Lithium-ion batteries have had a profound impact on our daily life, but inherent limitations make it difficult for Li-ion chemistries to meet the growing demands for portable electronics, electric vehicles and grid-scale energy storage. Therefore, chemistries beyond Li-ion are currently being investigated and need to be made viable for commercial applications. The use of metallic Li is one of the most favoured choices for next-generation Li batteries, especially Li-S and Li-air systems. After falling into oblivion for several decades because of safety concerns, metallic Li is now ready for a revival, thanks to the development of investigative tools and nanotechnology-based solutions. In this Review, we first summarize the current understanding on Li anodes, then highlight the recent key progress in materials design and advanced characterization techniques, and finally discuss the opportunities and possible directions for future development of Li anodes in applications.

Reviving the lithium metal anode for high-energy batteries

The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Rechargeable lithium-sulfur batteries.

Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.

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Laser Scribing of High-Performance and Flexible Graphene-Based Electrochemical Capacitors

Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g−1), low density (0.59 g cm−3) and the lowest negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.

Lithium metal anodes for rechargeable batteries

A supercapacitor with graphene-based electrodes was found to exhibit a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g. These energy density values are comparable to that of the Ni metal hydride battery, but the supercapacitor can be charged or discharged in seconds or minutes. The key to success was the ability to make full utilization of the highest intrinsic surface capacitance and specific surface area of single-layer graphene by preparing curved graphene sheets that will not restack face-to-face. The curved morphology enables the formation of mesopores accessible to and wettable by environmentally benign ionic liquids capable of operating at a voltage >4 V.

Graphene-based supercapacitor with an ultrahigh energy density

A nano-scaled graphene plate material and a process for producing this material. The material comprises a sheet of graphite plane or a multiplicity of sheets of graphite plane. The graphite plane is composed of a two-dimensional hexagonal lattice of carbon atoms and the plate has a length and a width parallel to the graphite plane and a thickness orthogonal to the graphite plane with at least one of the length, width, and thickness values being 100 nanometers or smaller. The process for producing nano-scaled graphene plate material comprises the steps of: a). partially or fully carbonizing a precursor polymer or heat-treating petroleum or coal tar pitch to produce a polymeric carbon containing micron- and/or nanometer-scaled graphite crystallites with each crystallite comprising one sheet or a multiplicity of sheets of graphite plane; b). exfoliating the graphite crystallites in the polymeric carbon; and c). subjecting the polymeric carbon containing exfoliated graphite crystallites to a mechanical attrition treatment to produce the nano-scaled graphene plate material.

Nano-scaled graphene plates

Herein reported is a fundamentally new strategy for reviving rechargeable lithium (Li) metal batteries and enabling the emergence of next-generation safe batteries featuring a graphene-supported Li metal anode, including the highly promising Li–sulfur, Li–air, and Li–graphene cells with exceptionally high energy or power densities. All the Li metal anode-based batteries suffer from a high propensity to form Li dendrites (tree-like structures) at the anode upon repeated discharges/charges. A dendrite could eventually penetrate through the separator to reach the cathode, causing internal short-circuiting and even explosion, the main reason for the battery industry to abandon rechargeable lithium metal batteries in the early 1990s. By implementing graphene sheets to increase the anode surface areas, one can significantly reduce the anode current density, thereby dramatically prolonging the dendrite initiation time and decreasing the growth rate of a dendrite, if ever initiated, possibly by a factor of up to 1010 and 105, respectively.

Reviving rechargeable lithium metal batteries: enabling next-generation high-energy and high-power cells

Herein reported is a fundamentally new strategy for the design of high-power and high energy-density devices. This approach is based on the exchange of lithium ions between the surfaces (not the bulk) of two nanostructured electrodes, completely obviating the need for lithium intercalation or deintercalation. In both electrodes, massive graphene surfaces in direct contact with liquid electrolyte are capable of rapidly and reversibly capturing lithium ions through surface adsorption and/or surface redox reaction. These devices, based on unoptimized materials and configuration, are already capable of storing an energy density of 160 Wh/kgcell, which is 30 times higher than that (5 Wh/kgcell) of conventional symmetric supercapacitors and comparable to that of Li-ion batteries. They are also capable of delivering a power density of 100 kW/kgcell, which is 10 times higher than that (10 kW/kgcell) of supercapacitors and 100 times higher than that (1 kW/kgcell) of Li-ion batteries.

Graphene surface-enabled lithium ion-exchanging cells: next-generation high-power energy storage devices.

A solid nanocomposite particle composition for lithium metal or lithium ion battery electrode applications. The composition comprises: (A) an electrode active material in a form of fine particles, rods, wires, fibers, or tubes with a dimension smaller than 1 μm; (B) nano graphene platelets (NGPs); and (C) a protective matrix material reinforced by the NGPs; wherein the graphene platelets and the electrode active material are dispersed in the matrix material and the NGPs occupy a weight fraction w g of 1% to 90% of the total nanocomposite weight, the electrode active material occupies a weight fraction w a of 1% to 90% of the total nanocomposite weight, and the matrix material occupies a weight fraction w m of at least 2% of the total nanocomposite weight with w g +w a +w m =1. For a lithium ion battery anode application, the matrix material is preferably amorphous carbon, polymeric carbon, or meso-phase carbon. Such a solid nanocomposite composition provides a high anode capacity and good cycling stability. For a cathode application, the resulting lithium metal or lithium ion battery exhibits an exceptionally high cycle life.

Bor Z. Jang

Papers

Graphene-based supercapacitor with an ultrahigh energy density

Nano-scaled graphene plates

Reviving rechargeable lithium metal batteries: enabling next-generation high-energy and high-power cells

Graphene surface-enabled lithium ion-exchanging cells: next-generation high-power energy storage devices.

Nano graphene reinforced nanocomposite particles for lithium battery electrodes