In 2019, goodenough finally won the Nobel Prize in chemistry, and lithium-ion batteries will finally hold the dominant position of batteries. Today, whether it is power batteries, mobile power supplies, or flexible health care devices, lithium-ion batteries are everywhere.

However, lithium-ion batteries have an intrinsic ceiling. Nowadays, people have higher requirements for the cost, life and safety of batteries. So, does lithium-ion battery still have the power to move forward? Can we make revolutionary progress based on lithium-ion batteries?

On March 30, 2021, a domestic mobile phone manufacturer released a new mobile phone. One of the core highlights is that it uses a super fast charging silicon negative lithium-ion battery with a capacity of up to 5000mAh.

Before that, silicon anode technology was mainly used in the development of new power batteries for new energy vehicles, and it has not been used on a large scale, let alone on mobile phones. Xiaomi has broken down. I don't know if it's a dimension reduction blow? However, it is also a great initiative to go down from the automotive field to the mobile phone field.

Today, we will tell some stories about silicon anode, hoping to inspire researchers in related fields.

The most important index of battery is energy density. The core of improving this performance is the cathode material and anode material, especially the anode material. At present, the main cathode material of lithium-ion battery is metal oxide, while the main anode material is graphite. The theoretical capacity is 372 MAH. G-1.

Graphite has excellent conductivity, so that electrons can be easily transferred to the metal wires of the circuit. However, the ability of graphite to store lithium ion in the discharge process is not so good, which requires six carbon atoms to combine with one lithium ion. This defect limits the lithium content carried by the electrode, thus limiting the energy that the battery can store.

In this respect, silicon can do better! Each Si atom can be combined with four lithium ions. Theoretically, silicon-based anode materials can store 10 times more energy than graphite anode materials, and the theoretical capacity is as high as 4200mah / g, which is the goal that electrochemists have been pursuing for decades.

It is very easy to prepare anode materials with massive Si, but there are many problems, including two core problems, which affect the electrical conduction, reduce the capacity, and eventually lead to battery failure, greatly shorten the service life of the battery

1) Volume expansion: the volume expansion is as high as 420% in the process of charging and discharging, which easily leads to the rupture of particles and motor.

2) SEI film: in the process of charge and discharge, the side reaction occurs, forming an unstable and non-conductive solid electrolyte interface SEI film.

So, what to do?

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Scheme of silicon anode modified by nanotechnology

In 2008, an unknown young scientist came up with a new solution. He led the team to invent a silicon nanowire anode, which effectively slowed down the pressure and stress effect and completely defeated the bulk silicon anode material. After 10 cycles, the anode material can maintain 75% of its theoretical energy storage capacity.

Although it is only a preliminary attempt, this young scientist has inadvertently started the trend of battery nanotechnology. When everyone is improving the performance of anode materials through traditional material modification, he is committed to closely combining nanotechnology and battery electrochemistry, and has developed a series of new battery nanotechnologies. Since then, the research of battery nanotechnology has become a whirlwind in the field of battery research.

This young man, his name is Cui Yi.

Cui Yi is one of the pioneers and representatives in the field of silicon anode technology. While doing research at the University of California, Berkeley, inspired by Steven Chu, director of Lawrence Berkeley National Laboratory and Nobel laureate, Cui Yi began to contact the battery field he had never touched before. Chu believes that nanotechnology provides a new and important tool for clean energy. Researchers can not only control the chemical composition of the material on the smallest scale, but also control the arrangement of atoms in the material, so as to really understand how the chemical reaction takes place!

After more than ten years of in-depth research, Cui Yi showed you how to use nanotechnology to solve the key and difficult problems in battery chemistry that have long existed and hindered the development of science and technology

1) Si was used as anode material of lithium ion battery instead of standard graphite;

2) Lithium is used as anode material;

3) Batteries based on li-s chemistry will be more powerful than any lithium-ion battery.

Cui Yi's team has been committed to applying nanotechnology to improve the performance of silicon anode for lithium-ion batteries for many years. According to Professor Cui Yi's lecture, this paper summarizes the nanotechnology of 11 generations of silicon anode batteries developed by them（ This data is up to 2016. Now it has been five years, and there should be more than 11 generations.)