Investigation of the high-voltage spinel cathodes for high-energy-density lithium-ion batteries

Since their first commercialization in the early 1990s, lithium-ion batteries (LIBs) have been widely used in portable devices, electric vehicles (EVs), and hybrid electric vehicles (HEVs), revolutionizing our way of life. Compared to other battery systems such as nickel-cadmium, nickel-metal hydride, and lead-acid batteries, LIBs are unique in their ability to provide high energy density, high output potential, low self-discharge, and to function over a wide working temperature, as well as many other features. The 2019 Nobel Prize in Chemistry was awarded for the development of LIBs, further recognizing the success of LIB commercialization. However, existing commercial LIBs are the current limitation for the rapid development of both EVs and HEVs due to their limited energy densities. Considering that cathode material accounts for the high weight and cost in state-of-the-art LIBs, replacing these materials with cheaper and higher-energy-density candidates is the key to improving battery energy density. In this regard, high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is the most promising cathode material to replace current LiCoO2 in the next-generation high-energy-density LIBs. The Co-free LNMO spinel owns a series of advantages over other candidates, including high energy density and high operating voltage, relatively low-cost to the Co-containing counterparts, good thermal stability, high ionic conductivity, etc. However, the rapid capacity decay of LNMO cathode during battery cycling severely hinders its wide application and potential commercialization. Corresponding modification strategies are in urgent need to improve the electrochemical performance of LNMO material

Ultrathin Few-Layer GeP Nanosheets via Lithiation-Assisted Chemical Exfoliation and Their Application in Sodium Storage

2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ultrathin few-layer materials have attracted intensive research attention because of their distinctive and unique properties. Few-layer GeP (FL-GP) is potentially interesting for application in electronics and optoelectronics because of its appropriate band gap and good stability under ambient conditions. Nevertheless, it is a challenge to achieve ultrathin few-layer or single layer GeP from exfoliation of bulk crystals. Here, a lithiation-assisted chemical exfoliation technique is employed to achieve FL-GP, in which the interlayer spacing can be efficiently enlarged after a preliminary lithium ion intercalation, allowing the bulk crystal to be readily exfoliated in a following ultrasonication. As a result, ultrathin FL-GP is obtained. In a demonstration, the FL-GP/reduced graphene oxide (rGO) demonstrates remarkable sodium storage performance. The FL-GP with a two-dimensional structure shortens the ion transport pathways and alleviates the volume variation during sodiation. Meanwhile, the rGO in the composite improves the conductivity of the whole electrode. The as-prepared FL-GP/rGO electrode exhibits a high capacity of 504.2 mAh g−1 at 100 mA g−1, remarkable rate performance, and superior cycling stability in the half cells. FL-GP/rGO//Na3V2(PO4)3 full cells are also assembled and demonstrated satisfactory electrochemical performance, indicating potential application of the as-prepared anode materials

Progress and perspectives for electrochemical CO2 reduction to formate

Electrochemical CO2 reduction (CO2RR) is an environmentally friendly approach to transform greenhouse gas CO2 to value-added chemical feedstocks and fuels. One of the most promising CO2RR products is formate with widespread commercial applications across chemical, food, and energy related industrials. An ideal high performing CO2 electrolyser to synthesis formate should operate stably with high formate conversion efficiencies, at high current densities and low voltage that meeting industrial technoeconomic requirements. Significant progresses have been achieved in the past decades in the development of advanced catalysts, electrolyte engineering, and electrolyser designs that improved overall CO2 electrolysis performance. In-depth fundamental understanding of electrocatalytic reaction mechanisms was achieved through advanced in-situ analytical techniques. Although lab-scale electrolysers are relatively well-developed, it is still not reaching maturity level for industrial formate manufacturing that requires stable and efficient cell performance at economic scales. Here, CO2RR mechanistic studies including the employed advanced techniques for formate production are reviewed. Recent advances in the syntheses of p-block post-transition and transition metal-based catalysts and their performances are discussed. The main strategies for performance improvements including catalyst optimisation, electrolyte control, and cell designs, are critically assessed. Finally, we offer perspectives on future developments of CO2RR to formate

Coupling Topological Insulator SnSb2Te4 Nanodots with Highly Doped Graphene for High-Rate Energy Storage

Topological insulators have spurred worldwide interest, but their advantageous properties have scarcely been explored in terms of electrochemical energy storage, and their high-rate capability and long-term cycling stability still remain a significant challenge to harvest. p-Type topological insulator SnSb2Te4 nanodots anchoring on few-layered graphene (SnSb2Te4/G) are synthesized as a stable anode for high-rate lithium-ion batteries and potassium-ion batteries through a ball-milling method. These SnSb2Te4/G composite electrodes show ultralong cycle lifespan (478 mAh g−1 at 1 A g−1 after 1000 cycles) and excellent rate capability (remaining 373 mAh g−1 even at 10 A g−1) in Li-ion storage owing to the rapid ion transport accelerated by the PN heterojunction, virtual electron highways provided by the conductive topological surface state, and extraordinary pseudocapacitive contribution, whose excellent phase reversibility is confirmed by synchrotron in situ X-ray powder diffraction. Surprisingly, durable lifespan even at practical levels of mass loading (\u3e10 mg cm−2) for Li-ion storage and excellent K-ion storage performance are also observed. This work provides new insights for designing high-rate electrode materials by boosting conductive topological surfaces, atomic doping, and the interface interaction

Coupling Topological Insulator SnSb2Te4 Nanodots with Highly Doped Graphene for High-Rate Energy Storage

Topological insulators have spurred worldwide interest, but their advantageous properties have scarcely been explored in terms of electrochemical energy storage, and their high-rate capability and long-term cycling stability still remain a significant challenge to harvest. p-Type topological insulator SnSb2Te4 nanodots anchoring on few-layered graphene (SnSb2Te4/G) are synthesized as a stable anode for high-rate lithium-ion batteries and potassium-ion batteries through a ball-milling method. These SnSb2Te4/G composite electrodes show ultralong cycle lifespan (478 mAh g−1 at 1 A g−1 after 1000 cycles) and excellent rate capability (remaining 373 mAh g−1 even at 10 A g−1) in Li-ion storage owing to the rapid ion transport accelerated by the PN heterojunction, virtual electron highways provided by the conductive topological surface state, and extraordinary pseudocapacitive contribution, whose excellent phase reversibility is confirmed by synchrotron in situ X-ray powder diffraction. Surprisingly, durable lifespan even at practical levels of mass loading (\u3e10 mg cm−2) for Li-ion storage and excellent K-ion storage performance are also observed. This work provides new insights for designing high-rate electrode materials by boosting conductive topological surfaces, atomic doping, and the interface interaction

Insight into the improved cycling stability of sphere-nanorod-like micro-nanostructured high voltage spinel cathode for lithium-ion batteries

Currently, developing cathode material with high energy density and good cycling performance is one of the key challenges for lithium-ion batteries. LiNi0.5-xMn1.5+xO4 (LNMO) spinel cathode has attracted great attention as the most promising cathode candidate due to its extraordinarily high operating voltage, but its inferior long-term cycling stability has limited its further development. In this work, we successfully designed LNMOs with specific facets and different morphologies, among which the hybrid sphere-nanorod-like micro-nanostructured LNMO possesses excellent cycling performance, with capacity of over 107.8 mAh g−1 after 1000 cycles at 10 C and superior rate capability up to 10 C. Its superior rate capability is found to originate from the large Li-O bond length by Rietveld refinement, which contributes to decreased charge transfer resistance and ease of Li insertion/extraction at tetrahedral sites. On the other hand, the excellent cycling stability comes from its having the least structural deformation from mechanistic reactions, which involve the longest solid-solution reaction, the highest spinel structural tolerance/stability up to Δ = ~0.69 Li, and a highly reversible two-phase reaction during charge and discharge in the hybrid LNMO, as revealed by the in operando synchrotron X-ray powder diffraction results. Moreover, the hybrid LNMO exhibits surface planes (210) with the highest Mn defect formation energy, prohibiting Mn3+ disproportionation and further stabilizing its cycling stability. This work not only demonstrates the importance of crystallographic and morphological controls on the high-voltage spinel performance, but also opens a window for battery engineers and researchers to develop battery technology for high-power applications

Understanding Rechargeable Battery Function Using In Operando Neutron Powder Diffraction

The performance of rechargeable batteries is influenced by the structural and phase changes of components during cycling. Neutron powder diffraction (NPD) provides unique and useful information concerning the structure-function relation of battery components and can be used to study the changes to component phase and structure during battery cycling, known as in operando measurement studies. The development and use of NPD for in operando measurements of batteries is summarized along with detailed experimental approaches that impact the insights gained by these. A summary of the information gained concerning battery function using in operando NPD measurements is provided, including the structural and phase evolution of electrode materials and charge-carrying ion diffusion pathways through these, which are critical to the development of battery technology

Revisiting the Role of Discharge Products in Li–CO2 Batteries

Rechargeable lithium-carbon dioxide (Li–CO2) batteries are promising devices for CO2 recycling and energy storage. However, thermodynamically stable and electrically insulating discharge products (DPs) (e.g., Li2CO3) deposited at cathodes require rigorous conditions for completed decomposition, resulting in large recharge polarization and poor battery reversibility. Although progress has been achieved in cathode design and electrolyte optimization, the significance of DPs is generally underestimated. Therefore, it is necessary to revisit the role of DPs in Li–CO2 batteries to boost overall battery performance. Here, a critical and systematic review of DPs in Li–CO2 batteries is reported for the first time. Fundamentals of reactions for formation and decomposition of DPs are appraised; impacts on battery performance including overpotential, capacity, and stability are demonstrated; and the necessity of discharge product management is highlighted. Practical in situ/operando technologies are assessed to characterize reaction intermediates and the corresponding DPs for mechanism investigation. Additionally, achievable control measures to boost the decomposition of DPs are evidenced to provide battery design principles and improve the battery performance. Findings from this work will deepen the understanding of electrochemistry of Li–CO2 batteries and promote practical applications

Insight into the improved cycling stability of sphere-nanorod-like micro-nanostructured high voltage spinel cathode for lithium-ion batteries

Currently, developing cathode material with high energy density and good cycling performance is one of the key challenges for lithium-ion batteries. LiNi0.5-xMn1.5+xO4 (LNMO) spinel cathode has attracted great attention as the most promising cathode candidate due to its extraordinarily high operating voltage, but its inferior long-term cycling stability has limited its further development. In this work, we successfully designed LNMOs with specific facets and different morphologies, among which the hybrid sphere-nanorod-like micro-nanostructured LNMO possesses excellent cycling performance, with capacity of over 107.8 mAh g−1 after 1000 cycles at 10 C and superior rate capability up to 10 C. Its superior rate capability is found to originate from the large Li-O bond length by Rietveld refinement, which contributes to decreased charge transfer resistance and ease of Li insertion/extraction at tetrahedral sites. On the other hand, the excellent cycling stability comes from its having the least structural deformation from mechanistic reactions, which involve the longest solid-solution reaction, the highest spinel structural tolerance/stability up to Δ = ~0.69 Li, and a highly reversible two-phase reaction during charge and discharge in the hybrid LNMO, as revealed by the in operando synchrotron X-ray powder diffraction results. Moreover, the hybrid LNMO exhibits surface planes (210) with the highest Mn defect formation energy, prohibiting Mn3+ disproportionation and further stabilizing its cycling stability. This work not only demonstrates the importance of crystallographic and morphological controls on the high-voltage spinel performance, but also opens a window for battery engineers and researchers to develop battery technology for high-power applications

Ultrathin Few-Layer GeP Nanosheets via Lithiation-Assisted Chemical Exfoliation and Their Application in Sodium Storage

2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ultrathin few-layer materials have attracted intensive research attention because of their distinctive and unique properties. Few-layer GeP (FL-GP) is potentially interesting for application in electronics and optoelectronics because of its appropriate band gap and good stability under ambient conditions. Nevertheless, it is a challenge to achieve ultrathin few-layer or single layer GeP from exfoliation of bulk crystals. Here, a lithiation-assisted chemical exfoliation technique is employed to achieve FL-GP, in which the interlayer spacing can be efficiently enlarged after a preliminary lithium ion intercalation, allowing the bulk crystal to be readily exfoliated in a following ultrasonication. As a result, ultrathin FL-GP is obtained. In a demonstration, the FL-GP/reduced graphene oxide (rGO) demonstrates remarkable sodium storage performance. The FL-GP with a two-dimensional structure shortens the ion transport pathways and alleviates the volume variation during sodiation. Meanwhile, the rGO in the composite improves the conductivity of the whole electrode. The as-prepared FL-GP/rGO electrode exhibits a high capacity of 504.2 mAh g−1 at 100 mA g−1, remarkable rate performance, and superior cycling stability in the half cells. FL-GP/rGO//Na3V2(PO4)3 full cells are also assembled and demonstrated satisfactory electrochemical performance, indicating potential application of the as-prepared anode materials