Lithium Metal Preparation Process

1. Brief Overview of the Electrolytic Metal Lithium Production Process

The primary raw materials for electrolysis are lithium chloride and potassium chloride (with potassium chloride added to lower the melting temperature of the molten salt). Lithium chloride and potassium chloride are fed into a semi‑closed electrolytic cell in specific proportions. Once the arc is struck and current is applied, the salts within the cell melt. After melting, alternating current is switched off and direct current is applied; under the influence of the DC current, metal ions accumulate at the cathode to form liquid metallic lithium, which is manually removed in intermittent batches. The resulting metallic lithium is then purified through low‑temperature distillation to obtain battery‑grade lithium, ultimately yielding lithium strips and lithium alloys. The lithium slag is subjected to hydrolysis treatment.

The electrolysis process employs a new technology featuring multiple anodes inserted from the top, resulting in lower lithium chloride consumption and lower specific power consumption compared to similar electrolytic cells.

Electrolysis reaction equation: 2LiCl = 2Li + Cl₂↑

Lithium slag hydrolysis reaction equation: Li₂O + H₂O = 2LiOH

Sodium Hypochlorite Production via Chlorine Absorption: The chlorine‑containing tail gas generated at the anode of the electrolysis cell is collected by a hood and then drawn by a fan to the absorption treatment unit. The absorption process employs multiple turbulent packed‑tower units, with each tower equipped with two induced draft fans—one in use and one as a standby—and every two towers share a single exhaust stack (25 meters high). The absorbent solution is a sodium hydroxide solution. To prevent chlorine gas leakage due to equipment failure during the absorption process, the production system implements interlocked control among the induced draft fan, the circulation pump, and the silicon rectifier: should either the induced draft fan or the circulation pump fail, the silicon rectifier will automatically shut down. The chlorine absorption efficiency of a single absorption tower is 90%, while the chlorine absorption efficiency of a complete absorption tower group—consisting of three towers per group—can reach as high as 99.9%. The treated tail gas meeting emission standards is discharged through a 25‑meter‑high exhaust stack.

The sodium hypochlorite solution produced through absorption typically has an effective chlorine concentration of around 12%, and is mainly used for water purification, as well as for disinfection and pulp bleaching.

Reaction equation: Cl₂ + 2NaOH = NaClO + NaCl + H₂O

2. Brief Overview of the Battery-Grade Metallic Lithium Production Process

Battery‑grade metallic lithium is produced using a domestically developed, pioneering vacuum low‑temperature distillation purification technology, which significantly reduces the cost of metallic lithium purification while greatly enhancing the reliability and safety of equipment operation.

The fundamental principle behind vacuum low-temperature distillation for purifying metallic lithium is as follows: At a given temperature, different metallic elements exhibit varying vapor pressures. By leveraging the distinct differences between evaporation and condensation rates, impurity elements—primarily metallic sodium and other heavy metals—can be separated from metallic lithium, thereby achieving the desired level of purification. At different temperatures, the ratio of an impurity element’s vapor pressure to that of metallic lithium is referred to as the relative volatility, denoted by A. The calculation formula is: A = Px/Pli, where Px represents the vapor pressure of the impurity element and Pli denotes the vapor pressure of metallic lithium. When A > 1, the volatility of the impurity element exceeds that of metallic lithium; when A < 1, the volatility of the impurity element is lower than that of metallic lithium; and when A = 1, the volatility of the impurity element is equal to that of metallic lithium. During the heating process of the lithium feedstock, precisely controlling the temperature of the material within the distillation furnace enables the effective separation of impurity elements contained in the raw lithium, ultimately achieving the goal of distilling and purifying metallic lithium. The advantages of this process include: through precise adjustment of distillation temperature and duration, high‑purity metallic lithium with varying purity requirements can be produced, while minimizing lithium loss and reducing energy consumption; the process boasts a simple configuration and convenient operation, allowing for continuous production with relatively low capital investment.

After electrolysis, the lithium is transferred to a melting furnace maintained at a temperature of 210 ± 15°C for melting. To facilitate the separation of lithium slag and effectively prevent severe oxidation of metallic lithium during the melting process, special No. 26 white oil must be added to the melting furnace. The white oil should be replaced with fresh oil on a regular schedule, while used white oil is stored in iron drums and sent back to the manufacturer for recycling once a sufficient quantity has been accumulated. Before the oil‑gas mixture drawn by the induced draft fan enters the blower, it must first pass through an oil‑gas separator; after the white oil has condensed, the effluent is discharged via the exhaust stack. Throughout the entire melting process, the temperature is consistently maintained at around 210 ± 15°C, allowing impurities such as oxides, nitrides, and electrolytes—due to their higher densities and melting points compared to metallic lithium—to naturally settle out. Subsequently, the upper layer of liquid metallic lithium is fed into a feeding tank maintained at 210 ± 15°C and a vacuum level below 10 Pa, after being filtered through a precision filter to remove higher‑melting‑point impurities. Next, the liquid metallic lithium is kept at 210 ± 15°C in the feeding tank for degassing, then transferred to a distillation column operating under a vacuum of less than 1 Pa and a temperature of 500 ± 15°C for 4–8 hours of distillation. Because sodium has a low melting point and a high saturation vapor pressure, it is distilled off first and recovered via a sodium collection system, yielding battery‑grade metallic lithium with an extremely low sodium content. Following this, the lithium undergoes a second fine filtration under argon protection, after which high‑purity technical lithium is transferred into a sealed glove box. Under an argon atmosphere (with water and oxygen levels ≤ 10 ppm), the metallic lithium is cast into shape, cooled by oil quenching, demolded, trimmed, inspected, and packaged, ultimately producing battery‑grade metallic lithium ingots that meet the required specifications in terms of shape and dimensions, with a purity of 99.95%.

1,000 tons of electrolytic metallic lithium per year

(1) The annual consumption quotas for 1,000 tons of electrolytic metallic lithium raw materials and utility services are shown in the table below. Consumption quotas are calculated per ton of qualified metallic lithium.

(2) Material Balance Sheet

According to the synthesis process flow, the reaction in the production process is: 2LiCl = 2Li + Cl. ₂ ↑ Kerr ₂ +2NaOH=NaClO +NaCl+H ₂ O The input, recovery, and emission data for each ton of product (unit: t) are shown in the following material balance table.

Metallic lithium products

Images of Production Equipment for Electrolytic Preparation of Metallic Lithium