Mitigating the Surface Degradation and Voltage Decay of Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material through Surface Modification Using Li2ZrO3.
ABSTRACT: In the quest to tackle the issue of surface degradation and voltage decay associated with Li-rich phases, Li-ion conductive Li2ZrO3 (LZO) is coated on Li1.2Ni0.13Mn0.54Co0.13O2 (LNMC) by a simple wet chemical process. The LZO phase coated on LNMC, with a thickness of about 10 nm, provides a structural integrity and facilitates the ion pathways throughout the charge-discharge process, which results in significant improvement of the electrochemical performances. The surface-modified cathode material exhibits a reversible capacity of 225 mA h g-1 (at C/5 rate) and retains 85% of the initial capacity after 100 cycles. Whereas, the uncoated pristine sample shows a capacity of 234 mA h g-1 and retains only 57% of the initial capacity under identical conditions. Electrochemical impedance spectroscopy reveals that the LZO coating plays a vital role in stabilizing the interface between the electrode and electrolyte during cycling; thus, it alleviates material degradation and voltage fading and ameliorates the electrochemical performance.
Project description:Lithium metal batteries are among the strong contenders to meet the increasing energy demands of the modern world. Metallic lithium (Li) is light in weight, possesses very low standard negative electrochemical potential and offers an enhanced theoretical capacity (3860?mA?h g-1). As a negative electrode Li paves way to explore variety of elements including oxygen, sulfur and various other complex oxides as potential positive electrodes with a promise of much higher energy densities than that of conventional positive electrodes. However, there are technical challenges in utilizing metallic lithium due to its higher reactivity towards liquid electrolytes and higher affinity to form Li dendrites, leading to serious safety concerns. Here, we report on preparation of niobium (Nb) metal-coated binder-free and highly hydrophilic polypropylene separator prepared via radio frequency (RF) magnetron sputtering. Thin layer of niobium metal (Nb) particles were deposited onto the polypropylene (PP) sheet for various time periods to achieve desired coating thickness. The as-prepared separator revealed excellent hydrophilic behaviour due to enhanced surface wettability. Symmetric cells display reduced interface resistance and uniform voltage profiles for 1000 cycles with reduced polarization at higher current densities suggesting smooth stripping and plating of Li and homogeneous current distribution at electrode/electrolyte interface under room temperature conditions. Nb nanolayer protected separator with LiNi0.33M0.33Co0.33O2 (LNMC) and composite sulfur cathodes revealed an enhanced cycling stability.
Project description:Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100-200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01-1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g(-1) at 100 mA g(-1) after 50 cycles. Even at a high current density of 1600 mA g(-1), a capacity of 406 mAh g(-1) can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.
Project description:The corrosion of Li- and Mn-rich (LMR) electrode materials occurring at the solid-liquid interface will lead to extra electrolyte consumption and transition metal ions dissolution, causing rapid voltage decay, capacity fading, and detrimental structure transformation. Herein, a novel strategy is introduced to suppress this corrosion by designing an Na+-doped LMR (Li1.2Ni0.13Co0.13Mn0.54O2) with abundant stacking faults, using sodium dodecyl sulfate as surfactant to ensure the uniform distribution of Na+ in deep grain lattices-not just surface-gathering or partially coated. The defective structure and deep distribution of Na+ are verified by Raman spectrum and high-resolution transmission electron microscopy of the as-prepared electrodes before and after 200 cycles. As a result, the modified LMR material shows a high reversible discharge specific capacity of 221.5 mAh g-1 at 0.5C rate (1C = 200 mA g-1) after 200 cycles, and the capacity retention is as high as 93.1% which is better than that of pristine-LMR (64.8%). This design of Na+ is uniformly doped and the resultanting induced defective structure provides an effective strategy to enhance electrochemical performance which should be extended to prepare other advanced cathodes for high performance lithium-ion batteries.
Project description:LiMnPO4 is an attractive cathode material for the next-generation high power Li-ion batteries, due to its high theoretical specific capacity (170 mA h g(-1)) and working voltage (4.1 V vs Li(+)/Li). However, two main drawbacks prevent the practical use of LiMnPO4: its low electronic conductivity and the limited lithium diffusion rate, which are responsible for the poor rate capability of the cathode. The electronic resistance is usually lowered by coating the particles with carbon, while the use of nanosize particles can alleviate the issues associated with poor ionic conductivity. It is therefore of primary importance to develop a synthetic route to LiMnPO4 nanocrystals (NCs) with controlled size and coated with a highly conductive carbon layer. We report here an effective surface etching process (using LiPF6) on colloidally synthesized LiMnPO4 NCs that makes the NCs dispersible in the aqueous glucose solution used as carbon source for the carbon coating step. Also, it is likely that the improved exposure of the NC surface to glucose facilitates the formation of a conductive carbon layer that is in intimate contact with the inorganic core, resulting in a high electronic conductivity of the electrode, as observed by us. The carbon coated etched LiMnPO4-based electrode exhibited a specific capacity of 118 mA h g(-1) at 1C, with a stable cycling performance and a capacity retention of 92% after 120 cycles at different C-rates. The delivered capacities were higher than those of electrodes based on not etched carbon coated NCs, which never exceeded 30 mA h g(-1). The rate capability here reported for the carbon coated etched LiMnPO4 nanocrystals represents an important result, taking into account that in the electrode formulation 80% wt is made of the active material and the adopted charge protocol is based on reasonable fast charge times.
Project description:Lithium metal is deemed as an ideal anode material for next-generation lithium ion batteries (LIBs) due to its high specific capacity and low redox potential. However, uncontrolled lithium dendrite formation during electrochemical deposition leads to a low Coulombic efficiency and serious safety issues, dragging metallic lithium anodes out of practical application. One promising strategy to suppress lithium dendrite issues is employing a three-dimensional host with admirable conductivity and large surface area. Herein, a vertical graphene nanosheet grown on carbon cloth (VG/CC) synthesized is adopted as the Li deposition host. The three-dimensional VG/CC with a large surface area can provide abundant active nucleation sites and effectively reduce the current density, leading to homogeneous Li deposition to overcome the dendrite issue. The Li@VG/CC anode exhibits a dendrite-free morphology after a long cycle and superior electrochemical performance to that of planar Cu current collector. It delivers a small voltage hysteresis of 90.9 mV at a high current density of 10 mA cm-2 and a Coulombic efficiency of 99% over 100 cycles at 2 mA cm-2. Our results indicate that this all-carbon-based nanostructure host has great potential for next-generation Li metal batteries.
Project description:A facile, one-pot hydrothermal method was used to synthesize Nickel selenide (NiSe) nanoparticles decorated with reduced graphene oxide nanosheets (rGO), denoted as NiSe/rGO. The NiSe/rGO exhibits good electrochemical performance when tested as anodes for Na-ion batteries (SIBs) and Li-ion batteries (LIBs). An initial reversible capacity of 423 mA h g-1 is achieved for SIBs with excellent cyclability (378 mA h g-1 for 50th cycle at 0.05 A g-1). As anode for LIBs, it delivers a remarkable reversible specific capacity of 1125 mA h g-1 at 0.05 A g-1. The enhanced electrochemical performance of NiSe/rGO nanocomposites can be ascribed to the synergic effects between NiSe nanoparticles and rGO, which provide high conductivity and large specific surface area, indicating NiSe/rGO as very promising Na/Li storage materials.
Project description:Organic compounds are desirable for sustainable Li-ion batteries (LIBs), but the poor cycle stability and low power density limit their large-scale application. Here we report a family of organic compounds containing azo group (N=N) for reversible lithiation/delithiation. Azobenzene-4,4'-dicarboxylic acid lithium salt (ADALS) with an azo group in the center of the conjugated structure is used as a model azo compound to investigate the electrochemical behaviors and reaction mechanism of azo compounds. In LIBs, ADALS can provide a capacity of 190 mAh g-1 at 0.5 C (corresponding to current density of 95 mA g-1) and still retain 90%, 71%, and 56% of the capacity when the current density is increased to 2 C, 10 C, and 20 C, respectively. Moreover, ADALS retains 89% of initial capacity after 5,000 cycles at 20 C with a slow capacity decay rate of 0.0023% per cycle, representing one of the best performances in all organic compounds. Superior electrochemical behavior of ADALS is also observed in Na-ion batteries, demonstrating that azo compounds are universal electrode materials for alkali-ion batteries. The highly reversible redox chemistry of azo compounds to alkali ions was confirmed by density-functional theory (DFT) calculations. It provides opportunities for developing sustainable batteries.
Project description:As promising cathode materials for lithium-ion batteries (LIBs), Fe-containing Li-rich compounds of Li1+x Fe0.1Ni0.15Mn0.55O y (0 ? x ? 0.3 and 1.9 ? y ? 2.05) have been successfully synthesized by calcining the spherical precursors with appropriate amounts of lithium carbonate. The structures, morphologies, and chemical states of these compounds are characterized to better understand the corresponding electrochemical performances. With an increase of lithium content, Li1+x Fe0.1Ni0.15Mn0.55O y evolves from a complex layered-spinel structure to a layered structure. The lithium content also affects the average size and adhesion of the primary particles. At 0.1 C, sample x = 0.1 shows the highest first charge/discharge specific capacities (338.7 and 254.3 mA h g-1), the highest first Coulombic efficiency (75.1%), the lowest first irreversible capacity loss (84.4 mA h g-1), the highest reversible discharge specific capacity, and good rate capability. Notably, voltage fading can be alleviated through the adjustment of structural features. Such superior electrochemical performances of sample x = 0.1 are ascribed to the hierarchical micro-/nanostructure, the harmonious existence of complex layered-spinel phase, and the low charge-transfer resistance. An integral view of structure evolution from layered to spinel during synthetic control and cycling process is provided to broaden the performance scope of Li-Fe-Ni-Mn-O cathodes for LIBs.
Project description:Low ionic conductivity at room temperature and limited electrochemical window of poly(ethylene oxide) (PEO) are the bottlenecks restricting its further application in high-energy density lithium metal battery. Herein, a differentiated salt designed multilayered PEO-based solid polymer electrolyte (DSM-SPE) is exploited to achieve excellent electrochemical performance toward both the high-voltage LiCoO2 cathode and the lithium metal anode. The LiCoO2/Li metal battery with DSM-SPE displays a capacity retention of 83.3% after 100 cycles at 60 °C with challenging voltage range of 2.5 to 4.3 V, which is the best cycling performance for high-voltage (?4.3 V) LiCoO2/Li metal battery with PEO-based electrolytes up to now. Moreover, the Li/Li symmetrical cells present stable and low polarization plating/stripping behavior (less than 80 mV over 600 h) at current density of 0.25 mA cm-2 (0.25 mAh cm-2). Even under a high-area capacity of 2 mAh cm-2, the profiles still maintain stable. The pouch cell with DSM-SPE exhibits no volume expansion, voltage decline, ignition or explosion after being impaled and cut at a fully charged state, proving the excellent safety characteristic of the DSM-SPE-based lithium metal battery.
Project description:Our work reports the hydrothermal synthesis of a bimetallic composite CoMoS, followed by the addition of cellulose fibers and its subsequent carbonization under Ar atmosphere (CoMoS@C). For comparison, CoMoS was heat-treated under the same conditions and referred as bare-CoMoS. X-ray diffraction analysis indicates that CoMoS@C composite matches with the CoMoS4 phase with additional peaks corresponding to MoO3 and CoMoO4 phases, which probably arise from air exposure during the carbonization process. Scanning electron microscopy images of CoMoS@C exhibit how the CoMoS material is anchored to the surface of carbonized cellulose fibers. As anode material, CoMoS@C shows a superior performance than bare-CoMoS. The CoMoS@C composite presents an initial high discharge capacity of ?1164 mA h/g and retains a high specific discharge capacity of ?715 mA h/g after 200 cycles at a current density of 500 mA/g compared to that of bare-CoMoS of 102 mA h/g. The high specific capacity and good cycling stability could be attributed to the synergistic effects of CoMoS and carbonized cellulose fibers. The use of biomass in the anode material represents a very easy and cost-effective way to improve the electrochemical Li-ion battery performance.