Shape matters!

Sometimes the difference between ordinary material and breakthrough technology is not chemistry but material geometry. Two materials can be built from the exact same atoms and still behave nothing alike. In batteries, this difference can determine where a battery can be used.

“Why can a diamond that cuts glass, and graphite that writes on paper, be the same material?” – is a hook often used in high school classes to make students interested in chemistry. To this day, this example perfectly describes that often crucial properties and phenomena in chemistry and material sciences are explained by surprisingly simple things such as molecular geometry, material form, shape, and size. And this goes beyond molecular structure.

Morphology matters a lot. The same substance can consist of spherical particles or have a completely irregular form. It may be silky smooth on the surface or have pimples, cracks, and pores. These small nuances impact the properties of items we use on a daily basis. And the closer you zoom in on material with your analytical device, the more complicated it may get.

This is particularly important in the battery industry where geometry, shape, and surface properties of cathodes and anodes matter on many levels. So how does shape decide the outcome in real materials?

Imagine two office buildings of the same size, but with completely different architectures. The first building is a long hallway with offices on both sides of the hallway and two building entrances on both ends. You can enter only from those and walk along the hallway till you get to your office room. If the hallway becomes crowded or blocked, movement through the building slows considerably because there are no alternative routes.

The second building has several entrances, floors, and hallways. Obviously, it would allow more employees in a short time to reach their offices. And in case a staircase or hallway is blocked, there is an alternative route. Similar logic can be applied to the working principle of some of the most common lithium-ion batteries we use every day. Charging and discharging batteries is just lithium ions running back and forth between cathode and anode. When lithium enters cathode material, it moves along its crystal structure and, like a kid in school, sits at the site designated for it, although.

For example, LFP (lithium iron phosphate), a common cathode material, has a crystal structure with 1D lithiation channels, meaning lithium ions move primarily along one-dimensional channels inside the crystal (Hu, Huang, Yang & Pan 2020). LMO (lithium manganese oxide), on the other hand, has a crystal structure with a 3D network and several pathways for lithium to travel. And while actual battery performance is managed by numerous parameters related to cell design and chemistry, you can expect that LFP will charge and discharge slower compared to LMO battery, making the latter better in applications that require more energy output per unit of time (power). (Thackeray 1997.)

There is an increasing interest in research in the field of nanomaterials. This includes both reducing already used materials to nano size in order to modify and improve their properties as well as developing new, more exotic materials such as carbon-based nanotubes, nanofibers, and graphene. Going nano provides several benefits.

Previously mentioned LFP also has low ionic conductivity, meaning there is a resistance that makes it harder for lithium ions to travel inside the battery. Reducing particle size to “nano” is the second most important method to improve conductivity. In smaller particles, the travel length of ions is simply shorter, and there are more surfaces for reactions to occur. And the role of nano increases as we are transitioning to new technologies. (Hu, Huang, Yang & Pan 2020.)

Currently, silicon is one of the most studied anode materials after graphite, due to the potential of storing much more energy per unit of weight. Still, most commercial anodes marketed as silicon anodes are a mixture of graphite and silicon, because the use of pure silicon is significantly limited by expansion of the material. Silicon expands and shrinks in size during charging and discharging of the battery. Continuous volume changes lead to cracking and pulverization of the silicon particles, separating them from current collectors, causing loss of electrical contact. Simultaneously, pulverization causes stable surface layers to continuously refresh, depleting lithium from the battery. Not to mention physical stress that impacts the whole battery system. A partial solution comes again from nanoparticles. 

Decreasing particle size reduces strain on the particles, and while this doesn’t eliminate volume changes, it reduces cracking and pulverization of battery anodes. Nanoparticles, however, tend to form clumps, or ”agglomerate” trapping air between them and taking up more space, which makes it harder to fit more anode material inside the battery cell. They are also harder to manufacture, requiring either more complicated production methods or energy-intensive milling process. (Pavlovskii, Pushnitsa, Kosenko, Novikov & Popovich 2026.)

Another way to solve the silicon volume change problem is to introduce empty space in the silicon. Void space can be added within silicon particles, making them hollow like a ping pong ball. Vice versa, silicon can be surrounded by empty space and encapsulated in a carbon shell, like a chocolate egg with a toy inside. Alternatively, the particle surface may have well-distributed pores. Each method has its own pros and cons, but the main logic is similar, introduction of empty space where particles can freely expand without causing outward stress, cracking, and pulverization. (Pavlovskii, Pushnitsa, Kosenko, Novikov & Popovich 2026.)

Porosity has other purposes as well. Similarly to how a sponge sucks up water, a more porous surface allows a battery electrolyte to better penetrate and wet battery material, improving transportation of lithium ions. This impacts various battery performance metrics, but as with nanoparticles, it impacts how much material can fit inside the battery.

Beyond size, shape is an important factor. Most of the battery cathode materials are highly ordered with crystal structures such as previously mentioned LFP and LMO, but the situation is different on the anode side. Silicon can have ordered structure (crystalline) or disordered (amorphous). When expanding, they behave differently, while amorphous silicon expands more uniformly in all directions, in crystalline silicon expansion is more significant in some directions, making it more prone to cracking and pulverization.

Graphite, the dominant anode material on the market, consists of the highly ordered planes, like a library filled with similar shelves, that store lithium when you charge the battery. While it is great in lithium-ion batteries, new technologies demand new materials. Graphite isn’t suitable anode material for emerging sodium-ion batteries, because it is harder for graphite to store larger sodium ions. Therefore, more elastic and disordered “hard carbon” is used, which resembles a chaotic warehouse full of different shelves arranged who knows where and some shelves even knocked over. (Saju, Chattopadhyay, Xu, Alhashim, Pramanik & Ajayan 2024; Manna, Billa & Puravankara 2026; Kim, Yang, Lee & Shim 2025.)

Manufacturing active battery components isn’t just about making a correct molecule. It is heavily dependent on particle engineering and production of correct chemistry, with desired crystal or amorphous structure, right shape, particle size, and porosity.

Some of the used battery materials like graphite are already close to their theoretical limits, meanwhile others have still room for improvement. While particle engineering can’t solve all the problems, it can bring some of the materials closer to their theoretical limits. It also allows the use of new materials and battery technologies that provide better performance or even enable utilization of alternative raw material sources. The remaining question is: How do we take particle engineering outside the lab into a pilot and industrial scale, in a sustainable and profitable way.

This article is part of the Battsi and Ekoakku project.