Nickel-rich Cathode Research Articles

Molecular anchoring of free solvents for high-voltage and high-safety lithium metal batteries

Constraining the electrochemical reactivity of free solvent molecules is pivotal for developing high-voltage lithium metal batteries, especially for ether solvents with high Li metal compatibility but low oxidation stability ( <4.0 V vs Li+/Li). The typical high concentration electrolyte approach relies on nearly saturated Li+ coordination to ether molecules, which is confronted with severe side reactions under high voltages ( >4.4 V) and extensive exothermic reactions between Li metal and reactive anions. Herein, we propose a molecular anchoring approach to restrict the interfacial reactivity of free ether solvents in diluted electrolytes. The hydrogen-bonding interactions from the anchoring solvent effectively suppress excessive ether side reactions and enhances the stability of nickel rich cathodes at 4.7 V, despite the extremely low Li+/ether molar ratio (1:9) and the absence of typical anion-derived interphase. Furthermore, the exothermic processes under thermal abuse conditions are mitigated due to the reduced reactivity of anions, which effectively postpones the battery thermal runaway.

Mg/Al Double-Pillared LiNiO2 as a Co-Free Ternary Cathode Material Ensuring Stable Cycling at 4.6 V.

Cobalt-free (Co-free) and nickel-rich (Ni-rich) cathode materials have attracted significant attention and undergone extensive studies due to their affordability and superior energy density. However, the commercialization of these Co-free materials is hindered by challenges such as cation disorder, irreversible phase changes, and inadequate high-voltage performance. To overcome these challenges, a Co-free ternary cathode material of Mg/Al double-pillared LiNiO2 (NMA) synthesized via a wet-coating and lithiation-sintering technique is proposed. Fundamental studies reveal that Mg and Al have the potential to form a distinctive double-pillar structure within the layered cathode, enhancing its structural stability. To be specific, the strategic placement of Mg and Al in Li and Ni layers, respectively, effectively reduces Li+/Ni2+ disorder and prevents irreversible phase transitions. Additionally, the inclusion of Mg and Al refines the primary grains and compacts the secondary grains in the cathode material, reducing stress from cyclic usage and preventing material cracking, thereby mitigating electrolyte erosion. As a result, NMA demonstrates exceptional electrochemical performance under a high charge cutoff voltage of 4.6 V. It maintains 70% of initial specific capacity after 500 cycles at 1 C and exhibits excellent rate performance, with a capacity of 162 mAh g-1 at 5 C and 149 mAh g-1 at 10 C. As a whole, the produced NMA achieves a high structural stability in cases of excessive delithiation, providing a groundbreaking solution for the development of cost-effective and high-energy-density cathode materials for lithium-ion batteries.

Kirkendall effect-induced uniform stress distribution stabilizes nickel-rich layered oxide cathodes

Nickel-rich layered oxide cathodes promise ultrahigh energy density but is plagued by the mechanical failure of the secondary particle upon (de)lithiation. Existing approaches for alleviating the structural degradation could retard pulverization, yet fail to tune the stress distribution and root out the formation of cracks. Herein, we report a unique strategy to uniformize the stress distribution in secondary particle via Kirkendall effect to stabilize the core region during electrochemical cycling. Exotic metal/metalloid oxides (such as Al2O3 or SiO2) is introduced as the heterogeneous nucleation seeds for the preferential growth of the precursor. The calcination treatment afterwards generates a dopant-rich interior structure with central Kirkendall void, due to the different diffusivity between the exotic element and nickel atom. The resulting cathode material exhibits superior structural and electrochemical reversibility, thus contributing to a high specific energy density (based on cathode) of 660 Wh kg−1 after 500 cycles with a retention rate of 86%. This study suggests that uniformizing stress distribution represents a promising pathway to tackle the structural instability facing nickel-rich layered oxide cathodes.

Stabilizing LiNi0.8Co0.1Mn0.1O2 cathode by combined moisture and HF digestion/adsorption for high-performance lithium metal batteries

Nickel-rich layered oxide cathodes such as LiNi0.8Co0.1Mn0.1O2 are promising to significantly increase the energy density of lithium metal batteries beyond 350 Wh kg−1. However, serious issues regarding cycle stability still remain when matching with conventional non-aqueous carbonate electrolytes that contain fluorine such as lithium hexafluorophosphate (LiPF6). Hydrolysis of LiPF6 generates corrosive hydrofluoric acid (HF), which destroys the cathode structure and accelerates the cathodic dissolution/anodic deposition of transition metal (TM) ions. Here, we demonstrate that ball milling NCM811 with carbon-coated aluminum nitride (AlN-C) remarkably enhances the capacity retention. AlN-C acts both as a scavenger and as an adsorption center to digest and adsorb H2O and HF, respectively. Thereby, it prevents the dissolution of TM ions, which would result in capacity decay and damage to the lithium metal anode. It is demonstrated that the addition of AlN-C via wet ball milling with NCM811 enables retaining a specific capacity of 149.9 mA h g−1 after 250 cycles (capacity retention: 85.2 %) at 1 C even in a high moisture electrolyte containing ∼0.2 % (v/v) H2O. Therefore, this work shows up a pathway to a rational enhancement of the capacity retention and cycle life of nickel-rich cathodes.

Smart-responsive sustained-release capsule design enables superior air storage stability and reinforced electrochemical performance of cobalt-free nickel-rich layered cathodes for lithium-ion batteries

Nickel-rich layered oxide stands as one of the most promising cathodes in demand for higher energy density of lithium-ion batteries (LIBs) in next generation. While increasing nickel content brings more capacity, it also makes this kind of cathode more vulnerable to the ambient, both the air outside the cell and the electrolyte inside, causing aggravated storage, structural and thermal instability. The cathode surface, as the first line of defense against the ambient attack, is the essential place to address these issues. Enlightened by the mechanism of “sustained-release capsule”, here we decorate the polydimethylsiloxane (PDMS), a skin with exceptional moisture-resistance and chemical stability, onto the surface of LiNi0.9Mn0.1O2. This PDMS skin demonstrated the smart response to the surrounding environment that the hydrophobic surface guarantees the ambient air storage stability by cutting off residual alkali accumulation and the protective role of coating could be relayed as another functional mechanism once entering the battery. The detrimental HF species generated from water-induced electrolyte decomposition are effectively captured and eliminated to defend cathode corrosion and enhance interfacial stability during long-term cycling. Attributed to the seamless protection from the outside to the inside of the battery, this well-capsuled Ni-rich cathode exhibits negligible capacity fading compared with fresh state even after long ambient exposure, and realizes superior cycling and thermal stability. This work demonstrates new guidelines to design smart-responsive coatings for cathode materials to reduce their susceptibility to the surrounding environment, towards improving both ambient storage stability and cycling stability.

Mechanism Behind the Loss of Fast Charging Capability in Nickel-Rich Cathode Materials.

Fast charging technology for electric vehicles (EVs), offering rapid charging times similar to conventional vehicle refueling, holds promise but faces obstacles owing to kinetic issues within lithium-ion batteries (LIBs). Specifically, the significance of cathode materials in fast charging has grown because Ni-rich cathodes are employed to enhance the energy density of LIBs. Herein, the mechanism behind the loss of fast charging capability of Ni-rich cathodes during extended cycling is investigated through a comparative analysis of Ni-rich cathodes with different microstructures. The results revealed that microcracks and the resultant cathode deterioration significantly compromised the fast charging capability over extended cycling. When thick rocksalt impurity phases form throughout the particles owing to electrolyte infiltration via microcracks, the limited kinetics of Li+ ions create electrochemically unreactive areas under high-current conditions, resulting in the loss of fast charging capability. Hence, preventing microcrack formation by tailoring microstructures is essential to ensure stability in fast charging capability. Understanding the relationship between microcracks and the loss of fast charging capability is essential for developing Ni-rich cathodes that facilitate stable fast charging upon extended cycling, thereby promoting widespread EV adoption.

Nickel-Rich Cathode Yarn for Wearable Lithium-Ion Batteries

Nickel-Rich Cathode Yarn for Wearable Lithium-Ion Batteries

Investigating the Path Dependent Aging Behavior of Nickel Cobalt Aluminum Oxide Cathode Batteries During High C-rate Cycling Conditions

Nickel-rich cathode material batteries such as the nickel cobalt aluminum oxide with graphite anode are common in the automotive sector due to their high energy density and power performance capabilities, however, they are limited in lifetime performance. Accelerated degradation in specific operation conditions, such as high C-rates are known to significantly contribute to this issue. To better understand a chronological dependence of these high-stress conditions occurring during battery lifetime, a path dependent aging study is performed using profiles inspired by high-performance race operation. The focus on C-rates >1C during charging and discharging using real-world inspired profiles- known to induce particle cracking or lithium plating- addresses the need to understand aging behavior in less studied, but highly relevant high-performance automotive context. The aging conditions were tailored to induce specific degradation modes to better identify potential degradation mode coupling. Using differential voltage and capacity analysis techniques, degradation modes were identified which likely contributed to path dependent aging behavior, including loss of lithium inventory and loss of active material in the positive electrode. Two critical paths were identified in this study where later high C-rate conditions in the form of fast-charging at temperatures of 25 °C resulted in accelerated aging and where loss of lithium inventory induced stresses in the positive electrode, accelerating loss of active material.

Mg/Fe site-specific dual-doping to boost the performance of cobalt-free nickle-rich layered oxide cathode for high-energy lithium-ion batteries

Layer-type LiNi0.9Mn0.1O2 is promising to be the primary cathode material for lithium-ion batteries (LIBs) due to its excellent electrochemical performance. Unfortunately, the cathode with high nickel content suffers from severely detrimental structural transformation that causes rapid capacity attenuation. Herein, site-specific dual-doping with Fe and Mg ions is proposed to enhance the structural stability of LiNi0.9Mn0.1O2. The Fe3+ dopants are inserted into transition metal sites (3b) and can favorably provide additional redox potential to compensate for charge and enhance the reversibility of anionic redox. The Mg ions are doped into the Li sites (3a) and serve as O2−-Mg2+-O2− pillar to reinforce the electrostatic cohesion between the two adjacent transition-metal layers, which further suppress the cracking and the generation of harmful phase transitions, ultimately improving the cyclability. The theoretical calculations, including Bader charge and crystal orbital Hamilton populations (COHP) analyses, confirm that the doped Fe and Mg can form stable bonds with oxygen and the electrostatic repulsion of O2−-O2−can be effectively suppressed, which effectively mitigates oxygen anion loss at the high delithiation state. This dual-site doping strategy offers new avenues for understanding and regulating the crystalline oxygen redox and demonstrates significant potential for designing high-performance cobalt-free nickel-rich cathodes.

Enhanced reversibility of single crystal Ni-rich cathode materials via Ti doping

Single crystal nickel-rich cathodes have been widely studied in the field of lithium-ion batteries (LIBs) due to their high volumetric energy density and good structural/electrochemical stability. However, a larger particle size (∼ 5 µm) prolongs the diffusion path of Li+ and leads to poor rate performance. In this work, a modification strategy of Ti4+ doping was used to prepare single-crystal Ni-rich cathodes LiNi0.88Co0.06Mn0.06O2 with good rate performance. Compared to the polycrystalline Ni-rich cathode, the modified cathodes will have wider lithium channels to strip and embed lithium ions more easily. Concurrently, the secure Ti-O bonds can not only maintain the transition metal layer but also inhibit the “air sensitive effect”. After 100 cycles, the electrochemical performance shows that the modified cathodes with 1 at.% Ti4+ doping have a comparatively high original capacity of 193.8 mAh g − 1 and an upgraded capacity retention of ∼ 93.6 % (2.8–4.3 V) at 1 C. A better rate performance (118.6 mAh g − 1) can be achieved at 10 C. This discovery will provide a good research direction for improving the insufficiency of single crystal nickel-rich cathodes.

Pushing High Capacity with Thermodynamically Stable Interface for Single Crystalline Nickel-rich Cathode

Pushing High Capacity with Thermodynamically Stable Interface for Single Crystalline Nickel-rich Cathode

Stabilizing LiNi0.8Co0.1Mn0.1O2 cathodes with a mixed ionic-electronic conducting Li0.34La0.55MnO3-x multifunctional coating formed via in-situ conversion of surface Li residual

In this work, we for the first time utilize the harmful surface Li residual on NCM811 to in-situ form a mixed Li+/electron conducting Li0.34La0.55MnO3-x (LLMO) coating. The formation of the (electro)chemically stable LLMO coating not only achieves effective surface cleaning, but also stabilizes the cathode surface against electrolyte attack, alleviating structure degradation and intergranular cracking. Equally importantly, the mixed conducting LLMO layer affords considerably high Li+ and electronic conductivities (2.35 ×10−5 S/cm and 1.86 ×10−3 S/cm respectively), accelerating the charge-transfer process at the interface. The in-situ LLMO-coated NCM811 exhibits notable improvements in both rate and cycling performance, featuring a capacity retention rate of 82.51% over 100 cycles at 1 C in stark contrast to 48.26% of the pristine NCM811. When combined with a dendrite-suppressed Li@Pb@carbon cloth composite Li metal anode in a full battery, a high capacity retention rate of 86.96% over 200 cycles at 1 C and a N/P ratio of 37.7 is achieved, significantly outperforming that with NCM811 (42.24%, 40.2). This study provides a novel and comprehensive solution to stabilize nickel-rich layered cathode materials for high-energy-density Li-metal batteries.

State of Charge-Dependent Impedance Spectroscopy as a Helpful Tool to Identify Reasons for Fast Capacity Fading in All-Solid-State Batteries.

Thiophosphate-based all-solid-state batteries (ASSBs) are considered the most promising candidate for the next generation of energy storage systems. However, thiophosphate-based ASSBs suffer from fast capacity fading with nickel-rich cathode materials. In many reports, this capacity fading is attributed to an increase of the charge transfer resistance of the composite cathode caused by interface degradation and/or chemo-mechanical failure. The change in the charge transfer resistance is typically determined using impedance spectroscopy after charging the cells. In this work, we demonstrate that large differences in the long-term cycling performance also arise in cells, which exhibit a comparable charge transfer resistance at the cathode side. Our results confirm that the charge transfer resistance of the cathode is not necessarily responsible for capacity fading. Other processes, such as resistive processes on the anode side, can also play a major role. Since these processes usually depend on the state of charge, they may not appear in the impedance spectra of fully charged cells; i.e., analyzing the impedance spectra of charged cells alone is insufficient for the identification of major resistive processes. Thus, we recommend measuring the impedance at different potentials to get a complete understanding of the reasons for capacity fading in ASSBs.

Revealing proton-coupled exchange mechanism in aqueous ion-exchange synthesis of nickel-rich layered cathodes for lithium-ion batteries

Ion exchange is a promising synthetic method for alleviating severe cation mixing in traditional layered oxide materials for lithium-ion batteries, leading to enhanced structural stability. However, the underlying mechanisms of ion exchange are still not fully understood. Such a fundamental study of the ion-exchange mechanism is needed for achieving the controllable synthesis of layered oxides with a stable structure. Herein, we thoroughly unearth the underlying mechanism that triggers the ion exchange of Ni-rich materials in aqueous solutions by examining time-resolved structural evolution combined with theoretical calculations. Our results reveal that the reaction pathway of ion exchange can be divided into two steps: protonation and lithiation. The proton is the key to achieving charge balance in the ion exchange process, as revealed by X-ray adsorption spectroscopy and inductive coupled plasma analysis. In addition, the intermediate product shows high lattice distortion during ion exchange, but it ends up with a most stable product with high lattice energy. Such apparent discrepancies in lattice energy between materials before and after ion exchange emphasize the importance of synthetic design in structural stability. This work provides new insights into the ion-exchange synthesis of Ni-rich oxide materials, which advances the development of cathode materials for high-performance lithium-ion batteries.

A breathable inorganic–organic interface for fabricating a crack-free nickel-rich cathode with long-term stability

A thin molecular level surface modification layer is constructed for a nickel-rich layered oxide cathode to boost long-term cycling stability.

Simultaneous modulation of cathode/anode and electrolyte interfaces via a nitrile additive for high-energy-density lithium-metal batteries.

Nickel-rich layered oxides have great potential for commercial development applications, so it is critical to address their stability over long cycles. Ensuring long-term cycle stability relies heavily on the stability of the interface between the electrode and electrolyte in Li|LiNi0.8Co0.1Mn0.1O2 (NCM811) batteries. In this work, a denser, more stable and thinner nickel-rich cathode/electrolyte interface was constructed by electrolyte engineering with succinonitrile (SN) as an additive. The increase of organic compound content in the formed Ni-rich cathode/electrolyte interface can fully release the stress and strain generated during repetitive charge-discharge processes, and significantly reduce the irreversible phase transition during the nickel-rich cathode charge-discharge processes. Additionally, this interface impedes the breakdown of electrolytes and the dissolution of transition metals. Furthermore, the addition of SN additives also forms a more stable lithium metal anode/electrolyte interface. Notably, batteries containing SN additives (0.5, 1.0 and 1.5 wt%) show excellent electrochemical performance compared to base electrolytes. Particularly, the improvement is most significant with an SN addition of 1.0 wt%. After 250 cycles at 1C rate, the capacity retention rate of the battery improved by 32.8%. Thus, this work provides a new perspective for simultaneously constructing a stable interface of nickel-rich cathode and lithium metal anode with a high energy density in lithium metal batteries.

Aluminium doping in single-crystal nickel-rich cathodes: insights into electrochemical degradation and enhancement

Al doped single-crystal nickel-rich NCMA cathode materials are considered one of the most promising candidates for automobile Li-ion batteries due to their high compacted density and superior cycling stability.

Enhancing humidity resistance of nickel-rich layered cathode materials by low water-soluble CaF2 coating.

A low water-solubility but hydrophilic coating of CaF2 is demonstrated to be effective in mitigating the susceptibility of nickel-rich cathodes to moisture and even water. The ability of the cathode to resist water erosion is not inherently linked to either hydrophobicity or hydrophilicity, but lies in robust chemical bonding within the protective layer exhibiting low water solubility.

Rational rock-salt phase engineering of a nickel-rich layered cathode interface for enhanced rate and cycling stability

Engineering the rock-salt phase by Al–N co-doping has been realized for nickel-rich layered cathodes, enhancing Li+ diffusion kinetics, electric conductivity, chemical stability, and mechanical coherence for mitigating chemo-mechanical degradation.

Synthesis of Fe/Mg-doped NMC6 22 from Spent Nickel Catalyst as Lithium-Ion Battery Cathode

The co-precipitation approach, along with nickel-rich (NMC622) cathode materials, magnesium, and Fe doping, was used to produce nickel-rich NMC (NMC622) cathode materials from spent nickel catalysts. Both X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were utilized in order to carry out the characterization of the NMC622 materials. The structural study showed that the doped materials had a structure that was equal to that of Li[Ni0,6Mn0,2Co0,2Xy]O2, which has a layered hexagonal structure similar to that of α-NaFeO2. The electrochemical test found that Mg 1 mol% had the highest discharge capacity at 99.61 mAh/g. This was determined by the results of the test. The use of magnesium as a dopant in structurally stable, Ni-rich NMC materials led to an increase in the electrochemical capacity of the Mg-doped NMC. Magnesium exhibited a significant amount of potential as a dopant. It is necessary to do additional research into the functional testing of magnesium as a doping material in order to maximize its use for a longer cycle life and improved thermal stability lithium ion batteries.