What has 2025 button cell battery nanotechnology achieved?

In the past decade, through the development and research of new electrode materials and new storage mechanisms, lithium-based rechargeable battery (lithium-ion battery) technology has made great progress, and battery performance has been continuously improved. Thanks to the continuous exploration and discovery of nanotechnology, many key and difficult basic problems in traditional battery materials are very likely to be solved.

1. What major problems does nanotechnology aim to solve in the field of traditional batteries?

1. Volume changes lead to cracking and fragmentation of active particles and electrodes

Traditional embedded electrode materials have small volume changes during charging and discharging. For new high-capacity electrode materials, due to the embedding and de-embedding of a large number of Li species during charging and discharging, huge volume changes occur. After many cycles, active particles and electrode materials will crack and break, affecting electrical conduction and causing capacity reduction, eventually leading to battery failure and greatly shortening the battery life. It is reported that the volume expansion rate of alloy-type negative electrode materials is 420% for Si, 260% for Ge and Sn, and 300% for P. The traditional graphite negative electrode is only 10%. 2

So, how does nanotechnology solve the problem of volume change?

Solution for Si negative electrode

A natural advantage of nanomaterials is that they are small in size and can effectively resist mechanical damage at the particle and electrode level. High-capacity electrode materials have a basic parameter called critical crushing size. The value of this parameter depends on a series of parameters such as the reaction type of the material (such as alloy reaction, conversion reaction), mechanical properties, crystallinity, density, morphology, and volume expansion rate. Moreover, the electrochemical reaction rate has a significant impact on the cracking and crushing of particles. The faster the charge and discharge rate, the greater the stress generated. When the particle size is smaller than this critical size, the stress caused by the lithiation reaction can be effectively controlled, thereby alleviating the cracking and crushing behavior of the particles.

Studies have shown that the critical size of Si nanocolumns is 240-360nm, and the critical size of Si nanowires is 300-400nm. This range is mainly affected by the electrochemical generation rate. The critical size of crystallized Si nanoparticles is about 150nm. 3

Therefore, the particle fragmentation problem can be solved by using various nanostructured materials below the critical size, such as nanopillars, nanowires, nanoparticles, nanotubes, nanorods, and nanocomposites. As for the electrode fragmentation problem, it is mainly achieved by bonding Si nanoparticles to the current collector using a series of adhesive methods.

S cathode solution

S has the advantages of high specific capacity and low cost, and is one of the most practical 2025 button cell battery cathode materials. When S is completely converted into Li2S through lithiation reaction, its theoretical volume expansion rate is as high as 80%. Therefore, S cathode, like other high-capacity electrode materials, also has the problem of pulverization. In addition, the lithiation process of S generally produces a variety of soluble polysulfide intermediates, and the expansion of the S cathode will cause the intermediates to leak out of the electrode, reducing the performance of the battery.

It is well known that these soluble intermediates can be prevented from leaking by wrapping. During the charge and discharge process,

The protective shell of the core-shell structure will break, causing the leakage of polysulfide intermediates. Therefore, researchers designed yolk-shell structures such as STiO2, S polymers, or other confined structures with hollow shells, which effectively solved the problems of polysulfide leakage and pulverization caused by volume expansion.

2. Stability of SEI film (solid-electrolyte interphase)

In lithium batteries, the reduction potential of organic carbonates in common electrolytes is higher than the working voltage of negative electrode materials. Therefore, during the battery charging process, the electrolyte will be reduced and a layer of SEI film will be formed on the electrode surface. This film can conduct lithium ions but is not conductive, so it will grow longer and thicker on the surface of the negative electrode material. The passivation effect of the stable SEI film on the negative electrode material helps to achieve high coulomb efficiency and long-term stability of the negative electrode material. However, the volume change causes the SEI to change continuously and it is difficult to maintain stability.

How does nanotechnology achieve the stability of the SEI film?

Si negative electrode

For Si negative electrode, the hollow encapsulation strategy is mainly used to achieve the stability of the SEI film. For example, the design of various yolk-shell structures such as SiC, SiCNT, AlTiO2, etc. not only provides an electrolyte barrier layer, but also reserves space for the volume expansion of active particles, thereby effectively improving battery performance.

Li metal anode

In the field of lithium-ion batteries, lithium metal is currently the anode material with the highest theoretical energy density, and it is also an excellent choice for high-energy Li-S batteries and Li-air battery anodes. However, during the charging process, the volume expansion of Li metal is amazingly large. Therefore, how to control the SEI film of lithium metal anode is even more difficult.

Through a similar scheme, researchers construct a nano-interface protection layer between lithium metal and electrolyte, such as interconnected hollow carbon nanospheres, or ultra-thin two-dimensional BN/Grphene nanocomposites. In this way, during the charging and discharging process, the SEI film stabilizes with the presence of the interface protection layer, and does not gradually thicken. This strategy also solves the dendrite problem of lithium metal anode.

3. Electron and ion transport

The rapid transport of charge carriers within active particles and electrodes is crucial for improving battery performance! High conduction paths for electrons and short transport distances for ions help improve rate discharge capabilities and activate insulating electrode materials. Compared with micron-scale materials, nanomaterials are smaller in size and have advantages in electron and ion transport.

For particles, lithium ion insertion/deinsertion processes and electron transport are faster in nanoparticles than in micron-scale particles due to the shorter transport distance. Common methods to improve particle conductivity include: wrapping with a conductive layer or embedding in a conductive matrix.

For electrodes, the rapid transport of electrons and ions is crucial for high mass loading of batteries. The following three strategies are mainly used: 1) Constructing conductive nanoactive materials on metal current collectors, such as self-supporting nanowire arrays, interconnected hollow carbon nanospheres, etc.; 2) Depositing active materials on the surface of nanostructured metal current collectors. 3) Depositing active materials in 3D conductive mesh structures.

4. Long-distance electrode atomic/molecular motion

In traditional embedded batteries, the electrode structure and size do not change much because there is no bond breaking and bonding. However, due to the continuous breaking and combining of bonds, the volume and structure of high-capacity electrode materials change greatly during the charge and discharge cycle, leading to collapse. Therefore, these high-capacity electrode materials have been considered difficult to use.

In rechargeable lithium batteries, the structural changes and phase changes of these high-capacity electrode materials cause the long-distance diffusion of active atoms/molecules, which seriously affects the battery performance. Generally speaking, the movement of active atoms/molecules in electrodes can be divided into three types: 1) phase change and related atomic/analytical diffusion, such as the solid-liquid phase change of the S positive electrode in Li-S batteries. 2) The growth of lithium dendrites during the lithium precipitation process of secondary Li metal batteries; 3) The huge volume expansion caused by the large intake of Li in high-capacity electrodes.

Nanotechnology solutions are mainly based on physical and chemical nano-confinement.

2. Major challenges facing battery nanotechnology

As the size of active particles decreases to the nanometer level, various problems also arise: high specific surface area, low packing density and high cost.

1) High specific surface area increases the risk of side reactions related to electrolyte decomposition and lithium consumption, resulting in low coulombic efficiency.

2) Low stacking density results in low volume capacity.

3) High cost makes it difficult to mass produce the material, and large-scale experiments are required to verify its practicality, making it difficult to use it on a large scale.

A good electrode material must strengthen its disadvantages while ensuring the advantages of micron particles.

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