CN100391034C - Lithium battery electrode material Li2S/Co nanometer compound film and its preparation method - Google Patents

Abstract

The invention belongs to the technical field of electrochemistry, and specifically relates to an electrode active material for lithium ion batteries and a preparation method thereof. The material is a nanocomposite film composed of Li ₂ S and transition metal element Co, which can be prepared by a pulse laser deposition method, and the particle size of the Li ₂ S/Co nanocomposite is less than 50nm. The specific capacity of the thin film electrode varies with the transition metal element Co in the range of 400-650mAh/g, and shows good stability in the process of repeated charge and discharge. The thin film electrode material has high specific capacity, good cycle performance and simple preparation method, and is suitable for thin film lithium ion batteries.

Description

A kind of lithium battery electrode material Li2S/Co nanocomposite thin film and preparation method thereof

technical field

The invention belongs to the technical field of electrochemistry, and specifically relates to a Li ₂ S/Co nanocomposite film and a preparation method thereof.

Background technique

Lithium-ion batteries have attracted great attention due to their advantages such as high operating voltage and high energy density. At present, lithium-ion batteries have been widely used in mobile phones, notebook computers, digital video cameras, cameras and other electronic equipment, and may be used as green energy in automobiles and other vehicles. At present, the commonly used cathode materials for lithium-ion batteries mainly include LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ . Although this type of cathode material has good electrochemical performance, it is restricted by factors such as high price, low specific capacity, complicated preparation and purification process, especially the problem of low specific capacity, which seriously limits its better development. . Although people have done a lot of research, it is still difficult to make the specific capacity exceed 180mAh/g.

In the research field of lithium-ion batteries, sulfur, as a material with high theoretical capacity (1672mAh/g) and low price and cost, is generally valued. However, elemental sulfur is difficult to be directly used as an electrode material due to its inherent insulating properties and the easy decomposition of reaction products in the electrolyte. Recently, Jiulin Wang et al. (Jiulin Wang. et al. Adv. Funct. Mater. 2003, 13, No 6, June) embedded sulfur particles in conductive organic matter, and successfully obtained lithium with good cycle performance and a capacity of 600mAh/g sulfur battery. Nobuya Machida et al. (Nobuya Machida. et al. Solid State Ionics. 175, 247-250 (2004)) mixed sulfur element with metal copper and a small amount of acetylene black to make powder electrode materials by ball milling, and also produced a powder electrode material with a capacity exceeding 980mAh/g lithium-sulfur battery. However, MNObrovac et al. (MNObrovac.et al.Electrochem.Solid-State Lett.5(4)A70-A73(2002)) tried to mix Li ₂ S and Fe by ball milling, and then charge and discharge, but its reversible capacity was only 170mAh /g or so, and the attenuation is fast. So far, no research has reported Li ₂ S/Co mixtures as electrode materials for lithium-ion batteries.

The invention proposes to use the nanoscale mixture of Li ₂ S and metal Co to prepare thin-film electrode materials by pulse laser deposition, and provides a high-capacity electrode material not only containing electrochemically active lithium, but also having good charge-discharge cycle performance. The main principle is as follows: the pulsed laser deposition technology is used to highly disperse and mix Li ₂ S and Co, and obtain a nanocomposite film on the substrate. Among them, the particle size of the film is less than 50nm, preferably below 20nm, which can greatly reduce the electrochemical internal resistance of the reaction system, improve the utilization rate of active materials in the reaction system, and finally improve the electrochemical capacity and cycle performance of the system.

Contents of the invention

The object of the present invention is to provide a lithium ion battery electrode material with good charge-discharge cycle performance and high electrochemical capacity and a preparation method thereof.

The electrode active material of the lithium ion battery proposed by the invention. It is a nanocomposite thin film prepared by pulsed laser deposition after uniformly mixing Li ₂ S and transition metal Co, wherein the molar ratio of Li ₂ S and transition metal Co is 1:x, 2>x>0.5.

Among the above electrode materials, the particle size of Co is less than 50nm, preferably less than 20nm; the particle size of Li ₂ S is less than 50nm, typically less than 20nm.

The advantage of the present invention is that the nano-mixture of Li ₂ S and transition metal Co is directly used to form an electrochemically active electrode material, which not only can provide a lithium source during charge and discharge, but also has good charge and discharge cycle performance and high Specific capacity (up to 400-650mAh/g); the preparation process of the mixture does not require the high-temperature reaction or high-energy ball milling process of traditional electrode materials, but only needs to adopt certain methods to make the composite below the nanometer level (50nm). Therefore, it has the obvious advantages of simple preparation process and excellent electrochemical performance.

Describe the preparation steps of electrode active material among the present invention below:

Preparation of thin-film materials by pulsed laser deposition——mix Li ₂ S with a molar ratio of 1:x (2>x>0.5) and transition metal Co uniformly and press it into a target material, and prepare a composite nano-mixture by pulsed laser deposition Electrode film material. The preparation conditions are as follows: the substrate is made of stainless steel, the distance between the substrate and the target is 35-45mm; the deposition atmosphere is argon, and the pressure is kept at 8-10Pa; the deposition temperature is room temperature; the laser is the fundamental frequency generated by the Nd:YAG laser 355nm pulsed laser generated by triple frequency, pulse frequency 10Hz, pulse width 10ns, energy density 1.5-2.5J/cm ^-2 ; deposition time 0.5-1h.

Description of drawings

Fig. 1 is the charge-discharge curve of Li ₂ S/Co nanocomposite film.

Detailed ways

Example 1

The chemically pure Li ₂ S with a molar ratio of 1:1 is fully mixed with Co powder; then the mixture powder is pressed into a target material for pulse laser deposition, and a composite nano-mixture electrode film material is prepared by pulse laser deposition. Preparation conditions: the substrate is a stainless steel sheet, the distance between the substrate and the target is 40mm; the deposition process is carried out in argon, and the pressure is kept at 10Pa; the deposition temperature is room temperature; the laser wavelength is 355nm, the pulse frequency is 10Hz, the pulse width is 10ns, and the energy The density is 2 J/cm ^-2 ; the deposition time is 0.5 hours.

According to SEM, the particle size in the deposited film is about 20nm. It shows that the deposited film is composed of Li ₂ S/Co nanocomposite material. The TEM electron diffraction measurement shows that the deposited film is a Li ₂ S/Co nano-mixture, in which Li ₂ S is a face-centered cubic structure, and Co is a hexagonal structure, which contains a small amount of CoS _x compound, which is inevitable during the deposition process. The thin film was used as a working electrode, and a high-purity lithium sheet was used as a counter electrode to assemble a simulated battery. The electrolyte is 1MLiPF ₆ +EC+DMC (the volume ratio of EC to DMC is 1/1), and the battery is assembled in a dry box filled with argon. The charging and discharging of the battery is carried out on the Land battery test system. The hybrid thin film electrode exhibits good electrochemical performance. The battery discharge platform is about 1.5V, and the capacity reaches about 600mAh/g (with photos).

For the _Li2S /Co nanocomposite film preparation process, the relevant parameter conditions are changed within the aforementioned range, and the _Li2S /Co film with the same or similar electrochemical performance as in Example 1 can be obtained, and can be used as a lithium The electrode materials of ion batteries are not listed here.

Claims (2)

1. an electrode active material that is used for lithium ion battery is characterized in that by mol ratio be 1: x, the Li of 2＞x＞0.5 ₂After S and transition metal Co evenly mix, the composite Nano mixture film that adopts pulsed laser deposition to be prepared from, Li in the film ₂The S particle diameter is less than 50nm, and the Co particle diameter is less than 50nm.

2. a preparation method who is used for the electrode active material of lithium ion battery as claimed in claim 1 is characterized in that with mol ratio be 1: x, the Li of 2＞x＞0.5 ₂S be pressed into target material after Co evenly mixes, the method by pulsed laser deposition is prepared into composite Nano mixture electrode film material; Its preparation condition is: substrate adopts stainless steel substrates, and the distance of substrate and target is 35-45mm; Deposition atmosphere is an argon gas, keeps pressure 8-10Pa; Depositing temperature is a room temperature; Laser energy density is 1.5-2.5J/cm ^-2, sedimentation time is 0.5-1 hour.

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