Abstract
Doping is a well-known strategy to enhance the electrochemical energy storage performance of layered cathode materials. Many studies on various dopants have been reported; however, a general ...relationship between the dopants and their effect on the stability of the positive electrode upon prolonged cell cycling has yet to be established. Here, we explore the impact of the oxidation states of various dopants (i.e., Mg
2+
, Al
3+
, Ti
4+
, Ta
5+
, and Mo
6+
) on the electrochemical, morphological, and structural properties of a Ni-rich cathode material (i.e., LiNi
0.91
Co
0.09
O
2
). Galvanostatic cycling measurements in pouch-type Li-ion full cells show that cathodes featuring dopants with high oxidation states significantly outperform their undoped counterparts and the dopants with low oxidation states. In particular, Li-ion pouch cells with Ta
5+
- and Mo
6+
-doped LiNi
0.91
Co
0.09
O
2
cathodes retain about 81.5% of their initial specific capacity after 3000 cycles at 200 mA g
−1
. Furthermore, physicochemical measurements and analyses suggest substantial differences in the grain geometries and crystal lattice structures of the various cathode materials, which contribute to their widely different battery performances and correlate with the oxidation states of their dopants.
The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (e.g., lithium metal, graphite, and silicon) leads to rapid capacity fade and ...poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi0.61Co0.12Mn0.27O2, over the course of 3000 charge–discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid–electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (e.g., fast charging) or stoichiometric restraints (e.g., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathode in a disrupted SEI. This insidious effect is found to initiate at a very early stage of cell operation (<200 cycles) and can be effectively inhibited by substituting a small amount of aluminum (∼1 mol %) in the cathode, resulting in much reduced transition-metal dissolution and drastically improved cyclability. Our results may also be applicable to studying the unstable electrodeposition of lithium on other substrates, including Li metal.
•Biochar amendment reduced ESP and increased the water stable aggregate percentage.•Increases in the percentage water stable aggregate enhanced maize growth.•Biochar decreased maize Na uptake ...resulting in decreased salt stress.•Biochar was a beneficial amendment for reclaimed tidal land.
Reclaimed tidal land soil (RTLS) often contains high levels of soluble salts and exchangeable Na that can adversely affect plant growth. The current study examined the effect of biochar on the physicochemical properties of RTLS and subsequently the influence on plant growth performance. Rice hull derived biochar (BC) was applied to RTLS at three different rates (1%, 2%, and 5% (w/w)) and maize (Zea mays L.) subsequently cultivated for 6weeks. While maize was cultivated, 0.1% NaCl solution was supplied from the bottom of the pots to simulate the natural RTLS conditions. Biochar induced changes in soil properties were evaluated by the water stable aggregate (WSA) percentage, exchangeable sodium percentage (ESP), soil organic carbon contents, cation exchange capacity, and exchangeable cations. Plant response was measured by growth rate, nutrient contents, and antioxidant enzyme activity of ascorbate peroxidase (APX) and glutathione reductase (GR). Application of rice hull derived biochar increased the soil organic carbon content and the percentage of WSA by 36–69%, while decreasing the ESP. The highest dry weight maize yield was observed from soil which received 5% BC (w/w), which was attributed to increased stability of water-stable aggregates and elevated levels of phosphate in BC incorporated soils. Moreover, increased potassium, sourced from the BC, induced mitigation of Na uptake by maize and consequently, reduced the impact of salt stress as evidenced by overall declines in the antioxidant activities of APX and GR.
Detailed analysis of the microstructural changes during lithiation of a full‐concentration‐gradient (FCG) cathode with an average composition of LiNi0.75Co0.10Mn0.15O2 is performed starting from its ...hydroxide precursor, FCG Ni0.75Co0.10Mn0.15(OH)2 prior to lithiation. Transmission electron microscopy (TEM) reveals that a unique rod‐shaped primary particle morphology and radial crystallographic texture are present in the prelithiation stage. In addition, TEM detected a two‐phase structure consisting of MnOOH and Ni(OH)2, and crystallographic twins of MnOOH on the Mn‐rich precursor surface. The formation of numerous twins is driven by the lattice mismatch between MnOOH and Ni(OH)2. Furthermore, the twins persist in the lithiated cathode; however, their density decrease with increasing lithiation temperature. Cation disordering, which influences cathode performance, is observed to continuously decrease with increasing lithiation temperature with a minimum observed at 790 °C. Consequently, lithiation at 790 °C (for 10 h) produced optimal discharge capacity and cycling stability. Above 790 °C, an increase in cation disordering and excessive coarsening of the primary particles lead to the deterioration of electrochemical properties. The twins in the FCG cathode precursor may promote the optimal primary particle morphology by retarding the random coalescence of primary particles during lithiation, effectively preserving both the morphology and crystallographic texture of the precursor.
Crystallographic twins form by the precipitation of MnOOH in full‐concentration‐gradient precursors, Ni0.75Co0.10Mn0.15(OH)2, for Li‐ion batteries. The twins persist in cathodes through lithiation, but with varying density depending on the temperature of lithiation. The twin density influences the size and crystallographic orientation of primary particles in cathodes, which unequivocally affect their electrochemical properties.
Potassium–sulfur (K–S) batteries are emerging as low‐cost and high‐capacity energy‐storage technology. However, conventional K–S batteries suffer from two critical issues that have not yet been ...successfully resolved: the dissolution of potassium polysulfides (KPS) into the liquid electrolyte and the formation of K dendrites on the K metal anode, which lead to inadequate cycling efficiencies with a low reversible capacity. Herein, a high‐capacity and long cycle‐life K–S battery consisting of a highly concentrated electrolyte (HCE) (4.34 mol kg−1 potassium bis(fluorosulfonyl)imide in a 1,2‐Dimethoxyethane) and a sulfurized polyacrylonitrile (SPAN) cathode is presented The application of a HCE efficiently suppresses the dendritic growth of K, as evidenced by operando optical imaging and phase field modeling, owing to the reduced K‐ion depletion on the electrode surface and a uniform Faradaic current density over the K metal anode surface. Additionally, because S is covalently bonded to the C backbone of PAN in the SPAN structure, the SPAN cathode inhibits the dissolution of KPS. These features generate synergy that the proposed K–S battery can provide a practical areal capacity of 2.5 mAh cm−2 and unprecedented lifetimes with high Coulombic efficiencies over 700 cycles.
Highly concentrated electrolyte using 4.34 mol kg−1 potassium bis(fluorosulfonyl)imide dissolved in a 1,2‐dimethoxyethane solvent enables the dendrite‐free K metal anode and shows good compatibility with sulfurized polyacrylonitrile cathode, thereby demonstrating the unprecedented high‐areal capacity and long lifetime of potassium–sulfur batteries.
This Perspective discusses the prospective strategies for overcoming the stability and capacity trade-off associated with increased Ni content in layered Ni-rich LiNi x Co y Mn z O2 (NCM) and LiNi ...x Co y Al z O2 (NCA) cathodes. The Ni-rich NCM and NCA cathodes have largely replaced the LiCoO2 cathodes in commercial batteries because of their lower cost, higher energy density, good rate capability, and reliability that has been extensively field-tested. Nevertheless, they suffer from microcrack generation along grain boundaries and Ni3+/4+ reactivity that rapidly deteriorate electrochemical performance. Doping and coating have been efficient strategies in delaying the onset of the damage, but they fail to overcome the degradation. There are, however, alternative strategies that directly counter the inherent degradation through micro- and nanostructural modifications of the Ni-rich NCM and NCA cathodes.
Fluorine doping of a compositionally graded cathode, with an average concentration of LiNi
0.80
Co
0.05
Mn
0.15
O
2
, yields a high discharge capacity of 216 mA h g
−1
with unprecedented cycling ...stability by retaining 78% of its initial capacity after 8000 cycles. The cathode is cycled at 100% depth of discharge (DOD), unlike the currently deployed layered cathode whose DOD is limited to 60-80% to compensate for capacity fading and guarantee the required battery life. Additionally, the capacity and cycling stability of the cathode easily surpass those of the existing state-of-the-art batteries, while achieving the energy density goal of 800 W h kg
−1
cathode
for electric vehicles (EV) with ultra-long cycle life. The structural and chemical stabilities of the cathode were provided by the compositional partitioning and unique microstructure of the compositionally graded cathode combined with the ordered site-intermixing of Li and transition metal (TM) ions discovered
via
transmission electron microscopy. F doping induced the formation of a 2
a
hex
× 2
a
hex
×
c
hex
superlattice from ordered Li occupation in TM slabs and
vice versa
, which has been proven to be essential for suppressing microcrack formation in deeply charged states, while maintaining the structural stability of the cathode during extended cycling. Furthermore, the proposed cathode allows for the recycling of used EV batteries in energy storage systems, thereby alleviating the negative environmental impact by reducing the CO
2
emissions and cost associated with disposing of dead batteries.
The observed ultra-long battery life of 8000 cycles demonstrated by the Ni-rich compositionally graded NCM cathode stems mainly from the cation ordered structure.
Electrochemical properties and structural and thermal stability of LiNi0.65Co0.13Mn0.22O2 (FCG65), LiNi0.75Co0.08Mn0.17O2 (TSFCG75), and LiNi0.85Co0.05Mn0.10O2 (TSFCG85) with concentration ...gradients of Ni and Mn were evaluated to comprehensively demonstrate the effectiveness of compositional gradation for a wide range of Ni-rich LiNi x Co y Mn1–x–y O2 (NCM) cathodes. The discharge capacities of FCG65, TSFCG75, and TSFCG85 were 194.2, 206.8, and 222.2 mAh g–1, respectively with capacity retention of over 90% after 100 cycles. The high capacities and enhanced cycling stability relative to those of conventional Ni-rich NCM cathodes were attributed to the compositional partitioning, strong crystallographic texture, and unique particle morphology. In addition, the highly correlated particle orientation helped to reduce the anisotropic internal strain induced by Li removal/extraction from the Ni-rich NCM cathodes. The accelerated aging test (storing the delithiated cathodes in an electrolyte at elevated temperature) reconfirmed the superior stability of the TSFCG85 cathode compared to the commercial LiNi0.82Co0.14Al0.04O2 cathode, which exhibited fast structural degradation. Thus, NCM cathodes with concentration gradients represent a viable solution that simultaneously addresses the specific energy density, cycling and chemical stability, and safety issues of Ni-enriched NCM cathodes for general electromobility.
Many remediation options have been applied to the heavy metal-contaminated agricultural soils nearby abandoned mining sites mainly due to hazard effects of heavy metals to human through agricultural ...crop dietary. Hence, the current study was carried to examine the heavy metal immobilizing effect of biochar produced from rice hull and subsequent heavy metal uptake by lettuce. Rice hull biochar was incorporated into a heavy metal-contaminated upland soil at six application rates (0, 0.5, 1, 2, 5, and 10 % (v/v)) and soil biochar mixtures were examined using both incubation and pot trials for cultivation of lettuce. Incubation studies showed that biochar incorporation induced significant declines (>80 %) in the phytoavailable metal pool as assessed via 1 M NH₄NO₃ extraction, possibly due to increased heavy metal adsorption onto the applied biochar and increases in soil pH. Similar results were also observed in pot trials, where the uptake of heavy metals by lettuce was significantly reduced as biochar application rate increased. Despite the significant decline in soil phytoavailable metal pools, lettuce growth still declined as biochar application rate increased. This was attributed to the adsorption of available nitrogen on to the biochar resulting in nitrogen deficiency. Therefore, when the biochar is used for metal immobilization in agricultural soils, maintaining soil nutrient status should be also considered to ensure optimum growth of the crop plants besides metal immobilization rate.
A self-passivating Li2ZrO3 layer with a thickness of 5–10 nm, which uniformly encapsulates the surfaces of LiNiO2 cathode particles, is spontaneously formed by introducing excess Zr (1.4 atom %). A ...thin layer of Li2ZrO3 on the surface is converted into a stable impedance-lowering solid–electrolyte interphase layer during subsequent cycles. The Zr-doped LiNiO2 cathode with an initial discharge capacity of 233 mA·h·g–1 exhibited significantly improved capacity retention (86% after 100 cycles) and thermal stability, compared to the undoped LiNiO2. While the spontaneously formed Zr-rich coating layer provides surface protection, the Zr ions in the LiNiO2 lattice delay the detrimental phase transition occurring in the deeply charged state of LiNiO2 and partially suppress the anisotropic strain emerging from the phase transition. Further optimization of the proposed simultaneous coating and doping strategy can mitigate the inherent structural instability of the LiNiO2 cathode, making it a promising high-energy-density cathode for electric vehicles.
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