How new Cathode formulations are opening up market opportunities for Lithium ion

Battery specifiers can now choose Lithium ion cells with a range of alternative cathode formulations, each delivering different performance characteristics. Neil Oliver summarises the mainstream choices available today, and the pros and cons of each option.

When providing power for portable electronic devices, rechargeable Lithium ion technology has been the default choice for many years. The high volumetric and gravimetric energy density of Lithium ion has revolutionised the way we use portable devices in our everyday lives – providing compact, lightweight portable power that is safe and convenient to use. One drawback of Lithium ion has always been its ability to deliver power. The Cobalt cathode formulation (LiCoO₂) that provides the high capacity needed for portable electronics cannot provide the high currents at sustained voltages required for motor driven applications such as power tools or electric vehicles. So what are the alternatives?

Lithium ion cells with a Manganese formulated Cathode (LiMn₂O₄) provide high discharge currents but have lower capacity and the choice of Manganese is an expensive one.

In recent years, most cell manufacturers have migrated to a hybrid cathode technology termed ‘NMC’ where a combination of Nickel, Manganese and Cobalt (Li(NiCoMn)O2) are used to offer the high capacity traits of Cobalt but with the thermal stability and power capability of Manganese. These cells are finding common use in power tools, electric bikes and other motor driven applications. The technology now allows a single 18650 (18mm diameter and 65mm height) NMC formulated cell to be discharged continuously at up to 30 Amps which is more than ten times that permitted by cells with a pure Cobalt cathode. Fast charge currents of up to 9 Amps also cut charge times to minutes rather than hours. NMC formulated cells provide excellent low temperature operation - down as low as -40°C in certain applications. As with all things in life (and chemistry) there is a trade-off and the mAh capacity of such an 18650 size NMC cell is ~50% of a Cobalt cell - but the high discharge capability means that the trade-off is easily acceptable as Cobalt cannot function under such demanding conditions.

An alternative to NMC is the much publicised Lithium ion Phosphate (LiPoFe4) technology which also offers very high power density and excellent cycle life. One disadvantage with Phosphate is its lower running voltage (~3.3V rather than ~3.7V for NMC or Cobalt) meaning that more cells are required per battery. Phosphate cells also have a lower energy density than NMC.

As a developer and manufacturer of rechargeable batteries for professional applications, Accutronics is best placed to determine the correct cell technology for any given application. As more of our customers move away from older technologies such as Nickel Cadmium and Nickel Metal Hydride we find that NMC formulated cells are often a very good choice, especially where high discharge currents are required. The most common application of NMC is in motor driven applications such as power tools and mobility devices - but NMC is also ideal for professional motor driven applications such as robots, medical ventilators, patient lifting aids and surgical tools. Such devices normally require between four and ten 3.7V cells connected in series to obtain the required operating voltage.

Accutronics design the necessary electronic protection and capacity balancing systems required to ensure safe and efficient charging and discharging of the battery. We can also provide ‘Smart Battery’ fuel gauging and battery management circuitry for those applications where enhanced features are required to further improve the usability of the battery system. Smart Battery technology places the battery at the centre of the power management decision making process so the battery will only request and allow charging when it is safe and appropriate. Similarly, it will allow discharge until its stored energy is consumed and then signal that it is approaching empty and finally that it is depleted. Host systems and chargers can either request information from the battery or the battery itself will broadcast critical alarm conditions which need attention. Smart battery technology offered by Accutronics can provide a real end user benefit to all battery powered professional applications in terms of maximising efficiency, safety, functionality and performance.

To discuss your battery requirements with our Customer Service team please contact Accutronics on +44 (0) 1782 566688 or email sales@accutronics.co.uk

Alternatively you can contact Neil Oliver directly at neil.oliver@accutronics.co.uk