Full-cell Li-ion Battery Electrodes

The materials themselves are the most fundamental design factors that determine the electrochemical potential window, reaction chemistry (including reaction kinetics and mechanism), and cell type (e.g., aqueous, non-aqueous, polymer, or solid-state). They also affect the cyclability, thermal stability, and overall performance of full-cell Li-ion batteries. Therefore, most research is directed toward developing novel material structures for the main components of full-cell LiBs.

Since the inception of LiBs, full-cell components have been intensively studied, and research continues to identify improvements with a focus on materials. It is well known that materials are the key factor in promoting electrochemical reactions, resulting in high specific capacity and energy density within the electrochemical potential window. In detail, the main components of LiBs include electrodes (negative and positive electrodes), binders (polymer materials), current collectors (metal foils of copper or aluminum), separators (polyolefin sheets), and electrolytes (a mixture of salts and liquids). The properties of these components—including their electronic and crystal structures, chemical, electrical, and mechanical properties, and intrinsic conductivity—play a crucial role in developing favorable reaction chemistry, enhancing thermal and mechanical stability, and improving the performance of full-cell LiBs.

Electrode is one of the main components of LiB, which determines the electrochemical potential window, specific capacity, energy and power density, comprehensive performance and electrochemical reaction mechanism. Therefore, the design and improvement of electrode materials are crucial to achieve high energy and power density. Ideally, the electrode should have high intrinsic conductivity, wide potential window, excellent cycling and rate performance, low cost, and strong stability and safety to improve the overall performance of LiB. Over the years, two main design strategies, intrinsic and extrinsic, have been explored to achieve these desired properties of LiB in many aspects.

Intrinsic design strategies mainly focus on the development of stoichiometric composition, optimization of crystal defects and control of crystal orientation, and these aspects are discussed in detail.

Chemical composition: The chemical composition determines the crystal structure and determines key properties such as mechanical strength (adhesion/cohesion), stability (structural, chemical and thermal), phase transitions and intrinsic conductivity (electrical and ionic). It also specifies the number of Li+ ions that can be inserted or extracted in the crystal structure, which directly affects the electrochemical performance of the electrode material. Furthermore, the building blocks represent the “genes” of the material, providing insights into the local chemical coordination and molecular chemistry, establishing the physical and chemical properties of the electrode.
Understanding the correlation between the building blocks and these physical/chemical properties provides key evidence for understanding the charge transfer properties, which are essential for intrinsic properties such as structural/thermal stability, electronic/ionic conductivity, and Li+ ion transport. These properties are crucial for improving the electrochemical performance of Li-ion batteries. Therefore, it is imperative to design and develop structurally tunable electrode materials to accommodate additional Li+ ions, improve intrinsic conductivity, expand the voltage window, enhance diffusion kinetics, and provide excellent electrochemical performance for LiBs.

Point defects: Similarly, point defects such as Frenkel defects (atoms migrate from lattice sites to interstitial sites, creating interstitial defects), Schottky defects (involving the simultaneous presence of cation and anion vacancies), and oxygen vacancies (lack of oxygen atoms or presence of hydroxyl ions in the crystal structure) play an important role in defining the local structure of electrode materials.
These defects can enhance the intrinsic conductivity of lithium-ion batteries, improve thermal and structural stability, promote pseudocapacitive dynamics, limit volume expansion, and enhance the electrochemical performance of lithium-ion batteries. In general, electrode materials with symmetrical compositions tend to act as semiconductors, while non-stoichiometric materials (doped or defect-induced) behave like metals, which helps to mitigate structural, chemical, and thermal changes. However, compared with Frenkel and Schottky defects, the impact of oxygen vacancies has not been fully investigated, and further research is needed to develop innovative LiBs.

Crystal orientation: Crystal orientation affects specific faces, crystal structure, and surface energy, which in turn affects the thermodynamics and reaction kinetics of the surface/interface. In batteries, supercapacitors, and fuel cells, physical and chemical interactions at interfaces play an important role in promoting electrochemical energy storage activities. In addition, single crystals have the advantages of small specific surface area, good structural stability, high mechanical and thermal stability, good reaction uniformity, and good crystallinity. The effect of crystal orientation has also been studied. These studies aim to significantly improve the electrochemical performance of lithium-ion battery electrode materials, including safety, capacity retention, and cycle life. Electrode materials with low activation energy and adsorption kinetics on a large number of crystal faces are expected to achieve high energy density and rate performance in LiB. The interest in exploring single crystal electrodes and their potential applications continues to grow, highlighting the need for advanced research methods to meet future energy challenges.
On the other hand, extrinsic design strategies mainly focus on the effects of size reduction, morphological changes, and surface modifications of electrode materials.

Reducing particle size: The particle size, particle size distribution, and shape of particles affect the contact area, diffusion resistance, diffusion path, energy density, and overall electrochemical performance of LiB. Reducing particle size shortens the transport length of Li+ ions, reduces the diffusion barrier of Li+ ions, enhances ion diffusion, increases the contact area between electrode active materials, current collectors, and electrolytes, and ensures the electroactivity of electrode materials. However, smaller particle size also increases the surface area, which can promote electrochemical activity and lead to more side reactions, which may cause thermal problems and internal short circuits in LiB. Particle size distribution affects the physicochemical properties and overall surface energy activity of electrode materials. Wide size distribution leads to high energy density, but poor battery uniformity due to particle size differences and surface energy differences. In contrast, uniform size distribution, although difficult to manufacture, can provide stable electroactivity, thereby improving the cycling performance of lithium-ion batteries by reducing stress strain during charging.
In addition, particle shape directly affects the effective surface area and mass flow characteristics, especially the tapping density, which affects the diffusion path and reaction kinetics of Li+ ions, thereby enhancing the cycling performance of LiB. However, particles from single crystal structures are expensive, difficult to manufacture and handle, and require a highly regulated reaction environment.

Morphological changes: The shape and morphology of electrode materials affect multiple factors such as porosity, tap density, diffusion path, surface area and interfacial contact area. These factors combined reduce the activation energy of electrochemical reactions, shorten the transport length of Li+ ions, enhance the diffusivity and electroactivity, improve the specific capacity and rate capability, and ultimately determine the electrochemical performance for energy storage applications. Different morphologies such as nanosheets, nanowires/nanorods/nanorobons/nanotubes, hierarchical nanostructures, microcubes, microspheres and microflowers develop according to the synthesis and calcination conditions. Nanowires/rods/ribbons/tubes and nanosheets, improve the compact density and provide a unidirectional diffusion path for Li+ ions. In contrast, microspheres/flowers, urchin-like structures, and 3D microspheres/microcubes with sizes around 5-10µm increase the packing density of the electrode, accommodate inactive ingredients (binders and conductive additives used in slurry manufacturing), provide extensive surface active sites for electrolyte penetration, and facilitate the diffusion of Li+ ions, leading to high energy density in LiBs. However, micron-sized particles extend the diffusion path of Li+ ions, limiting the rate performance and power density of LiBs. In addition, large cracks and deformations often occur between grain boundaries and on the electrode surface due to the accumulation of large amounts of stress during charging. These issues limit electronic and ionic conductivity, leading to capacity fading, electrode detachment, and battery degradation.

Surface modification: Surface modification is an easily implemented, cost-effective, and widely used strategy that can be achieved through techniques such as surface coating, etching, and ion doping. These methods improve ionic conductivity and create surface active sites that are conducive to electrolyte penetration, which is critical for the formation of a solid electrolyte interface (SEI) layer. This layer helps buffer volume expansion and contraction, maintain structural integrity, and mitigate capacity fading during cycling. Therefore, it is highly desirable to prepare electrodes with high voltage, high energy density, low cost, excellent intrinsic conductivity, and robust structural, chemical, and thermal stability. In addition, electrodes should have various morphologies with high surface area and porous properties. Surface modification techniques, including coating with carbonaceous materials or metal oxides, surface treatments (such as acid/base or metal oxide etching), and ion doping are essential for improving electronic and ionic conductivity and developing coatings. These modifications help to alleviate volume changes, suppress microstrain in the crystal structure, and improve surface adsorption characteristics for additional Li+ ions, thereby improving the electrochemical performance of lithium-ion batteries. Electrodes are classified into different types based on the chemistry of the electrochemical reactions during cycling, either intrinsically or extrinsically designed. A large number of reports have detailed the positive and negative electrode materials, synthesis methods, modifications, and studies on the electrochemical reaction mechanisms.

Ultrasonic coating systems are used to apply polyimide coatings to create separator layers in applications where a chemically inert protective coating is required. Polyimide coatings are an alternative to tape for complex geometries and small areas such as channels and holes, encapsulating hazardous materials and protecting lithium and other hazardous substances from harmful reactions or leaks. Polyimides are widely used as flexible encapsulation materials in batteries using radioactive or highly reactive elements, and they have good structural integrity.

Ultrasonic spraying technology for polyimide separator coating has the following advantages:

• Ultra-thin films with excellent porosity can be produced.
• The resulting coating is durable, mechanically stable, and stable in each layer.
• The nozzle has no moving parts that are prone to wear and has a long service life.
• It has ideal dielectric properties to meet a variety of electrical needs.
• Deep expertise in polyimide coatings and mature and reliable technology.
• Extensive experience and superb craftsmanship in microporous membrane coatings.
• The prepared film has extremely high uniformity, good repeatability and stable quality.
• The obtained high-temperature resistant coating can function normally in a temperature environment up to 400 degrees Celsius and has a wide range of applications.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

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