Lithium-ion battery new breakthrough is coming!

Liquid lithium batteries using new electrolytes,The charge and discharge can be completed within 10 minutes, and the ionic conductivity is increased by 4 times at room temperature.

At the same time, it also has an ultra-wide working temperature range, from -70 ℃ to 60 ℃, even in Mohe weather, it can work stably.

The new research results from Zhejiang University, the paper has been published in Nature.

New lithium-ion electrolyte: 10 minutes fast charge

As the temperature gradually warmed up, the "electric father" began to be less difficult to serve.

Although various new energy vehicle companies have tried their best to ensure the battery life in winter, it is an indisputable fact that the chemical reaction of lithium batteries slows down in low temperature environment, and even the electrolyte freezes at low temperature, resulting in the decline of battery performance.

In addition to low temperature, high temperature environment will also affect the working rate of liquid lithium ion battery.

One of the important factors isElectrolyte.

It is well known that the rate of charge and discharge of a battery is related to the speed at which lithium ions move in the battery.

Taking a low temperature environment as an example, when the ambient temperature is lower than − 20 ° C., the viscosity of the electrolyte increases (that is, the process of gradual solidification), resulting in a decrease in the movement speed of lithium ions, that is, a decrease in lithium ion conductivity.

At the same time, because the liquid lithium ion battery charge and discharge process, the electrolyte will form a passivation layer on the contact surface, that is, the SEI film.

Although the SEI film can prevent the solvent molecules of the electrolyte from entering and damaging, in a low temperature environment, the SEI film will become thicker and thicker, the impedance will increase, and the lithium ion conductivity will also be reduced.

However, the electrolyte proposed by the Zhejiang University team, based on FAN fluoroacetonitrile, can guarantee high ionic conductivity from -70 ℃ to 60 ℃.

For example, at -70 ℃, the battery of FAN electrolyte can also reach a high ionic conductivity of 11.9 mS/cm, which is more than four orders of magnitude higher than that of traditional carbonate electrolyte and surpasses the electrolyte of this state ionic conductivity.

And also has stability. The lithium ion battery using FAN electrolyte was charged and discharged at a rate of 6C at 60 ° C. The battery capacity remained at 80% after 600 cycles.

When the battery capacity is 1.2Ah, whether it is multiple cycles or the temperature drops to -80°C, only lithium-ion batteries using FAN electrolyte can provide a certain reversible capacity.

Even at the typical case, I .e., 25°C, the cell using the FAN electrolyte achieved an ionic conductivity of 40.3 mS/cm, more than four times higher than the typical electrolyte.

In other words, this new type of electrolyte allows lithium-ion batteries to have an ultra-wide operating temperature range while ensuring stable and cyclic operation, and its performance is greatly improved compared with traditional carbonate electrolytes.

The team said that under the same conditions, the battery using FAN electrolyte can be charged for 10 minutes, the power is charged to 80%, and the fast charging performance is excellent.

So, why the FAN electrolyte?

Ligand channel-facilitated transport mechanism

If you want to ensure the battery performance under temperature conditions, that is, to ensure the movement of lithium ions, or the conduction rate, you first need to understand the advantages and disadvantages of the existing conduction methods.

At present, in carbonate electrolyte, lithium ion has two main conduction modes, carrier transmission (Vehicular Transport) and structure transmission (Structural Transport), or hopping transmission (Hopping Transport).

When the carrier is transported, the solvent molecules form a solvated sheath (solvation sheath) in the shape of lithium ions. The composite is wrapped with lithium ions and moves in the electrolyte, which is equivalent to a carrier with lithium ions.

That is, at the time of carrier transport, the moving speed of lithium ions depends on the moving speed of the solvation sheath.

Structural transport is the movement of lithium ions between solvent molecules and anions, and the movement speed of lithium ions depends on the concentration of the electrolyte.

Although carrier transport can achieve high ionic conductivity in low concentration electrolyte and can form a stable SEI film, low temperature and high electrolyte concentration will reduce the movement speed of the solvation sheath and reduce the lithium ion conduction velocity.

Structural transport is more effective in high-concentration electrolytes, and in some cases, the high-speed movement of lithium ions can also damage the SEI film and affect battery performance.

So, is there a way or material that can simultaneously meet the high-speed movement of lithium ions and have a wide working temperature range?

When screening solvents, the Zhejiang University team found that FAN, namely fluoroacetonitrile solvent, has the characteristics of low solvent energy, low lithium ion transport energy barrier and small molecule size solvent.

Source: Zhejiang University

In other words, in the FAN solvent, the force between lithium ions and solvent molecules is weak, and it can move quickly with less energy, and it can move stably at low temperatures.

At the same time, the solvent has a small molecular size and a small solvation sheath, which can interact with lithium ions and adjust the solvation structure, form a continuous lithium ion transport ligand channel, and promote the chemical reaction of lithium ions.

The team thus proposed the concept of ligand channel-facilitated transport mechanism and introduced the transport index (TI) parameter to quantify the transport behavior of lithium ions.

When TI = 0, lithium ion transport through the carrier transport; when TI = 1, lithium ion transport through the structure; and in an electrolyte TI is equal to 0.5, the electrolyte can significantly promote the ligand channel transport.