• Energy Research

Electrochemically active LiMnPO4 nanoplates at lithiated/delithiated state were subjected to thermal stability and phase transformation evaluations for safety as a cathode material for Li-ion batteries. The phase transformation and oxygen evolution temperature of delithiated MnPO4 were characterized using in situ hot-stage X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric-differential scanning calorimetry-mass spectroscopy (TGA-DSC-MS), transmission electron microscopy and scanning electron microscopy (SEM)-energy dispersive X-ray analysis (EDAX).

The rechargeable lithium metal battery has attracted wide attention as a next-generation energy storage technology. However, simultaneously achieving high cell-level energy density and long cycle life in realistic batteries is still a great challenge. Here we investigate the degradation mechanisms of Li || LiNi0.6Mn0.2Co0.2O2 pouch cells and present fundamental linkages among Li thickness, electrolyte depletion and the structure evolution of solid–electrolyte interphase layers. Different cell failure processes are discovered when tuning the anode to cathode capacity ratio in compatible electrolytes. An optimal anode to cathode capacity ratio of 1:1 emerges because it balances well the rates of Li consumption, electrolyte depletion and solid–electrolyte interphase construction, thus decelerating the increase of cell polarization and extending cycle life. Contrary to conventional wisdom, long cycle life is observed by using ultra-thin Li (20 µm) in balanced cells. A prototype 350 Wh kg−1 pouch cell (2.0 Ah) achieves over 600 long stable cycles with 76% capacity retention without a sudden cell death. The development of Li metal batteries requires understanding of cell-level electrochemical processes. Here the authors investigate the interplay between electrode thickness, electrolyte depletion and solid–electrolyte interphase in practical pouch cells and demonstrate the construction of high-energy long-cycle Li metal batteries.

Immersion of a solid into liquid often leads to the modification of both the structure and chemistry of surface of the solid, which subsequently affects the chemical and physical properties of the system. For the case of the rechargeable lithium ion battery, consquence of such a surface modification is termed as solid electrolyte interphase (SEI) layer, which has been perceived to play a critical role in the stable operation of the batteries. However, the structure and chemical composition of the SEI layer and its spatial distribution and dependence on the battery operating conditions remain unclear. Using aberration-corrected scanning transmission electron microscopy, coupled with ultrahigh-sensitivity energy-dispersive X-ray spectroscopy, we probed the structure and chemistry of the SEI layer on several high-voltage cathodes. We show that layer-structured cathodes, when cycled at a high cut-off voltage, can form a Phosphorus-rich SEI layer on their surface, which is a direct evidence of Li-salt (LiPF6) ...

State-of-the-art lithium (Li)-ion batteries are approaching their specific energy limits yet are challenged by the ever-increasing demand of today’s energy storage and power applications, especially for electric vehicles. Li metal is considered an ultimate anode material for future high-energy rechargeable batteries when combined with existing or emerging high-capacity cathode materials. However, much current research focuses on the battery materials level, and there have been very few accounts of cell design principles. Here we discuss crucial conditions needed to achieve a specific energy higher than 350 Wh kg−1, up to 500 Wh kg−1, for rechargeable Li metal batteries using high-nickel-content lithium nickel manganese cobalt oxides as cathode materials. We also provide an analysis of key factors such as cathode loading, electrolyte amount and Li foil thickness that impact the cell-level cycle life. Furthermore, we identify several important strategies to reduce electrolyte-Li reaction, protect Li surfaces and stabilize anode architectures for long-cycling high-specific-energy cells. Jun Liu and Battery500 Consortium colleagues contemplate the way forward towards high-energy and long-cycling practical batteries.

Abstract In this work, Li/air batteries based on nonaqueous electrolytes were investigated in ambient conditions (with an oxygen partial pressure of 0.21 atm and relative humidity of ∼20%). A heat-sealable polymer membrane was used as both an oxygen-diffusion membrane and as a moisture barrier for Li/air batteries. The membrane also can minimize the evaporation of the electrolyte from the batteries. Li/air batteries with this membrane can operate in ambient conditions for more than one month with a specific energy of 362 Wh kg −1 , based on the total weight of the battery including its packaging. Among various carbon sources used in this work, Li/air batteries using Ketjenblack (KB) carbon-based air electrodes exhibited the highest specific energy. However, KB-based air electrodes expanded significantly and absorbed much more electrolyte than electrodes made from other carbon sources. The weight distribution of a typical Li/air battery using the KB-based air electrode was dominated by the electrolyte (∼70%). Lithium metal anodes and KB-carbon account for only 5.12% and 5.78% of the battery weight, respectively. We also found that only ∼20% of the mesopore volume of the air electrode was occupied by reaction products after discharge. To further improve the specific energy of the Li/air batteries, the microstructure of the carbon electrode needs to be further improved to absorb much less electrolyte while still holding significant amounts of reaction products.

Abstract Lithium (Li) metal battery technology has attracted world-wide attention because of its high energy density, but its practical application is hindered by several challenges, with one significant issue being the large volume change and cell swelling. While external pressure is known to have a profound effect on cell performance, there are currently no reports exploring the relationship between external pressure and the electroplating of Li+ in large-format pouch cells to enhance overall performance. Here we investigate the influence of externally applied pressure on the electroplating and stripping of lithium metal in 350 Wh/kg pouch cells. A hybrid constant gap and constant pressure design is designed to apply a minimal external pressure for practical application. The self-generated pressures are monitored and quantified which are further correlated to the observed charge-discharge processes. A two-stage cycling process is observed. In the first stage, Li+ ions utilized are mainly supplied by the cathode which shuttle between the cathode and anode with minimal Li loss which minimizes cell swelling but only happens when pressure is applied appropriately. In the second stage, Li from the Li foil anode participates in the reaction and the thickness of the anode gradually increases. However, even after extensive cycling, cell swelling remains less than 10%, comparable to that of state-of-the-art Li-ion batteries. In addition, the pressure distribution along the horizontal direction across the surface of Li metal pouch cell reveals a complex behavior of Li+ migration during the electroplating (charge) process. The external pressure encourages a preferred plating process of Li in the central region, necessitating the development of new strategies to address uneven Li plating and utilization to advance Li metal battery technology.

Lithium-rich, magnesium-rich (LMR) cathode materials have been regarded as very promising for lithium (Li-ion battery applications. However, their practical application is still limited by several barriers such as their limited electrochemical stability and rate capability. In this work, we present recent progress on the understanding of structural and compositional evolution of LMR cathode materials, with an emphasis being placed on the correlation between structural/chemical evolution and electrochemical properties. In particular, using Li[Li0.2Ni0.2Mn0.6]O2 as a typical example, we clearly illustrate the structural characteristics of pristine materials and their dependence on the material-processing history, cycling-induced structural degradation/chemical partition, and their correlation with electrochemical performance degradation. The fundamental understanding that resulted from this work may also guide the design and preparation of new cathode materials based on the ternary system of transitional metal oxides.