(1) Preface

Since mankind completed the Third Industrial Revolution and entered the electrical age, electric energy has been exploited and utilized to the maximum extent. As electric energy storage products, batteries have shown great potential and been applied in a wide range of scenarios. As the third generation of primary batteries, lithium-iron batteries are gradually attracting attention thanks to their high energy density and outstanding storage life. This paper elaborates on the working principle, advantages, applications and existing challenges of lithium-iron batteries.

(2) Battery Classification

First of all, various types of batteries are introduced. There are multiple classification standards for batteries. In terms of shape, they can be divided into cylindrical, prismatic and pouch types. According to cell materials, batteries include lithium-ion batteries, sodium-ion batteries, lithium polymer batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lead-acid batteries, alkaline batteries and so on.

(3) Overview of Lithium-Iron Batteries

The full name of lithium-iron battery is lithium/iron disulfide battery. It is a new type of high-energy lithium battery characterized by light weight, high energy and strong high-current discharge capability. Featuring stable discharge performance, long storage life and excellent safety performance, it is especially suitable for heavy-load occasions and has gradually become the optimal power source for portable electronic products.

It should be noted that lithium-iron batteries are different from the commonly mentioned lithium iron phosphate batteries (LiFePO₄). The full name of lithium iron phosphate battery is lithium iron phosphate battery, which belongs to secondary lithium-ion batteries (rechargeable). The lithium-iron battery is a primary battery (non-rechargeable) and falls into the category of lithium batteries.

Lithium-iron batteries generally have an energy density of approximately 297 Wh/kg and a nominal voltage of 1.5 V. The open-circuit voltage of a new cell is close to 1.8 V, and the terminal voltage under load is around 1.5 V. It is classified as a low-voltage lithium battery compared with other lithium battery systems. AA and AAA sizes are widely adopted in the market.

(4) Working Principle of Lithium-Iron Batteries

The operation of lithium-iron batteries follows basic redox reactions. Iron disulfide is generally used as the positive electrode material, while lithium metal or lithium alloy serves as the negative electrode material. Cells are manufactured via winding process. During discharge, iron disulfide is reduced and metallic lithium is oxidized. The electrochemical reactions are shown below:

Negative electrode (oxidation): Li→Li++e− Positive electrode (reduction): FeS2​+4e−→Fe+2S2− Overall discharge reaction: FeS2​+4Li→Fe+2Li2​S

(5) Characteristics of Lithium-Iron Batteries

(a) High Energy Density

Lithium/iron disulfide batteries usually achieve higher energy density than ordinary lithium batteries. The energy density of mainstream lithium iron phosphate batteries is below 200 Wh/kg, while ternary lithium batteries range from 200 Wh/kg to 300 Wh/kg. In contrast, lithium-iron batteries reach roughly 297 Wh/kg. High energy density enables favorable application in equipment with power output requirements.

(b) Low Material Cost

Iron disulfide is an abundant natural mineral with relatively low cost, granting lithium/iron disulfide batteries advantages in raw material expenses. Compared with ternary materials (mainstream cathode materials for lithium-ion batteries), its preparation difficulty is lower. It is also cheaper than nickel-metal hydride batteries of the same AA size, yet has no cost advantage versus ordinary alkaline batteries.

(c) Single-Use Property

The biggest disadvantage of lithium-iron batteries is that they can only be discharged once. For electrical equipment requiring long-term service, recyclable nickel-metal hydride batteries are more competitive despite lower energy density. Meanwhile, lithium-iron batteries are more expensive than alkaline batteries (also primary batteries). For this reason, alkaline batteries still dominate the primary battery market at present.

(d) Excellent Low-temperature Performance

The chemical reactions inside lithium-iron batteries are relatively active and maintain high energy conversion efficiency under low temperatures. Therefore, they work within a far wider temperature range than other primary batteries. Superior low-temperature performance expands their applicable scenarios.

(e) Light Weight and Convenient Storage

Lithium-iron batteries feature compact size and light weight. Cylindrical or button cells weigh only 70% of equivalent carbon-zinc batteries and 50% of alkaline batteries of the same size. Furthermore, lithium-iron batteries possess remarkable leakage resistance and excellent storage performance, with a storage life of up to 10 years. By comparison, alkaline batteries tend to leak electrolyte and swell, and their storable duration is relatively short.

(6) Applications of Lithium-Iron Batteries

Lithium-iron batteries are generally applied in heavy-load tools, toys and equipment.

Portable Electronic Devices

Lithium-iron batteries match portable electronic devices perfectly, especially equipment with specific requirements for discharge current and service life, such as game consoles, music players and cameras. Their high capacity and energy density can guarantee long endurance under heavy loads, obviously outperforming ordinary alkaline batteries.

Electric Toys

Lithium-iron batteries are also highly suitable for electric toys with high power demand. For instance, remote-controlled racing cars require large operating current and consume power rapidly, which fits the characteristics of lithium-iron batteries well.

Industrial Status

Lithium-iron batteries are often known as the third generation of primary batteries following carbon-zinc batteries and alkaline batteries. However, there is no obvious trend that alkaline batteries will be replaced at the current stage. Industry practitioners believe cost and selling prices restrict market development. Multiple factors lead to the persistently high prices of lithium-iron batteries in domestic market.

Currently, the lithium-iron battery industry is emerging yet growing slowly. Experts along the industrial chain have carried out targeted analysis, and the main restrictive factors are summarized as follows:

(a) High-cost Raw Materials plus Special Production Environment and Safety Requirements

The primary cause of high prices is the adoption of lithium metal strips for negative electrodes, whose cost is much higher than the zinc paste used in alkaline batteries. Lithium metal is highly active, so stricter temperature and humidity control is required in production workshops. Manufacturers need to install dehumidifiers and air-conditioning equipment and offer higher salaries for frontline operators. Additionally, the active lithium negative electrode, volatile electrolyte, combustible positive electrodes and separators require extra supporting safety facilities, which are unnecessary for carbon-zinc and alkaline battery production lines.

(b) High Dependence on External Supplies

Production equipment mainly relies on imports. Due to limited equipment suppliers, overseas manufacturers charge excessive prices. Once equipment breaks down, enterprises have to seek support from foreign suppliers, paying expensive fees for imported spare parts and maintenance services. Meanwhile, electrolytes largely depend on imports, and their compositions and formulas are kept as manufacturers’ trade secrets.

(c) Production Losses and High Defect Rate

Lithium-iron batteries demand high manufacturing precision, imposing strict standards for raw material selection and manual operation. Inferior raw materials, unqualified ingredients or human operational errors will raise the defect rate. The above internal and external factors make it difficult to cut the cost of lithium-iron batteries. On the other hand, China has issued environmental standards for carbon-zinc batteries and alkaline batteries since 2006. All mainstream alkaline batteries have realized mercury-free production, which deprives lithium-iron batteries of environmental advantages as substitutes.

With high energy density and outstanding low-temperature performance, lithium-iron batteries are becoming increasingly popular for portable electronic devices and heavy-load tools. Featuring high energy, light weight, relatively low raw material cost and long storage life, they are particularly suitable for scenarios requiring sustained power supply. Nevertheless, although the single-use characteristic limits widespread application, lithium-iron batteries are expected to occupy a position in the future battery market with technological progress and cost reduction.

Despite the slow development of the lithium-iron battery industry and challenges including high raw material costs and dependence on imported equipment, several domestic brands including Nais, Camelion and Betteries have made remarkable progress in technological research & development and market promotion. With upgraded environmental standards and growing consumer demand for high-performance batteries, lithium-iron batteries still boast broad development prospects and are expected to play a more important role in future battery technologies.