Batteries, energy storage and electric vehicles

The first principle

A battery stores energy as a chemical difference between two materials and releases it as current when an outside wire lets electrons pass from one to the other. Its trick is a separation of paths: ions travel inside the cell through the electrolyte while electrons are forced round the outside circuit, where they do work. Everything that matters about a battery, how far a car goes, how long a grid store lasts and which minerals a country must import, follows from the choice of the two electrode materials.

The core

How a lithium ion cell works

• Two electrodes, one shuttle. In a lithium ion cell the negative electrode is usually graphite and the positive electrode a lithium metal oxide or phosphate, with a liquid electrolyte between them and a porous separator that lets ions through but not electrons. On discharge, lithium atoms in the graphite give up electrons, which flow through the outside circuit, while the lithium ions cross the electrolyte and settle into the positive electrode; charging drives both back.
• Naming the electrodes. During discharge the graphite side is the anode, where oxidation happens, and the oxide side the cathode, where reduction happens; the industry keeps these names even while charging, when the roles reverse, which is why the cathode is said to decide the chemistry.
• Voltage comes from the materials. The voltage is set by how strongly each electrode holds lithium, about 3.6 to 3.7 volts for nickel based cells and about 3.2 volts for lithium iron phosphate, and cells are joined in series to raise voltage and in parallel to raise capacity, inside a pack watched by a battery management system.
• Four numbers judge a battery. Energy density, in watt hours per kilogram, decides range; power density decides how fast it can deliver; cycle life, the number of full charges before it falls to about 80 per cent of its capacity, decides how long it lasts; and cost per kilowatt hour decides who can buy it.
• Thermal runaway is the risk. If a cell is damaged, overcharged or overheated, the electrolyte and cathode can react, release heat and oxygen, and set off neighbouring cells, which is why phosphate cathodes, which hold their oxygen more tightly, are safer.

The chemistries

• Nickel manganese cobalt (NMC) packs the most energy and suits cars and phones, but needs nickel and cobalt and carries more fire risk.
• Lithium iron phosphate (LFP) stores less energy per kilogram but lasts longer, is safer and uses no nickel or cobalt, so it has become the choice for buses, three wheelers and grid storage.
• Sodium ion replaces lithium with abundant sodium and works well in cold, at lower energy density, so it suits stationary storage and cheap small vehicles.
• Solid state cells replace the liquid electrolyte with a solid, promising more energy and less fire risk, but they are still being scaled up.
• Flow batteries keep their energy in tanks of liquid electrolyte, often vanadium, so storage can be enlarged simply by enlarging the tanks, while lead acid, the oldest rechargeable, remains the cheapest for backup.

Dimensions

• Energy system. Solar peaks at noon and demand after sunset, so storage turns cheap daytime power into evening power; the grid needs cost and cycle life rather than light weight, which is why grid stores are measured in megawatt hours as well as megawatts.
• Pumped storage. Water is pumped uphill when power is cheap and run back through turbines when it is dear, returning about three quarters of the energy, and it still holds most of the world's stored grid energy; India had about 7 gigawatts (GW) working at the end of 2025 and about 12 GW under construction.
• Vehicles. An electric motor turns about 85 to 90 per cent of the battery's energy into motion, against about 20 to 30 per cent for a petrol engine, and it recovers energy in braking (regenerative braking), so an electric vehicle (EV) uses far less energy per kilometre; how clean it is depends on how clean the grid is.
• Resources. Lithium, nickel, cobalt and graphite are among the 30 minerals India named critical in 2023, and the Geological Survey of India inferred 5.9 million tonnes of lithium ore at Reasi in Jammu and Kashmir in 2023, an inferred resource, the lowest level of geological certainty; supply, mining law and the National Critical Mineral Mission as economics are in the Economy note on the energy sector.
• Environmental. A spent battery contains toxic and valuable metals, so recycling both protects soil and water and returns lithium, cobalt and nickel to the factory.
• Urban health. Two and three wheelers and buses dominate city traffic, so electrifying them first cuts local air pollution where people breathe it.

In practice

• Cell manufacturing. The production linked incentive (PLI) scheme for Advanced Chemistry Cell (ACC) battery storage, approved in May 2021 with Rs 18,100 crore, pays incentives for 50 gigawatt hours (GWh) of cell factories in India, because the cell is the costliest part of a pack and India still imports most cells.
• Grid batteries. Viability gap funding for battery energy storage systems (BESS), approved in September 2023 for 4,000 megawatt hours (MWh) with Rs 3,760 crore, was followed in June 2025 by a Ministry of Power scheme of Rs 5,400 crore for 30 GWh, paid from the Power System Development Fund.
• Pumped storage. The Central Electricity Authority's roadmap of 2026 aims at about 100 GW of pumped storage by 2035-36.
• Electric vehicles. The Faster Adoption and Manufacturing of (Hybrid and) Electric Vehicles (FAME) scheme ran in two phases from 2015 to 2024, and PM Electric Drive Revolution in Innovative Vehicle Enhancement (PM E-DRIVE), launched in 2024 with Rs 10,900 crore under the Ministry of Heavy Industries, supports electric buses, trucks, ambulances and charging stations; it was extended to March 2028, while its subsidy for two and three wheelers ended in March 2026.
• Recycling. The Battery Waste Management Rules, 2022 make producers responsible for collecting and recycling the batteries they sell, and set rising targets for recovered material and for recycled content in new batteries.

Issues and way forward

• Import dependence. India imports most of its cells and the refined minerals in them, and refining is concentrated in China, so cell factories under the PLI, recycling and minerals secured abroad have to grow together.
• Slow cell factories. Several ACC awardees missed their timelines, so faster land, power and clearances and penalties that are actually enforced are needed for the scheme to deliver.
• Charging. Range anxiety and too few public chargers hold back cars, so charging along highways and in housing societies, and common charging standards, matter as much as subsidies.
• Heat and safety. Indian summers stress cells and several scooter fires in 2022 led to tighter battery safety standards, so pack design, cooling and testing need constant attention.
• Long duration storage. Batteries suit a few hours of storage, while a grid that runs mostly on solar and wind also needs storage over days and seasons, which is where pumped hydro and hydrogen come in.
• Second life. Car batteries retire at about 80 per cent capacity, still good enough for stationary storage, so standards for reuse before recycling would stretch the value of every mined tonne.

Common confusions

• Energy and power. Energy, in kilowatt hours, is how much a battery stores, and power, in kilowatts, is how fast it can deliver; a grid store is described by both, for example 1 MW for 4 hours, that is 4 MWh.
• Battery and fuel cell. A battery stores its own reactants and must be recharged, while a fuel cell makes electricity as long as hydrogen is fed in.
• Anode and cathode. The anode is where oxidation happens and the cathode where reduction happens, so in a rechargeable cell the roles swap during charging even though the labels stay fixed.
• Resource and reserve. A resource is a mineral body that may exist, at inferred, indicated or measured certainty, while a reserve is the part proved to be mined at a profit; the Reasi lithium is a resource, not a reserve.
• Hybrid and electric vehicles. A hybrid has a petrol engine and a battery that helps it, while a battery electric vehicle runs on its battery alone and must be plugged in.

For the exam

• Keyword bank: electrochemical cell, intercalation, energy density, cycle life, thermal runaway, lithium iron phosphate, sodium ion, solid state battery, battery management system, battery energy storage system, pumped storage, regenerative braking, Advanced Chemistry Cell PLI, extended producer responsibility, second life.
• Previous year questions: Practise the previous year questions on this topic →
• Use in an answer:
  • Introduction with data: The Ministry of Power's viability gap funding of Rs 5,400 crore in June 2025 for 30 GWh of battery storage shows that storage has become the second half of India's renewable build.
  • Introduction with a source: The Advanced Chemistry Cell PLI scheme of 2021, with Rs 18,100 crore for 50 GWh of cell factories, was India's first attempt to make the cell and not only assemble the pack.
  • Conclusion: Every gigawatt of solar needs storage behind it, so cheap, safe and Indian made batteries are now as central to the energy transition as the panels themselves.
  • Conclusion: India's battery strategy has to close the loop, from minerals and cells to recycling, so that the metals mined once are used many times.