Secondary Battery

A rechargeable battery that can be repeatedly charged and discharged, serving as a core component of electric vehicles, ESS, and IT devices and as a foundational technology for next-generation industr

Secondary Battery

Overview

A secondary battery (二次電池, Secondary Battery) is a battery that converts chemical energy into electrical energy for use and can then be recharged via an external power source for repeated use. It is distinguished from primary batteries, which cannot be recharged once used, and serves as the heart of electric vehicles (EVs), energy storage systems (ESS), and IT devices such as smartphones and laptops. In particular, since the commercialization of lithium-ion batteries in the 1990s, secondary batteries have established themselves as core infrastructure for carbon neutrality and the transition to electrification, and today they are regarded as a national strategic industry and a representative field of advanced manufacturing technology.

Key Details

Operating Principle

A secondary battery consists of four core elements: the cathode, the anode, the electrolyte, and the separator. During charging, an external power source draws electrons from the cathode and moves them to the anode, while simultaneously lithium ions travel through the electrolyte to the anode and are stored there. During discharging, electrons flow in the opposite direction through an external circuit, generating current, and the lithium ions return to the cathode. In other words, the essence of a secondary battery is an electrochemical reversible reaction in which the "flow of electrons" and the "movement of ions" occur simultaneously. As charging and discharging are repeated, the electrode materials degrade and capacity decreases; this is called cycle life.

Main Types

Lead-acid battery: The oldest commercial secondary battery, used for automobile starting and UPS applications. It is inexpensive but has low energy density.
Nickel-cadmium (Ni-Cd): Highly durable, but cadmium poses environmental hazards.
Nickel-metal hydride (Ni-MH): Widely used in hybrid electric vehicles (HEVs) and more environmentally friendly than Ni-Cd.
Lithium-ion (Li-ion): The current mainstream of the market. With high energy density and output, it is used extensively in EVs and mobile devices.
Lithium iron phosphate (LFP): With excellent thermal stability and cost competitiveness, it is being reevaluated for ESS and entry-level EVs.
Next-generation batteries such as all-solid-state and sodium-ion: Development competition is underway for next-generation technologies aimed at resolving safety and cost issues.

Materials Industry Ecosystem

The largest share of the cost of a lithium-ion battery comes from the so-called "four core materials." The cathode material determines battery capacity and output and is classified into NCM, NCA, and others depending on the combination of nickel, cobalt, manganese, aluminum, and other elements. Graphite is the mainstream anode material and affects charging/discharging speed and lifespan. The separator prevents physical contact between the cathode and anode to avoid short circuits, and the electrolyte serves as the pathway for lithium ion movement. Recently, material and process innovations—such as silicon anode materials, high-nickel cathode materials, and dry electrode processes—are actively being pursued to reduce costs and improve performance.

Applications

The largest market is undoubtedly electric vehicles. Batteries are a core component accounting for about 30–40% of EV costs, and vertical integration and joint investments between automakers and battery companies are active. The second pillar is ESS, where demand is surging for power storage devices that compensate for the intermittency of renewable energy such as solar and wind power. In addition, the scope of applications continues to expand to IT devices such as smartphones, wearables, and laptops, power tools, electric ships, and urban air mobility.

Latest Trends

In 2024–2025, the secondary battery industry entered a restructuring phase amid a temporary demand stagnation called the "electrification chasm" and oversupply originating from China. As prices of raw materials such as lithium and nickel fell, battery cell prices fell along with them, intensifying price competition; while China's CATL and BYD are expanding global market share by leading with LFP batteries, Korea's three battery companies (LG Energy Solution, Samsung SDI, and SK On) are focusing on defending profitability and diversifying their portfolios.

On the technology side, preparations for the commercialization of all-solid-state batteries are the biggest topic. All-solid-state batteries using sulfide-based solid electrolytes can greatly reduce fire risk and increase energy density, and domestic and international companies and automakers are building pilot lines with the goal of mass production in 2027–2030. In addition, development of various form factors and chemistries targeting cost and safety—such as 46-pi cylindrical batteries, lithium manganese iron phosphate (LMFP) batteries, and sodium-ion batteries—is proceeding in parallel. Furthermore, as supply chain regulations such as the EU Battery Regulation and the AMPC and FEOC provisions of the U.S. Inflation Reduction Act (IRA) are strengthened, the "battery circular economy" stretching from raw material procurement to recycling and the diversification of supply chains have emerged as key agendas for the industry. The market for recycling and reuse (upcycling) of spent batteries is also growing rapidly.