Fun with chemistry

Batteries enter new phase

By David Appleyard

Battery technology has always evolved to meet consumer demand and today a host of new markets are opening up for energy storage applications. Electric vehicles and increasing renewable energy capacity are among the key drivers prompting research into a range of different chemical families. The goal is the development of low-cost, long-life, energy-dense and high-power batteries that can energize our future low-carbon world. 

Everywhere from pocket to grid

The cellular telephone in our pocket constitutes one tiny part of the world’s biggest consumer of battery technology – portable electronics.

Mobiles, tablets and laptops are a massive market, but while the lithium- or nickel-based battery within may power that latest gizmo, it does not necessarily represent the latest in battery technology development. Designed to supply just milliwatts of power, ideally for a period of several days, with a focus on light weight and sustained low output, such technology is not necessarily ideal for most of today’s emerging battery applications.

Professor David Greenwood at the University of Warwick in the UK, outlines the key market drivers: “Mobile energy for things like electric vehicles and large-scale energy storage for operating with the grid and the electrical distribution network. What those two growth sectors need is a bit different to the consumer electronics industry, which has driven battery development”.

This is a point echoed by Phil Hare, management consultant with analysis firm Poyry: “These are auspicious times for storage. Batteries actually seem to be coming to the fore, and I think are coming to the fore in part because of the crossover from developing electric cars. So costs are coming down enormously”.

IEC Technical Committee (TC) 21: Secondary cells and batteries, develops International Standards for all secondary cells and batteries, irrespective of type and chemistries (i.e. lithium-ion, lead-acid, nickel-based) or application (i.e. portable, stationary, traction, electric vehicles or aircraft). They cover all aspects such as safety, performance and dimensions and labelling, a new battery technology. Chemistry for flow batteries – another potential candidate for large-scale electrochemical energy storage – is now part of the TC remit.

Big batteries, big business

Big batteries are expected to become big business. Just how big is indicated from a recent report by US-based analysis firm Navigant which concludes that annual revenue for the commercial and industrial (C&I) energy storage industry is expected to reach USD 10,8 billion by 2025, from less than USD one billion in 2016.

As Alex Eller, research analyst with Navigant Research, explains: “Despite early challenges, global C&I energy storage system power capacity deployments are expected to grow from 499,4 MW in 2016 to 9,1 GW in 2025”.

A major driver of the demand for increased energy storage capacity has been the high penetration of variable output renewables, particularly wind and solar photovoltaic (PV). As an example, in 2013, regulators in California in the USA, which has a significant proportion of renewables, mandated the state’s three major utilities – Pacific Gas and Electric, Southern California Edison and San Diego Gas & Electric – to procure collectively 1 325 MW of energy storage by 2020, with installation by the end of 2024.

And in February this year, AES UK & Ireland commissioned its Advancion storage array at Kilroot power station in Carrickfergus in Northern Ireland, which provides 10 MW of grid-connected energy storage. Globally, AES owns and operates 116 MW of operational storage with a further 268 MW under construction or late stage development.

Evolving battery technology

New requirements for battery system performance characteristics may be emerging, but that does not necessarily indicate that lithium-ion or even older technologies like lead-acid are played out.

Greenwood highlights the evolving nature of battery technologies: “You have this family of chemistries around lead and lead-acid. There is another family of chemistries around nickel, the first of which was nickel-cadmium, while nickel metal hydride is the more modern version and then you have got a further family of chemistries which are around lithium and lithium-ion. There are many different flavours of lithium-ion, more than 40-odd; they are not all the same and they behave quite differently in places”.

He continues: “A lot of the new technologies that we are starting to look at are still lithium-based, but they're not working on transporting lithium ions, they're working on different reactions”. Greenwood cites a number of promising chemistries, including lithium-air, lithium iron phosphate and nickel cobalt manganese.

Indeed, in March 2016, sodium-ion battery technology company Faradion announced a partnership with WMG, University of Warwick and energy storage specialists Moixa Technology in a bid to commercialize this battery chemistry. By using highly abundant sodium salts rather than lithium, sodium-ion cells are anticipated to be 30% cheaper to produce.

Alongside endeavours to explore novel battery chemistries in more detail, the influence that the physical structure of the cell can have on performance is also driving research into new materials such as solid electrolytes or novel electrode structures.

Says Greenwood: “Typically the amount of energy that is held inside a battery cell is directly related to the amount of electrochemical material inside it, whereas the power that you get out of that cell is determined effectively by the active surface area inside the cell over which those reactions can take place”.

Ideally then, highly porous materials are used which allow rapid reactions for high power and can simultaneously pack in a large ratio of active material to support sustained reactions for high energy density. Graphene and other nanomaterials are showing promise in this area. IEC TC 113: Nanotechnology standardization for electrical and electronic products and systems is developing, for instance, Technical Specifications for "electrode nanomaterial used in nano-enabled energy storage devices such as lithium-ion batteries", and is also developing a range of publications related to this and to graphene-related applications.

The search for life

Lifespan is perhaps the major challenge for any emerging battery technology.

“The basic reactions are reasonably well understood, but like anything, it is the things that that you didn’t want to happen that are harder to control. There are many degradation mechanisms that come into play; the active sites in the electrochemical material effectively get clogged up with lithium deposits, or you can get problems with the electrochemical materials fracturing and coming away,” says Greenwood.

This degradation process has a significant impact on the size and mass of the current generation of battery technologies. In order to compensate for degradation over the eight or 10 years of an electric vehicle (EV) battery’s life, additional capacity is required initially if the system is to achieve design performance parameters after multiple charge and discharge cycles.

Furthermore, as some of these degradation processes are accelerated at states of very high or low charge, ‘buffer’ capacity is typically designed into battery systems to enable required performance whilst maintaining the charge state between, say, 10-90%.

All this adds weight, volume and cost

“A lot of the work that is going on around battery development nowadays is about really understanding those degradation modes, working out how to manage the battery in the best possible way so as to get the best out of it.”

Crash diet

One way battery performance may be improved is by reducing the mass of ‘ancillary’ components. Says Greenwood: “For your typical automotive battery at the moment, only about 40% of the mass of the battery is the electrochemically active material, the rest of it is all the support structure, the cooling structure, the control system, the electrical interconnects.

“There’s a lot you can do to understand how to better package that whole lot and get to a point where a great percentage of that battery pack is the chemically-active material, which is actually delivering on the primary purpose of the battery.”

Industry standards have a clear role to play here, explains Greenwood: “The standards really come in when we start to talk around applications for energy storage, because many of the sectors we have been talking about are relatively new to using electrical energy storage systems.”

Standard cell formats are one area of interest for consumers: “Manufacturers have their own proprietary standards that they are working to and that makes it incredibly difficult for users of those batteries to be able to standardize,” says Greenwood, in particular noting pouch and prismatic types of construction.

IEC TC 21 develops Standards for cell formats as part of its scope.

The power of chemistry

Looking forward, Greenwood envisages a number of developments over the coming decade or so. Within the five-year horizon: “It is all about being able to use much better the chemistry that we have got around us, to build electrode structures that give us the right mix of power and energy and which give us the durability that we need”.

Over the next 10 and more years: “That is when you start looking at things like lithium-air chemistries, which are still very much at laboratory scale. Typically these are operating with quite short life times at the moment. There is a lot of development work left to understand how we get the very best out of those chemistries and get them to a point where they can all be industrialized”.

“The different chemistries of batteries are still waiting in the wings,” concludes Hare, “and interestingly, lithium-ion batteries I think have a massive momentum behind them. We've already looked at lithium batteries, but the prospect of tuning those to meet the static applications is very intriguing.”

Hare envisages the prospect of lowering costs significantly by focusing on static applications, rather than requirements for lightness and power density.

He also posits another way to improve the lifetime performance of existing battery technology, using end-of-life EV batteries in static applications as well. With the performance specifications on EV batteries so much higher than required for, say, an average domestic static application, such as a solar PV system, the residual performance of an ‘end-of-life’ EV battery could be sufficient for many years.

“I think that's at an early stage, but there's a definite thought about that, and that's going to require all sorts of interesting questions about standardization.”

Chevy Volt battery Chevrolet Volt lithium-ion battery cutaway
Johnson micro hybrid battery Johnson 48V lithium-ion battery for so-called mild hybrid vehicles (Photo: Thomas Content, Milwaukee Wisconsin Journal Sentinel)
Li-ion drive battery installation on EV Underfloor battery compartment for electric vehicle