MICHELLEHAYWOOD
Battery powered
Diving can involve a lot of battery charging , and we need to understand powerful Li-ion batteries in particular , says Michelle Haywood
Lithium-ion batteries have a number of advantages over traditional battery technology . They charge faster , last longer and have a higher power density giving more battery life in a lighter weight battery . Lithium-ion batteries have become a common feature in consumer electronics and are the most popular type of rechargeable battery . They can produce a high voltage and have a low self-discharge rate . For most divers , lithium-ion batteries can be found in dive computers , cameras , torches as well as our mobile phones .
These batteries consist of four main components , a cathode , an anode , electrolyte and a separator . The cathode acts as the source of Lithium ions , and this determines the capacity and average voltage of a battery . The Lithium oxide used for the cathode is the active material and releases Lithium ions . The electrolyte is the medium that helps move the ions . It ’ s made of salts , solvents and additives . The salts allow the Lithium ions to move . The anode allows the current to pass through the external circuit . The separator in the middle prevents contact between the cathode and anode . Only Lithium ions can pass through microscopic holes .
The anode allows reversible absorption and emission of the Lithium ions released from the cathode . The anode is coated with active material . When the battery is being charged , the lithium ions are stored in the anode and not the cathode . When the battery is being used , the conducting wire connects the cathode to the anode and Lithium ions naturally flow back to the cathode through the electrolyte . The electrons are separated from the Lithium ions and move along the wire , carrying the electrical charge .
However , lithium-ion batteries do have a few drawbacks . The batteries are sensitive to high temperatures and inherently flammable . Battery packs that fail have a tendency to burst into flames in a runaway thermal reaction . The critical component is the separator which allows the maximum ion conductivity but prevents the electrical contact of the electrodes . Often , separators are polymers such as polyethylene or polypropylene and it ’ s these separators that are susceptible to a sudden rise in temperature . Thermal runaway reactions usually happen during charging . The heat generated during charging causes an accidental overheating of the reaction mixture .
Of course , the overheating situation can be made worse by how you charge the battery . Do you leave it inside the unit ? Or is it on a foam-filled shelf ( designed to prevent electronics getting damaged whilst a boat is in transit )? Or worse still – tucked under your pillow ? Do you keep electronics in a hot vehicle ? Physical damage is a key factor too . Lithium-ion batteries can burn fiercely when they go . As the temperature passes
240ᵒC , the cathode and the electrolytes start to decompose . These chemical reactions produce large amounts of heat that rapidly increase the temperature to 800ᵒC or higher . The cathode reactions release oxygen as they degrade , and that too feeds the fire .
Foam or CO₂ fire extinguishers aren ’ t much use against a fire that is feeding itself . Specialised Lithex fire extinguishers are now available , but they are pricey ( think over £ 300 for a 6-litre version ). Lithex fire extinguishers use Aqueous Vermiculite Dispersion ( AVD ) to effectively combat lithium-ion battery fires . AVD is a water-based mist containing thin , flat flakes of hydrated silicates . These tiny flakes of mineral are chemically and physically inert and non-toxic . The only thing given off when they are applied is steam . The mist of AVD creates a film over the top of the burning fire , which dries instantly . The particles bind together and create a nonflammable oxygen barrier between the fuel and the atmosphere . The water evaporates and cools the fire .
So , battery safety includes charging in a well-ventilated area ; making sure damaged batteries aren ’ t used ; not allowing batteries to overheat and – if you are on a liveaboard with a charging station – ask about Lithex fire extinguishers . Guidelines exist for using lithium-ion batteries installed on vessels ( Marine Guidance Note 550 ), but for those batteries that you bring with you , please take some responsibility . �
Lithium-ion batteries are commonly used in today ’ s super-bright diving torches
23