Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.

Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy storage

Three-Dimensional Holey-Graphene/Niobia Composite Architectures for Ultrahigh-Rate Energy Storage

Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives

The ever-growing demand for advanced rechargeable lithium-ion batteries in portable electronics and electric vehicles has spurred intensive research efforts over the past decade. The key to sustaining the progress in Li-ion batteries lies in the quest for safe, low-cost positive electrode (cathode) materials with desirable energy and power capabilities. One approach to boost the energy and power densities of batteries is to increase the output voltage while maintaining a high capacity, fast charge–discharge rate, and long service life. This review gives an account of the various emerging high-voltage positive electrode materials that have the potential to satisfy these requirements either in the short or long term, including nickel-rich layered oxides, lithium-rich layered oxides, high-voltage spinel oxides, and high-voltage polyanionic compounds. The key barriers and the corresponding strategies for the practical viability of these cathode materials are discussed along with the optimization of electrolytes and other cell components, with a particular emphasis on recent advances in the literature. A concise perspective with respect to plausible strategies for future developments in the field is also provided.

High-voltage positive electrode materials for lithium-ion batteries

Extreme fast charging, with a goal of 15 minutes recharge time, is poised to accelerate mass market adoption of electric vehicles, curb greenhouse gas emissions and, in turn, provide nations with greater energy security. However, the realization of such a goal requires research and development across multiple levels, with battery technology being a key technical barrier. The present-day high-energy lithium-ion batteries with graphite anodes and transition metal oxide cathodes in liquid electrolytes are unable to achieve the fast-charging goal without negatively affecting electrochemical performance and safety. Here we discuss the challenges and future research directions towards fast charging at the level of battery materials from mass transport, charge transfer and thermal management perspectives. Moreover, we highlight advanced characterization techniques to fundamentally understand the failure mechanisms of batteries during fast charging, which in turn would inform more rational battery designs. Along with high energy density, fast-charging ability would enable battery-powered electric vehicles. Here Yi Cui and colleagues review battery materials requirements for fast charging and discuss future design strategies.

Challenges and opportunities towards fast-charging battery materials

Increasing the areal capacity or electrode thickness in lithium ion batteries is one possible means to increase pack level energy density while simultaneously lowering cost. The physics that limit use of high areal capacity as a function of battery power to energy ratio are poorly understood and thus most currently produced automotive lithium ion cells utilize modest loadings to ensure long life over the vehicle battery operation. Here we show electrolyte transport limits the utilization of the positive electrode at critical C-rates during discharge; whereas, a combination of electrolyte transport and polarization lead to lithium plating in the graphite electrode during charge. Experimental measurements are compared with theoretical predictions based on concentrated solution and porous electrode theories. An analytical expression is derived to provide design criteria for long lived operation based on the physical properties of the electrode and electrolyte. Finally, a guideline is proposed that graphite cells should avoid charge current densities near or above 4 mA/cm2 unless additional precautions have been made to avoid deleterious side reaction.

https://iopscience.iop.org/article/10.1149/2.0321602jes/pdf

Optimizing areal capacities through understanding the limitations of lithium-ion electrodes

Quantifying Hysteresis and Voltage Fade in xLi2MnO3●(1-x)LiMn0.5Ni0.5O2 Electrodes as a Function of Li2MnO3 Content

Direct observations of structure–electrochemical activity relationships continue to be a key challenge in secondary battery research. 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium-ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.56Li2MnO3·0.56LiMn0.5Ni0.5O2, lithium- and manganese-rich transition-metal (TM) oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new 6Li resonances centered at ∼1600 ppm that are assigned to LiMn6-TMtet sites, specifically, a hyperfine shift related ...

Re-entrant Lithium Local Environments and Defect Driven Electrochemistry of Li- and Mn-Rich Li-Ion Battery Cathodes

Coin-cells are often the test format of choice for laboratories engaged in battery research and development as they provide a convenient platform for rapid testing of new materials on a small scale. However, reliable, reproducible data via the coin-cell format is inherently difficult, particularly in the full-cell configuration. In addition, statistical evaluation to prove the consistency and reliability of such data is often neglected. Herein we report on several studies aimed at formalizing physical process parameters and coin-cell construction related to full cells. Statistical analysis and performance benchmarking approaches are advocated as a means to more confidently track changes in cell performance. We show that trends in the electrochemical data obtained from coin-cells can be reliable and informative when standardized approaches are implemented in a consistent manner.

Brandon R. Long

Papers

Optimizing areal capacities through understanding the limitations of lithium-ion electrodes

Quantifying Hysteresis and Voltage Fade in xLi2MnO3●(1-x)LiMn0.5Ni0.5O2 Electrodes as a Function of Li2MnO3 Content

Re-entrant Lithium Local Environments and Defect Driven Electrochemistry of Li- and Mn-Rich Li-Ion Battery Cathodes

Enabling High-Energy, High-Voltage Lithium-Ion Cells: Standardization of Coin-Cell Assembly, Electrochemical Testing, and Evaluation of Full Cells

Advances in Stabilizing ‘Layered-Layered’ xLi2MnO3·(1-x)LiMO2 (M=Mn, Ni, Co) Electrodes with a Spinel Component