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On the charge

Dr Scott Brown

The UK throws away around 600 million household batteries every year, with two-thirds, many containing heavy metals such as lead and mercury, sent to landfill.

These will eventually break down and the dangerous chemicals may leach out, resulting in soil and water pollution, in turn causing damage to our natural ecosystems and wildlife.

But it doesn’t have to be that way, insists Dr Scott Brown, chief executive officer, Nexeon, this being the company whose new Li-ion battery technology uses silicon in place of carbon as the anode material.

What advantages does that bring?
“Our approach at Nexeon has the potential to improve significantly the performance of rechargeable batteries and, I believe, can have a major impact on environmental sustainability. Compared with carbon, silicon has ten times the capacity for lithium on a weight basis and three times its capacity by volume.”

In basic terms, that means better batteries, which are key to the faster adoption of electric vehicles, for example. By the same token, renewable energy technologies – e.g. wind and solar – need better energy storage systems to increase their effectiveness, while rechargeable batteries in consumer devices help to reduce the impact that batteries have on the environment.

“It is now widely accepted that silicon materials are the key to improved energy densities in Li-ion batteries,” Brown points out,” and that the winning technology will be both high performance and low cost.”

As a battery materials and licensing company working with product OEMs and battery companies to enable the next generation of lithium-ion batteries, Nexeon’s silicon materials enable much greater energy density and battery capacity to be achieved, providing lighter batteries with more power and longer lifetime between charges.

In the UK, Nexeon has commissioned a state-of-the art process development and manufacturing facility at Abingdon, Oxfordshire. This has been built to be highly versatile and to handle a wide range of materials and reagents. It also enables the company to understand how its materials will perform in commercial production conditions. What Brown describes as the ‘drop-in’ nature of Nexeon’s materials means they do not require substantial changes to existing Li-ion battery manufacturing processes.

“Getting the highest performance from Li-ion rechargeable batteries requires research and a sound understanding of each of the component parts of cells and the way they interact,” he points out. “Anode materials must be optimised to work in conjunction with conductive additives, electrolytes and binders. Real-world operating conditions are as important as theoretical parameters in delivering user benefits across challenging applications. Equally importantly, at Nexeon we are fortunate to be working with some of the best carbon, electrolyte and binder companies in the industry.”

Lithium-ion rechargeable batteries will remain the technology of choice for the foreseeable future, he believes, citing a number of advantages that Li-ion delivers when compared with other mature technologies by offering the best combination of: Energy density (light weight, small volume); low self-discharge (retains its charge when not in use); established and low-cost manufacturing and a wide range of formats.

“Other battery technologies are in development, but none is yet ready to challenge the performance of lithium ion. Today’s applications demand ever greater battery performance, so lithium ion batteries need to work even harder, as that is where the future lies. The lithium ions in a Li-ion cell move from the cathode to the anode as the cell is charged, and back again on discharge. To achieve ever-improving energy density, we need a cathode that contains more lithium and anodes that can absorb more lithium.”

Expansion issues
Traditional lithium-ion batteries use graphite in the anode: a graphite-based battery in a smartphone stores enough energy to watch movies for about two hours.

“Replacing the graphite with silicon will extend the viewing time significantly,” confirms Brown. So, why don’t all lithium-ion batteries already use silicon anodes, instead of graphite?

“Current forms of silicon expand on charging – and an expanding battery would break the phone.”

How exactly do you get over these expansion problems? Nexeon has identified a class of material that the company believes will be one of the ‘best-in-class’, in terms of energy density, while maintaining physical anode dimensions for long cycle life.

“The rate of take-up of electric and hybrid vehicles is limited principally by anxiety over the range available between charges. Advanced battery technology based on silicon anode lithium-ion batteries accelerates the progress of this important social development. Carbon anodes – the incumbent technology used in lithium-ion batteries – have almost reached their theoretical capacity limit and their future potential is limited.”

All of which makes the £10 million SUNRISE project on which Nexeon is embarked timely.

“Project SUNRISE addresses the silicon expansion and binder system issues, and allows more silicon to be used, further increasing the energy density that can be achieved in the cell,” explains Brown.

Innovative silicon anode material with a polymer binder represents a ‘drop-in’ replacement for current graphite anode systems. Lower cost and better performance power sources will reduce the time required for EVs to achieve mass adoption.

“We are about halfway through and have already produced silicon battery materials that have performed better than expected. Samples are now with potential customers for evaluation and initial feedback has been very positive.”

SUNRISE might well prove to be the gateway to creating far better materials for Li-ion batteries – an essential step to achieving electric vehicles (EVs) with greater range (400 miles and above), where range anxiety, cost, charge time or charging station availability are almost all related to limitations of the batteries. Silicon-enhanced batteries with longer life and higher energy density will also be of benefit in consumer electronics products and static energy storage applications.

Spice project
Nexeon is also embarked on a new project to optimise coating technology for its silicon material. This approach will result in improved cell performance and also extend the system compatibility of silicon anode materials, allowing use of lower-cost electrolyte formulations and lower overall battery cell costs. The project, named SPICE (Silicon Product Improvement through Coating Enhancement), is expected to take 18 months to complete. Focus will be on the use of an optimised coating for improved surface morphology, leading to improved conductivity of the underlying anode material for faster charge rates and sustained capacity of the battery during charge/discharge cycles.
“Using an optimised coating has several important performance advantages, and will further strengthen the case for adoption of silicon anode technology by OEMs and battery makers globally,” says Brown.

Nexeon’s CEO is greatly encouraged by the rate of take-up of silicon amongst EV manufacturers, notably its use in the fully-electric Model 3 Tesla, which has been winning high praise and garnering awards. “The fact that silicon has already been adopted in EVs is really good news, because the automotive industry is by nature very conservative and Tesla are proving a powerful, positive force in helping to break down such barriers.”

As for Nexeon itself, while taking care of the here and now, it would appear to be a company with its sights firmly fixed on exploiting the substantial future market opportunities that exist for advanced battery materials.

Author
Brian Wall

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