Efficient Solution-Scale Synthesis of Red Phosphorus Nanoparticles for High‑Performance Lithium‑Ion Battery Anodes

Abstract

Red phosphorus (RP) offers a theoretical specific capacity of 2596 mAh g⁻¹ and is earth‑abundant, making it a compelling anode material for lithium‑ion batteries (LIBs). Yet, scalable, low‑cost production of RP nanomaterials via solution chemistry remains challenging. Here, we present a simple, room‑temperature route that reacts PCl₃ with HSiCl₃ in the presence of amines to produce amorphous RP nanoparticles (RP NPs) of 100–200 nm in high yield. When employed as an anode, the RP NP electrode delivers 1380 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹, with Coulombic efficiencies approaching 100 % per cycle. This method provides a practical, scalable approach for producing high‑performance RP nanomaterials for LIBs.

Introduction

Fossil fuels are finite and environmentally detrimental, prompting a global shift toward rechargeable lithium‑ion batteries (LIBs) that combine high energy density with long cycle life [1,2,3]. However, conventional graphite anodes are limited by a capacity of only 372 mAh g⁻¹ [8,9], driving research into alternative high‑capacity materials [4–17]. Phosphorus, with its low cost, abundance, and theoretical capacity near 2600 mAh g⁻¹, has emerged as a prime candidate [18–22]. Among its allotropes, red phosphorus (RP) is the most promising for LIB anodes due to its stability and abundance [27], but its low electronic conductivity (≈10⁻¹² S m⁻¹) and ~300 % volume expansion during lithiation/delithiation [28,29] hinder practical use.

Strategies to overcome these drawbacks include embedding RP in carbon hosts [30–38] or engineering nanoscale RP to accommodate strain [41–44]. While several synthesis routes exist, scalable, low‑cost solution methods for RP nanomaterials remain scarce. In this work, we introduce a rapid, ambient‑temperature solution synthesis that leverages the reaction of PCl₃ with HSiCl₃ and amines to produce RP nanoparticles efficiently and economically.

Methods

Materials

Trichlorosilane (HSiCl₃) was sourced from TCI, n‑tripropylamine (Pr₃N) from Aladdin, and phosphorus trichloride (PCl₃) from Sinopharm Chemical Reagent Co. Ltd. Dichloromethane (CH₂Cl₂) was dried over CaH₂ before use. All reagents were used as received.

Synthesis of Red Phosphorus Nanoparticles

In a typical run, 0.55 mL Pr₃N and 0.5 mL HSiCl₃ were added to 20 mL anhydrous CH₂Cl₂ and stirred overnight at room temperature. The solution turned light yellow, then 0.5 mL PCl₃ was introduced, yielding orange RP NPs within seconds. The product was isolated by centrifugation and washed sequentially with anhydrous CH₂Cl₂, 1 M HF, and distilled water to remove unreacted PCl₃ and silica residues.

Electrochemical Measurements

Electrochemical performance was assessed in CR2032 coin cells with lithium metal as counter electrode. Working electrodes were prepared by mixing RP NPs, conductive graphite, and sodium carboxymethyl cellulose (CMC) in a 5:3:2 weight ratio in deionized water, blade‑coated onto Cu foil, and dried at 80 °C under vacuum. The final active‑material loading was ~0.5 mg cm⁻². Electrolyte was 1.0 M LiPF₆ in a 1:1 (v/v) ethylene carbonate/diethyl carbonate mixture. Charge–discharge profiles were recorded on a Neware battery tester at constant current mode.

Characterization

PXRD (Bruker D8, Cu Kα), SEM (Hitachi S‑4800), TEM (JEM‑2100), N₂ sorption (Micromeritics ASAP 2020), Raman (LabRAM Aramis, 633 nm), XPS (PHI 5000 VersaProbe), TGA (STA449F3), I‑V (Biologic VMP3), and CV (CHI650d) were employed to characterize structure, morphology, composition, and electrochemical behavior.

Results and Discussion

Synthesis and Characterization of RP NPs

RP NPs were synthesized via a facile solution method (Scheme 1). The reaction of PCl₃ with a pre‑formed mixture of HSiCl₃ and Pr₃N in CH₂Cl₂ at room temperature rapidly produces orange powders in seconds. The process relies on the reduction of PCl₃ by sub‑valent oligosilane chlorides generated through the disproportionation of HSiCl₃ in the presence of amine catalysts [45–47]. Without Pr₃N, no reaction occurs, underscoring the catalyst’s role. The overall yield is ~38 % based on phosphorus atoms, surpassing literature reports [43] and offering a cost‑effective alternative to PI₃‑based routes.

PXRD confirms the crystalline phase of red phosphorus, with broadened peaks at 13–16°, 25–38°, and 47–65° matching commercial RP patterns [21,36]. SEM images reveal irregular, spherical particles ranging from 100 to 200 nm, while SAED patterns confirm an amorphous structure (Fig. 2b). Raman spectra display peaks at 300–500 cm⁻¹ corresponding to bending and stretching modes of amorphous RP (Fig. 1b). TGA shows a weight loss between 380–430 °C, lower than commercial RP (450–500 °C) due to the high surface‑to‑volume ratio of nanoparticles. N₂ sorption yields a BET surface area of ~37 m² g⁻¹, significantly higher than commercial RP.

EDS and XPS analyses verify the elemental purity of RP NPs. XPS P 2p spectra exhibit peaks at 129.74 eV (2p₃⁄₂) and 130.74 eV (2p₁⁄₂), characteristic of P–P bonds, with a minor peak at 133.50 eV indicating surface oxidation. The conductivity of RP NPs (~1.7 × 10⁻⁷ S m⁻¹) exceeds that of commercial RP (10⁻¹² S m⁻¹) by five orders of magnitude (Fig. 4).

Electrochemical Performance

CV curves (0.1 mV s⁻¹) show a broad initial lithiation peak followed by distinct redox features at 0.5–0.75 V and 1.0–1.25 V, attributed to Li‑phosphorus alloy formation and decomposition. The first cycle exhibits a Coulombic efficiency of 58.2 % due to irreversible SEI formation, which stabilizes to ~100 % in subsequent cycles. Charge–discharge profiles at 0.1 A g⁻¹ demonstrate an initial capacity of 2818 mAh g⁻¹ and a first‑cycle irreversible loss of 1677 mAh g⁻¹. Despite the initial drop, the RP NP electrode retains 1380 mAh g⁻¹ after 100 cycles at 0.1 A g⁻¹, representing 89.1 % capacity retention with near‑unity Coulombic efficiency (Fig. 5d). Rate tests confirm robust performance, delivering 1801, 1430, 1245, 1227, 1184, and 871 mAh g⁻¹ at 0.1 to 1 A g⁻¹, respectively, and recovering the initial capacity when the rate returns to 0.1 A g⁻¹ (Fig. 5c). Compared with commercial RP, the RP NPs exhibit markedly improved cycling stability (Fig. 5e).

Conclusions

We have demonstrated a scalable, ambient‑temperature solution synthesis of red phosphorus nanoparticles via the reaction of PCl₃ with HSiCl₃ in the presence of amines. The resulting RP NPs deliver high reversible capacity (1380 mAh g⁻¹ after 100 cycles) and excellent Coulombic efficiency (~100 %) when used as LIB anodes, outperforming commercial RP. This straightforward method paves the way for cost‑effective, large‑scale production of high‑performance RP nanomaterials for next‑generation lithium‑ion batteries.