Abstract Lithium‐ion batteries are overreliant on cobalt containing cathodes. Current projections estimate that hundreds of millions of electric vehicles (EVs) will be on the road by 2050, and this ever‐growing demand threatens to deplete global cobalt reserves at an alarming rate. Moreover, cobalt supply chain issues have significantly increased cobalt prices throughout the last decade. As such, energy storage research and development need to reduce the reliance on cobalt to meet ever‐growing demand for lithium‐ion batteries. The present review summarizes the science and technology gaps and potential of numerous cobalt‐free Li‐ion cathodes including layered, spinel, olivine, and disordered rock‐salt systems. Despite the promising performance of these Co‐free cathodes, scale‐up and manufacturing bottlenecks associated with these materials must also be addressed to enable widespread adoption in commercial batteries. Overall, this review broadly highlights the enormous promise of “zero‐cobalt” Li‐ion batteries to enable sustainable production of EVs in the coming decades.
The Cover Feature shows a direct fluorination of prelithiated MoO2 using elemental fluorine, which leads to the formation of oxyfluoride and thereby improves both lithium-ion diffusivity and reversibility of the corresponding conversion reaction. The negative electrode derived through this process exhibits enhanced electrochemical performances, making it an attractive approach to address the issues of conversion electrodes. These findings open a new avenue to design high-capacity anodes for energy storage. More information can be found in the Full Paper by B. P. Thapaliya et al.
The cost and energy density of commercial Li-ion batteries (LIBs) are largely limited by the cathode. Currently, the LIB cathode market is dominated by intercalation type layered transition metal oxides of the general form LiNi x Mn y Co 1-x-y O 2 (NMC). As the LIB market continues to grow, there is an increasing risk of over-reliance on cobalt and nickel, which not only leads to increased cost and resource depletion, but also raises ethical concerns related to the cobalt mining industry. Hence, there is an urgent need to develop new cathodes based on earth abundant materials. Disordered rocksalt (DRX) oxides and oxyfluorides have emerged as a promising candidate for next generation LIB cathodes due to their high energy density and ability to utilize low-cost, earth abundant elements such as Mn and Ti. Studies have shown that anionic substitution of oxygen with fluorine enhances electrochemical performance and cycling stability of DRX cathodes. DRX cathodes are traditionally synthesized using high temperature solid-state and high energy mechanochemical routes. While these methods have yielded promising cathodes, they face challenges with fluorine substitution and process scalability. Keeping this in mind, the goal of this research is to develop alternate synthesis routes to prepare DRX oxyfluoride cathodes and identify key structure – property correlations to optimize cathode performance. Our team recently developed a sol-gel based approach to synthesize Li 1.2 Mn x Ti 0.8-x O 2-y F y (y=0-0.2; x=0.4-0.6) DRX oxides and oxyfluorides. This presentation will discuss recent development related to the synthesis, structure, and performance of these cathodes Acknowledgements This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) through the Vehicle Technologies Office (VTO).
Redox flow batteries (RFBs) are promising energy storage devices for grid-level applications due to their long cycle life and the ability to independently scale their energy and power densities. The energy density of conventional RFBs is dictated by their capacity (which is directly related to the solubility of the redox species in the electrolyte) and operating potential. Aqueous RFBs generally have low operating potentials ca. 1.5 V, resulting in poor energy densities (25 – 30 Wh/kg for an all vanadium RFB), whereas systems containing organic electrolytes with wider electrochemical windows have moderately higher energy densities. Our team recently demonstrated proof-of-concept for a revolutionary approach which uses mediated electrochemical reactions in a RFB configuration to drive reversible Na storage in a red P anode. Extremely high capacities ~1,000 mAh/g P have been demonstrated using this method. In this configuration, the anion radical mediators are recycled several times throughout the cell stack during a single charge/discharge cycle, effectively decoupling the RFB’s energy density from the redox species’ solubility in the electrolyte. By pairing this mediated red P anode with a sulfide-based cathode, energy densities up to 200 Wh/kg (~10x that of conventional RFBs) can potentially be achieved. This presentation will describe our recent progress developing polymer membranes and high energy density cathodes/catholytes for RFBs. The preparation and characterization of ionically conductive, mechanically robust poly(ethylene oxide) (PEO)-based membranes which are chemically resistant to and prevent crossover of the radical mediators will be discussed. The synthesis and electrochemical properties of a new class of high energy density sodium thiophosphate cathodes for RFBs will also be provided. Acknowledgements This research is supported by Dr. Imre Gyuk, Manager, Energy Storage Program, Office of Electricity Delivery and Reliability, U.S. Department of Energy and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy.
Freestanding nanofiber mat Li-ion battery anodes containing Si nanoparticles, carbon black, and poly(acrylic acid) (Si/C/PAA) are prepared using electrospinning. The mats are compacted to a high fiber volume fraction (≈0.85), and interfiber contacts are welded by exposing the mat to methanol vapor. A compacted+welded fiber mat anode containing 40 wt % Si exhibits high capacities of 1484 mA h g-1 (3500 mA h g-1Si ) at 0.1 C and 489 mA h g-1 at 1 C and good cycling stability (e.g., 73 % capacity retention over 50 cycles). Post-mortem analysis of the fiber mats shows that the overall electrode structure is preserved during cycling. Whereas many nanostructured Si anodes are hindered by their low active material loadings and densities, thick, densely packed Si/C/PAA fiber mat anodes reported here have high areal and volumetric capacities (e.g., 4.5 mA h cm-2 and 750 mA h cm-3 , respectively). A full cell containing an electrospun Si/C/PAA anode and electrospun LiCoO2 -based cathode has a high specific energy density of 270 Wh kg-1 . The excellent performance of the electrospun Si/C/PAA fiber mat anodes is attributed to the: i) PAA binder, which interacts with the SiOx surface of Si nanoparticles and ii) high material loading, high fiber volume fraction, and welded interfiber contacts of the electrospun mats.
We report the direct deposition of model sodium sulfide films by RF magnetron sputtering from Na2S and Na2S2 deposition targets. Analytical characterization and electrochemical cycling indicate that the deposited films are amorphous with stoichiometries that correspond to Na2S3 and Na2S2 formed from the Na2S and Na2S2 targets, respectively. We propose that the loss of Na in the case of the Na2S target is due to preferential sputtering of Na resulting from the higher energy required to break the Na–S bonds in Na2S. The development of thin film sodium sulfides opens a new route to understanding their fundamental properties, such as Na+ transport, conductivity, and reactivity.
All-solid-state batteries are a candidate for next-generation energy-storage devices due to potential improvements in energy density and safety compared to current battery technologies. Due to their high ionic conductivity and potential scalability through slurry processing routes, sulfide solid-state electrolytes are promising to replace traditional liquid electrolytes and enable All-solid-state batteries, but stability of cathode-sulfide solid-state electrolytes interfaces requires further improvement. Herein we review common issues encountered at cathode-sulfide SE interfaces and strategies to alleviate these issues.
Long duration energy storage devices, such as redox flow batteries (RFBs), are critical for enabling the widespread adoption of renewable energy sources such as wind and solar on the electric grid. Non-aqueous RFBs (NARFBs) have emerged as a possible alternative to aqueous RFBs (e.g., all-vanadium and Zn/Br systems), as they have the potential to use supporting electrolytes with wide operating voltage windows (>3 V) and a variety of redox couples. One NARFB of interest is a hybrid RFB that utilizes an alkali metal anode, such as sodium, and a polysulfide catholyte. However, the realization of a hybrid NARFB for long duration energy storage requires the development of new membranes with robust mechanical properties, good (electro)chemical stability, high ionic conductivity, and low polysulfide permeability. In this work, we have utilized a cation exchange pentablock copolymer membrane with sodium sulfonate and sodium trifluoromethanesulfonimide (TFSI) functionalities. We studied various crosslinking methods with the goal of reducing electrolyte uptake and polysulfide crossover of the membrane, while maintaining high ion transport. One lightly crosslinked membrane exhibits a 40% reduction in electrolyte uptake compared to the uncrosslinked membrane, but at the expense of a reduction in ionic conductivity from 2.5 x 10 -4 S/cm to 4.2 x 10 -5 S/cm at 20 °C. Our continued efforts in developing techniques to improve membrane properties will also be discussed.
The global demand for lithium-ion batteries (LIBs) is ever-increasing as many nations seek to achieve a net carbon neutrality by the late 2030s. LiNi x Mn y Co 1– x – y O 2 , (NMC) is one of the most widely-used Li-ion cathode active materials. Despite its excellent performance (e.g., reversible capacities up to ~220 mA h g –1 and 500+ cycles), NMC contains both Ni and Co, which are expensive and have vulnerable supply chains. Li-excess disordered rock salt (DRX) materials are promising new cathode materials that utilize earth-abundant transition metals such as Mn and Ti. Through a combination of cationic and anionic charge compensation, DRX materials can attain specific energies ≥700 Wh kg –1 . Doping F – into the DRX structure (Li 1+ x Mn y Ti 2–1– x – y O 2– z F z ) has been reported to improve the material’s cycling stability. Despite their promising properties, most DRX cathodes are prepared through solid-state synthesis routes which require high-energy milling, provide little-to-no control over the particle morphology, and are difficult to scale. In this work, we developed a scalable combustion synthesis route (the glycine nitrate process) to produce high purity, high performance DRX cathodes. More specifically, we prepared two DRX precursors with nominal compositions of Li 1.2 Mn 0.5 Ti 0.3 O 1.95 and Li 1.2 Mn 0.7 Ti 0.1 O 1.85 . When the precursors were heated under Ar to 1000 °C for 1 – 4 h, only 50% Li 1.2 Mn 0.5 Ti 0.3 O 1.95 adopted a DRX structure, and no DRX formed for Li 1.2 Mn 0.7 Ti 0.1 O 1.85 . However, adding LiF to the precursors facilitates DRX phase formation during annealing and yields high purity DRX powders with the nominal compositions Li 1.25 Mn 0.5 Ti 0.3 O 1.95 F 0.05 and Li 1.35 Mn 0.7 Ti 0.1 O 1.85 F 0.15 . In situ X-ray diffraction was employed to study the synthesis process, revealing DRX begins to form at just 600 °C, which is much lower than traditional solid-state routes. Furthermore, electrochemical tests on the Li 1.35 Mn 0.7 Ti 0.1 O 1.85 F 0.15 cathode reveal these materials attain excellent performance with initial reversible capacities up to 215 mA h g –1 and stable cycling performance. These promising results demonstrate that combustion synthesis is a viable method for the scale-up of DRX materials. This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and was sponsored by the Vehicle Technologies Office (VTO) under the Office of Energy Efficiency and Renewable Energy (EERE). Some measurements were conducted at the Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.
Prior research on carbon-coated silicon (Si@C) for Si-based lithium-ion batteries have shown improved electrochemical performance upon coating. However, the underlying mechanisms responsible for the enhancement in performance have not been fully explored and are typically attributed to the protective influence of the carbon coating around the Si particles as well as the improved electronic conductivity of the electrode. In this work, we investigate the contribution of coating on the processing of the electrodes as well as on the formed solid electrolyte interphase (SEI). Si@C particles were prepared by chemical vapor deposition (CVD) technique to achieve a homogeneous carbon layer on the Si surface. The influence of coating time as well as processing temperature was investigated. X-ray photoelectron spectroscopy (XPS), neutron reflectivity (NR) measurements, and transmission electron microscopy (TEM) reveal the coating characteristics such as its extremely thin nature, ~2.5 nm, allowing us to rule out the protective function of carbon coating to prevent Si volume expansion as the governing mechanism for the improved electrochemical behavior. Instead, Raman mapping of the electrodes reveal a uniform distribution of Si and carbon conductive additive, indicating that the coating on the Si particles can facilitate slurry processing which yields to more homogeneous electrodes. Consequently, this leads to the commonly reported improved electronic connections within the electrodes as supported by electrochemical impedance spectroscopy (EIS) data. Furthermore, SEI studies using XPS reveal similar SEI characteristics of the Si electrodes after cycling in half and full cell format. In summary, we assign the improved performance of Si@C on the beneficial effect of carbon coating on the processing of Si electrodes, but not on the electrochemical passivation.
