With the rise of solid-state batteries, can China still take the lead?

The annual Spring Festival travel rush begins. Traffic jams and long charging queues have become a torment for all those who drive pure electric vehicles back home.

Spring Festival travel rush

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How to enable pure electric vehicles to run for more than 1,000 kilometers and how to enable pure electric vehicles to provide maximum convenience in intercity travel have become the ardent needs of all consumers. When liquid batteries approach the highest threshold of the chemical system, solid-state batteries become the focus of all car companies and battery companies. Among them, all-solid-state batteries are considered to be a new battery technology that may subvert the electric vehicle industry.

An all-solid-state battery is a battery in which all components are solid materials, especially the liquid electrolyte currently used must be replaced by a solid electrolyte.

Ouyang Minggao, academician of the Chinese Academy of Sciences and professor of Tsinghua University, told Caijingqiche (ID: caijingqiche) at the unveiling ceremony of the "China All-Solid-State Battery Industry-Academic-Research Collaborative Innovation Platform" (hereinafter referred to as CASIP) that all-solid-state batteries are the preferred solution for the next generation of batteries. One, Japan, South Korea, the United States and Europe are vigorously researching, which is a key commanding height in the competition for next-generation battery technology.

Therefore, how to win the next electrification war and how to make consumers more willing to accept pure electric vehicles is a new proposition for Chinese academic and industrial circles.

01 What are the benefits of all-solid-state batteries?

According to the 2024 "New Energy Vehicle Users' Car Anxiety Insight Report" by Autohome and Sina Auto, the three main concerns consumers have when purchasing new energy vehicles include high future battery replacement costs, insufficient cruising range, and safety performance. Difference.

Specific to concerns about battery life, new energy car owners are most concerned about increased energy consumption under high and low temperature conditions, accounting for the highest proportion of 36%. In addition, there are also major concerns about the decline of battery life in the future.

In addition, charging-related issues have also attracted widespread attention from car owners, such as long waiting times in charging queues, long fast charging times, and adaptation issues at public charging piles.

In terms of safety performance, users are most worried about battery safety issues, especially the battery fire problem caused by collision or high temperature environment. The proportion of worries in this regard is as high as 81% and 67% respectively. However, limited by objective laws, current power batteries, no matter how safe they are, may burn and catch fire under extreme conditions.

The "high energy density", "high safety" and "high charging speed" of all-solid-state batteries seem to be the ultimate answer to all the anxieties of electric vehicle owners.

Shi Jianpeng, deputy director of the R&D Center of Dongfeng Motor Group Co., Ltd., said at the founding conference of the "China All-Solid-State Battery Industry-Academic-Research Collaborative Innovation Platform" that "battery development should be an iteration every 30 years."

Academician Ouyang Minggao also believes that "we have reached a new round of material innovation cycle, and this cycle is around 2030." According to this estimate, the commercial use of all-solid-state batteries will arrive in about six years? Don’t worry, let’s first take a look at what an all-solid-state battery is and how it works.

All-solid-state batteries may sound a bit confusing at first. “All-solid-state”? Are the batteries under electric cars now in liquid form? How to install a liquid battery in the car?

In fact, the power batteries currently widely installed in cars are mainly lithium batteries. Although they look solid in appearance, the inside of the battery is filled with liquid electrolyte, but the material wrapping them is solid. People usually think that the battery is just a solid. A solid piece.

Liquid batteries usually refer to batteries that use liquid electrolytes, mainly lead-acid batteries and lithium batteries. In this type of battery, the positive and negative electrode materials are separated by a liquid electrolyte medium, usually an organic solvent containing lithium salts.

Taking lithium batteries as an example, when the battery is charged, the positive electrode releases lithium ions, which move to the negative electrode through the electrolyte and are embedded in it. When discharging, the process is reversed and lithium ions are released from the negative electrode and move back to the positive electrode.

The key advantages of lithium batteries are their high energy density and mature manufacturing processes. However, the downside of liquid electrolytes is potential safety risks such as leakage, overheating and even fire.

The charging and discharging of the lithium battery itself will also generate lithium dendrites inside the battery. The lithium dendrites that gradually grow after multiple charges and discharges (usually more than a thousand times) may pierce the battery separator and directly connect the positive and negative electrodes of the battery. Cause the battery to short-circuit and catch fire and explode. Although chemically stable lithium iron phosphate batteries (LiFePO4) are safer than ternary lithium batteries, they sacrifice a certain amount of energy density.

In fact, under extreme conditions, lithium batteries can catch fire, and the electrolyte of lithium batteries will decompose to form oxygen when burning, making the combustion more violent. Once a lithium battery catches fire, all people can do is wait for it to burn out completely. When the fire brigade arrived, they could only water the area to cool it down.

In order to solve the nitrogen safety problem of liquid batteries, battery companies have also worked hard to ensure the safety of batteries in terms of battery production materials, management systems and structural design, but they still cannot break through the constraints of chemical materials and physical laws.

All-solid-state batteries are different. The main difference between all-solid-state batteries and traditional liquid lithium-ion batteries lies in the state of the electrolyte. All-solid-state batteries use solid electrolytes rather than liquid ones.

The advantages of all-solid-state batteries include greater safety, longer service life and higher energy density. They also operate over a wider temperature range. Because the electrolytes are all solid, there is no problem of leakage and ignition. Even if lithium dendrites puncture the separator, there will be no problem. The solid electrolyte also helps lithium ions better shuttle between the positive and negative electrodes, improving energy density. The charging and discharging power is also greatly improved.

02 All-solid-state batteries are difficult to manufacture

Although all-solid-state batteries have the advantages of high safety, high energy density, and long service life, their commercialization and industrialization are full of difficulties.

The current challenge of all-solid-state batteries is that the manufacturing process is complex and the cost is high. Although some vehicles have been equipped with solid-state batteries, generally speaking, solid-state batteries are still in the research and development stage and are still a certain distance away from mass production and commercial use.

To make a good all-solid-state battery, we must first solve the material problem. All-solid-state batteries need to find solid electrolyte materials with high ionic conductivity (to allow lithium ions to pass through), high stability, and need to be cost-effective.

Since the 1970s, many scientists at home and abroad have done a lot of basic research work on solid electrolytes. The early solid electrolytes were lithium nitride, oxides, etc. Later, solid electrolytes such as sulfides, halides, etc. also appeared. . There are currently three main types of all-solid-state battery electrolytes: polymers, sulfides, and oxides.

Taking sulfide as an example, the initial performance of sulfide electrolytes was not very good. However, in the past decade, sulfide solid electrolytes have developed rapidly, and their ionic conductivity has even surpassed that of liquid electrolytes. Sulfide has the highest ionic conductivity and is a softer material that bonds better to electrodes.

At present, among foreign companies, Japanese and Korean companies mainly take the sulfide route, while European and American companies such as QuantumSpace mainly take the oxide route.

According to data from the paper "A Performance and Cost Overview of Selected Solid-State Electrolytes: Race between Polymer Electrolytes and Inorganic Sulfide Electrolytes", the cost of Li10GeP2S12 (a sulfide solid-state electrolyte) is US$695/10 grams. In comparison, liquid electrolytes cost $0.012/kg. The cost difference between the two is about 5,000 times.

Wang Jiantao, deputy director of the National Power Battery Innovation Center and deputy general manager of Guolian Automotive Power Battery Research Institute Co., Ltd., also said that the cost reduction of solid electrolytes still relies on breakthroughs in the cost of raw materials at the front end of the industrial chain. He also said that the chemical stability and air stability of sulfide electrolytes are very poor, and mass production is difficult.

At the same time, sulfide solid electrolytes are easily affected by moisture. The hydrogen sulfide produced after being affected by moisture is a highly toxic substance that is extremely harmful to human health. For this reason, the moisture-proof work of sulfide is particularly important. At present, the stability of sulfide can be improved by adding oxygen. .

The second is the solid-solid interface challenge. This challenge mainly lies in the contact and compatibility between the solid electrolyte and the electrode.