Phosphate and Borate-Based Composite Interface of Single-Crystal LiNi0.8Co0.1Mn0.1O2 Enables Excellent Electrochemical Stability at High Operation Voltage.

The application of nickel-rich cathodes in lithium-ion batteries has been hampered by its rapid capacity/voltage fading and limited performance of rate. In this work, a passivation technique is used to create a stable composite interface on single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM811) surface, which greatly improves the cycle life-span and high-voltage constancy of cathode with 4.5 and 4.6 V cut-off voltage. The improved Li+ conductivity of the interface enables a firm cathode-electrolyte interphase (CEI), which reduces interfacial side reactions, lowers the risk of safety hazards, and improves irreversible phase transitions. As a result, the electrochemical performance of single-crystal Ni-rich cathode are remarkably enhanced. The specific capacity of 152 mAh g-1 can be delivered at a charging/discharging rate of 5 C under 4.5 V cut-off voltage, much higher than 115 mAh g-1 of the pristine NCM811. After 200 cycles at 1 C, the composite interface modified NCM811 demonstrates outstanding capacity retention of 85.4% and 83.8% at 4.5 V and 4.6 V cut-off voltage, respectively.

Ion Transport and Electrochemical Reaction in LiNi0.5Co0.2Mn0.3O2-Based High Energy/Power Lithium-Ion Batteries.

The high energy/power lithium-ion battery using LiNi0.5Co0.2Mn0.3O2 (NCM523 HEP LIB) has an excellent trade-off between specific capacity, cost, and stable thermal characteristics. However, it still brings a massive challenge for power improvement under low temperatures. Deeply understanding the electrode interface reaction mechanism is crucial to solving this problem. This work studies the impedance spectrum characteristics of commercial symmetric batteries under different states of charge (SOCs) and temperatures. The changing tendencies of the Li+ diffusion resistance Rion and charge transfer resistance Rct with temperature and SOC are explored. Moreover, one quantitative parameter, § ≡ Rct/Rion, is introduced to identify the boundary conditions of the rate control step inside the porous electrode. This work points out the direction to design and improve performance for commercial HEP LIB with common temperature and charging range of users.

Electrochemistry-Driven Interphase Doubly Protects Graphite Cathodes for Ultralong Life and Fast Charge of Dual-Ion Batteries.

Dual-ion batteries (DIBs) with graphite as cathode material, show superiority in terms of sustainability, affordability, and environmental impact over Li-ion batteries that rely on transition-metal based cathodes. However, graphite cathodes severely suffer from poor structural stability during anion storage at high potentials because of the co-intercalation and oxidative decomposition of electrolytes. This work presents an in situ electrochemistry-driven route to create a bifunctional interphase through implantation of diethylenetriaminepenta(methylene-phosphonic acid) (DTPMP) on the surface of graphite particles. The reaction mechanisms and functions of DTPMP are investigated both experimentally and theoretically. The DTPMP-derived interphase not only improves the antioxidative stability of electrolytes but also benefits the desolvation of PF6 - anions, which doubly protect the graphitic structure and give rise to fast-charge and ultralong cycling performance of graphite cathodes in DIBs.

A monofluoride ether-based electrolyte solution for fast-charging and low-temperature non-aqueous lithium metal batteries.

The electrochemical stability window of the electrolyte solution limits the energy content of non-aqueous lithium metal batteries. In particular, although electrolytes comprising fluorinated solvents show good oxidation stability against high-voltage positive electrode active materials such as LiNi0.8Co0.1Mn0.1O2 (NCM811), the ionic conductivity is adversely affected and, thus, the battery cycling performance at high current rates and low temperatures. To address these issues, here we report the design and synthesis of a monofluoride ether as an electrolyte solvent with Li-F and Li-O tridentate coordination chemistries. The monofluoro substituent (-CH2F) in the solvent molecule, differently from the difluoro (-CHF2) and trifluoro (-CF3) counterparts, improves the electrolyte ionic conductivity without narrowing the oxidation stability. Indeed, the electrolyte solution with the monofluoride ether solvent demonstrates good compatibility with positive and negative electrodes in a wide range of temperatures (i.e., from -60 °C to +60 °C) and at high charge/discharge rates (e.g., at 17.5 mA cm-2). Using this electrolyte solution, we assemble and test a 320 mAh Li||NCM811 multi-layer pouch cell, which delivers a specific energy of 426 Wh kg-1 (based on the weight of the entire cell) and capacity retention of 80% after 200 cycles at 0.8/8 mA cm-2 charge/discharge rate and 30 °C.

Prefabrication of "Trinity" Functional Binary Layers on a Silicon Surface to Develop High-Performance Lithium-Ion Batteries.

The silicon (Si) anode is widely recognized as the most prospective next-generation anode. To promote the application of Si electrodes, it is imperative to address persistent interface side reactions caused by the huge volume expansion of Si particles. Herein, we introduce beneficial groups of the optimized binder and electrolyte on the Si surface by a co-dissolution method, realizing a "trinity" functional layer composed of azodicarbonamide and 4-nitrobenzenesulfonyl fluoride (AN). The "trinity" functional AN interfacial layer induces beneficial reductive decomposition reactions of the electrolyte and forms a hybrid solid-electrolyte interphase (SEI) skin layer with uniformly distributed organic/inorganic components, which can enhance the mechanical strength of the overall electrode, restrain harmful electrolyte depletion reactions, and maintain efficient ion/electron transport. Hence, the optimized Si@AN11 electrode retains 1407.9 mAh g-1 after 500 cycles and still delivers 1773.5 mAh g-1 at 10 C. In stark contrast, Si anodes have almost no reserved capacity at the same test conditions. Besides, the LiNi0.5Co0.2Mn0.3O2//Si@AN11 full-cell maintains 141.2 mAh g-1 after 350 cycles. This work demonstrates the potential of developing multiple composite artificial layers to modulate the SEI properties of various next-generation electrodes.

Ultrafast Charge and Long Life of High-Voltage Cathodes for Dual-Ion Batteries via a Bifunctional Interphase Nanolayer on Graphite Particles.

Dual-ion batteries (DIBs) with Co/Ni-free cathodes especially graphite cathodes are very attractive energy storage systems in the long run because of the cost effectiveness and sustainability. However, graphite cathodes severely suffer from poor structural stability during anions storage at high potentials owing to the oxidative decomposition of electrolytes and volume expansion. This work proposes an artificial cathode/electrolyte interphase (CEI) strategy by implanting polyphosphoric acid (PPA) nanofilms tightly on natural graphite (NG) particles via interfacial hydrogen bonding. The electrochemical results show that the PPA-modified graphite cathodes possess enhanced charge-discharge reversibility, accelerated electrode reaction kinetic, decreased resistance, decelerated self-discharge, and prolonged cycling life. Through post-analyses on the cycled graphite cathodes, the improved performance is mainly attributed to the PPA-based CEI, which effectively mitigates the electrolyte decomposition and protects the graphitic structure. More interestingly, the hydrogen bonding interactions between poly(vinyldifluoride) (PVDF) binder and PPA as validated through density functional theory calculations and practical experiments can increase the contact sites of PVDF chains on NG@PPA particles. Meanwhile, the cross-linking effect of PPA can enhance the mechanical strength of PVDF, thus the long life of NG@PPA cathode is also correlated with the improved mechanical stability of the entire electrode.

Solvation and Interfacial Engineering Enable -40 °C Operation of Graphite/NCM Batteries at Energy Density over 270 Wh kg-1.

Li-ion batteries (LIBs) that can operate under low temperature (LT) conditions are essential for applications in orbital missions, subsea areas, and electric vehicles. Unfortunately, severe capacity loss is witnessed due to tremendous kinetic barriers that emerge at LT. Herein, to surmount such kinetic limitations, a low dielectric environment is tamed throughout the bulk electrolyte, which efficaciously brought the Li+ desolvation energy down to 30.76 kJ mol-1 . At the meantime, the adoption of sodium cations (Na+ ) is proposed as a hetero-cation additive, and a Li-Na hybrid and fluoride-rich interphase is further identified via preferential reduction of Na+ -(solvent/anion) clusters, which is found to efficiently facilitate Li+ migration through the LiF/NaF grain boundaries. Based on a N/P ratio of 1.1, the graphite/LiNi0.5 Co0.2 Mn0.3 O2 (NCM) full cell (cathode loading of ≈18.5 mg cm-2 ) delivers a capacity as high as 125.1 mAh g-1 under -20 °C with prolonged cycling to 100 cycles. Finally, a 270 Wh kg-1 graphite/NCM pouch cell is assembled, which affords a discharge capacity of 108.7 mAh g-1 under -40 °C during the initial cycles. With an eye to both fundamental and practical aspects, this work will propel additional advancements and allow LIBs to fill more roles under extreme operation temperatures than ever before.

Building Polymeric Framework Layer for Stable Solid Electrolyte Interphase on Natural Graphite Anode.

The overall electrochemical performance of natural graphite is intimately associated with the solid electrolyte interphase (SEI) layer developed on its surface. To suppress the interfacial electrolyte decomposition reactions and the high irreversible capacity loss relating to the SEI formation on a natural graphite (NG) surface, we propose a new design of the artificial SEI by the functional molecular cross-linking framework layer, which was synthesized by grafting acrylic acid (AA) and N,N'-methylenebisacrylamide (MBAA) via an in situ polymerization reaction. The functional polymeric framework constructs a robust covalent bonding onto the NG surface with -COOH and facilitates Li+ conduction owing to the effect of the -CONH group, contributing to forming an SEI layer of excellent stability, flexibility, and compactness. From all the benefits, the initial coulombic efficiency, rate performance, and cycling performance of the graphite anode are remarkably improved. In addition, the full cell using the LiNi0.5Co0.2Mn0.3O2 cathode against the modified NG anode exhibits much-prolonged cycle life with a capacity retention of 82.75% after 500 cycles, significantly higher than the cell using the pristine NG anode. The mechanisms relating to the artificial SEI growth on the graphite surface were analyzed. This strategy provides an efficient and feasible approach to the surface optimization for the NG anode in LIBs.

Construction of a LiF-Rich and Stable SEI Film by Designing a Binary, Ion-, and Electron-Conducting Buffer Interface on the Si Surface.

Stabilizing a solid electrolyte interface (SEI) film on the Si surface is a prerequisite for realizing silicon (Si) anode applications. Interfacial engineering is one of the effective strategies to construct stable SEI films on Si surfaces and improve the electrochemical performance of the Si anodes. This work develops a silver (Ag)-decorated mucic acid (MA) buffer interface on the Si surface and the obtained Si@MA*Ag anode retains 1567 mAh g-1 after 500 cycles at 2.1 A g-1 and exhibits 1740 mAh g-1 at 126 A g-1, which are significantly higher than those of the bare Si anode of 247 and 145 mAh g-1 under the same conditions, respectively. Analysis indicates that the improved electrochemical performance is because of the depressed volume effect of the Si particles and the sustained integrity of the electrode laminate during cycling, the enhanced lithium diffusion on the Si surface, and the improved electronic conductivity of the Si anode, as well as the facilitated formation of inorganic components in the SEI film.

In Situ Construction of a Multifunctional Interface Regulator with Amino-Modified Conjugated Diene toward High-Rate and Long-Cycle Silicon Anodes.

Silicon (Si) is deemed to be the next-generation lithium-ion battery anode. However, on account of the poor electronic conductivity of Si materials and the instability of the solid electrolyte interphase layer, the electrochemical performance of Si anodes is far from reaching the application level. In this work, a multifunctional poly(propargylamine) (PPA) interlayer is constructed on the Si surface via a simple in situ polymerization method. Benefiting from the electronic conductivity, ionic conductivity, robust interphase interactions for hydrogen bonding, and stability of multifunctional PPA, the optimized Si@PPA-7% electrode shows improved lithium storage capability. A high capacity of 1316.3 mAh g-1 is retained after 500 cycles at 2.1 A g-1, and 2370.3 mAh g-1 can be delivered at 42 A g-1, which are in stark contrast to the unmodified Si electrode. Furthermore, the rate and cycle capabilities of the LiFePO4//Si@PPA-7% full cell are also obviously better than those of LiFePO4//Si.

Electrolyte Design Enabling a High-Safety and High-Performance Si Anode with a Tailored Electrode-Electrolyte Interphase.

Silicon (Si) anodes are advantageous for application in lithium-ion batteries in terms of their high theoretical capacity (4200 mAh g-1 ), appropriate operating voltage (<0.4 V vs Li/Li+ ), and earth-abundancy. Nevertheless, a large volume change of Si particles emerges with cycling, triggering unceasing breakage/re-formation of the solid-electrolyte interphase (SEI) and thereby the fast capacity degradation in traditional carbonate-based electrolytes. Herein, it is demonstrated that superior cyclability of Si anode is achievable using a nonflammable ether-based electrolyte with fluoroethylene carbonate and lithium oxalyldifluoroborate dual additives. By forming a high-modulus SEI rich in fluoride (F) and boron (B) species, a high initial Coulombic efficiency of 90.2% is attained in Si/Li cells, accompanied with a low capacity-fading rate of only 0.0615% per cycle (discharge capacity of 2041.9 mAh g-1 after 200 cycles). Full cells pairing the unmodified Si anode with commercial LiFePO4 (≈13.92 mg cm-2 ) and LiNi0.5 Mn0.3 Co0.2 O2 (≈17.9 mg cm-2 ) cathodes further show extended service life to 150 and 60 cycles, respectively, demonstrating the superior cathode-compatibility realized with a thin and F, B-rich cathode electrolyte interface. This work offers an easily scalable approach in developing high-performance Si-based batteries through Si/electrolyte interphase regulation.

In Situ Developed Si@Polymethyl Methacrylate Capsule as a Li-Ion Battery Anode with High-Rate and Long Cycle-Life.

The development of Si-based lithium-ion batteries is restricted by the large volume expansion of Si materials and the unstable solid electrolyte interface film. Herein, a novel Si capsule with in situ developed polymethyl methacrylate (PMMA) shell is prepared via microemulsion polymerization, in which PMMA has high lithium conductivity, high elasticity, certain viscosity in electrolytes, as well as good electrolyte retention ability. Taking advantage of the microcapsule structure with the PMMA capsid, the novel Si capsule anode retains 1.2 mA h/cm2 at a current density of 2 A/g after 200 electrochemical cycles and delivers higher than 66% of its initial capacity at 42 A/g.

In Situ Transformed Solid Electrolyte Interphase by Implanting a 4-Vinylbenzoic Acid Nanolayer on the Natural Graphite Surface.

A solid electrolyte interphase (SEI) layer on a graphite anode plays a crucial role in deciding electrochemical properties of the electrode including the first Coulombic efficiency, rate capability, operating temperature, and long-term cycling stability. However, the ultrathin functional SEI layer is always naturally grown via electrolyte reduction decomposition reactions. Herein, we report a new strategy of in situ transformed solid electrolyte interphase of high stability by implanting a 4-vinylbenzoic acid (4-VBA) nanolayer on a mildly oxidized graphite surface. A 4-VBA layer of 40 nm contributes to the transformation of a robust and stable SEI layer, which not only significantly enhances the overall electrochemical performances of the natural graphite electrode but also greatly prolongs the cycle life of the full cell with the LiNi0.6Co0.2Mn0.2O2 cathode. The effectively suppressed surface evolution aroused from the stable organic SEI transformed from the implanted 4-VBA nanolayer explains the enhanced electrochemical properties.

Simultaneously formed and embedding-type ternary MoSe2/MoO2/nitrogen-doped carbon for fast and stable Na-ion storage.

To obtain an electrode material that is capable of manifesting high Na-ion storage capacity during long-term cycling at a rapid discharge/charge rate, ternary heterophases MoSe2/MoO2/carbon are rationally designed and synthesized through a supermolecule-assisted strategy. Through using supermolecules that are constructed from MoO4 2- and polydopamine as the precursor and sulfonated polystyrene microspheres as the sacrificial template, the in situ formed ternary phases MoSe2/MoO2/carbon are fabricated into a hollow microspherical structure, which is assembled from ultrathin nanosheets with MoSe2 and MoO2 nanocrystallites strongly embedded in a nitrogen-doped carbon matrix. In the ternary phases, the MoSe2 phase contributes to a high Na-ion storage capacity by virtue of its layered crystalline structure with a wide interlayer space, while the surrounding MoO2 and porous nitrogen-doped carbon phases are conducive to rate behaviour and cycling stability of the ternary hybrids since both the two phases are beneficial for electronic transport and structural stability of MoSe2 during repeated sodiation/desodiation reaction. The as-prepared MoSe2/MoO2/carbon manifests excellent rate behaviour (a Na-ion storage capacity of 461 mA h g-1 at an extremely high current density of 70 A g-1) and outstanding cycle performance (610 mA h g-1 after 1000 cycles).

Dimethylacrylamide, a novel electrolyte additive, can improve the electrochemical performances of silicon anodes in lithium-ion batteries.

To enhance the electrochemical properties of silicon anodes in lithium-ion batteries, dimethylacrylamide (DMAA) was selected as a novel electrolyte additive. The addition of 2.5 wt% DMAA to 1.0 M LiPF6/EC : DMC : DEC : FEC (3 : 3 : 3 : 1 weight ratio) electrolyte significantly enhanced the electrochemical properties of the silicon anode including the first coulombic efficiency, rate performance and cycle performance. The solid electrolyte interphase (SEI) layers developed on the silicon anode in different electrolytes were investigated by a combination of electrochemical and spectroscopic studies. The improved electrochemical performances of the Si anode were ascribed to the effective passivation of DMAA on the silicon anode. The addition of DMAA helped develop a uniform SEI layer, which prevented side reactions at the interface of silicon and electrolyte.

Quantitative Characterization of the Surface Evolution for LiNi0.5Co0.2Mn0.3O2/Graphite Cell during Long-Term Cycling.

Many factors have been brought forward to explain the capacity degradation mechanisms of LiNixCoyMnzO2 (NCM)/graphite cells at extreme conditions such as under high temperature or with high cutoff voltage. However, the main factors dominating the long-term cycling performance under normal operations remain elusive. Quantitative analyses of the electrode surface evolution for a commercial 18650 LiNi0.5Co0.2Mn0.3O2 (NCM523)/graphite cell during ca. 3000 cycles under normal operation are presented. Electrochemical analyses and inductively coupled plasma-optical emission spectroscopy (ICP-OES) confirm lithium inventory loss makes up for ca. 60% of the cell's capacity loss. Electrochemical deterioration of the NCM523 cathode is identified to be another important factor, which accounts for more than 30% of the capacity decay. Irregular primary particle cracking due to the mechanical stress and the phase change aroused from Li-Ni mixing during repetitive cycles are identified to be the main contributors for the NCM cathode deterioration. The amount of transition metal dissolved into electrolyte is determined to be quite low, and the resulting impedance rise after about 3000 cycles is obtained to be twice that of the reference cell, which are not very significant affecting the long-term cycling performance under normal operations.

3D Interconnected and Multiwalled Carbon@MoS2 @Carbon Hollow Nanocables as Outstanding Anodes for Na-Ion Batteries.

Currently, the specific capacity and cycling performance of various MoS2 /carbon-based anode materials for Na-ion storage are far from satisfactory due to the insufficient structural stability of the electrode, incomplete protection of MoS2 by carbon, difficult access of electrolyte to the electrode interior, as well as inactivity of the adopted carbon matrix. To address these issues, this work presents the rational design and synthesis of 3D interconnected and hollow nanocables composed of multiwalled carbon@MoS2 @carbon. In this architecture, (i) the 3D nanoweb-like structure brings about excellent mechanical property of the electrode, (ii) the ultrathin MoS2 nanosheets are sandwiched between and doubly protected by two layers of porous carbon, (iii) the hollow structure of the primary nanofibers facilitates the access of electrolyte to the electrode interior, (iv) the porous and nitrogen-doping properties of the two carbon materials lead to synergistic Na-storage of carbon and MoS2 . As a result, this hybrid material as the anode material of Na-ion battery exhibits fast charge-transfer reaction, high utilization efficiency, and ultrastability. Outstanding reversible capacity (1045 mAh g-1 ), excellent rate behavior (817 mAh g-1 at 7000 mA g-1 ), and good cycling performance (747 mAh g-1 after 200 cycles at 700 mA g-1 ) are obtained.

Layer-by-Layer Polyelectrolyte Assisted Growth of 2D Ultrathin MoS2 Nanosheets on Various 1D Carbons for Superior Li-Storage.

Transitional metal sulfide/carbon hybrids with well-defined structures could not only maximize the functional properties of each constituent but engender some unique synergistic effects, holding great promise for applications in Li-ion batteries and supercapacitors and for catalysis. Herein, a facile and versatile approach is developed to controllably grow 2D ultrathin MoS2 nanosheets with a large quantity of exposed edges onto various 1D carbons, including carbon nanotubes (CNTs), electrospun carbon nanofibers, and Te-nanowire-templated carbon nanofibers. The typical approach involves the employment of layer-by-layer (LBL) self-assembled polyelectrolyte, which controls spatially the uniform growth and orientation of ultrathin MoS2 nanosheets on these 1D carbons irrespective of their surface properties. Such unique structures of the as-prepared CNTs@MoS2 hybrid are significantly favorable for the fast diffusions of both Li-ions and electrons, satisfying the kinetic requirements of high-power lithium ion batteries. As a result, CNTs@MoS2 hybrids exhibit excellent electrochemical performances for lithium storage, including a high reversible capacity (1027 mAh g(-1)), high-rate capability (610 mAh g(-1) at 5 C), and excellent cycling stability (negligible capacity loss after 200 continuous cycles).

From Dispersed Microspheres to Interconnected Nanospheres: Carbon-Sandwiched Monolayered MoS2 as High-Performance Anode of Li-Ion Batteries.

Hierarchical structured carbon@MoS2 (C@MoS2) microspheres and nanospheres composed of carbon-sandwiched monolayered MoS2 building blocks are synthesized through a facile one-pot polyvinylpyrrolidone (PVP) micelle-assisted hydrothermal route. The dimension and carbon content of C@MoS2 spheres are effectively controlled by singly adjusting the concentration of PVP, which plays the dual functions of soft-template and carbon source. As the anode materials of Li-ion batteries, C@MoS2 nanospheres present considerably higher capacity, better rate behavior and cycling stability than C@MoS2 microspheres. The reasons are attributed to the unique interconnected nanospherical morphology and the internal hierarchical construction of C@MoS2 nanospheres with expanded MoS2/carbon interlayer spacing.