RCPL secures patent for Mg-battery with a solid electrolyte | Targets commercialisation in early 2025

A recently granted patent (Indian Patent grant: 496952; PCT/IN2023/050538) highlights a development by Chennai-based Ramcharan Company Pvt. Ltd. (RCPL) in the field of a solid-state Mg-battery utilizing eco-friendly solid electrolyte and the associated fabrication method. The company said it has achieved PoC (proof of concept) for a recyclable solid-state magnesium battery, showcasing global leadership in eco-friendly energy solutions beyond lithium patents.

According to a Mordor Intelligence report, the Next Generation Advanced Battery Market size is estimated at USD 1.87 billion in 2024, and is expected to reach USD 2.64 billion by 2029, growing at a CAGR of 7.24% during the forecast period (2024-2029).

Magnesium battery

Scientists have been exploring various metals, including sodium, potassium, aluminium, zinc, and calcium, as potential replacements for lithium-ion batteries. Among these, magnesium has garnered attention due to its unique properties.

– Magnesium is divalent, meaning its oxidation results in two electrons and an Mg2+ ion, contributing to a high specific capacity and volumetric energy density.

– The theoretical volumetric capacity of a magnesium-ion battery, at 3833 mAh/mL, is nearly double that of lithium (2062 mAh/mL).

– While practical lithium-ion batteries typically have a volumetric capacity of less than 200 mAh/mL, the higher theoretical capacity suggests the potential for increased practical value with magnesium-ion batteries.

Challenges and opportunities with Mg-ion batteries

While magnesium-ion batteries offer increased energy capacities and several advantages over lithium-ion counterparts, certain challenges exist. Due to magnesium’s higher weight compared to lithium, batteries using magnesium tend to be naturally heavier for a given energy capacity. The theoretical energy density of magnesium-ion batteries is 2205 mAh/g, in contrast to 3861 mAh/g for lithium-ion batteries. Despite this, practical lithium-ion batteries typically achieve less than 150 mAh/g, whereas early tests with a sulfur cathode have demonstrated that magnesium-ion batteries can reach 1000 mAh/g.

The advantages of magnesium-ion (Mg2+) batteries include the absence of dendrite formation and the resolving safety concerns associated with lithium-ion (Li+) batteries. These batteries also offer a longer lifespan and faster charging due to the avoidance of dendrite formation during the charging process. Magnesium (Mg), being the eighth-most abundant element in the earth’s crust, presents a sustainable resource for battery production.

However, challenges arise from the higher electrical charge of magnesium ions, leading to increased hindrance from ions of the opposite charge in the battery’s electrolyte. This results in decreased energy when the ions move from the electrolyte to the electrode. Additionally, the use of liquid electrolytes in magnesium batteries poses a risk of rapid corrosion to other elements, presenting a major concern that needs addressing in the development of magnesium-ion battery technology.

To address the bottleneck, utilizing polymer gel or solid-state electrolytes with high Mg2+ ion conductivity at room temperature, stable up to 600°C, is proposed. This involves the incorporation of earth-abundant phyllosilicates as electrolyte as well as Cathode Active Material (CAM). Two industries have developed and tested proof-of-concept (PoC) solid-state Mg batteries:

• Toyota Research Institute employed organic CAM, such as Pyrene-2,4,6,8-tetraone, and Magnesium Carborane as solid electrolyte in a swaglok configuration, achieving a high power of 3 kW/kg (Ref: Hui D. et al Nature Energy, 1-8, (2020)).

• Ram Charan Company (P) Ltd – Entity1 utilized Mg-rich naturally abundant phyllosilicates as CAM and Fe-rich or Mg-enriched earth-abundant phyllosilicates as solid electrolyte, achieving a high power of 0.89 kW/kg (Ref: Indian Patent grant: 496952; PCTIN2023050538). This is expected to undergo scaling up and real-time application testing by the end of 2024.

Ramcharan Company (P) Ltd – Entity1 has developed Solid State Magnesium Batteries (SSMgBs) utilizing naturally available phyllosilicates as both the Cathode Active Material (CAM) and Solid State Electrolyte (SSE). The selection of phyllosilicates for CAM involves naturally Mg-rich material, which inherently possesses a higher concentration of Mg2+ ions in its octahedral sites. For the SSE, the native phyllosilicate is enriched with Mg2+ ions and employed as a flexible membrane. The battery cell, crafted with Mg-rich CAM, Mg-enriched SSE, and Mg metal anode, demonstrated a cyclability of up to 5000 cycles at higher C-rates (5C and 10C). It achieved the highest specific capacity of 1176 mAh/g, representing 86.31% of the theoretical specific capacity of Mg-rich phyllosilicate (approximately 1362.53 mAh/g).

Electrochemical Impedance studies on the flexible SSE of Mg-enriched phyllosilicates revealed Mg2+ ionic conductivity of 2.86 mS/cm, and that of Mg-rich CAM was 1.54 mS/cm. These ionic conductivity values are 2.86 and 1.54 times higher, respectively, than the reported 1mS/cm conductivity of polymer gel electrolytes for SSMgBs in the existing literature. The substantial ionic conductivity of CAM and SSE, as utilized in this work, holds promise for low-cost, high-energy, highly cyclable, and safe SSMgBs.

The gravimetric energy density of the fabricated battery cell is measured at 0.89 kWh/kg, twice as high as the current state-of-the-art value of 0.45 kWh/kg. The Mg-rich CAM and Mg-enriched SSE facilitate fast and reversible redox processes of plating and stripping of Mg2+ ions. This combination promotes kinetically and thermodynamically favoured cathode behaviour for Mg2+ ions’ solid-phase diffusion and rapid electrode kinetics. Coupling Mg-rich CAM with Mg-enriched SSE resulted in SSMgBs with a specific power of up to 0.89 kW/kg.

Kaushik Palicha, Director of Ramcharan Company (P) Ltd – Entity1, emphasized that the CAM and SSE chemistries employed in this technology development are inorganic materials with minimal reactivity with the Mg metal anode. They support reversible plating/stripping of Mg/Mg2+ at high current density, ensuring a safe, dendrite-free process and thermodynamically and kinetically favoured solid-state diffusion of Mg2+ ions.

What is the relevance of this patent?

• Features: Solid state, earth-abundant CAM, SSE, flexible SSE, high energy density (0.297 kWh/kg), and high ionic conductivity (2.4 mS/cm) at room temperature.

• Significance: PoC for next-gen batteries achieved by an Indian industry under the Make-in-India initiative. It is recyclable, cost-effective, and applicable across various industries.

This is the second solid-state patent in a non-lithium product from India. Globally, all companies are focused on solid-state lithium batteries, and the fact that we are able to produce this product consistently shows our differentiation as well as focus on a supply chain & recyclability.

TRL of the technology

The technology is currently at Technology Readiness Level 5. RCPL plans to reach a TRL 9 product by next year.

What are the potential areas of immediate application? 

From low-power toys and watch batteries to E-mobility, stationary storage, and space applications.

What is the path to market launch/commercialisation, and how will this technology be deployed on target applications?

Targeting early 2025.

Time required for commercialisation

Anticipated within one year from now.

Other entities RCPL is working with to help bring this technology to market

Automotive industries, Indian Aerospace, Battery manufacturing companies, Power and energy sector, FMCG Goods.

Also read: RCPL secures patent for Quasi-solid-state Magnesium-ion battery and method of fabrication