WO2018095202A1

WO2018095202A1 - Composite lithium battery and preparation method therefor

Info

Publication number: WO2018095202A1
Application number: PCT/CN2017/108595
Authority: WO
Inventors: 汤卫平; 朱蕾; 江小标; 吴勇民; 贾荻
Original assignee: 上海空间电源研究所
Priority date: 2016-11-25
Filing date: 2017-10-31
Publication date: 2018-05-31
Also published as: CN106410194A

Abstract

Disclosed are a composite lithium battery and a preparation method therefor. The composite lithium battery comprises a cathode, an anode, an electrolyte, and a diaphragm, wherein the cathode comprises a cathode active substance; the cathode active substance is prepared by compounding elemental sulfur and ferric phosphate or by compounding sulfide and lithium iron phosphate; the anode is a lithium metal anode or a composite anode of metallic lithium and carbon. By utilizing the high specific volume of sulfur and the high safety and long service life of a lithium iron phosphate material, the present invention avoids the defect of low discharge energy density of a conventional lithium iron phosphate ion battery, and resolves the deficiency of low safety and poor circulation properties of the lithium sulfur battery, so as to improve comprehensive properties of energy density, safety and circulation service life of the battery.

Description

Composite lithium battery and preparation method thereof

Technical field

The invention belongs to the field of lithium batteries, and relates to a composite lithium battery and a preparation method thereof.

Background technique

Energy is an important material basis for the development of the national economy and the improvement of people's living standards, and is also an important factor that directly affects economic development. Due to the growing scarcity of non-renewable energy sources such as oil, natural gas, coal, and the increasingly severe environmental pollution caused by the use of these energy sources, countries around the world are stepping up exploration of new energy sources or new sustainable energy use technologies. One. At the same time, in order to facilitate the use of clean, safe and renewable energy such as wind energy, solar energy, tidal energy, geothermal energy, etc., it needs to be converted into electric energy, that is, energy storage is required by using a high-capacity electrochemical power source. With advances in electronics, lower power requirements, and the development of portable devices, electrochemical cells are used extensively in consumer, industrial, and military applications. At the same time, the increase in battery capacity and power characteristics required by electrical equipment has also contributed to the popularization of chemical power sources.

Among many energy storage devices, lithium-ion batteries provide the highest energy density, and have the advantages of voltage stability, small self-discharge, long life and no memory effect. They are widely used in aerospace, portable equipment, power tools and so on. The energy density of lithium-ion batteries can reach 150Wh kg ^-1 , which still cannot meet the needs of modern society for the continuous growth of energy. The fundamental challenge is the limitation of the specific capacity of the positive and negative materials of the battery. At present, the positive electrode material of lithium ion battery mainly uses transition metal oxide or phosphate, and the negative electrode mainly uses graphite. Since the reaction principle of these materials is deintercalation reaction, the specific capacity of positive electrode material is about 150-200 mAh g ^-1 , and the ratio of negative electrode graphite The capacity is about 370mAhg ^-1 , which limits the capacity and energy density of lithium-ion batteries. Even with optimized technology, its energy density can be increased by up to 30%, which is far from meeting the 800km battery life of electric vehicles. At the same time, the increase in energy density increases the safety risk of lithium-ion batteries. In order to ensure the safety of the battery, a lithium iron phosphate battery having a low energy density but high safety has become a main power battery.

In order to meet the demand for energy density in the continuous development of electric vehicles, smart grids, etc.

Claims

Started to develop batteries for new electrochemical systems. Electrode materials based on conversion reactions and capable of reacting with more ions and electrons are a good choice. Recently, lithium-air and lithium-sulfur batteries have attracted wide attention due to their high energy density (3500Wh kg -1 and 2500Wh kg -1 , respectively ), and have become representative of new electrochemical system batteries. The negative electrode of the lithium-air battery is lithium metal, and the positive electrode absorbs oxygen from the environment and is redoxed inside the air electrode. However, due to the breakthrough of the technology of the key components of the lithium-air battery, its chargeability and cycle performance are facing enormous challenges. Compared with lithium-air batteries, lithium-sulfur batteries with positive and negative materials, which are elemental sulfur and lithium metal, are less challenging and are considered to be easier to use. Its theoretical energy density can reach 2600Wh kg -1 , which is about 5 times that of current commercial batteries. The theoretical specific capacities of positive and negative materials are 1672mAh g -1 and 3860mAh g -1 respectively . The high capacity of elemental sulfur is based on elemental sulfur. In the conversion reaction, a sulfur atom can react with two lithium atoms to form Li 2 S. Elemental sulfur is not only theoretically high in specific capacity, but also rich in reserves, environmentally friendly, and low in cost.

Although lithium-sulfur batteries have a large advantage in specific energy density, poor cycle performance and safety limit their practical applications. The research on the cycle process and mechanism of lithium-sulfur batteries shows that the sulfur-based cathode materials mainly have the following problems:

(1) Elemental sulfur is an electron and ionic insulator at room temperature (room temperature conductivity is 5×10-30S/cm), and a large amount of conductive agent needs to be added to improve the electronic conductivity and ionic conductivity of the positive electrode;

(2) Elemental sulfur will form a soluble polysulfide during discharge, which will cause the loss of active material in the electrolyte, resulting in poor cycle performance. The polysulfide ions diffuse to the negative electrode and directly react with the negative electrode to form a self-discharge reaction. The "shuttle effect" causes the battery to be inefficient in charging and discharging.

(3) Battery discharge insoluble end products Li 2 S 2 and Li 2 S are deposited on the surface of the positive electrode, causing passivation of the surface of the positive electrode, which seriously affects the electrochemical reaction of the battery.

In response to these problems, the R&D personnel have modified the lithium-sulfur battery to a certain extent. However, the current modification technology is based on the synthesis of sulfur-containing composite positive electrode, through the improvement of the microstructure of the positive electrode composite material, in order to achieve the purpose of overcoming and improving the electrochemical performance. However, since the loss of the active substance cannot be completely avoided, the disadvantages are fundamentally overcome. Although lithium-sulfur batteries have been researched and developed for decades, they still have not reached the root cause of industrialization.

Disclosure of invention

The object of the present invention is to overcome the defects that the active material in the existing lithium battery is easy to be lost, and to provide a relief of the low safety and poor cycle performance of the lithium-sulfur battery, and improve the specific energy density and safety of the battery.