Next-generation Li-ion Batteries Research Articles

Design and synthesis of cellulose nanofiber-derived CoO/Co/C two-dimensional nanosheet toward enhanced and stable lithium storage

Nano-sized two-dimensional carbonaceous materials have been widely used as the matrix for alloying-type and conversion-type anode materials for Li-ion batteries (LIBs) to improve structural stability and rate performance. However, relevant synthesis usually requires rigorous conditions and chronic reaction processes. Herein, we have designed a simple solvothermal reaction and heat treatment to prepare a novel CoO/Co/C two-dimensional nanosheet (CoO/Co/C 2DNS) by adopting cellulose nanofibers (CNFs) as the precursor. The unique characteristics of CNFs facilitate the uniform distribution of active materials on the surface and the construction of two-dimensional nanostructure via self-assembly. It is worth noting that CoO/Co/C 2DNS exhibits a striking synergistic effect since the porous 2D carbon framework offers additional pseudo-capacitance and enhances the electronic conductivity, while the ultrafine active materials encapsulated inside shorten the Li-ions diffusion pathways and relieve the volume change. Benefit from the unique structure, the composite anode delivered outstanding rate performance (∼500 mAh g−1 at 10 A g−1) and superior long-range cycling performance up to 800 cycles even at 2 A g−1. This work provides a new strategy for the synthesis of nano-sized 2D composite, offering a promising route to construct high performance conversion-type anodes for next-generation LIBs.

A Molten-Salt Method to Synthesize Ultrahigh-Nickel Single-Crystalline LiNi0.92 Co0.06 Mn0.02 O2 with Superior Electrochemical Performance as Cathode Material for Lithium-Ion Batteries.

Ni-rich layered oxides have been intensively considered as promising cathode materials for next-generation Li-ion batteries. Nevertheless, the performance degradation caused by intergranular cracks and electrode/electrolyte interface parasitic reactions restricts their further application. Compared with secondary particles, single-crystal (SC) materials have better mechanical integrity and cycling stability. However, the preparation of ultrahigh-nickel layered SC cathodestill remains a serious challenge. Herein, a novel LiOH-LiNO3 -H3 BO3 molten-salt method is proposed to synthesize SC LiNi0.92 Co0.06 Mn0.02 O2 with considerable crystallinity and uniformity. The critical impacts of calcination temperature and boric acid on the microstructure and electrochemical property of Ni-rich layered oxides are systematically investigated. The results show that the crystal growth is promoted and the stability of crystal structure is improved by this synthesis method. In particular, the optimal electrode demonstrates a superior initial discharge capacity of 214.8 mAh g-1 with a high capacity retention of 86.3% over 300 cycles as tested by pouch-type full cells at 45ºC. This work not only prepares an ultrahigh-nickel layered CS cathode with superior electrochemical performances, but also provides a feasible method for the synthesis of other CS layered cathode materials.

Li-MOF-based ions regulator enabling fast-charging and dendrite-free lithium metal anode

Li metal has been regarded as the holy grail for the next-generation Li-ion battery. Li dendrites issues, however, impede its practical application. In general, prolonging the sand time of Li nucleation and regulating homogeneous Li+ flux are effective approaches to suppress the dendrites formation and growth. Regarding this view, a functional polypropylene (PP) separator is developed to regulate ion transportation via a newly designed Li-based metal-organic framework (Li-MOF) coating. The Li-MOF crystallizes in the orthorhombic space group P212121 and features a double-walled three-dimensional (3D) structure with 1D channels. The well-defined intrinsic nanochannels of Li-MOF and the steric-hinerance effect both restrict free migration of anions, contributing to a high Li+ transference number of 0.65, which improve the Sand time of Li nucleation. Meanwhile, the Li-MOF coating with uniform porous structure promotes homogeneous Li+ flux at the surface of Li metal. Furthermore, the Li-MOF coating layer helps to build solid-electrolyte interphase (SEI) layer that comprises of inorganic LiF and Li3N, which further prohibits the dendrites growth. Consequently, a highly stable Li plating/stripping cycling for over 1000 h is achieved. The functional separator also enables high-performance full lithium metal cells, the high-rate and long-stable cycling performance of LiNi0.8Mn0.1Co0.1 (NMC811)-Li and LiCoO2 (LCO)-Li cells further demonstrate the feasibility of this concept.

Polydopamine‐induced nano‐coating layer for high stability of nickel‐rich cathode in secondary batteries

High-Ni layered-oxide cathodes are the most prospective cathode materials for next-generation Li-ion batteries (LIBs) in electric vehicles (EVs) owing to their high specific capacity. However, High-Ni layered-oxide cathode materials exhibit inferior cyclability and low thermal stability owing to the side reaction between Ni4+ and the electrolytes. To solve these surface-related problems, we proposed a strategy for forming LiNbO3 (LNO)—with outstanding thermal stability and ionic conductivity—on a Ni-rich layered-oxide surface using polydopamine (PDA). The PDA formed on the transition metal hydroxide surface has copious catechol OH groups, which attract the Nb ions in the solution to form a LNO coating layer during the calcination process. The LiNi0.8Co0.1Mn0.1O2 (pristine LNCM) electrode experiences enormous degradation when cycled after being subjected to severe conditions—such as a full charge and a 60°C storage test—but the LiNbO3-coated LNCM (LNO-LNCM) electrode exhibits particularly stable cycling performance. Furthermore, differential scanning calorimetry (DSC) results exhibited that the LNO coating notably ameliorated the thermal stability of the cathode material. As a result, our experimental results suggest that the development of cathode materials that can withstand greatly oxidized states and high-temperature environments is achievable.

Reversible anionic redox chemistry in layered Li4/7[□1/7Mn6/7]O2 enabled by stable Li–O-vacancy configuration

<h2>Summary</h2> The combination of anionic and cationic activities within Li-rich materials breaks through the traditional capacity limitation and achieves high-energy-density batteries. However, the utilization of anionic oxygen redox reactions always leads to detrimental lattice oxygen release, which accelerates structural distortion and electrochemical performance deterioration. In contrast to the typical Li–O–Li configuration in Li-rich layered oxides, not only can oxygen redox behaviors be triggered within layered Li_4/7[□_1/7Mn_6/7]O₂ (□: Mn vacancy) with Li–O-vacancy configuration, but lattice oxygen loss can be effectively suppressed. Upon Li⁺ (de)intercalations, Mn vacancy within the TM layer also enables reversible structural evolution and Li migration processes, further boosting high output capacity and long-term cycling stability. Besides, not only can the irreversible/reversible anionic/cationic redox reactions be clearly unraveled, but their capacity distributions can be roughly quantified upon cycling. Overall, our findings demonstrate that the introduction of Mn vacancy provides a promising configuration to achieve high-capacity cathode candidates for next-generation Li-ion batteries.

Al–Li alloys as bifunctional sacrificial lithium sources for prelithiation of high-energy-density Li-ion batteries

The low initial Coulombic efficiency of anodes such as Si@C can seriously affect the capacity of high-energy-density Li-ion batteries (LIBs). Supplement the initial irreversible lithium loss in the anode through prelithiation technology is the only way to realize the next generation of LIBs. In this work, we report the study of Al–Li alloy (ALA) as a prelithiation additive for LIBs cathodes. As a bifunctional sacrificial lithium source, ALA can not only provide an additional capacity of 1068 mAhg−1 to supplement the initial active lithium consumption, but also form aluminum and aluminum oxide to stabilize the cathode interface after the delithiation to improve the battery cycling stability. Therefore, the initial charge capacity of LiCoO2 (LCO) and LiNi0.6Co0.2Mn0.2O2 (NCM622) electrodes can be increased to 12.5%–18.5% by adding 2%–4% ALA. In addition, the energy density of the NCM811/Si@C pouch cell prelithiated by ALA can reach 541 Wh kg−1, which means that the cathode can maximize the capacity (from 189 mAh g−1 to 205 mAh g−1). In conclusion, this work develops a more inexpensive and efficient cathode prelithiation additive for next-generation LIBs.

Designing the Binder-Free Conversion-Based Manganese Oxide Nanofibers as Highly Stable and Rate-Capable Anode for Next-Generation Li-Ion Batteries

Designing the Binder-Free Conversion-Based Manganese Oxide Nanofibers as Highly Stable and Rate-Capable Anode for Next-Generation Li-Ion Batteries

Enhanced performance of Si-based Li-ion batteries through elastic cushioning with hollow graphene shells

Silicon (Si) is a promising anode material for next-generation Li-ion batteries. The nanometer-sized Si could alleviate the pulverization caused by large volume changes during deep cycling. However, compression between agglomerated Si particles causes Si cracking and electrode failure. Considering this, we engineered a mechanical cushioning space between Si particles via elastic hollow graphene shells (GSs) to flexibly buffer volume changes and maintain the stability of the electrode structure. The stress generated from the Si volume expansion during lithiation was mechanically buffered and gently released by compression of the hollow space of the GS. In this Si/GS composite electrode, GS also reduced the local agglomeration of Si particles and effectively improved the overall conductivity. Considering these advantages, the designed Si/GS electrode showed an enhanced cycling performance with more than 1200 mA h g−1 at 0.8 A g−1 and an excellent rate capability of 1025 mA h g−1 at 4 A g−1 after 200 cycles.

Coincident formation of trapped molecular O2 in oxygen-redox-active archetypical Li 3d oxide cathodes unveiled by EPR spectroscopy

• Molecular O 2 trapped in the bulk is the main oxidized oxygen species in Li 3 d oxide cathodes • The suppression of out-of-plane cation migration does not refrain the formation of molecular O 2 • The local structural reversibility on oxygen redox depends on the inhibition of cation disorder Li-excess 3 d transition metal oxides with additional capacity contribution via oxygen redox are promising high-energy-density cathodes for next-generation Li-ion batteries. However, the chemical state of oxidized oxygen in the bulk of charged materials has been manifested very challenging to clarify and remains elusive. We herein apply the electron paramagnetic resonance (EPR) spectroscopy to uncover the oxidized oxygen states formed in the bulk of archetypical Li 3 d oxide cathodes on oxygen redox, including O3-Li 1.2 Ni 0.2 Mn 0.6 O 2 and Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , O2-Li 1.033 Ni 0.2 Mn 0.6 O 2 , and disordered rocksalt Li 1.2 Ti 0.4 Mn 0.4 O 2 . The results substantiate the coincident formation of molecular O 2 trapped in the bulk of charged cathodes, which can be reduced back to O 2− on discharging. The implication is that in contrary to the conventional wisdom, the suppression of out-of-plane cation migration does not refrain the formation of molecular O 2 . Moreover, the NMR study suggests that the local structural reversibility on oxygen redox depends on the inhibition of cation disorder rather than the formation of specific oxidized oxygen. This study advances our basic understanding of oxygen redox in Li-excess 3 d transition metal oxide cathodes. The coincident formation of trapped molecular O 2 on charging in four archetypical oxygen-redox-active Li 3 d oxide cathodes was certified by advanced EPR spectroscopy.

Asphericity Can Cause Nonuniform Lithium Intercalation in Battery Active Particles

Uniform intercalation is desired to enable next-generation Li-ion batteries. While we expect nonuniformity in materials undergoing a phase change, single-phase intercalation materials such as nickel manganese cobalt oxide are believed to lithiate uniformly at the particle/electrolyte interface. However, recent imaging reveals nonuniform lithiation. Motivated by this discrepancy, we examine if aspherical particle shape can cause such nonuniformity since the conventional belief is based on spherical particle theory. We obtain real particle geometries using rapid lab-based X-ray computed tomography and subsequently perform physics-based calculations accounting for electrochemical reactions at the particle/electrolyte interface and lithium transport inside the particle bulk. The aspherical geometry breaks the symmetry and causes nonuniform reaction distribution. Such nonuniformity is exacerbated as the particle becomes more aspherical. The proposed mechanism represents a fundamental limit on achievable lithiation uniformity in aspherical particles in the absence of other mechanisms causing inhomogeneity, such as grain structure, nonuniform carbon-binder coating, etc.

Anionic redox reaction and structural evolution of Ni-rich layered oxide cathode material

The Ni-rich layer-structured oxide is one of the most promising candidate cathode materials for the high energy-density Li-ion batteries. However, the commercial applications of these materials are hindered with drawbacks such as structural instability and poor cycling performance at high potentials. Herein, we comprehensively studied the oxygen redox reaction and the structural reversibility of LiNi0.83Co0.12Mn0.05O2 at deep delithiation using the synchrotron X-ray absorption spectroscopy, scanning transmission electron microscopy and density functional theory calculations. The oxygen redox occurs due to the cation mixing upon delithiation in this material though there are no Li-O-Li configurations in its pristine form. The formation of the I41 structure was attributed to the migration of the transition metals in the deeply delithiated material, extending the route of the phase transformation from the layered to the rock-salt structure. These findings are helpful to enrich the understanding of the origin of the oxygen redox and reveal its impact on the structural transformations in the Ni-rich layered oxides. These will spur new strategies to enhance the performance of the cathode materials for the next-generation Li-ion batteries.

In situ crosslinkable acrylic random copolymer binders for silicon anodes in lithium‐ion batteries

Silicon is in the spotlight as a promising anode material for next-generation Li-ion batteries. However, its practical application is limited by a rapid decay in capacity due to considerable volume changes. Rational design of binders that can exhibit strong adhesion and robust mechanical properties is crucial for overcoming such challenges. Herein, we synthesize a series of multifunctional acrylic random copolymers comprising various ratios of acrylic acid and glyceryl groups by free-radical polymerization. The adhesive and mechanical properties of the binders are systematically modulated, and their impact on the electrochemical properties of a Si-nanoparticle anode are investigated. Owing to the presence of both acrylic acid and hydroxyl groups, the copolymers containing 7 mol% and 25 mol% glyceryl group undergo in situ crosslinking under mild thermal treatment (70°C for 24 h). In particular, the copolymer containing 7 mol% glyceryl group exhibits the highest specific capacity and capacity retention (1170 mAh g−1 and 54% after 100 cycles at 0.5 A g−1, respectively), which is superior to those of a conventional poly(acrylic acid) binder (880 mAh g−1 and 52% after 100 cycles at 0.5 A g−1). The enhanced electrochemical properties attribute to the improved adhesive and mechanical properties enabled by the network structure.

Argyrodite-type advanced lithium conductors and transport mechanisms beyond paddle-wheel effect

Development of next-generation solid-state Li-ion batteries requires not only electrolytes with high room-temperature (RT) ionic conductivities but also a fundamental understanding of the ionic transport in solids. In spite of considerable work, only a few lithium conductors are known with the highest RT ionic conductivities ~ 0.01 S/cm and the lowest activation energies ~0.2 eV. New design strategy and novel ionic conduction mechanism are needed to expand the pool of high-performance lithium conductors as well as achieve even higher RT ionic conductivities. Here, we theoretically show that lithium conductors with RT ionic conductivity over 0.1 S/cm and low activation energies ~ 0.1 eV can be achieved by incorporating cluster-dynamics into an argyrodite structure. The extraordinary superionic metrics are supported by conduction mechanism characterized as a relay between local and long-range ionic diffusions, as well as correlational dynamics beyond the paddle-wheel effect.

Restriction of voltage decay by limiting low-voltage reduction in Li-rich oxide materials

Li-rich layered oxides are recognized as promising candidates for next-generation Li-ion batteries owing to the high capacity of >250 mAh g−1, but the severe voltage fade has prevented their commercialization. It is widely known that high-voltage charge processes result in layered-to-spinel structural evolution and voltage fade in Li-rich layered oxides. This work emphasizes that limiting the low-voltage reduction can maintain the structure and voltage stability of Li-rich layered oxides after the 4.6 V high-voltage charge processes. A strategy of limiting the low-voltage (<2.8 V) reduction by cycling at 4.6–2.8 V was performed in traditional Li1.2Ni0.13Mn0.54Co0.13O2 and high-Ni Li1.2Ni0.222Mn0.504Co0.074O2. After 300 cycles, traditional Li1.2Ni0.13Mn0.54Co0.13O2 and high-Ni Li1.2Ni0.222Mn0.504Co0.074O2 cycling at 4.6–2 V showed midpoint discharge voltages of 2.83 V and 2.97 V with high voltage fade rates of 2.25 mV/cycle and 2.24 mV/cycle, respectively. While the two materials cycling at 4.6–2.8 V can maintain discharge midpoint voltages of 3.34 V and 3.49 V, with low voltage decay rates of 0.692 mV/cycle and 0.632 mV/cycle, respectively. To better understand the voltage performance, their electric structures were calculated by density functional theory. Physical characterizations were also used to analyze their differences in structural evolution. The results suggested that limiting low-voltage reduction in Li-rich layered oxides is highly necessary for maintaining their structure and voltage stability.

Elucidating the Humidity-Induced Degradation of Ni-Rich Layered Cathodes for Li-Ion Batteries.

Ni-rich layered oxides, in a general term of Li(NixCoyMn1-x-y)O2 (x > 0.5), are widely recognized as promising candidates for improving the specific energy and lowering the cost for next-generation Li-ion batteries. However, the high surface reactivity of these materials results in side reactions during improper storage and notable gas release when the cell is charged beyond 4.3 V vs Li+/Li0. Therefore, in this study, we embark on a comprehensive investigation on the moisture sensitivity of LiNi0.85Co0.1Mn0.05O2 by aging it in a controlled environment at a constant room-temperature relative humidity of 63% up to 1 year. We quantitatively analyze the gassing of the aged samples by online electrochemical mass spectrometry and further depict plausible reaction pathways, accounting for the origin of the gas release. Transmission electron microscopy reveals formation of an amorphous surface impurity layer of ca. 10 nm in thickness, as a result of continuous reactions with moisture and CO2 from the air. Underneath it, there is another reconstructed layer of ca. 20 nm in thickness, showing rock salt/spinel-like features. Our results provide insight into the complex interfacial degradation phenomena and future directions for the development of high-performance Ni-rich layered oxides.

Structural Heterogeneity Induced Li Dendrite Growth in Li0.33La0.56TiO3 Solid-State Electrolytes

Solid-state electrolytes (SSEs) are driving next-generation Li-ion batteries (LIBs) with higher energy density and improved safety compared with organic liquid electrolytes. However, the gradual Li dendrite growth during cycling is still a critical issue limiting the long-term service of SSEs, the mechanism of which remains largely unclear. Here, we investigate the Li dendrite growth-induced short circuiting of Li0.33La0.56TiO3 (LLTO) ceramic pellets through detailed electron microscopy and spectroscopy analysis. Under both electrochemical cycling and thermal chemical reaction between Li and LLTO, we find that the Li dendrites prefer to nucleate at the voids in the LLTO pellet, followed by vertical growth along the grain boundaries, and finally result in the buildup of internal stress and the cracking of LLTO. In addition, Li dendrite growth accompanies the decomposition of Li0.33La0.56TiO3 because of the reduction of Ti4+ to Ti3+, which inevitably alters the bulk diffusion of Li ions.

Effect of lithium salt type on silicon anode for lithium-ion batteries

Silicon (Si) is one of the most promising anode materials in the next generation of Li-ion batteries. However, the application of Si is restricted by its unsatisfactory electrochemical performance. This work investigates the influence of lithium salt type on the electrochemical performance of Si anode, and shows that lithium salt type plays an importing role in determining the electrochemical performance of Si anode. Through investigation and optimization, lithium hexafluorophosphate (LiPF6)-lithium bis(fluorosulfonyl)imide (LiFSI)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ternary composite lithium salt with a mole ratio of 7:1:2 exhibits the best cycling stability and rate capability. It retains a high capacity of 1879.8 mAh g−1 after 400 cycles at 0.5 C charge and discharge, and still maintains 1851.4 mAh g−1 at 30 C; which are significantly higher than the 583.3 and 316.4 mAh g−1 of the LiPF6-based electrolyte under the same conditions. The underlying mechanism is investigated, and the results indicate that the lithium type has an effect on both the Si anode and the lithium counter electrode, and the synergistic effect of LiPF6-LiFSI-LiTFSI enables high-rate and long-cycle Si anodes.

Dilute Electrolyte to Mitigate Capacity Decay and Voltage Fading of Co-Free Li-Rich Cathode for Next-Generation Li-Ion Batteries.

Li-rich cathodes have potential for use in next-generation Li-ion batteries (LIBs) owing to their high specific capacity and low cost. However, their intrinsic cycling decay and voltage fading limit practical applications. In addition, these cathodes contain Co, which is nonrenewable, scarce, and expensive. This situation severely limits the rapid and sustainable development of low-cost LIBs. This paper introduces a novel dilute electrolyte to overcome these limitations based on the Co-free Li-rich Li1.2Mn0.54Ni0.26O2 (LMNO) cathode. An even and robust cathode-electrolyte interface (CEI) formed on the surface of LMNO further protects it from side reactions in the dilute electrolyte. This Co-free Li-rich cathode exhibits the best electrochemical performance reported to date among Li-rich cathodes in terms of outstanding cycling stability (capacity retention of 99.8% at 0.5 C) and dramatically suppressed voltage fading (only 0.3% after 100 cycles). This study demonstrates the potential of Co-free Li-rich cathodes for applications in next-generation LIBs.

Cover Feature: Lithium Storage Properties of TiC‐Modified SnS2 Nanosheets (ChemElectroChem 6/2022)

The Cover Feature illustrates that SnS2/TiC nanosheets synthesized by combining a DC arc-discharge plasma method and subsequent sulfurization, possessing higher surface area, reversible capacity and specific capacity, are expected to be an ideal candidate anode material for high-performance anodes in next-generation Li-ion batteries. More information can be found in the Research Article by Y. Ren, Q. Shi and G. Zhang.

Encapsulating a Responsive Hydrogel Core for Void Space Modulation in High-Stability Graphene-Wrapped Silicon Anodes.

Due to its formidably high theoretical capacity (3590 mAh/g at room temperature), silicon (Si) is expected to replace graphite as the dominant anode for higher energy density lithium (Li)-ion batteries. However, stability issues stemming from silicon's significant volume expansion (∼300%) upon lithiation have slowed down commercialization. Herein, we report the design of a scalable process to engineer core-shell structures capable of buffering this volume expansion, which utilize a core made up of a poly(ethylene oxide)-carboxymethyl cellulose hydrogel and silicon protected by a crumpled graphene shell. The volume expansion of the hydrogel upon exposure to water creates a void space between the Si-Si and Si-rGO interfaces within the core when the gel dries. Unlike sacrificial spacers, the dehydrated hydrogel remains in the core and acts as an elastic Li-ion conductor, which improves the stability and high rate performance. The optimized composite electrodes retain ∼81.7% of their initial capacity (1055 mAh/(grGO+gel+Si)) after 320 cycles when an active material loading of 1 mg/cm2 is used. At more practical mass loadings (2.5 mg/cm2), the electrodes achieve 2.04 mAh/cm2 and retain 79% of this capacity after 200 cycles against a lithium half-cell. Full cells assembled using a lithium ion phosphate cathode lose only 6.7% of their initial capacity over 100 cycles, demonstrating the potential of this nanocomposite anode for use in next-generation Li-ion batteries.