Surface Side Reactions Research Articles

Bonding the Terminal Isocyanate-Related Functional Group to the Surface Manganese Ions to Enhance Li-Rich Cathode's Cycling Stability.

Capacity fading of Li-rich cathodes in the cycling process is mainly caused by the irreversible side reactions at the interface of electrode and electrolyte by reason of the lack of a corrosion resistant surface. In this work, isocyanate-related functional groups (-N═C═O groups and polyamide-like groups) were tightly bonded on the surface of Li-rich oxides through a urea decomposition gas heat-treatment. The surface isocyanate functionalization inhibits the side reaction of PF5 hydrolysis to give LixPFyOz and HF species at the surface of Li-rich materials in the cycle process. As compared to the untreated Li-rich sample U0, the samples with the spinel-like layer and isocyanate functionalized surface exhibited an enhanced cycle stability. The capacity retention of the treated sample U3 reached as high as 92.6% after 100 cycles at the current density of 100 mA/g, larger than 66.8% for the untreated sample. Even at a higher current density of 1000 mA/g, sample U3 gives a capacity retention of 81.7% after 300 cycles. The findings of this work reveal the importance of surface isocyanate functionalization in restraining the surface side reactions and also suggest an effective method to design Li-rich cathode materials with better electrochemistry performance.

Enhanced electrochemical performance of Ni-rich cathode material by N-doped LiAlO2 surface modification for lithium-ion batteries

LiNi0.6Co0.2Mn0.2O2 (NCM) cathodes are regarded as prospective cathodes for high-performance Lithium ion batteries due to its low costs and high energy density. Nevertheless, poor electrochemical performance severely hinders its further commercial applications. In this study, an effective surface modification strategy to fabricate N-doped LiAlO2 was coated on the surface of LiNi0.6Co0.2Mn0.2O2, and electrochemical performance are greatly enhanced. The nitrogen (N)-doped LiAlO2 (LAO) coated LiNi0.6Co0.2Mn0.2O2 not only exhibit best cycling performance with capacity retention of 87 % after 450 cycles at 1 C (210 mA g−1) under voltage range of 2.7-4.5 V, but also approaches 167 and 154 mAh g−1 at 5 C and 10 C, respectively. The N-doped LiAlO2 surface modified LiNi0.6Co0.2Mn0.2O2 not only suppresses the occurrence of surface side reaction, structural degradation and intergranular cracks, but also remove residual lithium from the LiNi0.6Co0.2Mn0.2O2 surface. Most importantly, in constructed this N-doped LiAlO2 layer, the LiAlO2 with the similar layered structure as LiNi0.6Co0.2Mn0.2O2 can tightly immobilize on the LiNi0.6Co0.2Mn0.2O2 surface, and the N-doping could induce the formation of oxygen vacancies and Al-N bond on surface of the LiAlO2 as well as enlarge interslab distance for the migrating Li+ in the LiAlO2 lattices. These finding not only promoted the commercial application of Ni-rich material, but also provided a new idea for other layered structure cathode.

Tailoring the Al distribution in secondary particles for optimizing the electrochemical performance of LiNi0.8Co0.1Mn0.1O2

Ni-rich materials, as one type of cathode materials for next-generation lithium-ion batteries, suffer from poor cycling stability due to severe structural degradation and surface deterioration. Lattice doping is an effective method to stabilize crystal structures, yet it has little effect on inhibiting surface side reactions. Herein, we demonstrate a strategy that can tailor the distribution of doping element Al in the entire secondary sphere in a controllable way to simultaneously stabilize the crystal structure and surface of the cathode material. The strategy takes advantage of the interdiffusion of elements at the solid-solid interface formed by aluminum-containing species that uniformly cover the surface of the Ni0.8Co0.1Mn0.1(OH)2 precursor at a high temperature. The extent of Al doping in the materials can be properly regulated by the amount of aluminum-containing species to generate uniform doping, gradient doping, and gradient doping with a thin Al coating layer. As a result, the Al gradient-doped cathode material exhibits excellent capacity retention of 81.9% after 500 cycles at 2C, which is much higher than the capacity retention of 54.3% for the pristine counterpart.

Enhancing the structure stability of Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode via encapsulating in negative thermal expansion nanocrystalline shell

Ni-rich cathode materials have attracted considerable attention due to the high electrochemical capacities and prominent price advantage, while their extensive applications are still impeded by the poor structure stability induced by the intrinsic Li+/Ni2+ cation mixing and mechanical stress accumulation upon cycling. To address these issues, a typical negative thermal expansion (NTE) material ZrV2O7 (ZVO) is firstly employed as coating layer on LiNi0.6Co0.2Mn0.2O2 (NCM622) particles to promote the electrochemical performances through enhancing the structure stability upon repeated cycling and operating at high temperature. The [email protected] wt% ZVO sample exhibits excellent cyclability (71.0% capacity retension after 500 cycles under 25 °C and 67.0% capacity retension after 200 cycles under 55 °C) and rate capability (60.7% at 5 C). Further in-situ XRD analysis confirms that the structure stability of NCM622 could be prominently stabilized both under electrochemical and thermal treatments after ZVO decoration. Intensive investigation implies the unique functionalities of ZVO in restraining the stress accumulation and volume expansion, thus contributing to the bulk structure stability and interface compatibility of modified NCM622, besides the traditional effect of surface deposition layers (physical separation between solid electrode/electrolyte and inhibited irreversible surface side reactions).

An effective dual-modification strategy to enhance the performance of LiNi0.6Co0.2Mn0.2O2 cathode for Li-ion batteries.

Ni-rich ternary layered oxides represent the most promising cathodes for lithium ion batteries (LIBs) due to their relatively large specific capacities and high energy/power densities. Unfortunately, their inherent chemical instability and surface side reactions during the charge/discharge processes lead to rapid capacity fading and poor cycling life, which seriously restrict their practical applications. Herein, we report a simple dual-modification strategy for preparing LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials by Li2SnO3 surface coating and Sn4+ gradient doping. The gradient Sn doping stabilizes the layered structure due to the strong Sn-O covalent bond and relieves the Li+/Ni2+ cation disorder by the partial oxidation of Ni2+ to Ni3+. Besides, the ionic and electronic conductive Li2SnO3 coating serves as a protective layer to eliminate the side reactions with electrolyte/air. In LIB testing, the dual-modified NCM622 cathode with 2% Sn delivers an enhanced cycling performance with 88.31% capacity retention after 100 cycles from 3.0 to 4.5 V at 1C compared to the bare NCM622. Meanwhile, the dual-modified NCM622 shows an improved reversible capacity of 136.2 mA h g-1 at 5C and enhanced electrode kinetics. The dual-modification strategy may enable a new approach to simultaneously relieve the interfacial instability and bulk structure degradation of Ni-rich cathode materials for high energy density LIBs.

NCA, NCM811, and the Route to Ni-Richer Lithium-Ion Batteries

The aim of this article is to examine the progress achieved in the recent years on two advanced cathode materials for EV Li-ion batteries, namely Ni-rich layered oxides LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Co0.1Mn0.1O2 (NCM811). Both materials have the common layered (two-dimensional) crystal network isostructural with LiCoO2. The performance of these electrode materials are examined, the mitigation of their drawbacks (i.e., antisite defects, microcracks, surface side reactions) are discussed, together with the prospect on a next generation of Li-ion batteries with Co-free Ni-rich Li-ion batteries.

Application of Artificial Interphase on Ni-Rich Cathode Materials in All Solid State Li-Ion Batteries

Among many cathode materials, nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM 811) has been spotlighted as one of the most feasible candidates for next-generation LIBs because of its high discharge capacity (~200 mAh/g). However, NCM 811 shows significant performance degradation, which is mostly attributed to cation mixing, surface side reactions, and intrinsic structural instability originating from the large volume changes during repeated cycling.Conventional lithium ion batteries (LIB) normally use flammable nonaqueous liquid electrolytes, resulting in a serious safety issue in use. In this respect, all solid state lithium ion batteries (SSLIBs) are regarded as a fundamental solution to address the safety issue by using a solid state electrolyte (SSE) in place of the conventional liquid one.This study assess the performance of NCM811 cathode for all-solid-state batteries based on hybrid PEO-ceramic solid electrolyte. Artificial CEI coating layer has been developed in order to prevent direct contact of electrolyte with the cathode, thus avoid the negative effects, such as side reactions, on NCM 811. The incorporation of ceramic materials results composite electrolytes, containing inert fillers, offer improved mechanical stability under high operating temperature.It is demonstrated that the polymer of hybrid electrolytes can penetrate into cathode, providing a good Li+ transfer channel inside the battery under high operating temperature. Moreover, the protective coating on NCM811 effectively improve the electrochemical stability.(This work is supported by Ministry of Science and Technology, Taiwan under contract number: MOST 108-3116-F002-008)

(Invited) Probing the in-Situ Surface Chemistry of Ni-Rich LiNi x Co y Mn z O2 (x+y+z=1) Cathode Materials Using Synchrotron-Based Ambient-Pressure X-Ray Photoelectron Spectroscopy

Ni-rich layered cathode materials are important candidates for lithium-ion batteries used for applications requiring high energy density, such as electric vehicles and mobile electronic devices. However, comparing with low Ni content NMC, Ni-rich NMCs frequently exhibit fast capacity decay and relatively shorter lifetime due to the formation of more reactive surface with high Ni content. Previous reports demonstrated that Ni-rich NMCs are sensitive to the CO2 and water in the air during ambient storage, because of these oxidizing gases can lead to the formation of surface impurities such as Li2CO3 and LiOH. [1] these surface impurities can react with electrolyte during the electrochemical cycling process and form a nonuniform cathode/electrolyte interface (CEI) layer. Surface instability of Ni-rich NMCs can also cause problems during the large-scale electrode preparation, and material storage. Research results reported in the literature have suggested that the degradation of Ni-rich NMCs could be attributed to the reduction of Ni and evolution of active oxygen species as well as the side reaction between the surface impurities and the electrolyte. [2-3] However, only limited experimental results have been reported about the formation mechanism of surface impurities and side reaction during the battery cycling for Ni-rich NMCs. Therefore, it is very important to develop an in-situ characterization method to reveal the CO2 and moisture effects on the surface chemistry of Ni-rich NMCs. Synchrotron-based Ambient-Pressure XPS (AP-XPS) is a powerful technique with controllable gas environments and tunable energy. These enable us to probe the surface chemistry evolution of the samples in-situ in atmospheric gas environments with different depth profile. Taking these advantages, we have systematically investigated the CO2 and moisture effect on the LiNi0.94Co0.06O2 cathode material with and without Al doping using AP-XPS technique. Preliminary results showed that only Ni2+ can be observed in NC sample surface after exposed to CO2 environment even measured at 2000 eV with probing depth of ~9 nm. In contrast, characteristic peak of Ni3+ still exists in NCA sample, even measured at 1200 and corresponding to probing depth of ~5.5 nm. These results show that better surface stability (less Ni2+ at surface) can be achieved by Al doping. We also comprehensively investigated the depth profile of CEI layer of NMC cathode materials with different Ni content and found that CEI composition really depends on Ni content, dopant as well as the cut off voltage for charging. These results will be presented at the meeting.[1] You et al. Angewandte Chemie, 572018 (2018) 6480-6485.[2] Shizuka et al. Journal of Power Sources, 166 (2007) 233-238.[3] Jung et al. Journal of The Electrochemical Society, 165 (2) (2018) A132-A141. Acknowledgement The work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. DOE through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under contract No. DE-SC0012704.

Regenerable copper anode for the Cu(I)-mediated reduction of FAD in the electroenzymatic styrene epoxidation reaction

Styrene monooxygenase (SMO) is a two-component flavoenzyme composed of NADH-dependent flavin reductase (SMOB) and FAD-specific styrene epoxidase (NSMOA) components. The enantioselective styrene epoxidation reaction catalyzed by this enzyme can be streamlined for chemosynthetic applications by substituting NADH and the reductase with an electrode to supply the epoxidase with reducing equivalents required for catalysis. Slow kinetics of adsorption and desorption of FAD from the electrode surface and unproductive side reactions of the reduced flavin with oxygen limit the efficiency of direct electroenzymatic catalysis. In the present work we develop a miniature spectroelectrochemical cell equipped with a copper electrode for the anodic synthesis of Cu(I) chelates of EDTA, glutamate, and citrate as FAD-reducing agents, and a platinum electrode for the electrolytic generation of oxygen. Copper oxidized in the flavin reduction reaction can be reclaimed subsequently as copper metal at the electrode surface. About 80% transformation of styrene is achieved in a single cell cycle of reduction and oxygenation at pH 7 and 25 °C in good agreement with that predicted by numerical simulation. When the cell is operated in two successive cycles, styrene oxide can be synthesized with an electroenzymatic epoxidation activity of 663U/g in 94% yield. This approach to electroenzymatic catalysis shows promise for the quantitative transformation of styrene to styrene oxide and may be applied more generally to other flavoprotein monooxygenases.

Regulating the Grain Orientation and Surface Structure of Primary Particles through Tungsten Modification to Comprehensively Enhance the Performance of Nickel-Rich Cathode Materials.

Nickel-rich layered oxides, as the most promising commercial cathode material for high-energy density lithium-ion batteries, experience significant surface structural instabilities that lead to severe capacity deterioration and poor thermal stability. To address these issues, radially aligned grains and surface LixNiyWzO-like heterostructures are designed and obtained with a simple tungsten modification strategy in the LiNi0.91Co0.045Mn0.045O2 cathode. The formation of radially aligned grains, manipulated by the WO3 modifier during synthesis, provides a fast Li+ diffusion channel during the charge/discharge process. Moreover, the tungsten tends to enter into the lattice of the primary particle surface, and the armor-type tungsten-rich heterostructure protects the bulk material from microcracks, structural transformations, and surface side reactions. First-principles calculations indicate that oxygen is more stable in the surface tungsten-rich heterostructure than elsewhere, thus triggering an improved surface structural stability. Consequently, the 2 wt % WO3-modified LiNi0.91Co0.045Mn0.045O2 (NCM@2W) material shows outstanding prolonged cycling performance (capacity retention of 80.85% after 500 cycles) and excellent rate performance (5 C, 188.4 mA h g-1). In addition, its layered-to-rock salt phase transition temperature is increased by 80 °C compared with that of the pristine cathode. This work provides a novel surface modification approach and an in-depth understanding of the overall performance enhancement of nickel-rich layered cathodes.

Improving Cycling Stability and Rate Capability of High-Voltage LiCoO2 Through an Integration of Lattice Doping and Nanoscale Coating

High-voltage LiCoO₂ has attracted much interest owing to the high specific energy density. But the poor cycling performance and inferior rate capacity of LiCoO₂ at a high voltage (≥4.5 V) has restricted the practical applications. Herein, we propose to improve the electrochemical performances of LiCoO₂ at high voltage through a synergy of Al-doping and Li₂TiO₃-coating. In compared to bare LiCoO₂, Al-doped LiCoO₂ and Li₂TiO₃-coated LiCoO₂, the cycle performance, the rate capability and the polarization of Al-doped and Li₂TiO₃-coated LiCoO₂ shows a larger improvement, which can be attributed to the synergic effects of Al-doping and Li₂TiO₃-coating. Firstly, Al doping expands the interlayer spacing which decreases the Li-ion diffusion barrier and enhances the coefficient of Li-ion diffusion. This benefits to the rate capability. Secondly, Al doping enhances the layered structure stability due to the larger Al-O bonding energy (ΔH298 Kt (Al-O) = 512 kJmol-1) than that of Co-O (ΔH298 Kt (Co-O) = 368 kJmol-1). Thirdly, the coating layer of Li₂TiO₃ mitigates the surface side reactions and further enhances the cycling performance. Moreover, the coating layer of Li₂TiO₃ as a Li+-conductor is also favorable to the Li+ diffusion and the rate capability. This synergic strategy can also be extended to the modification of other cathode materials.

A highly stabilized single crystalline nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode through a novel surface spinel-phase modification

For developing high-energy-density nickel-rich layered oxide cathodes with extended cycle life and rate capability, it is necessary to mitigate mechanical degradation caused by volume change and surface side reactions between cathode and electrolyte. To overcome these problems, a novel single crystalline LiNi0.8Co0.1Mn0.1O2 material is coated by Li-reactive materials. Results show that the degree of cation mixing is significantly reduced and it is caused by the coating layer. The residual lithium compounds on the surface of the material are greatly removed by the coating materials through the formation of spinel Co3O4 and LiMn2O4 layer. The electrochemical performance of the modified materials is significantly improved. They conserve 91.4% and about 89.9% of the initial capacity (186.6 mAh·g−1 and 186.5 mAh·g−1, respectively) at 1 C after 100 cycles. They also exhibit greater rate capability of 161.7 mAh·g−1 and 157.9 mAh·g−1 at 5 C, remaining 79.3% and 77.4% capacity of 0.1C. The enhancements are attributed to the coated spinel phase with excellent structural stability. This generated cubic spinel phase suppresses volume change and thus inhibits the formation of surface cracks, resulting in fine surface structure during charge and discharge process.

Exploring the activating voltages on the electrochemical performances of Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials

Lithium and manganese-rich oxide (LMR) is regarded as one of the next generation of the high energy density cathode materials. However, the activating voltages have a great impact on the electrochemical performances. Herein, we explore the effects of the activating voltages on the electrochemical performances of Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials. The activating voltages can mainly affect the capacity release, rather than the cycling characteristics. The comparison study reveals that the layered structure can transform into spinel and/or nickel enriched structure due to the cation migration and the hardly-being reduced transition metals, especially for the Ni4+ during activation. Meanwhile, the surface side-reactions would also deteriorate the lithium kinetic characteristics, but the formed by-products coated on the cathode surface can resist the further attack from electrolyte, which favors to the following cycles. The Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials activated to 4.6 V with 25 mA·g−1 can deliver capacities of 262.0 and 209.2 mAh·g−1 over 2.0–4.8/4.4 V at 1C (250 mA·g−1) and the highest energy densities. The appropriate activating voltages play critical roles in the optimization of the structure of LMR cathode materials and improving the electrochemical performances.

Realizing Superior Cycle Stability of a Ni‐Rich Layered LiNi0.83Co0.12Mn0.05O2 Cathode with a B2O3 Surface Modification

AbstractNi‐rich cathode is considered a promising cathode for its high specific capacity. However, a sharp capacity attenuation induced by interface problems limits the application of the cathode material. Herein, we propose a practical surface modification strategy by introducing diboron trioxide (B2O3) to the surface of LiNi0.83Co0.12Mn0.05O2 (NCM) cathode materials. B2O3‐modified NCM shows superior cyclic stability with a capacity retention of 87.7 % at 1 C after 200 cycles in comparison to 69.4 % for a bare NCM. On the basis of material and electrochemical characterizations, we conclude that the superior cycle stability of B2O3‐modified NCM material benefits from the formation of B2O3 coating and B3+ doping on the surface. The B2O3 coating layer that is confirmed by scanning and transmission electron microscopy can suppress surface side reactions and reduce the content of Li2CO3 on the surface. The B3+‐doping surface is verified by X‐ray diffraction and X‐ray photoelectron spectroscopy and triggers a reduction of a small amount of Ni3+ to Ni2+. Furthermore, the combination of surface B2O3 coating and B3+ doping inhibits the irreversible phase transitions and extension of microcracks in the NCM material. The above surface modification strategy provides a direction for the acquisition of long‐life cathode materials.

Structural Distortion-Induced Charge Gradient Distribution of Co Ions in Delithiated LiCoO2 Cathode.

Layered LiCoO2 has drawn tremendous attention as a modeling cathode for Li-ion batteries, while its structural instability, especially in the high delithiation region, remains unsolved. With the aim of revealing the structural fundamentals, LiCoO2 electrodes are investigated at a long delithiation range using both in situ and ex situ techniques. In the highly delithiated LiCoO2 electrode, the unique charge compensation process leads to a spatial charge gradient of Co2+/Co3+/Co4+ ions from surface to bulk, which can be further manipulated by structural distortion, Li extraction, and surface side reactions. The coordinated surface oxygen is shown to be electrochemically active and fully reversible in participating in the charge compensation during cycling. Moreover, the active lattice O can be significantly stabilized by introducing the undesired surface Li-Co antisites, which also play an effective role in accommodating the internal stress induced by volume changes. These findings effectively bridge the structural changes with the Li+/e- migration kinetics to elucidate the degradation of LiCoO2 cathode upon delithiation, demonstrating a rewarding avenue for improving the electrochemical performance of LiCoO2 itself and developing high energy density cathodes for the battery community as well.

Reversible phase transition enabled by binary Ba and Ti-based surface modification for high voltage LiCoO2 cathode

As a popular commercialized cathode material in lithium-ion batteries, the cycle life, practical reversible capacity, and rate capabilities of LiCoO2 (LCO) at high voltage are limited owning to structural irreversibility and surface side reactions. Here, we employ a binary Ba and Ti-based hybrid surface treatment on LiCoO2 (LCO@BT) by facile wet chemical routes. This strategy integrates the advantages of both interface particle doping and surface coating as the layered structure of LCO is stabilized by a binary hybrid surface treatment, and the modified layer promotes the surface Li+ diffusivity and protects the LCO cathode from steady corrosion induced by surface side reaction. On the basis of in-situ NMR characterizations, it is found that after the first electrochemical delithiation/lithiation the phase reversibly changes from O3–I-type in LCO@BT and back to O3–I-type LxCO@BT (0.98 ≤ x＜1) rather than to a two-phase domain of O3–I and O3-II phase in uncoated LxCO (x＜0.98). The target material is achievable in displaying an initial discharge capacity of 190.5 mAh g−1 and delivers a high capacity retention of 90.29% (172 mAh g−1) at 0.2C after 100 cycles which is superior to most LiCoO2 cathodes that are operated at high cut-off voltage of 4.5V.

The Role of Zr Doping in Stabilizing Li[Ni0.6 Co0.2 Mn0.2 ]O2 as a Cathode Material for Lithium-Ion Batteries.

Ni-rich layered LiNi1-x-y Cox Mny O2 systems are the most promising cathode materials for high energy density Li-ion batteries (LIBs). However, Ni-rich cathode materials inevitably suffer from rapid capacity fading and poor rate capability owing to structural instability and unstable surface side reactions. Zr doping has proven to be an effective method to enhance the cycle and rate performances by stabilizing the structure and increasing the Li+ diffusion rate. Herein, effects of Zr-doping on the structural stability and Li+ diffusion kinetics are thoroughly investigated in LiNi0.6 Co0.2 Mn0.2 O2 (LNCM) cathode material using atomic-resolution scanning transmission electron microscopy imaging, XRD Rietveld refinement, and density functional theory calculations. Zr doping mitigates the degree of cation mixing, decreases the structural transformation, and facilitates Li+ diffusion resulting in improved cyclic performance and rate capability. Based on the obtained results, an atomistic model is proposed to explain the effects of Zr doping on the structural stability and Li+ diffusion kinetics in LNCM cathode materials.

One-Step Integrated Surface Modification To Build a Stable Interface on High-Voltage Cathode for Lithium-Ion Batteries.

As one of the most promising cathode materials for next-generation energy storage applications, spinel LiNi0.5Mn1.5O4 (LNMO) has been highlighted due to many advantages. However, it is still hindered by poor electrochemical stability derived from the bulk/interface structure degradation and side reactions under high working voltage. In this work, fast ion conductor Li3V2(PO4)3 (LVPO) is adopted to modify the surface of spinel LNMO by a one-step facile method to harvest the maximum benefit of interface properties. It is found that 1 wt % LVPO-LNMO exhibits the most excellent cycling performances, retaining great capacity retention of 87.8% after 500 cycles at room temperature and 82.4% for 150 cycles at 55 °C. Moreover, the rate performance is also significantly improved (90.4 mAh g-1 under 20C). It is revealed that the LVPO-involved layer could effectively suppress the surface side reactions under high working voltage, which mainly contributes to an improved interface with desirable structural stability and excellent kinetics behavior without sacrificing the surface electrochemical activity in an electrochemical environment. Thus, the dissolution of transition-metal ions is effectively mitigated, avoiding further structure degradation of the bulk material. Especially, it is also established that the vanadium (V) ions in LVPO could be to a certain extent migrated into the surface lattice of LNMO to generate a V-involved transition layer (Li-Ni-Mn-V-O surface solid solution), which greatly co-contributes to the enhanced electrochemical performances owing to the prominently depressed charge-transfer resistance.

Single Additive with Dual Functional-Ions for Stabilizing Lithium Anodes.

The dendritic lithium formation and sustained lithium consumption caused by the uncontrollable side reactions between lithium and electrolytes seriously restrict the applications of lithium anodes in high-energy density batteries, especially in carbonate electrolytes. Ameliorating the surface status of lithium anodes is critical for modulating lithium deposition behavior and improving the cycling stability of lithium metal batteries. Herein, magnesium chloride salt is first reported as a carbonate electrolyte additive for lithium surface modification by in situ reaction. It is proved that both Cl- and Mg2+ play important roles in building a stable electrode/electrolyte interface with a fast Li+ diffusion property. The coexistence of inorganic LiCl and metallic Mg species in the interface can effectively decrease the surface side reactions, lower interphase resistance, promote Li ions diffusion, and result in uniform lithium deposition. The electrochemical tests show that the reversible utilization rate of lithium for Li/Cu asymmetrical cells increases by 10% and the polarization of Li/Li symmetrical cells is reduced noteworthily with such an additive. Furthermore, a significant improved cycling performance of Li/Li4T5O12 full cells is also achieved.

Seaweed-derived synthesis of Na3.12Fe2.44(P2O7)2/r-GO aerogels as air stable cathode materials for sodium-ion batteries

Due to the high theoretical capacity and open frameworks, the low-cost sodium iron pyrophosphate Na3.12Fe2.44(P2O7)2 has become a promising candidate for cathode materials of the sodium ion batteries (SIBs). However, NFPO is very sensitive to moisture and CO2, which causes serious surface oxidation reaction and results in degraded high-rate charge/discharge performance and cyclic stability. Herein, we developed a seaweed-derived synthesis strategy to prepare air stable NFPO/r-GO aerogels by using sodium alginate (SA) and reduced graphene oxide (r-GO) as precursors. X-ray photoelectron spectroscopy (XPS) proved that there were no residual Na species on the surface of prepared NFPO/r-GO aerogels and no any oxidized impurities after exposing in air for 100 days. When evaluating the NFPO/r-GO aerogels as cathode materials for SIBs, the sample exhibits excellent reversible capacity of 116.1 mAh g−1 at 0.1 C, 88.82% capacity retention after 5000 cycles and superior rate capacity of 72.3 mAh g−1 at 20 C. The superior electrochemical performances are mainly attributed the delicate structure, which can not only increase the electronic conductivity, but also improve air stability of NFPO by suppressing surface side reactions with moisture and CO2.