing foamed nickel into a wafer, and cleaning for later use;

step 2, adding graphene oxide powder into absolute ethyl alcohol, and performing ultrasonic dispersion for 30-60min to prepare a 1-5M graphene oxide solution;

step 3, cleaning the nano silicon, and then adding the nano silicon into absolute ethyl alcohol: preparing a silicon dispersion solution with the concentration of 1-5M in a mixed solution of 9:1 ethylene glycol;

step 4, soaking the foamed nickel into the graphene oxide solution, taking out the foamed nickel, and drying the foamed nickel in an inert atmosphere at the temperature of 60-90 ℃ for 10-15 min;

step 5, soaking the foamed nickel treated in the step 4 into a silicon dispersion solution, taking out and drying in an inert atmosphere at the temperature of 60-90 ℃ for 5-10 min;

step 6, repeating the steps 4 to 5 to prepare the silicon/graphene composite lithium battery cathode material with n silicon layers and n being more than or equal to 1 and less than or equal to 20;

step 7, pressing the silicon/graphene composite lithium battery cathode material prepared in the step 6 into a sheet at 8-10 Mpa by using a tablet press;

and 8, putting the slices into a vacuum tube furnace, and reducing graphene oxide in an inert atmosphere at 550-650 ℃, wherein the heat treatment process of the vacuum tube furnace is as follows: the temperature rising speed is 5 ℃/min, the temperature rises to 550-650 ℃, and the temperature is kept for 2 h; and obtaining the multilayer silicon/graphene composite lithium battery cathode material of the foamed nickel collector.

2. The preparation method of the multilayer silicon/graphene composite lithium battery anode material according to claim 1, wherein the cleaning process of the nickel foam in the step 1 is as follows: preparing a 4-6M hydrochloric acid solution, adding foamed nickel pressed into a wafer into the hydrochloric acid solution, ultrasonically cleaning for 10-20min, and then cleaning with absolute ethyl alcohol.

3. The preparation method of the multilayer silicon/graphene composite lithium battery anode material according to claim 1, wherein the cleaning process of the nano-silicon in the step 3 is as follows: dropping HF into absolute ethyl alcohol: deionized water 1: 1, preparing 4-6M HF solution; and then adding the nano silicon into an HF solution, carrying out ultrasonic cleaning for 10-20min, and then centrifuging or carrying out suction filtration.

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