1.5.5 Application Profile: Batteries
Short application description
The battery market is divided into three types; primary batteries, which are non-rechargable; secondary batteries, which are able to be recharged; and reserve batteries, which are intended to be used when a primary power source fails. The chapter mainly considers secondary or rechargeable batteries. These account for two thirds of the global battery market, a share valued at around USD 38 billion by Freedonia Group.
The battery market is expected to grow substantially in the coming years. This is partially driven by growth in existing battery applications - particularly laptops, ‘netbooks' and mobile devices. However, the primary driver will be new applications, particularly in the automotive industry. The number of Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEV - which utilise a combustion engine and a battery pack as dual power sources) is set to increase. A number of car manufacturers are following the lead of Toyota and Honda to develop EVs or HEVs; these range from new manufactures producing high-end sports cars; such as Tesla Motors; and major existing firms; including General Motors, with its Chevy Volt.
There are currently four main technology approaches to rechargeable batteries; lead acid; nickel cadmium; nickel metal hydride; and lithium ion batteries. The latter two technologies are increasing their share of the overall rechargeable market, primarily because their energy density - measured in Watt hours per kilogram (Wh/kg) is substantially higher. Lithium ion batteries have particularly gained market share in this decade, increasing their use in mobile devices and laptops.
Lithium-ion batteries use a positive electrode which is typically Lithium Cobalt Oxide (LiCoO2) and a graphite negative electrode. These are typically formed as two sheets, kept apart by a plastic separator. The electrodes are held within a liquid electrolyte (which can release oxygen when punctured or overcharged, causing and explosion). The electrodes are pressed together by a metal case.
The energy density advantage of Lithium-ion batteries is substantial; an average value would be 150 Wh/kg, a six-fold increase on the performance of lead acid batteries (at 25 Wh/kg). Another advantage of Lithium-ion technology is that there is significantly less power leakage than with other technologies, at just 5% per month. However, Lithium ion batteries also have drawbacks; if the positive and negative electrodes come into contact, the battery itself can explode. Exploding laptop batteries has forced manufactures to issue extensive, expensive product recalls. Other issues with Lithium ion batteries include a risk that they become ruined if they are completely discharged, and their heat sensitivity.
More recently, Lithium-ion polymer batteries have been developed. These hold a lithium salt electrolyte within a polymer composite. These can be lower cost, because they no longer need a welded case to hold the electrodes in place - the case can even be flexible. These are also more robust, in that the electrolyte is less prone to explode.
Impact of Nanotechnology
Nanotechnology for batteries is a very active field of research and development. A development by Yet-Ming Chiang at MIT used an iron phosphate material as a replacement for the Lithium Cobalt electrode. Later reductions of the iron phosphate size to less than 100nm further improved performance. This technology is less prone to explode, is smaller (because higher energy densities mean that a battery cell with given power can be smaller) and have a lower cost of materials. This technology was licensed to a number of firms, including A123 Systems.
Another MIT group, led by Gerbrand Ceder has also developed a lithium ion phosphate cathode material, which is capable of discharging its entire energy capacity within 10 seconds (compared to 90 seconds for a conventional Lithium-ion battery. This makes it more like a supercapacitor, used to deliver a high charge in a short burst.
The primary functional requirement for batteries is their power density, expressed as Wh/l or Wh/kg. Li-ion batteries currently have power densities in the range 100-200Wh/kg, with NiMH approaching 100 Wh/kg. New Li-ion batteries are predicted to deliver power densities in excess of 300 Wh/kg.
The charge/discharge efficiency of a battery describes how rapidly it can delivery charge and be recharged. The battery work by Gerbrand Ceder at MIT found a discharge speed of 10 seconds, which is substantially quicker than existing solutions. Note here the distinction between batteries, in which other attributes are also important, and supercapacitors, for which the primary intention is to deliver as high a charge in as short a time as possible.
Self Discharge Rate
Most batteries gradually lose their charge, even whilst a current is not being drawn. This is particularly a challenge for reserve batteries, which would need to retain a charge even after a long period (years) of inactivity.
Cycle durability is another measure of the lifetime of a battery, indicating the number of times it can go through a charge/recharge cycle. This was typically in the range 300-500 cycles, but LiFePO4 batteries, for example, have been found to last for 2000-3000 cycles.
For automotive applications, the risk of explosion is felt to a barrier to adoption of Li-ion batteries; the consequences would be more severe with larger battery packs, or if an explosion were to occur when the vehicle was being used. Companies like A123 Systems are therefore at pains to point out that the consequences of their batteries being punctured are far less severe than with conventional Li-ion batteries.
Operating Temperature Range
For most battery applications, an operating temperature range of -40°C to 80°C is necessary, and performance should not be substantially degraded at the extremes of this temperature range.
mPhase's smart NanoBattery uses a silicon based, superhydrophobic membrane to keep the electrolyte separate from the electrodes, maintaining the battery in an ‘off' state which drains no power. When an electric field is applied to the membrane, an electrowetting effect allows the electrolyte to flow through the membrane barrier, activating the battery.
ZPower Silver-Zinc Battery
ZPower's batteries have an element of nanotechnology, in that they employ a silver cathode which is coated with unspecified nanoparticles, presumably increasing surface area. The batteries also have a composite polymer zinc anode, and a layered separator which is designed to reduce dendrite growth. The battery is advertised as having 40% more running time and as being 90% recyclable. The technology is protected by an extensive patent portfolio, with 25 patents granted and 36 pending.
26650 Series Cell, A123 Systems
A123 systems 26650 cell was originally intended for use in power tools, and claimed a tenfold increase in power capacity over conventional lithium ion batteries, as well as rapid charging - to high capacity in five minutes.
Growth in the Lithium-ion battery market comes from a number of sources, including portable devices, power tools, and electric vehicles. The Li-ion market for automotive applications is projected to increase from US$ 337 million in 2012 to US$ 1.6 billion in 2015. A report by iRAP assessed the value of the nano-enabled battery market at USD 169 million at present, increasing to US$ 1.133 billion in 2013; a 46.3% annual growth rate. Within this, the market share of ‘large format modules'; battery packs for electric vehicles, increases from US$ 64 million (38%) to US$ 960 million (85%).
Selected Key Companies Profiles
Nanoexa (http://www.nanoexa.com) is a manufacturer of high power lithium batteries, and is based in California. The company develops manganese-rich electrode structures, which enable higher (up to double) the power storage of Lithium cobalt oxide.
mPhase's (http://www.mphasetech.com) subsidiary, AlwaysReady has developed the Smart NanoBattery. This is designed to provide back-up power and utilises a triggerable porous membrane which keeps the electrolyte separate from the electrodes. This means that in its off / dormant state the battery suffers no power loss.
A123 Systems (http://www.a123systems.com) has a case for being one of the most successful ‘nanotech' companies, now having 1800 employees. The company produces batteries which employ a doped nanophosphate material as an electrode; technology which A123 has licensed from MIT. The company's first product was high power rechargeable battery for power tools, and it has also developed a battery pack for use with hybrid vehicles. This is designed to supplement the factory battery of the Toyota Prius, offering greater energy storage capacity. A123 signalled its intention to float in August 2008, though the economic crisis may now have delayed this plan.
Seeo (http://www.seeo.com/) develops Li-ion batteries which have a solid polymer electrolyte. To overcome the conductivity challenge (liquid electrolytes are more conductive than polymers) a block co-polymer is used; this has the advantage of making the battery more stable. The company does not disclose revenue or headcount, but received an investment of US$ 1 million from Khosla Ventures in 2008.
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