Practical Li-ion Batteries Research Articles

Reversible Configurations of 3-Coordinate and 4-Coordinate Boron Stabilize Ultrahigh-Ni Cathodes with Superior Cycling Stability for Practical Li-Ion Batteries.

Ultrahigh-Ni layered oxide cathodes are the leading candidate for next-generation high-energy Li-ion batteries owing to their cost-effectiveness and ultrahigh capacity. However, the increased Ni content causes larger volume variations and worse lattice oxygen stability during cycling, resulting in capacity attenuation and kinetics hysteresis. Herein, a Li2SiO3-coated Li(Ni0.95Co0.04Mn0.01)0.99B0.01O2 ultrahigh-Ni cathode that well-addresses all the above issues, which is also the first time to realize the real doping of B ions is demonstrated. The as-obtained cathode delivers a reversible capacity of up to 237.4 mAh g-1 (924 Wh kg-1 cathode) and a superior capacity retention of 84.2% after 500 cycles at 1C in pouch-type full-cells. Advanced characterizations and calculations verify that the boron-doping is existed in terms of 3-coordinate and 4-coordinate configurations and their high electrochemical reversibility during de-/lithiation, which greatly stabilizes oxygen anions and impedes Ni-ion migration to Li layer. Furthermore, the B-doping engineers the primary particle microstructure for better relaxing the lattice strain and accelerating Li-ion diffusion. This work advances the energy density of cathode materials into the domain of above 900 Wh kg-1, and the concept will inspire more intensive study on ultrahigh-Ni cathodes.

Thermal runaway prevention through scalable fabrication of safety reinforced layer in practical Li-ion batteries

Integrating safety features to cut off excessive current during accidental internal short circuits in Li-ion batteries (LIBs) can reduce the risk of thermal runaway. However, making this concept practical requires overcoming challenges in both material development and scalable manufacturing. Here, we demonstrate the roll-to-roll production of a safety reinforced layer (SRL) on current collectors at a rate of 5 km per day. The SRL, made of molecularly engineered polythiophene (PTh) and carbon additives, interrupts current flow during voltage drops or overheating without adversely affecting battery performance. Impact testing on 3.4-Ah pouch cells shows that the SRL reduces battery explosions from 63% to 10%. This work underscores the potential of integrating material science with manufacturing technology to enhance battery safety.

Densification of Alloying Anodes for High Energy Lithium-Ion Batteries: Critical Perspective on Inter- Versus Intra-Particle Porosity.

High Li-storage-capacity particles such as alloying-based anodes (Si, Sn, Ge, etc.) are core components for next-generation Li-ion batteries (LIBs) but are crippled by their intrinsic volume expansion issues. While pore pre-plantation represents a mainstream solution, seldom do this strategy fully satisfy the requirements in practical LIBs. One prominent issue is that porous particles reduce electrode density and negate volumetric performance (WhL-1) despite aggressive electrode densification strategies. Moreover, the additional liquid electrolyte dosage resulting from porosity increase is rarely noticed, which has a significant negative impact on cell gravimetric energy density (Whkg-1). Here, the concept of judicious porosity control is introduced to recalibrate existing particle design principles in order to concurrently boost gravimetric and volumetric performance, while also maintaining the battery's cycle life. The critical is emphasized but often neglected role that intraparticle pores play in dictating battery performance, and also highlight the superiority of closed pores over the open pores that are more commonly referred to in the literature. While the analysis and case studies focus on silicon-carbon composites, the overall conclusions apply to the broad class of alloying anode chemistries.

A green aqueous binder to enhance the electrochemical performance of Li-rich disordered rock salt cathode material

Li-rich disordered rock-salt oxides (DRX) are considered an attractive cathode material in the future battery field due to their excellent energy density and specific capacity. Nevertheless, anionic redox provides high capacity while causing O2 over-oxidation to O2, resulting in voltage hysteresis and capacity decay. Herein, the crystal structure of Li1.3Mn0.4Ti0.3O1.7F0.3 (LMTOF) cathode is stabilized by using sodium carboxymethylcellulose (CMC) binders replacing traditional polyvinylidene difluoride (PVDF) binders. The electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) reveal that the CMC-based LMTOF electrode has higher electronic conductivity and lithium-ion diffusion kinetics. Moreover, CMC has been demonstrated to improve the O2– reversibility, reduce the amounts of byproducts from electrolyte decomposition and suppress transition metal dissolution by Na+/Li+ exchange reaction. Furthermore, the CMC-based LMTOF electrode also exhibits less volume change upon lithiation/delithiation processes compared to the PVDF-based electrode, resulting in enhanced structural stability during cycling. Benefiting from these features, the CMC binders can effectively improve the cycling life and rate performance of the LMTOF cathode, and the CMC-based LMTOF electrode shows good capacity retention of 94.5 % after 30 cycles at 20 mA/g and 66.7 % after 100 cycles at 200 mA/g. This finding indicates that CMC as a binder can efficiently stabilize the structure and improve the electrochemical performance of Li-rich disordered rock-salt oxides cathode, making it possible for practical Li-ion battery applications.

Si Nanowires: From Model System to Practical Li-Ion Anode Material and Beyond.

Nanowire (NW)-based anodes for Li-ion batteries (LIBs) have been under investigation for more than a decade, with their unique one-dimensional (1D) morphologies and ability to transform into interconnected active material networks offering potential for enhanced cycling stability with high capacity. This is particularly true for silicon (Si)-based anodes, where issues related to large volumetric expansion can be partially mitigated and the cycle life can be enhanced. In this Perspective, we highlight the trajectory of Si NWs from a model system to practical Li-ion battery anode material and future prospects for extension to beyond Li-ion batteries. The study examines key research areas related to Si NW-based anodes, including state-of-the-art (SoA) characterization approaches followed by practical anode design considerations, including NW composite anode formation and upscaling/full-cell considerations. An outlook on the practical prospects of NW-based anodes and some future directions for study are detailed.

Evolution of Phases at the Surface and Interface of Mn Based Spinel Cathode with Coating Layer - a Spectroscopic Investigation

Surface modifications, commonly termed coatings or artificial interphases, are known to mitigate secondary reactions of charged cathodes with organic electrolyte and limit surface reconstruction. As a result, better electrochemical stability has been observed for coated cathodes in both liquid and solid electrolyte-based Li ion batteries (LIBs). However, these coatings, in contact with electrolyte, can be dynamic and evolve during processing stages or electrochemical cycling.In this work we investigate the interphases between spinel cathodes and two coating layers, LiNbO3 and Al2O3. The spinel LiMn2O4 (LMO) cathode and its doped variant LiMn1.5Ni0.5O4 (LMNO), owing to their three-dimensional structure, have high-rate and high-power capability with moderate energy density. With conventional electrolytes, the surface transition metal undergoes reduction forming thin binary or layered ternary oxides when charged beyond 4.2V (vs Li), restricting Li ion transport, and thereby compromising accessible capacity. This along with dissolution of manganese by HF (generated at the liquid electrolyte-electrode interface) restricts long-term applicability in practical LIBs thus necessitating surface coating or doping. In our experiments we choose epitaxial thin-film cathodes and thin-film coating materials. These provide large interface, and hence interphase areas, of well-defined crystal orientation, facilitating characterisation to deepen our understanding of the surface reactions occurring. We form an epitaxial film of cathode material using pulsed laser deposition (PLD) followed by controlled deposition of Al2O3 via atomic layer deposition (ALD) or LiNbO3 via PLD.We will present the detailed characterisation analysis of coated and uncoated spinel thin films. The epitaxial nature and crystal structure of deposited thin films are confirmed using thin film X-ray diffraction. Structurally, the phase diagram of Li-Mn(Ni)-O is complicated with many possible crystal structures with varying lithium content as well as different oxidation states of manganese. Hence, we employ a combination of X-ray absorption and photoelectron spectroscopies (XAS/XPS) to look at the chemical states of Mn ion in the cathode and Nb and Al ions in LiNbO3 and Al2O3 coating layers. For the as deposited fresh samples, the effect of deposition conditions is evaluated using XAS of the Mn L-edge and Al K-edge. XPS depth profiles of elemental distribution in the thin film heterostructures are obtained at three different incident X-ray energies (up to 6.6 kV) – thus providing chemical information from the surface, coating and at the interface of coating and cathode layers. Subsequently we electrochemically cycled these films in organic electrolyte against Li metal anode and further spectroscopic investigations were carried out. The effect of Al2O3 vs LiNbO3 coatings on retaining the structure of cathode material is probed and we will discuss the understanding thereby developed.

Implanting Transition Metal into Li2 O-Based Cathode Prelithiation Agent for High-Energy-Density and Long-Life Li-Ion Batteries.

Compensating the irreversible loss of limited active lithium (Li) is essentially important for improving the energy-density and cycle-life of practical Li-ion battery full-cell, especially after employing high-capacity but low initial coulombic efficiency anode candidates. Introducing prelithiation agent can provide additional Li source for such compensation. Herein, we precisely implant trace Co (extracted from transition metal oxide) into the Li site of Li2 O, obtaining (Li0.66 Co0.11 □0.23 )2 O (CLO) cathode prelithiation agent. The synergistic formation of Li vacancies and Co-derived catalysis efficiently enhance the inherent conductivity and weaken the Li-O interaction of Li2 O, which facilitates its anionic oxidation to peroxo/superoxo species and gaseous O2 , achieving 1642.7 mAh/g~Li2O prelithiation capacity (≈980 mAh/g for prelithiation agent). Coupled 6.5 wt % CLO-based prelithiation agent with LiCoO2 cathode, substantial additional Li source stored within CLO is efficiently released to compensate the Li consumption on the SiO/C anode, achieving 270 Wh/kg pouch-type full-cell with 92 % capacity retention after 1000 cycles.

Engineering manganese-rich phospho-olivine cathode materials with exposed crystal {0 1 0} facets for practical Li-ion batteries

Manganese-rich LiMn1-yFeyPO4 (e.g., LiMn0.7Fe0.3PO4) is emerging as the most promising olivine cathode material after LiFePO4, which has a current market demand of >500000 tons per year. However, its commercial application is challenging because of its poor kinetic properties. Although nanocrystallization is a transformative paradigm for improving the kinetics, it results in the concomitant problem of increasing the specific surface area of the material, which leads to more interfacial side reactions. Here, we develop a polyol solvothermal method to boost the particle size (decrease the specific surface area) whilst simultaneously regulating the crystal orientation (improving the kinetics) of LiMn0.7Fe0.3PO4. Importantly, the synthesis can be used at the ton scale, with the off-take potential reaching 1000 tons per year. Cobalt doping and carbon coating are combined to further increase the kinetic properties. Electrochemical measurements demonstrate that the diffusion of the Li+ kinetics is increased by 58.6 % and 46.1 % for the Fe2+/3+ and Mn2+/3+ redox couple during charging and 92.0 % and 21.2 % during discharging, respectively. A capacity of 150 mAh g−1 at a 5C rate is then delivered. In full batteries (14000 mAh), the capacity retention reaches 89.6 % over 1000 cycles at a 1C rate.

High Initial Coulombic Efficiency of SiO Enabled by Controlling SiO2 Matrix Crystallization.

SiO is a promising anode material for practical Li-ion batteries because it can achieve a much higher capacity than graphite and a better capacity retention than Si. However, SiO suffers from poor initial Coulombic efficiency (ICE). Here, we report on a fundamentally different approach to increase the low ICE of SiO while achieving high capacity and long-term cycle stability compared to previous approaches such as electrochemical/chemical pre-lithiation processes. To enhance the ICE, the long-range/short-range orders of amorphous SiO2 in SiO are increased by the chemical reaction of a small amount of LiOH·H2O even at a much lower temperature (900 °C) than the reported. The increased crystallization of SiO2 substantially reduces the irreversible electrochemical reaction of SiO. As a result, the Li-added SiO shows substantially increased ICE, ∼82.7%, which is one of the highest values. Furthermore, we demonstrate that controlling the crystallization of SiO can enable us to achieve high ICE, high reversible capacity, and superior capacity retention (∼100% at 1C rate for 100 cycles) in SiO simultaneously. The understanding and findings will pave the way to design high-capacity SiO with high ICE and long-term stability for practical high energy density Li batteries.

Operando Quantified Lithium Plating Determination Enabled by Dynamic Capacitance Measurement in Working Li‐Ion Batteries

AbstractThe access to full performance of state‐of‐the‐art Li‐ion batteries (LIBs) is hindered by the mysterious lithium plating behavior. A rapid quantified lithium plating determination method compatible with actual working conditions is an urgent necessity for safe working LIBs. In this contribution, the relationship between electrical double layer (EDL) capacitance and electrochemical active surface area (ECSA) of graphite anodes during the Li‐ion intercalation and Li plating processes is unveiled. We propose an operando lithium plating determination method based on the dynamic capacitance measurement (DCM) test. Reasonable selection of alternating current (AC) frequency protects the anodic responses from the interference of cathodic responses, which allows DCM to be applied in practical LIBs. The onset of lithium plating can be quantitatively traced, demonstrating the promise for real‐time operando determination for lithium plating in a working battery.

Operando Quantified Lithium Plating Determination Enabled by Dynamic Capacitance Measurement in Working Li‐Ion Batteries

The access to full performance of state-of-the-art Li-ion batteries (LIBs) is hindered by the mysterious lithium plating behavior. A rapid quantified lithium plating determination method compatible with actual working conditions is an urgent necessity for safe working LIBs. In this contribution, the relationship between electrical double layer (EDL) capacitance and electrochemical active surface area (ECSA) of graphite anodes during the Li-ion intercalation and Li plating processes is unveiled. We propose an operando lithium plating determination method based on the dynamic capacitance measurement (DCM) test. Reasonable selection of alternating current (AC) frequency protects the anodic responses from the interference of cathodic responses, which allows DCM to be applied in practical LIBs. The onset of lithium plating can be quantitatively traced, demonstrating the promise for real-time operando determination for lithium plating in a working battery.

Weakly Solvating Solution Enables Chemical Prelithiation of Graphite-SiOx Anodes for High-Energy Li-Ion Batteries.

Although often overlooked in anode research, the anode's initial Coulombic efficiency (ICE) is a crucial factor dictating the energy density of a practical Li-ion battery. For next-generation anodes, a blend of graphite and Si/SiOx represents the most practical way to balance capacity and cycle life, but its low ICE limits its commercial viability. Here, we develop a chemical prelithiation method to maximize the ICE of the blend anodes using a reductive Li-arene complex solution of regulated solvation power, which enables a full cell to exhibit a near-ideal energy density. To prevent structural degradation of the blend during prelithiation, we investigate a solvation rule to direct the Li+ intercalation mechanism. Combined spectroscopy and density functional theory calculations reveal that in weakly solvating solutions, where the Li+-anion interaction is enhanced, free solvated-ion formation is inhibited during Li+ desolvation, thereby mitigating solvated-ion intercalation into graphite and allowing stable prelithiation of the blend. Given the ideal ICE of the prelithiated blend anode, a full cell exhibits an energy density of 506 Wh kg-1 (98.6% of the ideal value), with a capacity retention after 250 cycles of 87.3%. This work highlights the promise of adopting chemical prelithiation for high-capacity anodes to achieve practical high-energy batteries.

Scalable synthesis of interconnected hollow Si/C nanospheres enabled by carbon dioxide in magnesiothermic reduction for high-performance lithium energy storage

Silicon (Si) anode has great potential for use in practical Li-ion batteries due to large specific capacity beyond that of conventional graphite. The main challenges for Si are large volume changes (~400%) during (de)alloying with lithium caused material cracking and pulverization, instability of solid electrolyte interphase (SEI) layer and electric contact loss. Herein, we demonstrate a novel interconnected hollow Si/C nanospheres with thin shells consisting of Si crystals and highly wrinkled amorphous carbon layers synthesized by introducing carbon dioxide (CO2) as a green carbon source in magnesiotherimic reduction to accelerate the commercialized application of Si-based anodes. Interconnected carbon networks in the Si intervals and MgO as cores generate simultaneously via the reaction between CO2 and excess Mg vapor. Additionally, hollow structure can be realized after the removal of in-situ generated MgO templates by acid etching. Unique interconnected Si/C hybrid delivers a high capacity, impressive cycling performance and good Coulombic efficiency, benefiting from the improved Li+ ions transportation and electron transfer kinetics and the volume butter effects of hollow architecture. In particular, such new synthetic route is low-cost and easily scaled up, which probably facilitates the commercial application of Si/C hybrids for high energy Li-ion batteries.

Building a Cycle-Stable Fe-Si Alloy/Carbon Nanocomposite Anode for Li-Ion Batteries through a Covalent-Bonding Method.

Si is being intensively developed as a safe and high-performance anode for next-generation Li-ion batteries (LIBs); however, its battery application still remains challenging because of its low cycling Coulombic efficiency. To address this issue, we chose a conjugated polymer, polynaphthalene, as a carbon precursor and a low-cost commercial ferrosilicon (Fe-Si) alloy as the active phase to prepare a Fe-Si/C nanocomposite with a core-shell-like architecture through sand milling-assisted covalent-bonding method, followed by a carbonization reaction, thus forming a covalently bonded carbon coating on the surfaces of Fe-Si alloy nanoparticles. Benefitting from the greatly reduced volumetric expansion of Fe-Si alloy cores in the lithiation process and the stable interface provided by the outer carbon shell, the thus-prepared Fe-Si/C nanocomposite exhibits a high structural stability in repeated charge/discharge cycles. The experimental results reveal that the Fe-Si/C composite anode can demonstrate a high reversible capacity of 1316.2 mA h g-1 with an active mass utilization of 82.6%, a long-term cycle stability of more than 1000 cycles even at a considerably high current rate of 2.0 A g-1, and, in particular, a high cycling Coulombic efficiency of 99.7%, showing great prospect for application in practical LIBs.

Lithium Diffusion in Copper.

Copper is the conventional, broadly applied anode current collector in lithium-ion batteries, because Li does not form intermetallic alloys with Cu at room temperature. Fast diffusion and trapping of lithium in copper were, however, suggested in the past, and the involved diffusion mechanisms are still not clarified. By using three complementary methods, we determine grain boundary and lattice diffusion of lithium in copper. We show that indiffusion into copper is possible not only from metallic lithium deposits at the surface but also from a Li+-containing electrolyte. Lattice diffusion (D0 = 3.9 × 10-9 cm2/s; Ea = 0.68 eV) and grain boundary diffusion (D0 = 1.5 × 10-11 cm2/s; Ea = 0.36 eV) are found to be 13 orders of magnitude lower than previously published. Furthermore, for practical Li-ion battery considerations, lithium trapping in copper current collectors, which relies heavily on operating temperature and morphology, is discussed.

Problems and their origins of Ni-rich layered oxide cathode materials

Ni-rich layered oxides, LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) with x ​+ ​y ​+ ​z ​= ​1 and x ​≥ ​0.8, are regarded to be the best choice for the cathode material of high energy Li-ion batteries due to their combined advantages in capacity, working potential and manufacture cost. However, their application in practical Li-ion batteries is hindered by two essential problems of (1) performance degradation and (2) safety hazard over the whole life of battery. Performance degradation behaves as declines in battery's capacity and working voltage as well as the battery's swelling and impedance growth; Safety hazard arises from thermal runaway under abuse conditions such as overcharging, overheating, and electric shorting. It appears that nearly all problems can be ultimately attributed to the loss of oxygen, especially caused by the oxidation of lattice oxygen in H3 phase where the capacities are contributed by both of the Ni and O redox couples. In this review, the problems and their origins of Ni-rich layered oxides are overviewed, and the solutions attempted to mitigate these problems are outlined.

Surfactant-assisted synthesis of ultrathin two-dimensional Co3O4 nanosheets for applications in lithium-ion batteries and ultraviolet photodetector

Ultrathin two-dimensional (2D) Co3O4 nanosheets were prepared by surfactant-assisted self-assembly method. We demonstrate a high reversible capacity and an excellent rate capability of ultrathin 2D Co3O4 nanosheets as anodes in Li ion batteries. At a current density of 100 mA g−1, the nanosheets maintain an extraordinary capacity of 1868.6 mA h g−1 after 30 discharge/charge cycles, and nearly 100% capacity retention. When the current is increased to 400 mA g−1, 112% of the capacity can be retained. With their ease of large area synthesis and superior electrochemical properties, the 2D Co3O4 nanosheets will be interesting for practical Li ion batteries. Additionally, 2D Co3O4 nanosheets also showed both high stability and reproducibility as ultraviolet photodetector.

Mn-Doped Fe1- xMn xF3·0.33H2O/C Cathodes for Li-Ion Batteries: First-Principles Calculations and Experimental Study.

Increasing attention has been paid on iron fluoride as an alternative cathode material for Li-ion batteries (LIBs) owing to its high energy density and low cost. However, the poor electric conductivity and low diffusivity for Li-ions set great challenges for iron fluoride to be used in practical LIBs. Here, we employ first-principles calculations to probe the influence of Mn-doping on the crystal structure and electronic structure of FeF3·0.33H2O. The calculated results suggest that Mn-doping can enlarge the hexagonal cavity and reduce the band gap of FeF3·0.33H2O as well as improve its intrinsic conductivity. Furthermore, Fe1- xMn xF3·0.33H2O/C ( x = 0, 0.06, 0.08, and 0.10) nanocomposites were successfully fabricated by a hydrothermal method and ball-milling. Owing to the Mn-doping effect combined with highly conductive acetylene black (AB) modification, the typical Fe0.92Mn0.08F3·0.33H2O/C composite exhibits a high discharge capacity of 180 mA h g-1 at 50 mA g-1 after 100 cycles and delivers excellent cycling stability as well as good rate capability.

Red phosphorus composite anodes for Li-ion batteries

Thickness changes associated with charging and discharging challenge the practical application of electrodes composed of high-capacity materials towards batteries of both high energy density and long life. The investigation on the electrode level has found that the red phosphorus composite electrodes experience reversible expansion and shrinkage during lithiation/delithiation, except for the first cycle. The reversible thickness changes are acceptable for the practical application, and the thickness change is only 4 μm, which is about 7% of the total thickness when the capacity density of the electrode is 4.5 mAh cm−2. 4.5 mAh cm−2 is the upper limitation of the capacity density for practical Li-ion batteries. The capacity of the electrode material is 800 mAh g−1 with coulombic efficiency of 99.7%. Such high capacity, high coulombic efficiency, and low electrode thickness change show promise of the red phosphorus composite as a practical anode for lithium-ion batteries. This investigation pushes forward the practical application of red phosphorus composite anodes.

Origin of charge storage in cobalt oxide - Anchored graphene nanocomposites

Prospects of transition metal oxide (TMO) anodes in practical Li-ion batteries are limited despite their high capacity, owing to conversion reaction-driven inefficiencies and poor cycle life. Size confinement of TMOs and compositing them with carbon architectures is an established approach to realize high-performance electrodes. Here, we report cobalt oxide nanoparticles anchored on graphene (CoG) nanocomposite for Li-ion batteries; the anode exhibits a reversible capacity of 1270 mA h g−1 at 2 C rate and delivers 770 mA h g−1 even at a high rate of 50 C (44.5 Ag-1) of which >99% is retained at the end of 1000 cycles. Although many papers have reported exorbitant high capacity and rate performance for graphene–3d metal oxide composites, the nature of charge storage in these nanocomposites remains unidentified particularly in the voltage region of conversion reaction. By using cobalt oxide-anchored graphene as a model system, we reveal that the charge storage is a collective response from conversion/intercalation and pseudocapacitive processes. In addition, the CoG composite anode reported here provides excellent chemical stability and high durability as witnessed in terms of high capacity, impressive rate performance, and long cycle life. This study illustrates the benefits of nanoarchitecturing toward designing high-performance electrodes.