Emergency, Feature

LFP batteries are no saviour in emergency lighting

Good quality nickel-cadmium and nickel metal hydride batteries with the correct charging regimes will easily last for over four years, and although Ni-Cd contains cadmium, in Europe there is a robust and recognised recycling process in place

Phil Horsley of ARTS Energy argues that lithium iron phosphate batteries don’t represent the utopian ideal for emergency lighting equipment and that alternatives, such as nickel-cadmium and nickel metal hydride, have many key qualities.

 

THERE HAVE been recent press reports about the ‘demise’ of nickel-cadmium (Ni-Cd) and nickel metal hydride (Ni-MH) technologies in the emergency lighting market.

While it’s true that there have been bans on the use of Ni-Cd technology in power tool and consumer products in recent years in Europe, this is not the case in the USA.

Consequently production has decreased as the power tool was a large Ni-Cd market; however it’s worth remembering that emergency lighting batteries are classified as industrial and in Europe there is a robust and recognised recycling process in place which is widely used.

There have also been comments about the alleged superior performance of lithium phosphate (LFP) in this application, claims of double the life of Ni-Cd and Ni-MH batteries, although there is little evidence of this given.

Both Ni-Cd and Ni-MH cells are subjected to accelerated life testing to simulate life expectancy; these tests prove life expectancy of four-years plus as specified by the market and this is how it is done (using the Arrhenius equation).

Ni-Cd:

  • 6 months operating at 70°C (T Type)
  • 12 months operating at 70°C (U type)

Ni-MH:

  • 6 months operating at 70°C (T Type)
  • 12 months operating at 70°C (U type)

 

Indeed a good quality Ni-Cd and Ni-MH cell with the correct charging regimes will easily surpass the required four years, and now with the ARTS Energy ecolifeTM products, in Ni-Cd we have an eight-year life product, and in Ni-MH a 10-year life product with a five-year warranty.

LFP will have its place in the emergency lighting market due to its energy density and voltage profile per cell (3.2V) which gives size, weight and cost advantages. However, users must ensure that robust safety circuits are in place and suppliers should be carefully vetted to ensure quality.

For LFP, life testing cannot be done the same way with the same lead time, as increasing temperature degrades the chemistry.

The only real way to know is to test for the full-life requirement in the application or at a temperature below 60°C and as LFP is reasonably new in the application, this is yet to be proven.

It is also worth noting that LFP poorly operates below zero degrees Celsius and that it can’t be recharged below this temperature for safety reasons, whereas Ni-MH, and Ni-Cd in particular due to its robust chemistry, is suited to these environments. Ni-MH is particularly suited to low and high temperatures, from -30°C to 55 degrees Celsius and above.

Ultimate reliability is down to where the customer sources the Ni-Cd and Ni-MH products. Certainly some Ni-Cd batteries on the market are handmade in Chinese factories without internal and external environmental control, which makes it more difficult to guarantee consistency across batches, never mind the obvious health and safety concerns.

However ARTS Energy is the leading manufacturer in this technology and our products are produced in a fully-automated French factory which meets all the high-level regulations, quality and health and safety requirements, especially the EU’s more stringent ones.

While Ni-Cd contains cadmium, as long as the product is recycled through the correct aforementioned route, there is little environmental affect.

The Ni-MH chemistry is environmentally neutral and the product is 84 per cent recyclable.  Ni-Cd is 81 per cent recyclable and LFP is only 77 per cent recyclable (phosphate is strong drawback for recycling).

There are very few recycling companies taking back LFP products, as the costs of recycling of LFP are potentially prohibitive. Here are recycling costs per kilo from 2017:

  • LFP – £3.63
  • Ni-Cd – £0.87
  • Ni-MH – £0.06


(Source: G&P Batteries, Birmingham, UK)

And, within the EU Batteries Directive, we need to bear in mind that the recycling cost is covered by the producer of the battery, e.g. the manufacturer in that country, and/or the company introducing it into each European country.
 

ARTS Energy batteries are produced in an automated French factory which meets all the high-level regulations, quality and health and safety requirements, especially the EU’s more stringent ones.

Regarding energy consumption, if it’s true that LFP does carry a benefit due to pulse charging, but this is also true with Ni-MH. The later also uses intermittent charging, thus reducing energy consumption versus Ni-Cd.

The next subject raised to address is safety. It’s a fact that not all types of lithium battery are ‘safe’ for emergency lighting.

Australia has sanctioned it as safe but Japan has banned it. All lithium batteries including LFP, have to have extra electronic protection to avoid the risk of combustion from such things as a short circuit or overcharging.

LFP also uses phosphate as the cathode material which does make it ‘safer’ than lithium to use but still not safe.

Adding to this, there is not yet a standard in Europe for the use of lithium or LFP products in emergency lighting.

ARTS Energy has conducted many tests on LFP from many Far Eastern suppliers and has found as many variations in performance and safety as products tested.

All lithium products including LFP have an organic electrolyte to create the electro-chemical reaction needed.

It’s a fact that organic electrolyte, unlike the aqueous electrolyte used in Ni-Cd and Ni-MH, is highly flammable. Recently ARTS Energy conducted tests on all technologies to see the effect of an open flame on each battery. The findings were that with both Ni-Cd and Ni-MH, it had no effect or no further fuelling of the flame was seen; with lithium, there was an explosion and a ball of fire; and with LFP there was a strong venting effect like a blow torch of flame expelled from the battery

While mechanical damage – such as piercing of the battery casing – will not result in combustion or toxic chemical leakage, if there is a spark by a short circuit or open flame nearby, it is certainly a higher risk.

In summary, LFP will have its place in this market due to its energy density and voltage profile per cell (3.2V) which gives size, weight and cost advantages. However, users must ensure that robust safety circuits are in place and suppliers should be carefully vetted to ensure quality.

It is not the ‘saviour’ or the utopian product that it is often portrayed as. However, it’s true that Ni-Cd is likely to be phased out over the decade or two, but there is a very viable, environmentally and safe product already available which will give 10-years life, and that is Ni-MH.

 

  • ARTS Energy supply all battery technologies and uses its knowledge of power products to give its customer the right power source for the application. Article by commercial director Phil Horsley ([email protected], telephone +44 7785 283785).

 

  • See suppliers of emergency lighting and battery systems at LuxLive 2019, taking place on Wednesday 13 November and Thursday 14 November 2019 at London ExCeL. Entry is free. See more info and pre-register to stay in the loop HERE.