Lithium Cycling Research Articles

“Sticky” carbon coating enables high-area-capacity lithium storage of silicon-graphitic carbon hybrid

Pulverization and surface instability have been identified as the main impediments to the application of Si anodes in high-energy lithium-ion batteries (LIBs). In this study, a Si-graphitic carbon hybrid (SiG) is created via embedding Si nanoparticles in between expanding graphite interlayers, thus to be adopted as a model system to unravel structure-properties relations for LIBs applications. We explore the impact of artificial surface coating layers on the lithium cycling performance of SiG particles. In comparison with native SiG and carbon-coated SiG (CC-SiG), we find that the “sticky-carbon” coating, i.e., an epoxy-rich layer on top of the carbon coating, gave rise to superior cycle performance. In the “sticky carbon” coated SiG (SCC-SiG), the surface chemistry appears to have a pivotal role in both alleviating electrode disintegration and forming a favorable SEI rich in fluorine-polymers. These positive findings are examined in electrodes with mass loading ranging from 1.0 to 5.0 mg/cm2, achieving area capacities up to ∼5.0 mAh/cm2. A full cell adopting >6 mg/cm2 LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and SCC-SiG delivers stable cycling performances. It is hence unraveled that the carbon coating layer with reactive surface groups on the top is an unrecognized key for wide range of Si-based anodes.

In Situ Chemical Lithiation Transforms Diamond-Like Carbon into an Ultrastrong Ion Conductor for Dendrite-Free Lithium-Metal Anodes.

Lithium (Li)-metal anodes are of great promise for next-generation batteries due to their high theoretical capacity and low redox potential. However, Li-dendrite growth during cycling imposes a tremendous safety concern on the practical application of Li-metal anodes. Herein, an effective approach to suppress Li-dendrite growth by coating a polypropylene (PP) separator with a thin layer of ultrastrong diamond-like carbon (DLC) is reported. Theoretical calculations indicate that the DLC coating layer undergoes in situ chemical lithiation once assembled with the lithium-metal anode, transforming the DLC/PP separator into an excellent 3D Li-ion conductor. This in situ lithiated DLC/PP separator can not only mechanically suppress Li-dendrite growth by its intrinsically high modulus (≈100GPa), but also uniformly redistributes Li ions to render dendrite-free lithium deposition. The twofold effects of the DLC/PP separator result in stable cycling of lithium plating/stripping (over 4500 h) at a high current density of 3mA cm-2 . Remarkably, this approach enables more than 1000 stable cycles at 5 C with a capacity retention of ≈71% in a Li || LiFePO4 coin cell and more than 200 stable cycles at 0.2 C in a Li || LiNi0.5 Co0.3 Mn0.2 O2 pouch cell with cathode mass loading of ≈9mg cm-2 .

Efficient Lithium Metal Cycling at a Wide Range of Pressures from an Anion-Derived Solid-Electrolyte Interphase Framework

Novel electrolytes have been developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. The dependence of the performance on the operational pressure can provide valuable insights on the Li plating mechanisms in different electrolytes. Here, we study Li cycling performance evolution against pressure in 1 M LiFSI/fluorinated 1,4-dimethoxylbutane (FDMB) electrolyte, one of the highest-performing electrolytes for Li metal to date. We show that it enables excellent Coulombic efficiency (CE) in a pouch cell format under a wide range of initial pressures (30-600 psi). We discover that this is due to a completely different Li plating mode with superior deposition morphologies compared to that in a conventional carbonate electrolyte, which exhibits increasing cycle stability with increased pressure. We show that this is enabled by the properties of an anion-derived residual solid-electrolyte interphase (rSEI) framework on the electrode surface, an undercharacterized structure with profound implications for Li metal cycling. The plating morphology enabled by this anion-derived rSEI chemistry is likely the key to a prolonged cycle life in high performance electrolytes for Li metal.

Porous Polymer Gel Electrolytes Influence Lithium Transference Number and Cycling in Lithium-Ion Batteries

To improve the energy density of lithium-ion batteries, the development of advanced electrolytes with enhanced transport properties is highly important. Here, we show that by confining the conventional electrolyte (1 M LiPF6 in EC-DEC) in a microporous polymer network, the cation transference number increases to 0.79 while maintaining an ionic conductivity on the order of 10−3 S cm−1. By comparison, a non-porous, condensed polymer electrolyte of the same chemistry has a lower transference number and conductivity, of 0.65 and 7.6 × 10−4 S cm−1, respectively. Within Li-metal/LiFePO4 cells, the improved transport properties of the porous polymer electrolyte enable substantial performance enhancements compared to a commercial separator in terms of rate capability, capacity retention, active material utilization, and efficiency. These results highlight the importance of polymer electrolyte structure–performance property relationships and help guide the future engineering of better materials.

Large Scale Synthesis of Manganese Oxide/Reduced Graphene Oxide Composites as Anode Materials for Long Cycle Lithium Ion Batteries

Manganese oxides have been frequently used as cathodes in primary batteries. Applications of manganese oxides in secondary batteries are limited by low electrical conductivity and rapid capacity fading because of electrode pulverization and aggregation. In this study, a solid-state synthetic strategy is presented that successfully combines nanosize (∼50 nm) nickel doped α-MnO2 with reduced graphene oxides as highly stable composite anodes in lithium ion batteries. The synthesis approach is easy to scale up and suitable for industrial applications. The rationally designed Ni-α-MnO2/RGO was tested in galvanostatic half coin cells for Li+ charge–discharge studies. The results show that this composite maintains a high capacity of 615 mAh g–1 even after 200 cycles at a high current rate of 1 C (830 mA g–1), and with a high Coulombic efficiency near 99%. The anodes exhibit excellent rate capability in a wide range of rate testing from 0.2 to 10 C, without showing capacity decay. This superior anode performance is ascribed to the reduced size of α-MnO2 domains that are well dispersed in an RGO matrix, which affords good ionic/electrical conductivity, low charge transfer resistance and mitigates issues of volume expansion of the anodic active materials. This study opens up an avenue for developing the manufacturing of high-performance electrodes for real applications, such as batteries in electrical vehicles.

A Stable Fluorine‐Containing Solid Electrolyte Interface toward Dendrite‐Free Lithium‐Metal Anode for Lithium‐Sulfur Batteries

AbstractLithium‐sulfur (Li−S) batteries are considered to be a representative of the next generation of lithium‐ion batteries due to their high theoretical specific capacity (2600 Wh ⋅ Kg−1), and they have been extensively researched. However, the formation of lithium dendrites during the discharge process continuously consumes the electrolyte and the lithium anode, resulting in an increase in the cell‘s internal resistance and a capacity loss. Herein, we added an organic‐inorganic polymer hexafluoro‐cyclo‐triphosphazene (HFPP) to the electrolyte, which showed lower interfacial resistance and more effective lithium‐ion deposition. The lone‐pair electrons of the nitrogen atoms in HFPP promote the uniform diffusion of lithium ions and its 2D structure also enhances the mechanical stability of the solid electrolyte interphase (SEI) and inhibits the formation of lithium dendrites. Based on the regulating effect, the cells using HFPP as electrolyte additives showed an excellent discharge capacity of 1095 mAh ⋅ g−1 at 0.5 C and a reversible capacity of 763 mAh ⋅ g−1 after 200 cycles, indicating that HFPP is an effective additive for the protection of the lithium anode and cycling stability of Li−S batteries.

Boosting lithium batteries under harsh operating conditions by a resilient ionogel with liquid-like ionic conductivity

New chemistries are being developed to increase the capacity and power of rechargeable batteries. However, the risk of safety issues increases when high-energy batteries using highly active materials encounter harsh operating conditions. Here we report on the synthesis of a unique ionogel electrolyte for abuse-tolerant lithium batteries. A hierarchically architected silica/polymer scaffold is designed and fabricated through a facile soft chemistry route, which is competent to confine ionic liquids with superior uptake ability (92.4 wt%). The monolithic ionogel exhibits high conductivity and thermal/mechanical stability, featuring high-temperature elastic modulus and dendrite-free lithium cycling. The Li/LiFePO4 pouch cells achieve outstanding cyclability at different temperatures up to 150 °C, and can sustain cutting, crumpling, and even coupled thermal–mechanical abuses. Moreover, the solid-state lithium batteries with LiNi0.60Co0.20Mn0.20O2, LiNi0.80Co0.15Al0.05O2, and Li1.2Mn0.54Ni0.13Co0.13O2 cathodes demonstrate excellent cycle performances at 60 °C. These results indicate that the resilient and high-conductivity ionogel electrolyte is promising to realize high-performance lithium batteries with high energy density and safety.

Boosting ultrafast Li storage kinetics of conductive Nb-doped TiO2 functional layer coated on LiMn2O4

Interface engineering of LiMn2O4 (LMO) is a promising strategy to enhance the lithium storage capability and cycling stability of cathode materials in Li-ion batteries (LIBs). This is because the strategy prevents structural degradation; however, Li storage kinetics remains unsatisfactory, resulting in poor ultrafast cycling performance. Therefore, we fabricated an Nb-doped TiO2 (NTO) functional layer as a conductive passivation layer on the LMO surface by horizontal ultrasonic spray pyrolysis deposition. The NTO functional layer suppressed the volume expansion of LMO and exhibited high electrical and ionic conductivity, which resulted in improved structural stability of LMO (related to cycling stability) and increased electron/ion transfer rate (related to ultrafast cycling performance). In the TiO2 structure, Ti4+ ions were replaced by Nb5+ ions, which possess high electrical conductivity and a wide c-axis as a Li-ion diffusion route. As a result, the NTO-coated LMO cathode material showed an outstanding specific capacity of 112.7 mAh/g with a remarkable capacity retention of 96.2% after 100 cycles at a current density of 1 C and excellent ultrafast cycling capacity and stability of 70.0 mAh/g after 500 cycles at a current density of 10 C.

Petroleum Coke as the Active Material for Negative Electrodes in Lithium–Sulfur Batteries

The possibility of using carbon materials based on petroleum coke as the cheap and available active material for negative electrodes of lithium–sulfur rechargeable batteries is considered. The comparative studies of characteristics of lithium–sulfur cells with negative electrodes based on metal lithium, graphite, and petroleum coke are carried out. It is found that heat-treated petroleum coke can be successfully used as the active material for negative electrode of lithium–sulfur batteries with acceptable energy characteristics. All other conditions being the same, the lithium–sulfur cells with negative electrodes based on petroleum coke demonstrate the longer cyclability as compared with cells based on metal lithium or graphite. This is explained by the slower destruction of electrolyte components on the negative electrode during cycling of lithium–sulfur cells. It is shown that the use of negative electrodes based on petroleum coke in lithium–sulfur batteries allows their cyclability to be increased and their cost to be reduced.

Insight into bulk charge transfer of lithium metal anodes by synergism of nickel seeding and LiF-Li3N-Li2S co-doped interphase

Cycling lithium (Li) metal anode with a low negative/positive capacity (N/P) ratio is critical to build high-energy-density Li metal batteries (LMBs). Many strategies focusing on interfacial protection are limited to shallow conditions using excessive Li with a high negative/positive capacity (N/P) ratio > 50. Herein, we demonstrate a deeply enhanced charge transfer kinetic by a rational incorporation of nickel (Ni) seeds in the Li anodes with a tailored interfacial chemistry. The Ni seeds in the bulk Li anode not only act as well-dispersed nucleation sites to enable Ni-seeded growth of granular Li deposits, but also adsorb acetonitrile (AN) molecules when the Ni-seeded Li anodes are paired with an AN-based electrolyte using lithium bis-(fluorosulfonyl)imide as salt, forming a fast Li+ conducting interphase with co-produced LiF, Li3N and Li2S components. These benefits conduct an exchange current density ~ 20 times higher than that of the bare Li in conventional carbonate electrolytes. Stable cycling of LMBs with a practical cathode loading (~ 5 mAh cm−2) and a low N/P capacity ratio of 2 is also demonstrated, showing the prominence of this remedy for developing high-energy-density LMBs.

Optimal microstructural design of pitch-derived soft carbon shell in yolk-shell silicon/carbon composite for superior lithium storage

Silicon-carbon composites have proved to be effective in addressing the issues of silicon anodes, however, few works focus on understanding the effect of the microstructure of the carbon component on their electrochemical performance. Herein, we prepare a series of yolk-shell structured silicon-carbon nanocomposites with adequate voids through a facile and scalable process. By deliberately selecting the pitch species and delicately adjusting the heat treatment temperature, the microcrystal texture and pore structure of the soft carbon can be easily tuned. Finally, a well matching of the crystalline and pore structure ensure the rapid charge transport and the good structural robustness, further endowing the optimal lithium storage, cycle performance and rate capability of the electrodes. The Si/C composite with an optimized carbon shell delivers a reliable cycle stability with a capacity retention ratio of 55% after 300 cycles at 0.2 A g−1 and a remained capacity of 743 mAh g−1 at a high current density of 2.0 A g−1. Importantly, the correlation between the lithium storage of the Si/C composites and the microstructure features (crystallinity and pores) of the carbon shell has been established, which may provide an effective guidance for optimizing the microstructure design of the promising Si/C anode materials.

Efficient Lithium Metal Cycling over a Wide Range of Pressures from an Anion-Derived Solid-Electrolyte Interphase Framework

Advanced electrolytes were developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. Here, we study the Li cycling performance under different ...

Delineating the Lithium–Electrolyte Interfacial Chemistry and the Dynamics of Lithium Deposition in Lithium–Sulfur Batteries

AbstractStabilizing the metallic lithium anode is the major roadblock to realizing long cycle life lithium‐sulfur (Li–S) batteries with high energy density. The chemistry of the dynamically evolving solid‐electrolyte interphase layer on the lithium surface is critical to achieving reversible plating and stripping of lithium. Herein, electrolyte formulations are carefully varied and employed to modulate the composition, and thereby, the properties of the lithium‐electrolyte interface. The impact of these changes in the interfacial chemistry on the dynamics of lithium deposition is evaluated by tracking cyclability in an anode‐free full cell configuration. Critical insights are revealed on the role of different components of the electrolyte and their interplay, including various functional groups in the electrolyte salt, oxidizing effect of lithium nitrate, and the intrinsically stabilizing effect of polysulfide species, in determining the characteristics of lithium deposition and lithium cycling efficiency. The study illuminates the key elements underlying the unique chemistry of the lithium–electrolyte interface in Li–S batteries and it can spur further development of novel strategies toward stabilizing the lithium‐metal anode in the Li–S system.

Revealing the Role of Fluoride‐Rich Battery Electrode Interphases by Operando Transmission Electron Microscopy

AbstractThe solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride‐rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid‐cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride‐poor and fluoride‐rich interphases. The in situ imaging of lithium cycling reveals that a fluoride‐rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride‐rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure.

Effect of Size and Shape on Electrochemical Performance of Nano-Silicon-Based Lithium Battery.

Silicon is a promising material for high-energy anode materials for the next generation of lithium-ion batteries. The gain in specific capacity depends highly on the quality of the Si dispersion and on the size and shape of the nano-silicon. The aim of this study is to investigate the impact of the size/shape of Si on the electrochemical performance of conventional Li-ion batteries. The scalable synthesis processes of both nanoparticles and nanowires in the 10–100 nm size range are discussed. In cycling lithium batteries, the initial specific capacity is significantly higher for nanoparticles than for nanowires. We demonstrate a linear correlation of the first Coulombic efficiency with the specific area of the Si materials. In long-term cycling tests, the electrochemical performance of the nanoparticles fades faster due to an increased internal resistance, whereas the smallest nanowires show an impressive cycling stability. Finally, the reversibility of the electrochemical processes is found to be highly dependent on the size/shape of the Si particles and its impact on lithiation depth, formation of crystalline Li15Si4 in cycling, and Li transport pathways.

Grain boundary modification in garnet electrolyte to suppress lithium dendrite growth

Solid-state batteries (SSBs) have attracted many attentions due to its higher energy density and improved safety. As one of the most promising solid electrolytes, garnet Li7La3Zr2O12 (LLZO) has achieved significant advances in its cell performance, however, its application in Li-metal batteries is still hindered by lithium dendrite growth at voids or grain boundaries inside the solid electrolyte. Herein, a novel grain-boundary enhancement strategy was demonstrated by introducing Li6Zr2O7 (LZO), which can be decomposed into Li2O in situ, into Ta-doped LLZO (LLZT). The Li2O provides a sufficient inner Li2O atmosphere, achieving none mother powder sintering. The Li2ZrO3 stays at garnet grain boundaries or fills up the pores, which have been shown to effectively suppress the lithium dendrite growth. More importantly, the critical current density (CCD) of the Li | LLZT-LZO | Li symmetric cell achieved as high as 1.4 mA cm−2 at 25 °C and 2.0 mA cm−2 at 60 °C, and the long-term lithium cycling remained stable over 2000 h at 0.3 mA cm−2. Moreover, the Li-S battery maintained high discharge capacity of 816 mAh g−1 after 200 cycles at 0.5C. Therefore, our work provides a facile and effective strategy to prepare a safety-enhanced electrolyte for future applications of SSBs.

Modulating the electrical conductivity of a graphene oxide-coated 3D framework for guiding bottom-up lithium growth

An electrical conductivity-controlled 3D Li host for Li-metal batteries enables preferential bottom deposition/dissolution of lithium and stable cycling performance.

Implications of in situ chalcogen substitutions in polysulfides for rechargeable batteries

Selenium and tellurium in Li–S batteries: formation of polyselenosulfides enables improved sulfur redox kinetics while formation of polytellurosulfides improves lithium cycling efficiency.

In-situ grown flower-like C@SnO2/Cu2O nanosheet clusters on Cu foam as high performance anode for lithium-ion batteries

Tin dioxide (SnO2) is considered as one of promising anode materials in lithium-ion batteries due to its high specific discharge capacity, low cost and environmental friendliness. However, practical application of SnO2 is still hindered by severe capacity fading, poor cycling stability and inferior rate performance due to volume expansion during charge/discharge processes. To overcome this problem, composites of flower-like carbon layer (thickness: ~1.5 nm) enwrapped SnO2/Cu2O (thickness: ~20 nm; length: ~ 200 nm) anchored on Cu foam were in-situ synthesized by facile hydrothermal method and subsequent annealing. Compared with pure SnO2, such novel hierarchical structure effectively enhancs the conductivity and structural stability of the composites as integrated electrode for lithium-ion batteries. Electrochemical studies reveal superior lithium storage capability, cycle stability, and rate performance for C@SnO2/Cu2O nanosheet clusters with discharge capacity of 1726 mAh g−1 in first cycle and 814 mAh g−1 after 300 cycles at 0.5 C, as well as 425 mAh g−1 at 2 A g−1. Therefore, C@SnO2/Cu2O nanosheet clusters possess great potential for scientific research and future application in lithium-ion batteries.

Tellurium-Polysulfide Chemistry Enables Stable Operation of Lithium-Sulfur Batteries with Limited Lithium Inventory and Electrolyte Supply

The practical realization of lithium-sulfur (Li-S) batteries with high energy density is currently limited by the poor cyclability of the lithium-metal anode. Lithium plating and stripping in the liquid ether-based electrolyte is irreversible over long-term cycling and this leads to rapid capacity fade. Due to the reducing nature of lithium, parasitic side reactions with the electrolyte also occur with considerable severity during cell operation. This eliminates a significant portion of the available lithium inventory and electrolyte supply, and the cell fails prematurely. These problems can be sidestepped by employing surplus lithium and electrolyte in the cell, but this compromises the stack-level energy density. Stabilizing lithium deposition and reducing electrolyte decomposition is of critical importance to enabling commercially viable Li-S batteries with high energy density and long cycle life.The chemistry of Li-S batteries is unique due to the generation of polysulfide intermediates at the cathode that are soluble in the electrolyte. The polysulfides migrate to the anode side, which fundamentally alters its interfacial chemistry by forming reduced sulfide species (Li2S/Li2S2) on the lithium surface. These species are known to have an intrinsically stabilizing effect on lithium deposition, although it is not sufficient to enable stable operation of Li-S batteries at reasonable current densities. Nevertheless, the modification of electrolyte-soluble polysulfide species offers a unique opportunity for tuning the interfacial chemistry of the lithium-metal anode towards stabilizing lithium deposition and reducing electrolyte decomposition.Tellurium, which sits two position below sulfur in Group 16 of the periodic table, is an excellent candidate element for modifying the composition of polysulfide intermediates in Li-S batteries and forming potentially favorable components in the lithium SEI layer. It was found that elemental tellurium (Te0) could be facilely assimilated into polysulfide species to form soluble mixed polytellurosulfide species when left in an ethereal solution of Li2S6. This was confirmed by the characteristic isotopic signature of tellurium using mass spectrometry. The polytellurosulfide species were found to reduce on the surface of lithium metal to form red-colored lithium thiotellurate (Li2TeS3), which was confirmed by X-ray techniques. In contrast to Li2S, Li2TeS3 is expected to be a significantly better ionic conductor due to the reduced electron density around the sulfur atoms. This would help engender a uniform lithium-ion flux on the lithium surface, enabling homogenous lithium deposition.Based on the results above, elemental tellurium was simply added in a 1 : 10 molar ratio to the sulfur/Li2S cathode to modify the chemistry of Li-S batteries. During cell operation, the generated polysulfides (Li2Sn) reacted with the Te0 additive in the cathode to form polytellurosulfide (Li2TexSy) species in-situ. The crossover of these tellurium-containing species to the anode side was confirmed by the detection of a significant amount of Li2TeS3 on the lithium surface. The favorable properties of Li2TeS3 as a lithium SEI component enabled the formation of dense and uniform lithium deposits and significantly improved lithium cycling efficiency. In the anode-free full cell configuration, which pairs a Li2S cathode with a bare anode current collector and contains zero excess lithium (N/P ratio = 1), the addition of tellurium improved cycle life by a factor of 7. The loss of the limited lithium inventory in the anode-free cell was reduced from 2% per cycle to 0.25% per cycle.Time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed the drastically reduced electrolyte decomposition on lithium surface due to tellurium-stabilized lithium deposition. The reduced electrolyte decomposition could allow a limited electrolyte supply to be retained for a longer number of cycles, thus enabling extended cyclability under lean-electrolyte conditions. This was confirmed using large-area pouch cells employing a high-loading sulfur cathode (5.2 mg cm-2), a lithium-foil anode, and a low electrolyte/sulfur (E/S) ratio of 4.5 µl mg-1. Under such stringent cell design conditions, the pouch cells could be cycled stably for nearly 100 cycles with the addition of tellurium. In contrast, the control cell failed within 25 cycles.This work demonstrates a novel, effective, and robust strategy of adding tellurium to the sulfur/Li2S cathode for stabilizing lithium deposition and reducing electrolyte decomposition in Li-S batteries. This improves cycle life in energy-dense cell configurations operating with a limited lithium inventory or electrolyte supply. Importantly, this approach is scalable as no expensive or complicated pre-treatments or coatings of the lithium-metal anode are necessary. The unique chemistry of tellurium in the polysulfide-rich environment of Li-S batteries opens a new frontier in research in Li-S batteries, bringing them one step closer to reality. Figure 1