High-energy Li-ion Batteries Research Articles

Si Anode in High-Salt Concentration Ionic Liquid Electrolytes Based on Pyrrolidinium and Phosphonium Systems for High-Energy Li-Ion Batteries

In order to push further the development of next generation Li-ion batteries (LiBs), high energy density, good capacity retention and increased safety are key features that need to be taken into account when designing energy storage devices. To this date, commercial batteries for portable devices mainly use graphite as anode. However, with the advent of electric vehicles and intelligent power grids, there is an increasing demand for high capacity materials to meet the energy and power requirement of these applications. More recently, Si anode has received considerable attention because of its natural abundance and its ability to deliver high energy density, with a gravimetric capacity of 3579 mAhg-1 which is almost 10 times that of graphite (372 mAhg-1) [1-2]. Bearing in mind that commercial LiBs use carbonate electrolytes which are recognized to pose safety issues and have been identified to suffer from degradation during charge-discharge cycles, we explored in this study the performance of Si anode in ionic liquid electrolytes based on phosphonium and pyrrolidinium cations, systems that are currently the most studied in the field of Li batteries [3-4]. Ionic liquid electrolytes are an appealing alternative to carbonates mainly because of their low volatility and better stability. In the recent years, good electrochemical behavior has been observed in ionic liquids with high salt concentration [3-5]. In this work, we were able to demonstrate better electrochemical performance of Si anode in ionic liquid electrolytes with 3.2 m LiFSI compared to conventional carbonate electrolytes in terms of capacity and capacity retention at 50°C. Electrochemical performance obtained in the phosphonium and pyrrolidinium systems are compared for different concentrations and temperatures. Moreover, initial investigation of the SEI using NMR and XPS spectroscopy revealed that less degradation products are formed upon cycling in ionic liquid electrolytes compared to usual carbonates electrolytes. Overall, these results highlight the stability of ionic liquids which translate to good cycling performance and show promising potential of Si anode as a high-capacity material for high-energy and high-temperature applications. Cyclability and capacity retention for the phosphonium and pyrrolidinium system will be discussed in terms of ionic liquids components degradation and SEI formation and evolution, as probed by combined 19F, 7Li MAS-NMR, XPS and impedance spectroscopy.

Next Generation of Materials for Lithium-Ion Battery Anodes, Cathodes, Separators & Electrolytes

Energy density and cost of conventional Li-ion batteries (LIBs) are closely approaching their limits. The reliance of conventional cathodes on the use of toxic metals additionally endangers health and safety of miners in developing countries. Novel materials for conversion-type cathodes and alloying-type anodes offer an opportunity to double energy stored in LIBs, reduce their cost by the same factor, and improve cell safety. Conventional separators suffer from poor thermal stability, limited mechanical strength in tension and compression, relatively large minimum thickness of 6 micron (typically 10-25 micron for safer versions used in electric vehicle (EV) LIBs) and relatively high ionic resistance, undesired for ultra-fast charging. Ceramic and ceramic-composite nanofiber-based separators enable one to overcome the current limitations and produce safer LIBs with higher energy density and faster charging abilities. Finally, conventional organic electrolytes suffer from flammability, limited electrochemical stability in contact with anodes and cathodes of high-energy LIBs and undesired chemical and electrochemical reactions with cathode materials that accelerate LIB fading, particularly at elevated temperatures. Several classes of solid electrolytes may offer effective solutions to overcome such drawbacks. In this invited talk I will provide an overview of the activities of our group in these complementary fields and share my understanding of the industrial requirements for the technology adoption and successful commercialization.

Chemical stability and long-term cell performance of low-cobalt, Ni-Rich cathodes prepared by aqueous processing for high-energy Li-Ion batteries

Cobalt content in Li-ion battery cathodes has become a top concern due to its price volatility and limited source availability. Low-cobalt, Ni-rich active materials are promising candidates for next-generation cathodes due to their high capacities, and water-based processing of these materials can further reduce both cost and environmental impact. We systematically evaluated the water compatibility of four different LiNixMn1-x-yCoyO2 (NMC) powders with increasing nickel contents. Comprehensive characterization verified there is no major change to their bulk structures, and only slight surface modifications related to the removal of contaminant species. For the first time, we demonstrate that LiNi0.8Mn0.1Co0.1O2 (NMC 811) cathodes can be formulated in water and cycled 1000 times in full pouch cells with excellent capacity retention (~70% compared to ~76% for NMP-processed cells). When implemented in future battery production lines, aqueous processing of Ni-rich NMC will simultaneously enable cost reductions and higher cell energy densities.

Renewable agaric-based hierarchically porous cocoon-like MnO/Carbon composites enable high-energy and high-rate Li-ion batteries

Hierarchical pore structures in the composite electrode materials can offer greater accessibility to active sites for the lithium ions, shorter ion diffusion distances and quicker lithium ion diffusion, which can enable the high-rate and high-energy Li-ion batteries (LIBs). In this work, hierarchically porous cocoon-like MnO/C composites (PCM) have been prepared using natural agaric as raw materials via a sustainable and facile method associated with the hydrothermal and annealing treatment. The as-prepared porous PCM composites show a high reversible capacity of 981 mAh g−1 at 0.1 A g−1 and remain an high discharge capacity of 640 mAh g−1 after 900 cycles at 1 A g−1. Even at the high current density of 5 A g−1, the electrode can still deliver a high capacity of 440 mAh g−1. More importantly, the high MnO content (∼78 wt %) and micron-scale structure of PCM composite greatly improve the high specific capacity and tap density of electrode materials, and help to meet the requirements for practical application. Therefore, such novel preparation strategy of composite electrode from agaric also develops a new route to fully utilize the biomass resources for high-performance LIBs and other energy storage devices.

Problems and their origins of Ni-rich layered oxide cathode materials

Ni-rich layered oxides, LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) with x ​+ ​y ​+ ​z ​= ​1 and x ​≥ ​0.8, are regarded to be the best choice for the cathode material of high energy Li-ion batteries due to their combined advantages in capacity, working potential and manufacture cost. However, their application in practical Li-ion batteries is hindered by two essential problems of (1) performance degradation and (2) safety hazard over the whole life of battery. Performance degradation behaves as declines in battery's capacity and working voltage as well as the battery's swelling and impedance growth; Safety hazard arises from thermal runaway under abuse conditions such as overcharging, overheating, and electric shorting. It appears that nearly all problems can be ultimately attributed to the loss of oxygen, especially caused by the oxidation of lattice oxygen in H3 phase where the capacities are contributed by both of the Ni and O redox couples. In this review, the problems and their origins of Ni-rich layered oxides are overviewed, and the solutions attempted to mitigate these problems are outlined.

Enhancing the High-Voltage Cycling Stability of Nickel-Rich Oxide Cathode Using Functional Electrolyte

Increasing needs of electric vehicles and grid-based energy storage systems for the reduction of carbon dioxide gases require higher energy density lithium (Li)-ion batteries than commercial batteries. The energy density of Li-ion batteries can increase by increasing the specific capacity of cathode material, which can increase by raising the charge cut-off voltage. Among various cathode materials, nickel-rich layered oxides of Li(Ni1 –x –y Co x Mn y )O2 (NCM, 1–x–y ≥ 0.5) are promising high-capacity cathode materials for high-energy density Li-ion batteries because of higher capacity and lower cost than nickel-lean oxides. However, the limited anodic instability of the conventional carbonate-based organic electrolytes at the voltage higher than 4.2 V versus Li/Li+ and instability of cathode-electrolyte interface at highly charged state makes high-voltage charge of nickel-rich oxide cathode difficult. In order to mitigate the electrolyte and interface issues, we have been developing new functional electrolytes that provides high anodic stability above 4.3 V and highly stable cathode-electrolyte interface. High-voltage electrochemical and interfacial reaction studies and their correlation to cycling performance would be discussed in the meeting. Acknowledgements: This research was supported by Ministry of Trade, Industry & Energy (R0004645) and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/Bio Materials of BK Plus program by Ministry of Education of Korea.

Characterization of PEDOT-Quinone conducting redox polymers in water-in-salt electrolytes for safe and high-energy Li-ion batteries

Li-ion batteries (LIBs) raise safety and environmental concerns, which mostly arise from their toxic and flammable electrolytes and the extraction of limited material resources by mining. Recently, water-in-salt electrolytes (WiSEs), in which a large amount of lithium salt is dissolved in water, have been proposed to allow for assembling safe and high-voltage (>3.0 V) aqueous LIBs. In addition, organic materials derived from abundant building blocks and their tunable properties could provide safe and sustainable replacements for inorganic cathode materials. In the current work, the electrochemical properties of a conducting redox polymer based on poly(3,4-ethylenedioxythiophene) (PEDOT) with hydroquinone (HQ) pendant groups have been characterized in WiSEs. The quinone redox reaction occurs within the potential region where the polymer is conducting, and fast redox conversion that involves lithium cycling during pendant group redox conversion was observed. These properties make conducting redox polymers promising candidates as cathode-active materials for safe and high-energy aqueous LIBs. An organic-based aqueous LIB, with a HQ-PEDOT as a cathode, Li4Ti5O12 (LTO) as an anode, and ca. 15 m lithium bis(trifluoromethanesulfonyl)imide water/dimethyl carbonate (DMC) as electrolyte, yielded an output voltage of 1.35 V and high rate capabilities up to 500C.

Binder-Induced Interface Stabilization and Performance Improvement of Nickel-Rich Cathode

High-energy Li-ion batteries are well-suited for electric vehicle (EV) and energy storage applications. For the success of long-range energy storage systems, increasing the specific energy density of Li-ion batteries toward more than doubled compared to commercial batteries is on demand. Nickel (Ni)-rich multi-component layered oxide, represented by LiNi1−x−y Co x Mn y O2 (NCM, x+y £ 0.5), is a promising high-capacity cathode material for high-energy batteries, whose capacity increases by increasing the amount of Ni and/or by increasing charge cut-off voltage above 4.2 V versus Li/Li+. Their long term performance and high-voltage cycling performance however are often limited, due to high reactivity at highly charged state, instable cathode-electrolyte interface, and the occurrence of metal-dissolution, particle cracking and structural degradation, particularly.1-3 In order to mitigate those problems, we have been designing and developing novel functional binder,4 which provides a solution to the degradation problems of the Ni-rich cathodes coated with conventional polyvinylidenefluoride (PVdF) binder, through superior binding ability to cathode surface and the formation of a robust cathode-electrolyte interface structure. Improved cycling performance and interfacial stabilization of Ni-rich cathodes by the effects of our functional binder would be discussed in the meeting. Acknowledgements This research was supported by Ministry of Trade, Industry & Energy (10080025), National Research Foundation (NRF-2015R1D1A1A01060838) and Creative Human Resource Development Consortium for Fusion Technology of Functional Chemical/ Bio Materials of BK Plus program by Ministry of Education of Korea. References Y.-M. Lee, K.-M. Nam, E.-H. Hwang, Y.-G. Kwon, D.-H. Kang, S.-W. Song, J. Phys. Chem. C., 118, 10631 (2014).H.Q. Pham, K.-M. Nam, E.-H. Hwang, Y.-G. Kwon, H.M. Jung, S.-W. Song, J. Electrochem. Soc., 161 A2002 (2014).D.-T. Nguyen, J. Kang, K.-M. Nam, Y. Paik, S.-W. Song, J. Power Sources, 303, 150 (2016).H.Q. Pham, G. Kim, H.M. Jung, S.-W. Song, Adv. Funct. Mater., 28, 1704690 (2018).

Climate-Immune Extreme Fast Charging of High Energy Li-Ion Batteries

Fast charging is the enabler of mainstream adoption of electric vehicles (EVs). There is a race worldwide for building fast charging stations with the power up to 350kW, which are able to charge a 200-mile-range EV at 6C (10 minutes). State-of-the-art EV batteries (cell-level energy density >200 Wh/kg) could only withstand 2C (30 minutes) charging due to the issue of lithium plating. Even worse, the charge rate must be dramatically reduced at low temperatures to prevent lithium plating. Most recently, our group presented a controllable cell structure that enables lithium plating free (LPF) fast charging at all temperatures. [1] The key is to charge a cell always above a temperature that can prevent lithium plating. A rapid heating step will be performed before charging if the cell temperature is low. It is demonstrated that a 9.5Ah pouch cell with an energy density of 170 Wh/kg could be charged by 80% state of charge in 15 minutes even at -50oC, an extremely low temperature at which all conventional Li-ion cells would cease to work. Furthermore, the LPF cell sustained 4500 cycles of 15-min fast charging at 0oC with <20% capacity loss, which is equivalent to >12 years and >280,000 miles of EV lifetime, whereas a baseline conventional cell at the same condition only survived 50 cycles. Based on the LPF cell structure, we proposed an approach to enable 10-min extreme fast charging (XFC) of high energy EV cells. By numerical analysis, we revealed that the optimal temperature for Li-ion battery charging increases with the increase of charge rate and energy density. [2] Thus, we are now partnering with the U.S. Department of Energy (DOE) to develop an XFC battery that is charged at high temperatures (>60oC). The target is to achieve 6C charging of >225 Wh/kg cells with a life of >1000 cycles at <20% capacity loss. In this talk, we will give a comprehensive discussion of the LPF cell structure and operating strategy. We will also share our latest progress on the development of XFC cells.

Investigation on Solvent and Surface Modification Effects for Li Metal Anodes

Li metal anode is strongly considered to be one of the most promising candidates for high-energy Li-ion batteries. However, lithium dendrite growth, which could cause short-circuit and low Coulombic efficiency (CE), is one of the key issues for realizing practical applications of Li anode technologies. Various strategies have been proposed to suppress Li dendrite formation. In order to understand the Li dendrite formation and suppression behaviors for Li plating, we carried out extensive study on the effects of solvent and surface coating on the electrochemical behaviors of the Li metal anodes. Carbonate solvents having various components with/without additives have been employed for Li plating and stripping on Cu substrate. Polymeric coatings on Cu have also been tested for their effects on the morphology of Li deposition and SEI analysis. In particular, extensive real-time optical microscopy imaging and post mortem SEM analyses are carried out in conjunction with electrochemical characterizations to reveal the underlying mechanisms for the resulting effects. Figure 1

Microstructural feature analysis of commercial Li-ion battery cathodes by focused ion beam tomography

Four positive electrodes are extracted from two high-power and two high-energy Li-ion battery consumer cells, and then analyzed by focused ion beam-scanning electron microscopy (FIB-SEM) tomography. The active material phase, carbon black-binder phase and pore phase are quantitatively evaluated using adequate 3D analysis techniques by their volume fractions, surface areas, particle size distributions and tortuosities. The active material phase is composed of LiCoO2 (Sanyo 1500 mA h), or LiNiCoAlO2 (Sony 2600 mA h) or one of two LiNiCoAlO2-LiCoO2 blends (Kokam high-power 350 mA h and high-energy 560 mA h). Special emphasis was put on the three-dimensional distribution of the submicron-sized (yet highly agglomerated) carbon black-binder phase. Vacuum infiltration with a two-component silicone resin gave greyscale contrast between the carbon black-binder and pore phases for contour description at voxel sizes from 30 to 50 nm. This study elucidates the cathode microstructural features for high-energy and high-power application and provides a complete parameter set of commercial electrodes with differing chemical composition. This information can be used by the scientific community as input parameters in simulations and models, filling the gap between the experimental and the simulation fields.

Precursor pre-oxidation enables highly exposed plane {010} for high-rate Li-rich layered oxide cathode materials

Precursor synthesis technology is a key factor to improve the electrochemical properties of Li-rich layered oxide (LLO) cathode materials. However, the effect of precursor preparation strategies on the morphology and electrochemical properties of cathode materials has not been clearly elucidated. In this work, an LLO cathode material (denoted as LMNC-300) with highly exposed {010} planes and a lower amount of surface residual lithium is reported via pre-oxidation of a precursor at 300 °C. This LMNC-300 cathode material exhibits an initial Coulombic efficiency of 91.7% with a discharge capacity of 277.2 mA h g−1 at 0.1 C, an excellent high-rate capability with a discharge capacity of 175.1 mA h g−1 even at 5.0 C and a good cycling performance with a capacity retention of 92.6% after 200 cycles at 0.5 C. In addition, a pouch cell consisted of the LMNC-300 cathode and a commercial graphite anode presented good cycling stability with a capacity retention of 81.6% after 500 cycles at 2.0 C. The outstanding electrochemical performance can be ascribed to an accelerated Li+ diffusion dynamics. Therefore, the method reported in this work will be significant to understanding the effects of preparation strategies of transition metal precursors on the electrochemical performance of Li-rich layered cathode materials for high-energy density Li-ion batteries.

Sizing improvement of hybrid storage system composed with high energy and high power Li-ion batteries for automotive applications

In this article, an algorithm has been developed to study the influence of hybrid energy storages system management on the performance of this last one in terms of weight, volume, cost and stresses applied to the two storage systems witch compose our source. The main storage system is composed with a high energy or ultra high energy density batteries. Otherwise, the secondary one can be an ultra high power, high power batteries or supercapacitor. Simulation results show that gains in weight and volume are obtained using ultra high energy cells as the main battery or/and an ultra high power as secondary source. The power management is improved to ameliorate the performances of storage system for automotive application.

Metalophilic Gel Polymer Electrolyte for in Situ Tailoring Cathode/Electrolyte Interface of High-Nickel Oxide Cathodes in Quasi-Solid-State Li-Ion Batteries.

High-Ni layered oxides are potential cathodes for high energy Li-ion batteries due to their large specific capacity advantage. However, the fast capacity fade by undesirable structural degradation in liquid electrolyte during long-term cycling is a stumbling block for the commercial application of high-Ni oxides. In this work, a functional gel polymer electrolyte, grafted with sodium alginate, is introduced to increase the stability of high-Ni oxide cathodes at the levels of both the particle and electrode. An in situ generated ion-conducting layer appears on the interface through the chemical interaction between transition-metal cations of the cathode and the metalophilic reticulum group in sodium alginate. Such a tailoring layer can not only enhance the interfacial compatibility on the cathode/electrolyte interface, reducing the interfacial resistance, but also inhibit the HF corrosion, suppressing the dissolution of transition-metal cations and harmful gradient distribution of components through the oxide cathode at the electrode level. Meanwhile, detrimental microcracks in oxide microspheres and between primary crystallites are impressively inhibited at the particle level. The high-Ni oxide cathode with the metalophilic gel polymer electrolyte shows excellent cycle stability with large initial capacity of 204.9 mA h g-1 at a 1.0 C rate and high discharge capacity retention within 300 cycles at high temperature.

Material structure and chemical bond effect on the electrochemical performance of black phosphorus-graphite composite anodes

Black phosphorus (BP) is a little-studied but promising next-generation anode material for high-energy density Li-ion and Na-ion batteries. To understand the relationship between material property and electrochemical performance, black phosphorus-graphite (BP-G) composite materials are synthesized with two different BP-G molar ratios. This study demonstrates that the crystal structure and PC bond of BP-G composites are affected by the BP-G molar ratio, which are directly correlated to cycle stability and the lithiation/delithiation process. BP0.9G1 shows a medium-range ordered structure, retaining some features of BP and having fewer or weaker PC bonds. In contrast, BP0.3G1 has an amorphous-like structure with robust PC bonds, which is helpful in withstanding the large volume change upon lithiation or delithiation. As a result, fracture and pulverization of particles, which are clearly seen in BP0.9G1 electrode, are scarcely observed in the cycled BP0.3G1 electrode. The possibility of mechanical failure in the BP-based electrode induced by BP's hydrophilic nature and the formation of Cu3P is also discussed. This work not only contributes to improving the current understanding of phosphorus-based anodes, but also provides direct evidence of fracture and pulverization of BP particles during cycling.

Role of Polyacrylic Acid (PAA) Binder on the Solid Electrolyte Interphase in Silicon Anodes

To obtain high-energy density Li-ion batteries for the next-generation storage devices, silicon anodes provide a viable option because of their high theoretical capacity, low operating potential ve...

Collapse of LiNi1- x- yCo xMn yO2 Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries.

Volume variation and the associated mechanical fracture of electrode materials upon Li extraction/insertion are a main cause limiting lifetime performance of lithium-ion batteries. For LiNi1- x- yCo xMn yO2 (NCM) cathodes, abrupt anisotropic collapse of the layered lattice structure at deep charge is generally considered characteristic to high Ni content and can be effectively suppressed by elemental substitution. Herein, we demonstrate the lattice collapse is a universal phenomenon almost entirely dependent on Li utilization, and not Ni content, of NCM cathodes upon delithiation. With Li removal nearing 80 mol %, very similar c-axis lattice shrinkage of around 5% occurs concurrently for NCMs synthesized in-house regardless of nickel content (90, 70, 50, or 33 mol %); meanwhile, the a-axis lattice contracts for high-Ni NCM, but it expands for low-Ni NCM. We further reveal Co-Mn cosubstitution in NCM barely, if at all, affects several key structural aspects governing the lattice distortion upon delithiation. Our results highlight the importance of evaluating true implications of compositional tuning on high-Ni layered oxide cathode materials to maximize their charge-storage capacities for next-generation high-energy Li-ion batteries.

Understanding thickness and porosity effects on the electrochemical performance of LiNi0.6Co0.2Mn0.2O2-based cathodes for high energy Li-ion batteries

The targeted optimization of Li-ion batteries (LIBs) requires a fundamental understanding of the wide variety of interdependencies between electrode design and electrochemical performance. In the present study, the effects of thickness and porosity on the electrochemical performance and Li-ion insertion kinetics of LiNi0.6Co0.2Mn0.2O2-based (NCM-622) cathodes are investigated. Cathodes of different thickness and porosity are prepared and analyzed regarding their rate capability. The polarization behavior is investigated using electrochemical impedance spectroscopy. A simple mathematical model is employed to estimate the impact of Li-ion diffusion limitations in the electrolyte. The results are considered at both, the materials and the full-cell level. The design parameters are found to have distinct impact on the electrolyte, contact and charge transfer resistance as well as the Li-ion diffusion limitations in the electrolyte, significantly influencing the rate capability. The results attest an inherent tradeoff between energy and power density. The insights of this study can be used straightforward for the optimization of gravimetric and volumetric energy density of LIBs depending on the desired application.

Functional additives assisted ester-carbonate electrolyte enables wide temperature operation of a high-voltage (5 V-Class) Li-ion battery

Nowadays, wide temperature range and high-energy Li-ion batteries are increasingly required. However, it is difficult to get a compromise between subzero temperature performance and high temperature performance. Herein, methyl acetate co-solvent with a freezing point of −98.1 °C (50% by volume) is blended with carbonates to obtain a high-conductivity LiPF6-based electrolyte, which contains tris(trimethylsilyl) phosphite and 1,3-propanediolcyclic sulfate binary functional additives to significantly enhance cycling performance of a challenging high-voltage (5 V-class) battery system using a LiNi0.5Mn1.5O4 cathode and a graphitic mesocarbon microbead anode, unprecedentedly ranging from −60 °C to 50 °C. High reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode is innovatively proposed to be associated with graphitic mesocarbon microbead anode catalytic formation of methoxy free radical. More importantly, high reactivity between methyl acetate co-solvent and graphitic mesocarbon microbead anode can be greatly suppressed by species derived from functional additives. This paper highlights the crucial rule of both high Li+ conductivity and favorable graphite anode interface layer for achieving high performance wide temperature range Li-ion batteries.

In Situ Focused Ion Beam Scanning Electron Microscope Study of Microstructural Evolution of Single Tin Particle Anode for Li-Ion Batteries.

Tin (Sn) is a potential anode material for highenergydensity Li-ion batteries because of its high capacity, safety, abundance and low cost. However, Sn suffers from large volume change during cycling, leading to fast degradation of the electrode. For the first time, the microstructural evolution of micrometer-sized single Sn particle was monitored by focused-ion beam (FIB) polishing and scanning electron microscopy (SEM) imaging during electrochemical cycling by in situ FIB-SEM. Our results show the formation and evolution of cracks during lithiation, evolution of porous structure during delithiation and volume expansion/contraction during cycling. The electrochemical performance and the microstructural evolution of the Sn microparticle during cycling are directly correlated, which provides insights for understanding Sn-based electrode materials.