Overview

Sodium-ion batteries (referred to as sodium batteries) are a type of secondary battery that relies on the movement of sodium ions between the cathode and anode during the charge and discharge processes. Their working principle and structure are similar to those of the widely used lithium-ion batteries.

Both sodium and lithium belong to the same group of elements, exhibiting similar "rocking-chair" electrochemical charge and discharge behaviors in battery operation. During the charging process of a sodium-ion battery, sodium ions are extracted from the cathode and intercalated into the anode, with electrons being transferred through the external circuit.

The more sodium ions intercalated into the anode, the higher the charging capacity. Conversely, during discharge, the process is reversed; sodium ions move from the anode back to the cathode, increasing the discharge capacity as the number of sodium ions returning to the cathode increases.

Sodium Battery Working Principle

The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, involving the extraction and intercalation of sodium ions to achieve charge transfer. During discharge, sodium ions are extracted from the anode material and move into the cathode material. Electrons flow from the anode to the cathode through the circuit, releasing energy.

During charging, sodium ions are extracted from the cathode material and enter the anode material through the electrolyte. Simultaneously, electrons flow into the anode material through the external circuit. Ideally, the extraction and intercalation of ions during the charge and discharge processes should not cause structural changes in the materials and should not result in side reactions with the electrolyte.

However, due to the relatively large radius of sodium ions, the current technology inevitably causes structural changes in the materials during the extraction process, leading to decreased cycle performance and stability of the battery.

Working Principle of Sodium-ion Batteries

Sodium Battery Advantages

Energy Density: The energy density of sodium-ion battery cells typically ranges from 100-150 Wh/kg, whereas lithium-ion battery cells generally range from 120-200 Wh/kg, with high-nickel ternary systems exceeding 200 Wh/kg.

Currently, the energy density of sodium-ion batteries does not yet match that of ternary lithium batteries. However, the energy density of sodium-ion batteries can overlap or cover the 120-200 Wh/kg range of lithium iron phosphate batteries and the 30-50 Wh/kg range of lead-acid batteries.

Operating Temperature Range and Safety: Sodium-ion batteries have a wider operating temperature range, typically from -40°C to 80°C. In contrast, the operating range of ternary lithium-ion batteries is usually from -20°C to 60°C, with performance declining below 0°C.

Sodium-ion batteries maintain a state of charge (SOC) retention rate of over 80% at -20°C. Additionally, sodium-ion batteries have higher internal resistance compared to lithium-ion batteries, making them less prone to heating up during short circuits and thus offering higher safety.

World's Largest Sodium-ion Battery Energy Storage Station

Rate Performance: The charge and discharge rate performance of sodium-ion batteries is directly related to the migration capability of sodium ions at the cathode, anode, electrolyte, and their interfaces. Factors affecting sodium ion migration speed will impact the charge and discharge rate performance of sodium-ion batteries. Furthermore, the heat dissipation rate within the battery is a crucial factor affecting rate performance.

If the heat dissipation rate is slow, the heat accumulated during high-rate charge and discharge cannot be effectively dissipated, severely impacting the safety and lifespan of sodium-ion batteries. Due to the crystal structure of sodium cathode materials, sodium-ion batteries have good rate performance, meeting the needs of energy storage and large-scale power supply.

Charging Speed: Sodium-ion batteries can be fully charged in about 10 minutes, while ternary lithium batteries require at least 40 minutes, and lithium iron phosphate batteries require 45 minutes.

Comparison of Performance Among Sodium, Lithium, and Lead-acid Batteries

Industry Classification

Sodium-ion batteries can be classified into various types, including sodium-sulfur batteries, sodium-salt batteries, sodium-air batteries, aqueous sodium-ion batteries, organic sodium-ion batteries, and solid-state sodium-ion batteries.

In the energy storage sector, the currently scalable applications of sodium batteries mainly include high-temperature sodium-sulfur batteries and sodium-metal chloride battery systems based on solid electrolyte systems. These two systems both use metallic sodium as the active material for the anode and are more accurately referred to as sodium batteries. When referring to sodium-ion batteries, it typically means the latter three types.

Sodim-Sulfur Batteries: These have molten liquid sodium as the anode and elemental sulfur as the cathode, using solid ceramic Al2O3 as the electrolyte and separator. Sodium-sulfur batteries have a relatively high specific energy.

Sodium-Salt Batteries: These have liquid sodium as the anode, metal chloride materials as the cathode, and Na+ conductive Al2O3 ceramics as the electrolyte.

Sodium-Air Batteries: The cathode typically uses porous materials, which provide gas diffusion channels and sites for electrode reactions.

Organic Sodium-ion Batteries: These use hard carbon or sodium-intercalating materials for the anode, with cathode materials including transition metal oxides and polyanionic materials.

Aqueous Sodium-ion Batteries: These use different electrolytes compared to organic electrolyte batteries, providing higher safety performance.