Ultra-fast charging sodium metal battery

Chinese researchers built a sodium battery with ultra-fast charging and 90% capacity even after 2,000 cycles        

Researchers in China have developed a new quasi-solid-state electrolyte which could help sodium metal batteries charge faster, last longer and operate more safely. The team from Southeast University, working with HiNa Battery Technology and Yangzhou University, designed a dual-mediator electrolyte which addresses two major challenges in sodium metal batteries: slow sodium-ion transport and unstable interfaces that can lead to dendrite growth and battery failure. Quasi-solid-state electrolytes (QSEs) are critical for ultrafast-charging yet high-safety sodium metal batteries (SMBs), yet their implementation is hindered by sluggish Na+ transport in bulk and at interfaces. Dual interlocked mediator engineering which transcends conventional independent approaches by coupling cationic Sn2+ salt with anionic difluoro(oxalato)borate (DFOB⁻) salts to simultaneously regulating bulk ion transport and bilateral interface chemistry. During QSE preparation, Sn2+ initiates in situ cationic polymerization, while DFOB⁻ acts as a retarding agent to suppress runaway polymerization. The first interlocking effect in the Sn-FB QSE bulk builds a uniform network, enabling near-unity Na+ transference number (0.94) and robust puncture strength (8.5 kPa). During cell operation, Sn2+ is reduced to form a hybrid NaSn alloy-based solid-electrolyte interphase, while DFOB⁻ oxidizes to generate a robust yet thin cathode–electrolyte interphase, respectively. This second interlocking effect creates adaptable bilateral interphases that facilitate Na+ diffusion and mitigate interfacial degradation. As a result, the symmetric cells exhibit 6000 h stability, and full cells retain 80.1 mAh g–1 at an ultrafast-charging rate of 15C and retain 90% capacity at 3C over 2000 cycles. Furthermore, high-mass-loading full cells and pressure-free pouch cells are demonstrated, underscoring the potential of dual interlocked mediator engineering for practical SMBs.

Sodium batteries are attracting growing attention as a lower-cost alternative to lithium-ion systems because sodium is widely available and less vulnerable to supply chain constraints. However, achieving fast charging without sacrificing cycle life has remained difficult. The researchers report that their new electrolyte delivers a sodium-ion transference number of 0.94 while maintaining ionic conductivity of 1.3 mS cm⁻¹. Conventional quasi-solid-state electrolytes typically record transference numbers between 0.4 and 0.7, limiting charging performance. Realizing ultrafast charge (≥ 3C), however, hinges on electrolytes that concurrently provide high Na conductivity (σ) and Na+ transference number. Although conventional liquid electrolytes are effective, they amplify safety risks and promote inhomogeneous Na+ flux, aggravating dendritic failure, thus motivating quasi-solid-state electrolyte (QSE) designs that retain excellent interfacial wetting and scalability yet enhance intrinsic safety. Despite these advantages, the reported state-of-the-art QSEs remain two challenges under ultrafast-charging conditions. 

Limited ion transport in bulk: the strong Na⁺-polymer coordination and anion-dominated conduction depress and slow down bulk Na+ migration. 

Poor ion diffusion at bilateral interfaces: the compositionally mismatched solid-electrolyte interphase (SEI) and cathode–electrolyte interphase (CEI) layers fail to accommodate high Na⁺ fluxes, leading to heterogeneous electric fields, dendrite formation, and accelerated QSE degradation. Therefore, addressing these coupled Na+ transport in bulk and at bilateral interfaces challenges is pivotal to unlocking practical ultrafast-charging SMBs.

The electrolyte uses a combination of tin ions (Sn²⁺) and difluoro(oxalato)borate (DFOB⁻) ions. Together, they regulate both the electrolyte structure and the movement of sodium ions. According to the researchers, DFOB⁻ weakens interactions between sodium ions and the polymer network, freeing more sodium ions to move through the electrolyte. Simulations showed sodium-ion diffusion rates reaching 16.8 Ų ns⁻¹, roughly six times faster than those seen in conventional liquid electrolytes. The material also forms protective layers on both battery electrodes during operation. At the sodium metal anode, tin ions create a sodium-tin alloy-rich interface which promotes uniform sodium deposition. At the cathode, DFOB⁻ helps form a thin and mechanically robust protective layer that reduces electrolyte degradation. The dual-interlocked design also improves overall electrolyte stability by balancing ion coordination in the bulk and at interfaces, ensuring smoother sodium transport under high current conditions. This reduces concentration polarization and helps maintain consistent performance during fast charging cycles in both symmetric and full-cell configurations. These interfacial layers are designed to suppress dendrites, needle-like metallic structures that can trigger short circuits and shorten battery life. The performance results were among the strongest reported for sodium metal battery systems.

To synthesize a liquid sample (FB LE), 1.5 g of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and 0.1 g of sodium difluoro(oxalato)borate (NaDFOB) were dissolved in 10 mL of 1,3-dioxolane (DOL) in turn, followed by 1.0 mL of fluoroethylene carbonate (FEC) injected. On this base, a quasi-solid-state sample (Sn-FB QSE) was synthesized by in situ polymerization of LE with tin(II) trifluoromethanesulfonate (Sn(OTf)2) as the Lewis acid initiator while Sn QSE was polymerized without NaDFOB. All samples were kept at 25 °C for 48 h to ensure complete polymerization. In laboratory testing, sodium symmetric cells operated for 6,000 hours without dendrite-related failure at a current density of 0.1 mA cm⁻². The system also reached a critical current density of 3.0 mA cm⁻². When paired with sodium vanadium phosphate cathodes, the batteries still delivered 80.1 mAh g⁻¹ even at an ultra-fast charging rate equivalent to full charge in about four minutes. The cells also retained 90% of their capacity after 2,000 charge-discharge cycles at a high charging rate of 3C. The electrolyte remained stable up to 4.7 volts, potentially expanding its compatibility with higher-voltage cathode materials.

The Sn-FB QSE was synthesized via in situ polymerization of DOL, coupling Sn(OTf)2 as the Lewis acid initiator, and NaDFOB as the runaway polymerization retarder. For comparison, FB LE was synthesized without Sn(OTf), and Sn QSE was synthesized without NaDFOB. Vividly, a uniform polymerization product is presented in Sn-FB QSE. In contrast, FB LE presents its liquidity due to the lack of Sn2+ while Sn QSE presents its ununiform product after runaway polymerization due to the lack DFOB– and brings the uneven molecular weight distribution of PDOL. Electrostatic potential (ESP) distribution was applied to validate DFOB– works as polymerization retarder. Upon coordination with DFOB⁻, the blue coloration surrounding the Sn2+ center diminishes significantly, while the negative potential of DFOB⁻ shifts toward Sn2+. This visualizes the electron transfer occurs from the oxalate and fluorine atoms toward the Sn center, effectively dispersing the excess positive charge of the Sn2+ and thereby reducing its electrophilicity. Subsequently, 50 μL of the precursor solution for each sample was injected into the prepared cells and the obtained composite Sn-FB QSE/separator was only 27 μm. The more homogenous polymerization also contributes to a more robust structure in Sn-FB QSE. Therefore, puncture strength–deflection curves for both Sn QSE and Sn-FB QSE were recorded. The puncture strength in Sn-FB QSE reached approximately 8.5 kPa, nearly double that of Sn QSE (4.4 kPa), suggesting a notable improvement in mechanical robustness. This enhancement is attributed to a lower PDI index in Sn-FB QSE which forms a denser and more mechanically stable polymer network, implying its improvement in resisting sodium dendrite penetration.

The researchers also moved beyond coin-cell testing. Pressure-free pouch cells continued operating while being repeatedly folded and were able to power a smartphone. High-loading battery configurations and alternative cathode chemistries also showed promising results. In this work, a single-ion-conducting QSE with highly adaptable interphases was developed via a dual interlocked mediator engineering, incorporating Sn2+ salt as a in situ cationic polymerization initiator and DFOB– as a retarding agent to suppress the runaway polymerization in a PDOL-based system. This interlocking effect in Sn-FB QSE bulk not only yields a homogenous and mechanically robust network but also achieves = 0.94 by dissociating Na+-TFSI– and reducing Na–O interactions. Consequently, the other interlocking effect enables adaptable bilateral interphases. During cell operation, a hybrid NaSn alloy/inorganic-rich SEI was induced by Sn2+ together with other electrolyte species, which homogenizes the electric field and facilitates rapid Na+ transport and enables no-dendrite Na+ plating/stripping with low polarization for over 6000 h. Meanwhile, DFOB– oxidizes at the cathode to generate a thin yet robust CEI, mitigating electrolyte degradation and lowering interfacial Na+ diffusion resistance. Furthermore, a pressure-free pouch cell successfully operates for 19 cycles, and Sn-FB QSE is also compatible with high-mass-loading cathode NVP (5 mg cm–2) and NFM (17 mg cm–2), which underscores the potential of dual interlocked mediator engineering for practical ultrafast-charging and long-life SMBs. The team says the approach could be extended to lithium and potassium metal batteries while remaining compatible with existing battery manufacturing methods already existing. 

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World's first underwater data center

 China starts operations of world's first underwater data center 

China has begun operations of the world's first undersea data center directly powered by offshore wind, as the country races to solve the soaring energy demands of artificial intelligence with greener and more efficient infrastructure. Project combines renewable energy and AI-focused digital infrastructure. The Shanghai Lingang undersea data center demonstration project, built by a subsidiary of China Communications Construction, officially entered operation in the waters off Shanghai's eastern coast. Just over seven months from completing phase one of this mega-project, Chinese engineers have finished the build and switched on the world's first underwater data center (UDC) powered by offshore wind turbines. What's more, it doesn't need freshwater and cuts land use by more than 90% compared with above-ground centers.

The project combines offshore engineering, renewable energy and AI-focused digital infrastructure in a model Chinese officials and engineers describe as a potential template for next-generation computing systems. Located about 10 km's offshore in Shanghai's Lingang area, the project has a planned capacity of 24 megawatts, which is enough to power roughly 20,000 households. According to state media, the center is currently operating at 2.3 MW. This "room to move" is essentially future-proofing the UDC's usefulness, as companies turn their attention from initial builds to longevity when it comes to hardware upgrades and compute capacity. It was reported on the big build earlier, when the first stage had been constructed. At the time, there was no projected timeline for it to become operational. The underwater infrastructure, off the coast of Shanghai in the Lin-hang Special Area, was officially switched on recently, and it's far more impressive than it may sound on paper.

Its core innovation is what developers call a "direct offshore wind connection" model. Electricity generated by offshore wind farms is transmitted directly to submerged data modules through subsea photoelectric composite cables, bypassing traditional grid-routing systems. The system also uses seawater as a natural cooling source through a circulating copper-pipe heat exchange design, reducing electricity consumption by 22.8%, eliminating freshwater use entirely and cutting land usage by more than 90%. This center, built by a subsidiary of China Communications Construction, uses a circulating copper-pipe heat exchange system that reportedly reduces electricity consumption. Offshore wind farms are also estimated to generate 95% of the electricity needed to run its 192 server racks across four levels, significantly reducing reliance on existing power infrastructure. "For an undersea data center of the same scale, the electricity used for cooling would only account for about one-tenth of total power consumption," Tsinghua University Professor Li Zhen said. "If data centers of the same scale were placed underwater, even allowing extra margins, cooling consumption could fall to around 30-billion kW. That would save about 50 billion kWh of electricity each year."

The move is not only an engineering breakthrough, but also a paradigm shift in the relationship between computing power, energy and geographic space in China, industry experts said. The launch comes as China's AI boom fuels a rapid rise in demand for low-latency, high-density computing infrastructure. Shanghai has become one of China's leading AI hubs, home to large-model developers, autonomous driving firms, biotech companies, fintech groups and advanced manufacturing enterprises, industries where milliseconds can determine commercial performance. Data centers don’t need freshwater to function, but it remains the simplest cooling option, as it puts fewer demands on surrounding infrastructure, thanks to its lower levels of salts, minerals and biological impurities which can corrode pipes or reduce cooling efficiency over time. Unlike many inland facilities that still rely on freshwater, UDCs instead use the surrounding ocean as a heat sink, transferring this heat through sealed cooling systems.

The project also reflects a growing global scramble to tackle the energy and cooling crisis facing AI infrastructure. Data centers have become one of the world's fastest-growing electricity consumers as companies expand AI model training and inference capacity. Cooling alone accounts for a large share of energy consumption in conventional data centers, particularly in densely populated urban markets. Nonetheless, while UDCs may reduce freshwater demands and land use, underwater computing is still a largely unknown at commercial scale. Questions remain around how these facilities will endure, and what the ecological effects of continuously releasing heat into local marine environments might be. But considering tech companies are racing to put data centers in space to meet rising demand, real-world projects like China's UDC could serve as valuable test cases in the AI age, revealing whether moving computing infrastructure into new environments can offset existing land-based issues, or reveal entirely new ones.

Tsinghua University Professor Li Zhen said conventional data centers typically use about one-third of their total electricity consumption on cooling systems. China's data centers currently consume around 250 billion kilowatt-hours of electricity annually, with roughly 80 billion kWh used for environmental cooling. It is estimated that the reduction would be equivalent to not burning roughly 15 million metric tons of standard coal annually, significantly lowering carbon emissions. Globally, major technology companies are searching for new ways to reduce the environmental footprint of AI infrastructure as model sizes and inference demand expand rapidly. The combination of offshore renewable power and seawater cooling could become increasingly attractive in coastal markets where land, electricity and freshwater resources are constrained. For China, Li said, the country that has built the world's largest manufacturing supply chains is now attempting to build a new generation of industrial infrastructure for the AI era, one where electricity, cooling and computing are engineered as a single integrated system beneath the sea. Others can also get lead from it.

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