The Effect of Sodium Dihydrogen Phosphate in Lithium Batteries

1. As a key phosphorus source for synthesizing lithium iron phosphate (LFP) cathode materials

This is the largest and most important application of sodium dihydrogen phosphate in lithium batteries. Lithium iron phosphate has become the mainstream cathode material for mid- and low-end electric vehicles and energy storage batteries due to its high safety, long cycle life, and cost advantages.

In various processes for preparing lithium iron phosphate (LFP), such as solid-phase and liquid-phase methods, sodium dihydrogen phosphate is often used as a raw material to provide phosphorus (P). It reacts with an iron source (such as ferrous sulfate, FeSO₄) and a lithium source (such as lithium hydroxide, LiOH, or lithium carbonate, Li₂CO₃).

A common reaction pathway example (simplified):

NaH₂PO₄ + FeSO₄ + LiOH → LiFePO₄ + ...

(The actual reaction is more complex, often producing byproducts such as sodium sulfate, requiring multiple steps such as washing, filtration, and sintering.)

MSP

Mono Sodium Phosphate

Why choose sodium dihydrogen phosphate?

High Reactivity: As an acid salt, it generally has better solubility and reactivity in aqueous solutions than orthophosphates (such as sodium phosphate, Na₃PO₄). It mixes more easily with other metal ions (Fe⁺, Li⁺) at the atomic level, helping to form pure, uniformly particle-sized lithium iron phosphate.

Controllability: In liquid-phase reactions such as co-precipitation, using sodium dihydrogen phosphate allows for better control of the solution pH, thereby precisely controlling the particle morphology, size, and distribution of the iron phosphate (FePO₄) precursor or the final LFP product, which is critical to the electrochemical performance of the battery.

Cost and purity: Compared with other phosphorus sources, it has good economic performance and can be purified to obtain battery-grade high-purity products without introducing harmful impurities.

2. As a phosphorus source for other phosphate cathode materials

In addition to lithium iron phosphate, some cathode materials in new battery systems such as sodium-ion batteries may also use sodium dihydrogen phosphate as a raw material. For example:

Polyanionic cathode materials such as sodium vanadium phosphate (Na₃V₂(PO₄)₃). In the laboratory development and synthesis of these materials, sodium dihydrogen phosphate is a common phosphorus and sodium source.

3. Potentially Auxiliary Roles in Electrode Fabrication

(This application is relatively minor, but does exist)

pH Adjuster/Buffer: In electrode coating slurries, precise pH control is sometimes required to ensure slurry stability (e.g., to prevent corrosion of the aluminum current collector). The buffering properties of sodium dihydrogen phosphate can be used to fine-tune the pH environment.

Binder System Components: In certain aqueous binder systems, phosphates may participate in crosslinking or improve bonding properties.

Summary and Importance

The role of sodium dihydrogen phosphate in the lithium battery industry can be summarized as follows:

The "food and grass" in the saying "before the troops move, the food and grass must be prepared first." Although it doesn't directly appear in the final battery product, it is a fundamental raw material for manufacturing the core component—the lithium iron phosphate cathode.

Industry Chain Relationship:

Sodium dihydrogen phosphate → (as a phosphorus source) → iron phosphate/lithium iron phosphate cathode material → (as a cathode) → lithium battery cell → battery pack

Therefore, the price, purity, and supply stability of sodium dihydrogen phosphate directly impact the production cost and quality of downstream lithium iron phosphate cathode materials, and thus have a profound impact on the development of the entire lithium battery industry. With the explosive growth in global demand for lithium batteries, the demand for basic chemical raw materials such as battery-grade sodium dihydrogen phosphate has also continued to rise.

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