Suppressing dendritic metallic Li formation on graphite anode under battery fast charging

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

Fast charging of commercial lithium-ion batteries severely compromises long-term cycle durability, particularly in cells using high mass-loading thick electrodes. Such performance decay originates from interfacial kinetic limitations in the graphite anode as follows: (i) a sluggish Li+ desolvation at the electrolyte-graphite interface, (ii) a hindered Li+ diffusion across the solid electrolyte interphase (SEI), and (iii) a restricted Li+ insertion into the graphite, which collectively lead to an undesirable Li plating. Herein, we introduce an ultrathin and uniform MoO2/Mo2C biphasic passivation layer, achieved through a sequential cationic polyelectrolyte-assisted molybdate adsorption approach. The outer MoO2 layer does not only suppress an excessive SEI formation but also stabilizes the electrolyte interface by promoting the formation of Li2O and LiF-rich SEI that are both ionically conductive and chemically robust. The inner Mo2C layer provides a low Li+ adsorption energy (-0.97 eV), a reduced surface diffusion barrier (43 meV), and a high electrical conductivity (∼104 S cm-1), consequently enabling capacitive behavior and fast intercalation kinetics at the edge plane. The biphasic layer-passivated graphite anode delivers a fast-charging capability, reaching the 80% state of charge in just 7.4 min at a current density of 6 C and retaining 78.3% of its initial capacity after 600 fast-charge cycles with a practically viable high areal capacity of 3.2 mAh cm-2. These results represent a notable advancement over previously reported surface-engineered graphite anodes, particularly under industrially demanding conditions including high mass-loading and fast-charging.

Lithium-ion batteries (LIBs) are one of the most promising power sources for electric vehicles because of their high energy density and long lifetime. Graphite is widely used as anode electrode material in the state-of-the-art LIBs. However, a graphite anode is usually only compatible with an ethylene carbonate (EC)-based electrolyte. When contacting with a propylene carbonate (PC)-based electrolyte, which is advantageous over the EC-based one for its wider temperature range and higher low-temperature conductivity, the graphite anode may suffer from substantial exfoliation problem during the initial lithium intercalation step. Consequently, a PC-based electrolyte cannot be used in LIBs with graphite as the anode unless some solid electrolyte interphase (SEI) film-formation additives are introduced into the electrolytes. Usually this type of additives is reduced predominantly on the graphite electrode surface before PC is intercalated and reduced. These additives mainly contain some functional groups such as vinylene or cyclic unsaturated compounds. For example, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) have been widely studied and used as additives for PC-based electrolytes. They play an important role in the protection of the structure of the graphitic anode from destruction by PC, but they also have some shortcomings. Usually these additives result in a thick SEI protective layer, which could significantly reduce the rate capability and limit low-temperature performance and cycling stability at elevated temperatures because of its additional impedance and poor thermal stability. Recently, we developed a novel electrolyte additive that can suppress the PC reductive decomposition on the graphite anode without a thick and resistant SEI film. The additive may provide a novel protective mechanism for the graphite anode in the PC-containing electrolytes without or with suppressed SEI film formation. The SEI-film-suppression additive can not only significantly improve the compatibility between graphite anode and PC-containing electrolyte, but also exhibit superior rate capability and excellent cycling stability at elevated temperatures.We believe that this new electrolyte additive can be applied to LIBs and other electrochemical systems using PC-containing electrolytes and graphite anodes. The details of the results will be reported. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technology of the U.S. Department of Energy (DOE). The electron microscopy and XRD measurements were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL.

Understanding the trilemma of fast charging, energy density and cycle life of lithium-ion batteries

As the most advanced energy storage devices, lithium ion batteries (LIBs) have captured a great deal of attention and have been developed swiftly during the past decades. However, the improved fast-charging performance is more urgent than ever for time-saving and convenience, which is generally limited by the graphite anode. Recent studies have revealed that the fast-charging performance of graphite anodes is highly dictated by the properties of the electrolyte. Therefore, the investigations on fast-charging graphite based on designs of electrolytes are summarized from two aspects: solid electrolyte interphase (SEI) structures and solvated lithium ion structures. Finally, challenges and prospects for further research toward fast-charging graphite anodes are proposed.

The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (e.g., lithium metal, graphite, and silicon) leads to rapid capacity fade and poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi0.61Co0.12Mn0.27O2, over the course of 3000 charge-discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid-electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (e.g., fast charging) or stoichiometric restraints (e.g., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathode in a disrupted SEI. This insidious effect is found to initiate at a very early stage of cell operation (<200 cycles) and can be effectively inhibited by substituting a small amount of aluminum (∼1 mol %) in the cathode, resulting in much reduced transition-metal dissolution and drastically improved cyclability. Our results may also be applicable to studying the unstable electrodeposition of lithium on other substrates, including Li metal.

As the world enters into the era of electrifying transportation for cleaner energy, lithium-ion battery (LIB)-powered electric vehicles have drawn great attention in recent years. However, the fast-charging capability of LIBs has long been regarded as the technological obstacle to the wider adoption of battery electric vehicles (BEVs) in the market. A substantial challenge associated with fast charging is the formation of Li plating on the graphite anode as it is the major contributor of side reactions during cell operations. In this review, the fundamentals of Li plating and corresponding influencing factors (including state of charge [SOC], charging current density, temperature, and N/P ratio) for the Li-ion intercalation process are first elucidated under fast-charging conditions. Furthermore, conventional strategies to suppress Li plating by enhancing ion transport kinetics between interface and electrode through anode engineering and electrolyte design are also summarized and analyzed. Then, innovative strategies for achieving ultrahigh SOC of anodes by regulating Li plating morphology on host materials to construct hybrid anode storage are discussed in detail. Two types of strategies are compared in terms of cell performance, process simplicity, and safety concerns. Last, we highlight some research orientations and perspectives pertaining to the development of hybrid anode storage, providing effective approaches to address Li plating issues for fast-charging LIBs.

Reversible Li plating regulation on graphite anode through a barium sulfate nanofibers-based dielectric separator for fast charging and high-safety lithium-ion battery

To meet the growing demand for energy storage, lithium-ion batteries (LIBs) with fast charging capabilities has emerged as a critical technology. The electrode materials affect the rate performance significantly. Organic electrodes with structural flexibility support fast lithium-ion transport and are considered promising candidates for fast-charging LIBs. However, it is a challenge to create organic electrodes that can cycle steadily and reach high energy density in a few minutes. To solve this issue, accelerating the transport of electrons and lithium ions in the electrode is the key. Here, it is demonstrated that a ferrocene-based polymer electrode (Fc-SO3Li) can be used as a fast-charging organic electrode for LIBs. Thanks to its molecular architecture, LIBs with Fc-SO3Li show exceptional cycling stability (99.99% capacity retention after 10 000 cycles) and reach an energy density of 183Wh kg-1 in 72 seconds. Moreover, the composite material through insitu polymerization with Fc-SO3Li and 50 wt % carbon nanotube (denoted as Fc-SO3Li-CNT50) achieved optimized electron and ion transport pathways. After 10000 cycles at a high current density of 50C, it delivered a high energy density of 304Wh kg-1. This study provides valuable insights into designing cathode materials for LIBs that combine high power and ultralong cycle life.

Fast charging technology for electric vehicles (EVs), which promises rapid charging times similar to refueling conventional vehicles, holds promise but encounters hurdles due to kinetic issues within lithium-ion batteries (LIBs). These issues include both kinetic and thermodynamic challenges within batteries, resulting in restricted utilization of active materials, Li plating, excessive heat generation, and accelerated capacity degradation.1 Efforts to tackle issues associated with fast charging have predominantly concentrated on modifying the Li salts in the electrolyte or the structure and surface/interface of the anode materials.However, compared to the electrolyte or anode materials, the importance of the cathode in relation to fast charging has not been significantly highlighted. Because properties such as the energy density, thermal stability, and rate performance of LIBs are largely determined by the cathode material, 2 understanding the characteristics of the cathode under high-current-density conditions is essential to comprehensively understand fast charging.In this study, the mechanism responsible for the loss of fast charging capability of Ni-rich cathodes during prolonged cycling is examined via a comparative analysis of Ni-rich cathodes exhibiting different microstructures. The results demonstrate that microcracks and subsequent cathode degradation notably compromise the fast charging capability over extended cycling periods. Formation of thick rocksalt impurity phases throughout the particles due to electrolyte infiltration via microcracks leads to limited kinetics of Li+ ions, resulting in electrochemically inactive regions under high-current conditions, hence leading to the loss of fast charging capability. Therefore, preventing microcrack formation by microstructural modification is imperative to ensure stability in fast charging capability. These findings underscore the need to comprehensively understand the degradation of the cathode during extended cycling, particularly from the perspective of the kinetic loss of utilizable Li+ ions at high currents, rather than just the loss of capacity. Reference s : [1] Y. Liu, Y. Zhu, Y. Cui, Nat. Energy, 2019, 4, 540.[2] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121.

The lithium-ion battery (LIB) is a key technology for inexpensive, renewable, and safe energy storage system, but there are a few challenges that need to be addressed to make LIB more efficient. One critical challenge is increasing both energy density and fast charging capability. Increasing electrode thickness can increase the energy density of lithium-ion batteries. However, increasing electrode thickness increases transport limitations and the risk of lithium plating, which limit safe fast charging capability. This work analyzes prospective improvements to the conventional lithium-ion cell electrode structure that may facilitate high energy density and fast charging capabilities. A 2D lithium-ion battery model is applied to five different cell designs to understand the impact of thick electrode structure on performance at different charge and discharge rates for a single cell. These five different cell designs consist of one conventional cell and four cells with electrodes modified by varied electrolyte channel arrangements. The simulated electrodes were taken as Li(Ni1/3Mn1/3Co1/3)O2 (NMC) for the cathode and graphite for the anode. The simulated electrolyte was 1 M lithium hexafluorophosphate (LiPF6) in 1:1 ethylene carbonate (EC) and diethylene carbonate (DEC). All five cells were simulated under discharge at C/10, C/2 and 1C followed by charge at 1C, 3C, and 5C with no rest time prior to charge. Adding electrolyte channels on the anode side was found to facilitate lithium ion transport and reduce the risk of lithium plating. Modification of both electrodes did not present any benefit compared to the conventional cell. Analysis of cell behavior based on mass transport Fourier number and a dimensionless mass flux parameter was performed to compare different electrodes at different charge and discharge conditions. These dimensionless parameters provide a means for the general assessment of prospective electrode structure modifications.

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

Along with the rapid growth in robots, mobile electronics and electric vehicles (EVs) technology, lithium ion batteries (LIBs) are facing several technical challenges such as higher energy density and fast charging capability. Graphite, currently used anode materials for LIBs, has technical limitations to be used for robots, mobile electronics and EVs in terms of energy density and fast charging capability. To solve these problems, various anode materials have been suggested for alternative graphite anode material. In this work, titanium dioxide coated graphite was investigated as an anode material with fast charging capability for LIBs. The proposed core-shell structure, titanium dioxide coated graphite anode electrode exhibited an excellent rate capability of 96.4 % of the capacity retention at a rate of 10 C compare to that tested at a rate of 0.2 C without any degradation of reversible capacity and long-term cycle performance. The characterization, microstructure and electrochemical properties of the titanium dioxide coated graphite will be discussed in more detail.

Lithium metal batteries are widely considered to be a next-generation battery technology due to their high energy density, fast charging capability, and potential to power a wide range of applications, from portable electronics to electric vehicles.Compared to conventional lithium-ion batteries, which use graphite as the anode material, lithium metal batteries have the potential to offer significantly higher energy density. This is because lithium metal has a much higher theoretical capacity than graphite, meaning it can store more energy per unit weight or volume. As a result, lithium metal batteries could potentially offer longer run times and smaller form factors than lithium-ion batteries, which are already widely used in consumer electronics and electric vehicles.In addition to their high energy density, lithium metal batteries also offer fast charging capabilities. This is because the lithium metal anode can be charged more quickly than the graphite anode used in conventional lithium-ion batteries. This could enable faster charging times for electric vehicles and other applications, reducing the time required for recharging and improving their overall usability.However, one of the major challenges with lithium metal batteries is dendrite growth, which can occur when lithium metal ions deposit unevenly on the surface of the anode during charging. These dendrites are needle-like structures that can penetrate the separator and cause short-circuits, leading to reduced battery performance and safety issues. As a result, much of the research on lithium metal batteries has focused on developing strategies to prevent dendrite growth, such as using coatings or electrolytes with additives that can stabilize the lithium metal anode.Despite these challenges, lithium metal batteries continue to be a promising next-generation battery technology. Researchers are working on improving their energy density, charging speed, and safety, and they are exploring a range of applications, from portable electronics to electric vehicles and grid-scale energy storage. If these challenges can be overcome, lithium metal batteries could revolutionize the energy storage industry and enable a wide range of new and exciting applications.To address this issue, we have explored the use of various coatings on the lithium metal anode to prevent dendrite growth. In this study, ordered mesoporous silica with different pore sizes and pore structures, such as SBA-15 and KIT-6, were used as coatings between the lithium metal anode and separator.SBA-15 and KIT-6 are two types of mesoporous silica materials that are widely used in various applications due to their unique properties. The synthesis of these materials involves the use of templates to control the pore size and structure.They are synthesized using a combination of a surfactant(pluronic P123 or cetyltrimethylammonium bromide;CTAB) as the template and tetraethyl orthosilicate(TEOS) as the silica source. The synthesis involves mixing a solution of surfactant and TEOS in acidic conditions, followed by aging and calcination steps. The resulting materials have a highly ordered hexagonal pore structure(SBA-15) and body-centered cubic pore structure(KIT-6) with a pore size ranging from 5 to 20 nm.By coating the surface of the lithium metal with a uniform pore structure material such as ordered mesoporous silica, dendrite growth can be suppressed and lithium deposition can occur more uniformly.The uniform pore structure material acts as a physical barrier to lithium ion diffusion and helps to control the deposition of lithium ions onto the surface of the lithium metal. When lithium ions are deposited onto the surface of the lithium metal, they can form a layer of lithium that can grow and become thick over time. If the lithium layer is too thick, it can become unstable and form dendrites. However, the uniform pore structure material can help to limit the thickness of the lithium layer and promote the deposition of lithium ions in a more uniform manner, thus reducing the likelihood of dendrite formation.Additionally, the uniform pore structure material can help to reduce the concentration of lithium ions at the surface of the lithium metal, which is another factor that can contribute to dendrite growth. By limiting the concentration of lithium ions at the surface, the uniform pore structure material can help to prevent the formation of high-concentration regions that can promote dendrite growth.Overall, the mechanism by which a uniform pore structure material can suppress dendrite growth involves controlling the deposition of lithium ions onto the surface of the lithium metal, limiting the thickness of the lithium layer, and reducing the concentration of lithium ions at the surface. These factors help to promote more uniform lithium deposition and prevent the formation of dendrites, leading to improved battery performance and safety.

The difficulties to identify the rate‐limiting step cause the lithium (Li) plating hard to be completely avoided on graphite anodes during fast charging. Therefore, Li plating regulation and morphology control are proposed to address this issue. Specifically, a Li plating‐reversible graphite anode is achieved via a localized high‐concentration electrolyte (LHCE) to successfully regulate the Li plating with high reversibility over high‐rate cycling. The evolution of solid electrolyte interphase (SEI) before and after Li plating is deeply investigated to explore the interaction between the lithiation behavior and electrochemical interface polarization. Under the fact that Li plating contributes 40 % of total lithiation capacity, the stable LiF‐rich SEI renders the anode a higher average Coulombic efficiency (99.9 %) throughout 240 cycles and a 99.95 % reversibility of Li plating. Consequently, a self‐made 1.2‐Ah LiNi0.5Mn0.3Co0.2O2 | graphite pouch cell delivers a competitive retention of 84.4 % even at 7.2 A (6 C) after 150 cycles. This work creates an ingenious bridge between the graphite anode and Li plating, for realizing the high‐performance fast‐charging batteries.