CN107887587A - Composite cathode material for lithium ion cell and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of composite cathode material for lithium ion cell and preparation method thereof, and nanometer silicon face progress oxidation processes are obtained into Surface coating the nano-silicon of silica；The nano-silicon that Surface coating has silica is well mixed with lithium source, obtains presoma；Gained presoma is placed in the nano silicon material for being heated in inert gas and obtaining being coated with lithium metasilicate, is washed, centrifuged, obtaining composite cathode material for lithium ion cell after drying.The present invention is matrix by using the uniform native oxide in nano silicon material surface, carry out the uniform cladding that in-situ chemical reaction realizes lithium metasilicate, the stability between nano-silicon and air or electrolyte interface is effectively improved, so as to greatly improve the chemical property of nano silicon material.

Description

Lithium-ion battery composite negative electrode material and preparation method thereof

technical field

The invention relates to the technical field of lithium ion battery material preparation, in particular to a lithium ion battery composite negative electrode material and a preparation method thereof.

Background technique

With the development of human society, the energy crisis and environmental issues have increasingly become the focus of attention. The clean and efficient use of traditional energy and the development of new energy technologies have become the main trend. Lithium-ion batteries have high performance, safety and environmental protection It is currently the most promising high-energy green secondary battery for development and application prospects. However, in recent years, the demand for battery energy density in various fields has increased rapidly. In particular, the country has accelerated the promotion and application of new energy vehicles, and new high-energy Density batteries have become a hot spot in current research and development. The energy density of batteries mainly depends on electrode materials, and new electrode materials support the development of a new generation of chemical power sources. In the research of new non-carbon negative electrode materials, silicon-based materials have high theoretical specific capacity at room temperature. (3579mAh/g), low lithium extraction potential (0.02-0.6V vs. Li ⁺ /Li), environmental friendliness, abundant reserves and other advantages, it is considered to be the next generation high energy density lithium ion battery negative electrode with the most potential to replace graphite Material.

There are two key problems in the large-scale application of silicon-based materials. First, silicon is an alloy-type lithium storage material. During the process of deintercalating lithium, the crystal structure of silicon changes, causing a huge volume effect in the electrode material, resulting in electrode material powder. The active material loses effective electrical contact and shows poor cycle stability. Secondly, the direct contact between the silicon material and the electrolyte leads to the continuous growth of the interfacial SEI film. In this process, the limited electrolyte in the battery system will be continuously consumed and lithium from the positive electrode, eventually leading to a rapid decline in battery capacity. The main solution to these problems is the design of material nanostructures and the development of new electrolytes. Due to the large specific surface area of nanomaterials, the short diffusion path of lithium ions, and the reserved space between particles The advantages of large space can significantly improve the electrochemical performance of silicon-based materials. However, nano-silicon materials are easily oxidized into silicon dioxide due to their large specific surface area and high surface activity, and the oxidized nano-silicon materials show a low reversible ratio. Capacity, or even loss of electrochemical activity. The oxidation of nano-silicon puts forward stricter requirements for its storage and application in actual production.

Studying the native oxide layer on the surface of nano-silicon can promote the formation of a stable SEI film at the electrode/electrolyte interface, and reasonably controlling the thickness of the surface oxide layer can improve the electrochemical performance of the material. In the battery, the surface silicon dioxide will undergo the following reaction: SiO ₂ + Li→Si+Li _x SiO _y . The lithium silicate layer with good plasticity and mechanical properties can stably exist at the electrode/electrolyte interface, which can effectively protect the internal silicon material from electrolyte erosion. Lithium silicate is a fast ion conductor and has a higher density than silicon dioxide. High electronic conductivity. However, in the battery system, the gradual transformation of silicon dioxide into lithium silicate is an irreversible reaction, which will also consume part of the lithium ions in the battery. How to effectively realize the in-situ chemical reaction on the surface of nano-silicon to form a layer of lithium silicate coating, and greatly improve the stability of the interface between nano-silicon and electrolyte has a good application prospect.

Lithium silicate coating has been reported in the positive and negative electrodes of lithium-ion batteries: Chinese patent application number 201610045279.4 proposes to use lithium silicate to modify lithium titanate negative electrode materials. The method is to directly add lithium silicate for surface coating, which cannot Treatment of the surface oxide layer does not improve the electrochemical performance of the material; Chinese patent application number 201610887984.9 proposes a method for preparing a silicon/oxide composite negative electrode material with a lithium silicate interface layer. The method is to use lithium hydroxide to precipitate metal oxide The compound and the accompanying lithium silicate layer cannot effectively solve the problem of silicon surface oxidation. The lithium source in this patent can only promote the formation of lithium hydroxide of metal oxides, which has certain limitations.

Aiming at the problems in the related technologies, no effective solution has been proposed yet.

Contents of the invention

Aiming at the above-mentioned technical problems in the related art, the present invention proposes a composite negative electrode material for lithium-ion batteries, which can utilize the native oxide layer on the surface of the nano-silicon material, and perform an in-situ chemical reaction on the surface of the nano-silicon by pre-adding a lithium source to generate a layer of silicon. Lithium acid coating layer can greatly improve the stability of the interface between nano-silicon and electrolyte, and at the same time, it can alleviate the damage of the electrode due to the volume change of silicon. The preparation process is simple and controllable, which solves the problems of easy oxidation of nano-silicon and abnormal capacity. .

For realizing above-mentioned technical purpose, technical scheme of the present invention is realized like this:

On the one hand, the present invention provides a kind of preparation method of lithium-ion battery composite negative electrode material, comprises the steps:

Step 1): Oxidize the surface of nano-silicon to obtain nano-silicon coated with silicon dioxide;

Step 2): Nano-silicon coated with silicon dioxide on the surface and lithium source are evenly mixed to obtain a precursor;

Step 3): heating the precursor obtained in step 2) in an inert gas to obtain a nano-silicon material coated with lithium silicate;

Step 4): The obtained nano-silicon material is washed, centrifuged and dried to obtain a lithium-ion battery composite negative electrode material.

Further, the total mass ratio of silicon dioxide in the nano-silicon coated with silicon dioxide on the surface is 1-20%. Preferably, the mass ratio is 1%, 2%, 5%, 8%, 10%, 15%, 20%.

Further, the nano-silicon in the step 1) is one or more of silicon nanospheres, silicon nanowires, porous nano-silicon, and silicon-based composite materials. Preferably, the silicon-based composite material is silicon/graphite, silicon/graphene and the like.

Further, the method of oxidation treatment in step 1) includes: one or more of the methods of oxidizing the surface of nano-silicon by exposure to air, oxidizing the surface of nano-silicon by using an oxidant, and oxidizing the surface of nano-silicon by low-temperature heat treatment. kind. The nano-silicon is naturally oxidized when exposed to the air, by simulating the oxidation process of the material in practical application. The oxidizing agent used to oxidize the surface of nano-silicon can be slowly adding nano-silicon powder into hydrogen peroxide solution, the concentration of hydrogen peroxide is not higher than 30%, and after ultrasonic dispersion, magnetically stir in an oil bath at 60-90°C for 0.5-6 hours, filter the silicon powder in the solution, wash it with deionized water and ethanol in turn, and finally carry out vacuum drying to complete the surface treatment process of nano-silicon. The low-temperature heat treatment to oxidize the nano-silicon surface may be placing the nano-silicon material in a tube furnace to heat and hold for a certain period of time, and the heating temperature is not higher than 600°C.

Furthermore, the oxidizing agent is used to oxidize the nano-silicon surface, and the oxidizing agent includes hydrogen peroxide, a mixed solution of hydrogen peroxide and concentrated sulfuric acid, concentrated sulfuric acid solution, and the like.

Further, the lithium source is one or more of lithium carbonate, lithium oxalate, lithium acetate, lithium phosphate, lithium tartrate, lithium citrate, lithium molybdate, and lithium titanate.

Further, the molar ratio of lithium in the lithium source to silicon dioxide in nano-silicon coated with silicon dioxide on the surface is 0.4-8. Preferably, the molar ratio is 0.4, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0.

Further, the nano-silicon coated with silicon dioxide on the surface of the step 2) is dissolved in a solvent and dispersed evenly with the lithium source by ultrasonic, and the nano-silicon material coated with lithium silicate is obtained after removing the solvent.

Furthermore, the solvent is reasonably selected according to the selected lithium source, preferably water, ethanol, etc.; preferably water is deionized water.

Furthermore, the solvent removal method includes one or more of solvent evaporation, blast drying, vacuum drying, freeze drying, and spray drying.

Further, in the step 2), the nano-silicon coated with silicon dioxide on the surface is uniformly mixed with the lithium source in solid phase to obtain a nano-silicon material coated with lithium silicate.

Furthermore, the solid-phase mixing includes one or more of grinding, high-energy ball milling, and high-energy sand milling.

Further, the inert gas in step 3) includes argon, hydrogen-argon mixed gas, nitrogen and the like.

Further, the heating temperature in step 3) is controlled at 550-950° C., and the temperature is controlled at 550-950° C. for 1-12 hours. Preferably, the temperature is controlled at 900°C, 700°C, 550°C; the temperature holding time is 1h, 2h, 5h, 10h, 12h.

Further, the lithium silicate in step 3) includes one or more of lithium monosilicate, lithium disilicate, and lithium pentasilicate.

Further, the surface of the nano-silicon material coated with lithium silicate obtained in step 3) is also coated with a carbon layer.

Further, the solvent used for washing in step 4) is ethanol or deionized water.

Further, the drying in step 4) adopts vacuum drying.

On the other hand, the present invention provides a lithium ion battery composite negative electrode material prepared by the method described in the present invention, comprising nano-silicon and a lithium silicate layer coated on the surface of the nano-silicon.

On the other hand, the present invention provides a lithium ion battery composite negative electrode material prepared by the method of the present invention, comprising nano-silicon, a lithium silicate layer and a carbon layer coated on the surface of the nano-silicon.

On the other hand, the present invention provides a negative electrode of a lithium ion battery, which is prepared by using the composite negative electrode material of the lithium ion battery described in the present invention as a raw material.

In another aspect, the present invention provides a lithium ion battery, including the negative electrode of the lithium ion battery described in the present invention.

In order to improve the interface stability between nano-silicon and electrolyte and solve the problem that the surface of nano-silicon is easy to oxidize, the present invention designs a silicon dioxide layer based on the surface of nano-silicon, and adopts in-situ chemical reaction to form a lithium silicate coating layer. The nano-silicon negative electrode material, that is, the lithium-ion battery composite negative electrode material. As a general design concept, the nano-silicon material is used as an active material, and the surface is self-oxidized or oxidized to form a layer of nano-silicon dioxide. The oxidized nano-silicon material is mixed with a lithium source, and after high-temperature treatment, the silicon oxide and lithium The source reaction forms a lithium silicate layer, thereby preparing a lithium-ion battery composite negative electrode material.

In the preparation process of the present invention, if the selected lithium source has a polymer functional group, a part of the carbon layer will be formed while reacting at high temperature in an inert atmosphere, thereby forming a double protection of in-situ lithium silicate and pyrolytic carbon. layer structure.

The storage performance of the lithium-ion battery composite negative electrode material prepared by the invention is greatly improved in the air, and the electrode/electrolyte interface stability and electrochemical cycle stability in the battery are obviously improved.

The invention utilizes the problems such as easy oxidation and abnormal capacity performance of nano-silicon materials in the actual application process, and based on the original oxide layer on the surface of nano-silicon, adopts in-situ chemical reaction to coat the surface with lithium silicate. The synthesized lithium silicate has good mechanical properties and ionic conductivity, and the in-situ chemical coating can achieve uniform coating on the silicon surface, and can better isolate the silicon from being eroded by the electrolyte. The generated lithium silicate layer can stably exist at the electrode/electrolyte interface, and will not consume the electrolyte in the battery system or lithium in the positive electrode. Lithium silicate does not participate in the deintercalation reaction, and there will be no phenomenon such as phase transition that will cause the coating layer to fall off or pulverize. In addition, the lithium silicate layer exhibits better stability in the air, thereby better improving the storage performance of nano-silicon materials in practical applications.

Beneficial effects of the present invention: the lithium-ion battery composite negative electrode material prepared by the present invention uses the uniform native oxide layer on the surface of the nano-silicon material as a matrix to perform an in-situ chemical reaction to achieve uniform coating of lithium silicate, effectively improving the contact between nano-silicon and air. Or the stability between the electrolyte interface, thereby greatly improving the electrochemical performance of nano-silicon materials.

The preparation method of the lithium-ion battery composite negative electrode material provided by the invention adopts the high-temperature reaction of lithium source and nano-silicon, and has short preparation process, low cost, high controllability, high stability of the obtained material, and is suitable for mass production and application.

At present, there is no report on the preparation of composite anode materials for lithium-ion batteries by in-situ chemical reactions based on silicon oxidation.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is the XRD collection of illustrative plates of the material obtained in preferred embodiment 1 of the present invention;

Fig. 2 is the TEM collection of illustrative plates of preferred embodiment 1 gained material of the present invention;

Fig. 3 is the cycle performance figure that the material obtained in preferred embodiment 1 of the present invention is assembled into a button battery;

Fig. 4 is the microstructure characterization collection of materials obtained in preferred embodiment 2 of the present invention;

Fig. 5 is the cycle performance figure that the material obtained in preferred embodiment 2 of the present invention is assembled into a button battery;

Fig. 6 is the XRD spectrum of the material obtained in preferred embodiment 3 of the present invention;

Fig. 7 is the XPS spectrum of the material obtained in preferred embodiment 3 of the present invention.

In the figure: silicon, intensity, theta θ, degree °, voltage, specific capacity, cycle number, charge, discharge, counts, binding energy.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention belong to the protection scope of the present invention.

Unless otherwise defined, all professional terms used hereinafter have the same meaning as those skilled in the art generally understand. The professional terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention ｡

Unless otherwise specified, various reagents and raw materials used in the present invention are commercial products that can be purchased from the market or products that can be prepared by known methods.

Example 1

After 0.8 g of nano-silicon particles were placed in humid air for one week, the nano-silicon was dissolved in 50 mL of deionized water at 10°C. Then add 0.05g of lithium carbonate, stir evenly, disperse ultrasonically, control the temperature to be constant during the process, and then freeze-dry the solution to obtain the precursor.

The obtained precursor was placed in an argon atmosphere tube furnace, heated to 900°C at 5°C/min, kept at a constant temperature for 2h, and cooled naturally to obtain a nano-silicon material coated with lithium silicate.

Subsequently, the nano-silicon material coated with lithium silicate is washed with deionized water, centrifuged at a high speed, and vacuum-dried to obtain a lithium-ion battery composite negative electrode material.

The physical and chemical properties of the obtained lithium-ion battery composite negative electrode material are shown in Figure 1, Figure 2, and Figure 3. The XRD results in Figure 1 show that the surface of the lithium-ion battery composite anode material is composed of lithium metasilicate and lithium silicate phases, without other impurity phase peaks, and the characteristic peaks of silicon still maintain a good crystal form. From the TEM image in Figure 2, it can be seen that there is a layer of silicon dioxide with uniform thickness on the surface of nano-silicon after oxidation. After treatment, the surface amorphous silicon dioxide layer is transformed into a layer of uniform lithium silicate layer. The resulting lithium-ion battery composite anode material was assembled into a button battery to measure its cycle performance. As shown in Figure 3, at a current density of 200 mA/g, the capacity of the oxidized nano-silicon is only 2400 mAh/g, which is far lower than its theoretical capacity. The specific capacity, and the first coulombic efficiency is only 76%, while the first coulombic efficiency of the nano-silicon material after in-situ chemical reaction treatment is increased to 86%. In addition, there is no change in the charge-discharge curve before and after treatment, indicating that lithium silicate is not electrochemically active, and the specific capacity of the lithium-ion battery composite negative electrode material after coating is reduced. This is because the reversible specific capacity is based on all silicon materials, lithium silicate The introduction reduces the mass ratio of the active silicon material. It can be seen from the cycle performance that the cycle stability of the lithium-ion battery composite negative electrode material obtained after treatment has been greatly improved, which is attributed to the fact that the lithium silicate coating layer improves the stability of the interface between silicon and electrolyte.

Example 2

Take 0.5g of nano-silicon and add 50ml of 10% hydrogen peroxide, stir and ultrasonically disperse, filter and dry in vacuum at 80°C. At room temperature, dissolve the treated nano-silicon in 50ml of ethanol, stir and ultrasonically disperse, add 0.5g of anhydrous lithium acetate, continue to stir and ultrasonically disperse uniformly for 1h. The solution was then freeze-dried to obtain the precursor.

The obtained precursor was placed in an argon atmosphere tube furnace, heated to 700°C at 5°C/min, kept at a constant temperature for 5h, and cooled naturally to obtain nano-silicon materials coated with lithium silicate and carbon layers.

Subsequently, the nano-silicon material coated with lithium silicate and carbon layer is washed with deionized water, centrifuged at a high speed, and vacuum-dried to obtain a lithium-ion battery composite negative electrode material.

The microstructure characterization of the obtained lithium-ion battery composite anode material is shown in Figure 4, and the cycle performance is shown in Figure 5. The high-temperature thermal decomposition products of anhydrous lithium acetate (C ₂ H ₃ LiO ₂ ) in an inert atmosphere are mainly water, lithium oxide and organic carbon phase. Lithium oxide and silicon dioxide form a lithium silicate layer, and the organic carbon phase is coated on the surface of the material. An amorphous carbon layer is formed. It can be seen from Figure 4 that after treatment, the nano-silicon still maintains a good crystal form and spherical structure, and the surface is a coating layer where lithium silicate and amorphous carbon coexist. The resulting lithium-ion battery composite negative electrode material was assembled into a button battery to measure its cycle performance. As shown in Figure 5, under the high-current test condition, the capacity retention rate of the oxidized nano-silicon was only 24.% after 200 cycles, while after The capacity of the obtained lithium-ion battery composite negative electrode material after treatment remained at 70.9%. It can be seen from the cycle performance that the cycle stability of the lithium-ion battery composite negative electrode material obtained after treatment has been greatly improved, which is attributed to the designed coating layer in which lithium silicate and carbon coexist. Lithium silicate and carbon layer can effectively hinder the direct contact between electrolyte and silicon, electrolyte can form a stable solid electrolyte layer on the surface of carbon layer, lithium silicate layer and carbon layer with good mechanical properties can effectively inhibit the volume expansion of silicon .

Example 3

Take nano-silicon and add 50ml of 10% hydrogen peroxide, stir and ultrasonically disperse, filter and dry in vacuum at 80°C. At room temperature, the treated nano-silicon and lithium oxalate were mixed in a mass ratio of 2:1. The mixture was milled in a high-speed vibrating ball mill at 1200 rpm for 3 h to obtain a precursor.

The obtained precursor was placed in an argon atmosphere tube furnace, heated to 900°C at 5°C/min, kept at a constant temperature for 5h, and cooled naturally to obtain a nano-silicon material coated with lithium silicate.

Subsequently, the nano-silicon material coated with lithium silicate is washed with deionized water, and vacuum-dried after high-speed centrifugation to obtain a lithium-ion battery composite negative electrode material.

Figure 6 is the XRD spectrum of the obtained lithium-ion battery composite negative electrode material. The results show that the lithium-ion battery composite negative electrode material is composed of nano-silicon, lithium disilicate and lithium pentasilicate, and the nano-silicon still maintains a good crystal structure without other impurities. Matter is generated. Figure 7 is the XPS spectrum of oxidized nano-silicon and lithium silicate-coated nano-silicon. The results show that after oxidation treatment, the silicon dioxide on the surface of nano-silicon is much higher than the characteristic peak of silicon. The characteristic peak of silicon element in the obtained material silicon dioxide after lithium silicate treatment is reduced. The new characteristic peaks appearing between 100-103 correspond to the silicon element in lithium silicate, which indicates that the main component of nano-silicon surface is lithium silicate phase.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. a kind of preparation method of composite cathode material for lithium ion cell, it is characterised in that comprise the following steps：

Step 1）：Nanometer silicon face progress oxidation processes are obtained into Surface coating the nano-silicon of silica；

Step 2）：The nano-silicon that Surface coating has silica is well mixed with lithium source, obtains presoma；

Step 3）：By step 2）Gained presoma is placed in the nano silicon material that heating in inert gas obtains being coated with lithium metasilicate；

Step 4）：Gained nano silicon material is washed, centrifuged, obtains lithium ion battery composite cathode material after drying Material.

2. preparation method according to claim 1, it is characterised in that the Surface coating has in the nano-silicon of silica Silica accounts for its total mass ratio as 1 ~ 20%；

The step 1）Middle nano-silicon is silicon nanosphere, silicon nanowires, porous nano silicon, one kind in silicon based composite material or several Kind.

3. preparation method according to claim 1, it is characterised in that the step 1）The mode of middle oxidation processes includes： Nano-silicon exposes autoxidation in atmosphere, nanometer silicon face is aoxidized using oxidant and using Low Temperature Heat Treatment to receiving One or more in the mode that rice silicon face is aoxidized.

4. preparation method according to claim 1, it is characterised in that the lithium source be lithium carbonate, lithium oxalate, lithium acetate, One or more in lithium phosphate, lithium tartrate, lithium citrate, lithium molybdate, lithium titanate；

It is 0.4 ~ 8 that lithium and Surface coating, which have the mol ratio of silica in the nano-silicon of silica, in the lithium source.

5. preparation method according to claim 1, it is characterised in that step 2）In, the Surface coating has silica Nano-silicon dissolving in a solvent after it is uniform with lithium source ultrasonic disperse, obtain being coated with the nano-silicon material of lithium metasilicate after removal solvent Material；Or the Surface coating has the nano-silicon of silica and lithium source solid phase mixing uniformly to obtain being coated with the nano-silicon of lithium metasilicate Material；

The mode for removing solvent includes one in solvent evaporation, forced air drying, vacuum drying, freeze-drying, spray drying Kind is several；

The solid phase mixing includes the one or more in grinding, high-energy ball milling, high energy sand milling.

6. preparation method according to claim 1, it is characterised in that step 3）Described in inert gas include argon gas, nitrogen Gas；

Step 3）Described in the temperature control that heats at 550 ~ 950 DEG C, the temperature control keeps 1 ~ 12h at 550 ~ 950 DEG C；

The step 3）Middle lithium metasilicate includes the one or more in a lithium metasilicate, lithium bisilicate, five lithium metasilicates.

7. preparation method according to claim 1, it is characterised in that the step 3）What is obtained is coated with receiving for lithium metasilicate Rice silicon materials surface is also wrapped on carbon-coating.

8. composite cathode material for lithium ion cell prepared by a kind of any described method of claim 1 ~ 7, it is characterised in that bag Include nano-silicon and be coated on the lithium silicate of nanometer silicon face；

Or including nano-silicon, be coated on the lithium silicate and carbon-coating of nanometer silicon face.

9. a kind of negative electrode of lithium ion battery, it is characterised in that including with the lithium ion battery composite cathode material described in claim 8 Expect to prepare for raw material.

10. a kind of lithium ion battery, it is characterised in that including the negative electrode of lithium ion battery described in claim 9.