Ouyang Minggao: Development trend of power battery technology in the next few years

On the afternoon of January 7, 2018, the hot issues exchange meeting of the China Electric vehicle 100 Forum (2018) with the theme of "grasping the trend of global change and achieving high-quality development" was held in Tsinghua University. Chen Qingtai, chairman of the China Electric Vehicle Association of 100, Ouyang Minggao, executive director of the China Electric Vehicle Association of 100, and Zhang Yongwei, secretary general of the China Electric Vehicle Association of 100, attended the meeting. Ouyang Minggao, academician of the Chinese Academy of Sciences, mainly made an in-depth analysis and prospect on the technical problems of batteries. China bus network after interview and finishing, after my review, its views are released as follows:

Domestic power battery technology progress: 300 wh/kg can be achieved

Lithium-ion power batteries are expected to achieve the goal of 300 Wh/kg by 2020. At present, domestic and foreign technology research and development are basically at the same level, but safety research needs to be strengthened.

According to Professor Ouyang Minggao, there are currently three teams in the new energy vehicle project to achieve 300 watt-hour/kg battery research and development by 2020, namely Ningde Times, Tianjin Lishen and Hefei Guoxuan.

The technical routes currently adopted by the three teams are basically the same. The positive electrode is high nickel ternary and the negative electrode is silicon carbon negative electrode. The battery technical indexes of the three companies are close to the application requirements. In other words, the battery with a specific energy technical index of 300 Wh/kg planned to be industrialized in 2020 has made a substantial breakthrough.

In Ningde era, soft-pack batteries were mainly used, not square batteries. The cycle life of the battery was about 1000 times, and the energy density reached 304 watt-hours/kg. Its 300 watt-hours/kg monomer could make a battery PACK system of 200-210 watt-hours/kg. The safety indexes also all passed the national requirements. The other two are similar.

Of course, there are still some enterprise security standards that have not been fully met.

Ouyang Minggao said that by the end of 2017 and the beginning of 2018, the energy density monomer of major battery enterprises in our country has reached about 230 WHR/kg, and the PACK system is about 150 WHR/kg.

We only need to increase 50-70 Wh/kg in 2018 and 2019. The 300 watt-hour/kg target required by the Ministry of Industry and Information Technology can be achieved. Professor Ouyang believes that this indicator can be achieved.

As for the monomer density of 350 watt-hours/kg and the system density of 260 watt-hours/kg, Professor Ouyang said that that is our goal.

How to achieve 300-400 WHs/kg: conversion of positive and negative materials

In order to achieve the goal of 350 Wh/kg or higher, Professor Ouyang said that there are currently two new types of technology systems: lithium-sulfur batteries and lithium-air batteries. The progress at home and abroad is relatively slow, and no breakthrough has been seen in 2017. Progress.

The weight ratio energy of lithium-sulfur battery is basically equivalent to the volume ratio energy. In principle, the weight ratio energy of lithium-sulfur battery is basically equivalent to the volume ratio energy, so it is quite difficult to optimize the volume ratio energy.

The volume specific energy of passenger car and car batteries is more important than weight specific energy. If the batteries of passenger cars and cars are 400 watt-hours/kg per kilogram, the volume specific energy is only 400 watt-hours/liter, which is not Conducive to electric passenger car applications.

The lithium-ion battery is different. When its weight specific energy is 300 watt-hour/kg, the volume specific energy can reach 600 watt-hour/liter.

Another technology, lithium-air batteries, integrates all the difficulties of zinc-air batteries, hydrogen fuel cells, and lithium secondary batteries. Hydrogen fuel cells have a competitive advantage.

Facing the industrialization in 2025, we still want to hit the target of 400 Wh/kg of single battery. How can this be done.

Professor Ouyang introduced that in 2017, China has made some breakthroughs in high-capacity lithium-rich cathode materials, and innovative lithium-ion batteries based on high-capacity lithium-rich cathodes and high-capacity silicon-carbon anodes are more feasible than lithium-sulfur and lithium-air batteries.

Professor Ouyang said: To achieve 300 Wh/kg is actually to change the negative electrode from carbon to silicon carbon. To achieve 400 Wh/kg, we need to change the positive electrode material.

At present, there are several kinds of optional cathode materials, and the breakthrough is the high-capacity lithium-rich manganese-based cathode material. There are now two units in China that have undertaken cutting-edge basic projects. Among them, the Institute of Physics has improved the voltage attenuation of the lithium-rich manganese-based cathode cycle. After 100 weeks of battery use, the voltage attenuation has dropped to less than 2%. It should be said that this is a major progress.

In addition, the team of Peking University has developed a lithium-rich manganese-based positive electrode with a specific capacity of 400 mA Wh/g for the first time. The material can completely achieve the goal of 400 Wh/kg or even higher.

Global Battery Technology Hotspot: All-solid-state Battery Technology

Solid-state batteries are undoubtedly the hottest technical term in the global battery field in 2017.

Although the industrialization of research and development continues to heat up, but by the solid/solid interface stability and metal lithium negative charging two major issues, the real all-solid lithium metal negative battery is not yet mature, but the inorganic sulfide as a solid electrolyte lithium ion battery breakthrough.

Looking at the development path of solid-state batteries in general, the electrolyte is from liquid, semi-solid, solid-liquid mixed to solid, and finally to all-solid. As for the negative electrode, it will be from graphite negative electrode to silicon carbon negative electrode. Our country is now transforming from graphite negative electrode to silicon carbon negative electrode, and finally it is possible to metal lithium negative electrode, but there is still technical uncertainty.

It is 25 years since the invention of lithium-ion batteries, and the concept of all-solid-state lithium batteries appeared earlier than lithium-ion batteries. The all-solid lithium battery referred to in the early stage refers to the all-solid metal lithium battery with lithium metal as the negative electrode.

At present, there are many research institutions and industrial units working on solid-state batteries in China, including Qingdao Energy Institute of Chinese Academy of Sciences, Ningbo Institute of Materials, Institute of Physics, etc., as well as Ningde Times New Energy and AVIC Lithium Battery. Recently, Ningbo Materials Institute and Ganfeng Lithium Industry plan to mass produce solid-state batteries in 2019.

The so-called "all-solid lithium battery" is a lithium battery in which the electrode and electrolyte materials used in the working temperature range are solid and do not contain any liquid components, so it is called "all-solid electrolyte lithium battery". All-solid-state lithium batteries, every word of this word cannot be less and cannot be changed. For example, "all-solid-state" is different from "solid-state". "Lithium battery" and "lithium-ion battery" are not the same concept.

All-solid-state lithium batteries are divided into all-solid-state lithium primary batteries and all-solid-state lithium secondary batteries, and primary batteries are already useful. All-solid-state lithium secondary batteries are further divided into all-solid-state lithium ion batteries and lithium metal batteries. The so-called all-solid-state metal lithium battery means that its negative electrode uses lithium metal. Our domestic products now use carbon, silicon carbon or lithium titanate as the negative electrode.

All-solid-state lithium batteries have several potential technical advantages:

1 High security. The absence of an organic solvent as an electrolyte causes electrolyte combustion problems.

2 high energy density. The solid electrolyte solves the problem of electrolyte leakage and has a high volume specific energy.

3 wide range of cathode material selection. Because the negative electrode is lithium metal, the positive electrode does not contain lithium, the voltage window of the electrolyte will be wider, and the specific energy can also be improved.

4 system than high energy. Since the electrolyte has no fluidity, it can be easily connected in series to form a high-voltage monomer, which is beneficial to the improvement of the group efficiency and energy density of the battery system.

Problems with all-solid-state lithium batteries:

1 the ionic conductivity of solid electrolyte materials is low. Now there are three kinds of solid electrolyte, namely polymer, oxide, sulfide. The polymer electrolyte battery needs to be heated to 60 degrees before the ionic conductivity comes up and the battery can work normally. What we are going to break through is the solid electrolyte of sulfide.

2 solid/solid interface contact and poor stability. Liquids combine with solids to penetrate easily. But solid and solid contact and stability is not too good,. Although the lithium ion conductivity of sulfide electrolytes has been improved, there are still problems with interfacial contact and stability.

3 Rechargeable problem of lithium metal. In the solid electrolyte, the lithium surface also has the problems of chalking and dendrite growth. Its cyclicity, and even safety, need to be studied.

4 high manufacturing costs.

Based on the above problems, the real all-solid-state metal lithium battery technology still has technical uncertainties and is immature. Existing or breakthrough, there are performance advantages and industrialization prospects, mainly solid-state lithium-ion batteries.

What is the difference between solid-state lithium ion batteries and all-solid-state lithium batteries?

Solid-state batteries are not necessarily all solid electrolytes. They are mixed with liquid and solid, depending on the mixing ratio. For real solid-state lithium-ion batteries, the electrolyte is solid, but there is a small amount of liquid electrolyte in the cell;

The so-called semi-solid battery means that the solid electrolyte and the liquid electrolyte each account for half, or half of the cell is solid and half is liquid. According to this, there are quasi-solid batteries, which are mainly solid and a small amount of liquid.

Now solid-state lithium batteries continue to heat up, the United States, Europe, Japan, South Korea, China, are in the investment.

Among them, the United States is dominated by small companies and entrepreneurial companies, based on disruptive technologies. There are two start-up companies in the United States that have achieved good results. One is S-akit3, which can reach 500 kilometers, the other is Solid-State, and the other is invested by several large companies such as BMW.

Japan is basically a solid-state lithium-ion battery, most famously Toyota. Toyota solid-state lithium-ion batteries will be commercialized by 2022. The anode of Toyota's solid-state lithium-ion battery is graphite, sulfide electrolyte, and high-voltage cathode. The single battery has a capacity of 15 amers and a voltage of more than 10V. It will be commercialized in 2022.

The South Korea is a graphite negative electrode, not a lithium metal negative electrode.

The situation in China, Japan, and South Korea is similar, because we already have a large-scale lithium-ion battery industry chain in our country, so we must continue the inherent technical route, and do not overthrow it and waste resources for technological innovation.

Power consumption is more of a concern than driving range

According to the above progress analysis, the expert group represented by Ouyang Minggao made an optimization iteration on the development trend of technical battery technology as follows for industry reference.

In 2020, the specific energy is 300 watt-hours/kg, the specific power is 1000 watt-hours/kg, the cycle is more than 1000 times, the cost is 0.8 yuan/watt-hour, the corresponding material is high nickel three yuan. Our country is now shifting from nickel: cobalt: manganese ratio 3:3:3 to 6:2:2, that is, high nickel, nickel becomes 6, then to 8:1:1, nickel becomes 8, cobalt further drops to 1, and even cobalt further drops to 0.5. The negative electrode should be transformed from carbon negative electrode to silicon carbon negative electrode. This is our current technological change.

By 2025, the performance of cathode materials will be further improved, including lithium-rich manganese-based materials and other materials. From 2020 to 2025, from 300 watt-hour/kg to 400 watt-hour/kg, the cost per watt-hour is from 0.6 yuan to 0.8 yuan. The reasonable mileage of the corresponding pure electric car is about 300-400 kilometers.

By 2030, experts hope to make a breakthrough in electrolytes, and at the same time, solid-state batteries will achieve large-scale industrialization, and the specific energy of battery cells is expected to impact 500 Wh/kg. In 2030, regular cost-effective models should be able to reach more than 500 kilometers.

All of this requires the cooperation of other technologies. Therefore, Professor Ouyang Minggao said that his current concern is not the mileage, but the power consumption of electric vehicles, which is also the core issue of the current vehicle integration technology.

In particular, the winter of pure electric vehicles is still a problem that has not been completely solved, including the impact of low temperature on the battery, and the high power consumption for heating.

Although these problems and technologies will be gradually solved, Professor Ouyang Minggao still said that pure electric vehicles will always have the problem that energy is not too sufficient, so energy saving of pure electric vehicles may be an eternal theme.