Impact of Electrolyte on Direct-Contact Prelithiation of Silicon-Graphite Anodes in Lithium-Ion Cells with High-Nickel Cathodes.

Silicon-based anodes offer high specific capacities to enhance the energy density of lithium-ion batteries, but are severely hindered by the immense volume expansion and subsequent breakage of the solid-electrolyte-interphase (SEI) during cycling. Herein, we utilize an effective strategy, known as direct-contact prelithiation, to mitigate the challenges associated with expansion and surface instability in SiOx/graphite (SG) anodes. It involves introducing lithium into the anode via physical contact with lithium metal and electrolyte before cycling. Prelithiation of SG anodes with an advanced localized high-concentration electrolyte is shown to develop a mechanically robust artificial SEI that tolerates better the electrode volume expansion. The modified SG anode paired with the high-Ni cathode LiNi0.90Mn0.05Co0.05O2 delivers a high initial capacity of 191 mA h g-1 with 80% capacity retention over 150 cycles, compared to 46% retention with a conventional electrolyte. The bolstered SEI layer with reduced surface reactivity is due to the reduced electrolyte consumption and regulated SEI formation during cycling. Furthermore, the advanced electrolyte and fortified SG anode help reduce cathode degradation, transition-metal dissolution, and loss of active lithium. This study highlights viable prelithiation strategies to stabilize Si-based anodes for high-energy-density batteries through electrolyte design.

Three-Dimensional Carbon Nanotubes Buffering Interfacial Stress of the Silicon/Carbon Anodes for Long-Cycle Lithium Storage.

Silicon/graphite composites show a high specific capacity and improved cycling stability. However, the intrinsic difference between silicon and graphite, such as unequal volume expansion and lithium-ion diffusion kinetics, causes persistent stress at the silicon/graphite interface and the expansion of the electrical isolation region. Herein, carbon nanotubes (CNTs) were successfully introduced into silicon/carbon composites via ball milling and spray drying, which effectively relieved the stress concentration at the direct contact interface and formed a three-dimensional conductive structure. In addition, CNTs and amorphous carbon acting as "lubricants" further improved the inherent differences between silicon and graphite. As a result, the Si/CNTs/G@C-1 anode increased the cycling performance and rate capability, with a reversible capacity of up to 465 mAh g-1 after 500 cycles at 1 A g-1 and superior rate performance of 523 mAh g-1 at 2 A g-1. It is believed that this strategy may provide a feasible preparation of large-scale high-content silicon-based nanocomposite anodes in lithium-ion batteries.

Revisiting the Electrochemical Impedance Spectroscopy of Porous Electrodes in Li-ion Batteries by Employing Reference Electrode.

Electrochemical impedance spectroscopy (EIS), characterized by its non-destructive and in-situ nature, plays a crucial role in comprehending the thermodynamic and kinetic processes occurring with Li-ion batteries. However, there is a lack of consistent and coherent physical interpretations for the EIS of porous electrodes. Therefore, it is imperative to conduct thorough investigations into the underlying physical mechanisms of EIS. Herein, by employing reference electrode in batteries, we revisit the associated physical interpretation of EIS at different frequency. Combining different battery configurations, temperature-dependent experiments, and elaborated distribution of relaxation time analysis, we find that the ion transport in porous electrode channels and pseudo-capacitance behavior dominate the high-frequency and mid-frequency impedance arcs, respectively. This work offers a perspective for the physical interpretation of EIS and also sheds light on the understanding of EIS characteristics in other advanced energy storage systems.

Sequential Effect of Dual-Layered Hybrid Graphite Anodes on Electrode Utilization During Fast-Charging Li-Ion Batteries.

To recharge lithium-ion batteries quickly and safely while avoiding capacity loss and safety risks, a novel electrode design that minimizes cell polarization at a higher current is highly desired. This work presents a dual-layer electrode (DLE) technology via sequential coating of two different anode materials to minimize the overall electrode resistance upon fast charging. Electrochemical impedance spectroscopy and distribution of relaxation times analysis revealed the dynamic evolution of electrode impedances in synthetic graphite (SG) upon a change in the state of charge (SOC), whereas the natural graphite (NG) maintains its original impedance regardless of SOC variation. This disparity dictates the sequence of the NG and SG coating layers within the DLE, considering the temporal SOC gradient developed upon fast charging. Simulation and experimental results suggest that DLE positioning NG and SG on the top (second-layer) and bottom (first-layer), respectively, can effectively reduce the overall resistance at a 4 C-rate (15-min charging), demonstrating two times higher capacity retention (61.0%) over 200 cycles than its counterpart with reversal sequential coating, and is higher than single-layer electrodes using NG or NG/SG binary mixtures. Hence, this study can guide the combinatorial sequence for multi-layer coating of various active materials for a lower-resistivity, thick-electrode design.

Regulation of high value-added carbon nanomaterials by DC arc plasma using graphite anodes from spent lithium-ion batteries.

With the extensive use of lithium-ion batteries (LIBs), neglecting to recycle graphite anodes from LIBs leads to environmental pollution and the waste of graphite resources. Thus, developing an efficient and environment-protecting approach to reusing spent graphite anodes is necessary. Here, high value-added graphene sheets (GS), carbon nanohorns (CNHs), fluorine-doped CNHs (F-CNHs), and amorphous carbon nanoballs (ACNs) were prepared from spent graphite anodes of LIBs via DC arc plasma. In order to control the conversion of spent graphite anodes into various carbon nanomaterials, the growth mechanism of carbon nanomaterials is investigated by quenching rate. Benefiting from the extremely high quenching rates (>1.8 × 106 K/s) produced by DC arc plasma, the particle size of the prepared ACNs and CNHs is small and evenly distributed. The CNHs show a "dahlia-like" structure, and the number of graphene layers is only 3-8. Furthermore, the structural transformation mechanism of carbon nanomaterials is researched by deposition temperature. The ACNs, few-layer GS, and CNHs produced by the high quenching rates are unstable and prone to structural transformation. When these carbon nanomaterials are deposited on the cathode surface and cathode holder, the ACNs, "dahlia-like" CNHs, and GS undergo processes of fusing and overlaying at high temperatures, respectively, resulting in the agglomeration and increased particle size of ACNs and "seed-like" CNHs. Meanwhile, the GS is bent and converted into carbon nanocages (CBCs). Overall, the carbon nanomaterials prepared using spent anodes from LIBs by arc plasma are a facile, environment-friendly, and economical strategy to achieve high value-added utilization of the graphite.

Interphase Engineering Enhanced Electro-chemical Stability of Prelithiated Anode.

Prelithiation is an essential technology to compensate for the initial lithium loss of lithium-ion batteries due to the formation of solid electrolyte interphase (SEI) and irreversible structure change. However, the prelithiated materials/electrodes become more reactive with air and electrolyte resulting in unwanted side reactions and contaminations, which makes it difficult for the practical application of prelithiation technology. To address this problem, herein, interphase engineering through a simple solution treatment after chemical prelithiation is proposed to protect the prelithiated electrode. The used solutions are carefully selected, and the composition and nanostructure of the as-formed artificial SEIs are revealed by cryogenic electron microscopy and X-ray photoelectron spectroscopy. The electrochemical evaluation demonstrates the unique merits of this artificial SEI, especially for the fluorinated interphase, which not only enhances the interfacial ion transport but also increases the tolerance of the prelithiated electrode to the air. The treated graphite electrode shows an initial Coulombic efficiency of 129.4%, a high capacity of 170 mAh g-1 at 3 C, and negligible capacity decay after 200 cycles at 1 C. These findings not only provide a facile, universal, and controllable method to construct an artificial SEI but also enlighten the upgrade of battery fabrication and the alternative use of advanced electrolytes.

Quantifying the Influence of Li Plating on a Graphite Anode by Mass Spectrometry.

The prominent problem with graphite anodes in practical applications is the detrimental Li plating, resulting in rapid capacity fade and safety hazards. Herein, secondary gas evolution behavior during the Li-plating process was monitored by online electrochemical mass spectrometry (OEMS), and the onset of local microscale Li plating on the graphite anode was precisely/explicitly detected in situ/operando for early safety warnings. The distribution of irreversible capacity loss (e.g., primary and secondary solid electrolyte interface (SEI), dead Li, etc.) under Li-plating conditions was accurately quantified by titration mass spectroscopy (TMS). Based on OEMS/TMS results, the effect of typical VC/FEC additives was recognized at the level of Li plating. The nature of vinylene carbonate (VC)/fluoroethylene carbonate (FEC) additive modification is to enhance the elasticity of primary and secondary SEI by adjusting organic carbonates and/or LiF components, leading to less "dead Li" capacity loss. Though VC-containing electrolyte greatly suppresses the H2/C2H4 (flammable/explosive) evolution during Li plating, more H2 is released from the reductive decomposition of FEC.

Interface Engineering via Regulating Electrolyte for High-Voltage Layered Oxide Cathodes-Based Li-Ion Batteries.

Li-rich and Ni-rich layered oxides as next-generation high-energy cathodes for lithium-ion batteries (LIBs) possess the catalytic surface, which leads to intensive interfacial reactions, transition metal ion dissolution, gas generation, and ultimately hinders their applications at 4.7 V. Here, robust inorganic/organic/inorganic-rich architecture cathode-electrolyte interphase (CEI) and inorganic/organic-rich architecture anode-electrolyte interphase (AEI) with F-, B-, and P-rich inorganic components through modulating the frontier molecular orbital energy levels of lithium salts are constructed. A ternary fluorinated lithium salts electrolyte (TLE) is formulated by mixing 0.5 m lithium difluoro(oxalato)borate, 0.2 m lithium difluorophosphate with 0.3 m lithium hexafluorophosphate. The obtained robust interphase effectively suppresses the adverse electrolyte oxidation and transition metal dissolution, significantly reduces the chemical attacks to AEI. Li-rich Li1.2 Mn0.58 Ni0.08 Co0.14 O2 and Ni-rich LiNi0.8 Co0.1 Mn0.1 O2 in TLE exhibit high-capacity retention of 83.3% after 200 cycles and 83.3% after 1000 cycles under 4.7 V, respectively. Moreover, TLE also shows excellent performances at 45 °C, demonstrating this inorganic rich interface successfully inhibits the more aggressive interface chemistry at high voltage and high temperature. This work suggests that the composition and structure of the electrode interface can be regulated by modulating the frontier molecular orbital energy levels of electrolyte components, so as to ensure the required performance of LIBs.

50C Fast-Charge Li-Ion Batteries using a Graphite Anode.

Li-ion batteries have made inroads into the electric vehicle market with high energy densities, yet they still suffer from slow kinetics limited by the graphite anode. Here, electrolytes enabling extreme fast charging (XFC) of a microsized graphite anode without Li plating are designed. Comprehensive characterization and simulations on the diffusion of Li+ in the bulk electrolyte, charge-transfer process, and the solid electrolyte interphase (SEI) demonstrate that high ionic conductivity, low desolvation energy of Li+ , and protective SEI are essential for XFC. Based on the criterion, two fast-charging electrolytes are designed: low-voltage 1.8 m LiFSI in 1,3-dioxolane (for LiFePO4 ||graphite cells) and high-voltage 1.0 m LiPF6 in a mixture of 4-fluoroethylene carbonate and acetonitrile (7:3 by vol) (for LiNi0.8 Co0.1 Mn0.1 O2 ||graphite cells). The former electrolyte enables the graphite electrode to achieve 180 mAh g-1 at 50C (1C = 370 mAh g-1 ), which is 10 times higher than that of a conventional electrolyte. The latter electrolyte enables LiNi0.8 Co0.1 Mn0.1 O2 ||graphite cells (2 mAh cm-2 , N/P ratio = 1) to provide a record-breaking reversible capacity of 170 mAh g-1 at 4C charge and 0.3C discharge. This work unveils the key mechanisms for XFC and provides instructive electrolyte design principles for practical fast-charging LIBs with graphite anodes.

Rechargeable LiNi0.65 Co0.15 Mn0.2 O2 ||Graphite Batteries Operating at -60 °C.

The rechargeability of contemporary lithium-ion batteries (LIBs) is challenging at low temperatures, mainly due to the hurdles faced by graphite anodes. Herein, by exploiting the Li-solvent co-intercalation into graphite, its low-temperature rechargeability is boosted. Experimental characterizations aided by theoretical calculations demonstrate that the co-intercalation process is featured by low interfacial resistance with a small charge transfer activation energy (0.23 eV atom-1 ) and an extremely low diffusion energy barrier (0.09 eV atom-1 ) which leads to nearly temperature-independent diffusion coefficients of the solvated Li-ion in graphite, enabling graphite to be stably charged-discharged at -60 °C with 73.7 % of its room-temperature capacity. Consequently, the full-cell consisting of a LiNi0.65 Co0.15 Mn0.2 O2 cathode and a graphite anode shows impressive rechargeability under -60 °C. This work provides an alternative approach to develop low-temperature rechargeable LIBs.

Practical Approaches to Apply Ultra-Thick Graphite Anode to High-Energy Lithium-Ion Battery: Carbonization and 3-Dimensionalization.

Lithium-ion batteries with ultra-thick electrodes have high energy density and low manufacturing costs because of the reduction of the inactive materials in the same battery volume. However, the partial usage of the full capacity and the low rate capability are caused by poor ionic and electronic conduction. In this work, the effects of two approaches, such as electrode binder carbonization by heat treatment and 3-dimensionalization by the laser structuring of ultra-thick graphite anodes to lithium-ion batteries for high energy density, are investigated. During the heat treatment, the polyvinylidene fluoride (PVDF) binder is carbonized to form fluorinated graphitic carbons, thereby increasing the number of lithium-ion storage sites and the improvement of the electrode capacity by 14% (420 mAh g-1 and 20 mAh cm-2). Further, the carbonization improves the rate capability by 31% at 0.1 C by simultaneously reducing the ionic and electronic resistances. Furthermore, after the laser structuring of the carbonized electrode, the areal discharge capacity increases to 50% at the increasing current rates, resulting from drastically improved ionic conduction. In addition to the electrochemical characteristics, these two approaches contribute considerably to the fast wetting of the electrolyte into the ultra-thick electrode. The carbonization and laser structuring of the ultra-thick graphite anodes are practical approaches for high-energy batteries to overcome the thickness limitation.

Weak Cation-Solvent Interactions in Ether-Based Electrolytes Stabilizing Potassium-ion Batteries.

Conventional ether-based electrolytes exhibited a low polarization voltage in potassium-ion batteries, yet suffered from ion-solvent co-intercalation phenomena in a graphite anode, inferior potassium-metal performance, and limited oxidation stability. Here, we reveal that weakening the cation-solvent interactions could suppress the co-intercalation behaviour, enhance the potassium-metal performance, and improve the oxidation stability. Consequently, the graphite anode exhibits K+ intercalation behaviour (K||graphite cell operates 200 cycles with 86.6 % capacity retention), the potassium metal shows highly stable plating/stripping (K||Cu cell delivers 550 cycles with average Coulombic efficiency of 98.9 %) and dendrite-free (symmetric K||K cell operates over 1400 hours) properties, and the electrolyte exhibits high oxidation stability up to 4.4 V. The ion-solvent interaction tuning strategy provides a promising method to develop high-performance electrolytes and beyond.

Unblocked Electron Channels Enable Efficient Contact Prelithiation for Lithium-Ion Batteries.

Contact prelithiation is strongly considered for compensating the initial capacity loss of lithium-ion batteries, exhibiting great potential for ultralong cycle life of working batteries and the application of large-scale energy-storage systems. However, the utilization of the sacrificial Li source for contact prelithiation is low (<65%). Herein the fundamental mechanism of contact prelithiation is described from the perspective of the Li source/anode interfaces by regulating the initial contact state, and a clear illustration of the pathogeny for capacity attenuation is successfully delivered. Specifically, creating plentiful electron channels is an access to making contact prelithiation with a higher Li utilization, as the mitigated local current density that reduces the etching of Li dissolution and SEI extension on electron channels. A vacuum thermal evaporation for depositing the Li film enables the contact interface to possess an adequate electron channel construction, rendering a Li utilization of 91.0%, and the dead Li yield is significantly reduced in a working battery.

Eliminating Graphite Exfoliation with an Artificial Solid Electrolyte Interphase for Stable Lithium-Ion Batteries.

Although graphite materials with desirable comprehensive properties dominate the anode market of commercial lithium-ion batteries (LIBs), their low capacity during fast charging precludes further commercialization. In the present work, natural graphite (G) is reported not only to suffer from low capacity during fast charging, but also from charge failure after many charging cycles. Using different characterization techniques, severe graphite exfoliation, and continuously increasing solid electrolyte interphase (SEI) are demonstrated as reasons for the failure of G samples. An ultrathin artificial SEI is proposed, addressing these problems effectively and ensuring extremely stable operation of the graphite anode, with a capacity retention of ≈97.5% after 400 cycles at 1 C. Such an artificial SEI modification strategy provides a universal approach to tailoring and designing better anode materials for next-generation LIBs with high energy densities.

Resolution of Lithium Deposition versus Intercalation of Graphite Anodes in Lithium Ion Batteries: An In Situ Electron Paramagnetic Resonance Study.

In situ electrochemical electron paramagnetic resonance (EPR) spectroscopy is used to understand the mixed lithiation/deposition behavior on graphite anodes during the charging process. The conductivity, degree of lithiation, and the deposition process of the graphite are reflected by the EPR spectroscopic quality factor, the spin density, and the EPR spectral change, respectively. Classical over-charging (normally associated with potentials ≤0 V vs. Li+ /Li) are not required for Li metal deposition onto the graphite anode: Li deposition initiates at ca. +0.04 V (vs. Li+ /Li) when the scan rate is lowered to 0.04 mV s-1 . The inhibition of Li deposition by vinylene carbonate (VC) additive is highlighted by the EPR results during cycling, attributed to a more mechanically flexible and polymeric SEI layer with higher ionic conductivity. A safe cut-off potential limit of +0.05 V for the anode is suggested for high rate cycling, confirmed by the EPR response over prolonged cycling.

Recycling of photovoltaic silicon waste for high-performance porous silicon/silver/carbon/graphite anode.

The rapid development photovoltaic industry has generated a huge amount of waste ultra-fine silicon cutting powder. The management and value-added recovery of silicon cutting waste is highly important for both environmental remediation and economic efficiency. In this work, silicon waste was used as a cost-effective raw material for the preparation of silicon/graphite anode for lithium-ion batteries. First, porous Si embedded with Ag particles (pSi/Ag) was produced by silver-assisted chemical etching (Ag-ACE). Then, pSi/Ag was loaded on a micron-sized graphite matrix (pSi/Ag/G), and organic carbon (C) produced by the pyrolysis of polyvinylpyrrolidone (PVP) acted as a link to closely connect pSi/Ag and graphite to form the pSi/Ag/C/G composite. The incorporated Ag particles and the porous structure improve electron transfer and mitigate the volume expansion effect of silicon. The novel design and structure of the anode can maintain the integrity of the electrode during cycling, and thus strongly improve cycling stability. The prepared pSi/Ag/C/G composite exhibited a large initial discharge capacity of 2353 mAh/g at 0.5 A/g and good initial coulombic efficiency of 83%, delivering a high capacity of 972 mAh/g at 1 A/g after 200 cycles. This work confirmed the possibility of the preparation of lithium battery silicon-carbon anode from silicon waste and provides a promising new avenue for value-added utilization of silicon cutting waste materials.

Inhibiting Solvent Co-Intercalation in a Graphite Anode by a Localized High-Concentration Electrolyte in Fast-Charging Batteries.

Lithium-ion batteries with routine carbonate electrolytes cannot exhibit satisfactory fast-charging performance and lithium plating is widely observed at low temperatures. Herein we demonstrate that a localized high-concentration electrolyte consisting of 1.5 M lithium bis(fluorosulfonyl)imide in dimethoxyethane with bis(2,2,2-trifluoroethyl) ether as the diluent, enables fast-charging of working batteries. A uniform and robust solid electrolyte interphase (SEI) can be achieved on graphite surface through the preferential decomposition of anions. The established SEI can significantly inhibit ether solvent co-intercalation into graphite and achieve highly reversible Li+ intercalation/de-intercalation. The graphite | Li cells exhibit fast-charging potential (340 mAh g-1 at 0.2 C and 220 mAh g-1 at 4 C), excellent cycling stability (ca. 85.5 % initial capacity retention for 200 cycles at 4 C), and impressive low-temperature performance.

Ecotoxicological assessment and electrochemical remediation of doxorubicin.

Doxorubicin (DOX) is an anthracycline widely used in treatments of several cancers, so it has found in hospital effluents with a significant concentration (above 1 µg L-1). Electrochemical remediation is an alternative to promote its degradation. The aim of this work was to evaluate the ability of nanostructured graphite electrodes with metallic oxides to degrade DOX by electro-oxidation (EO). Graphite, TiO2@graphite and AuO-TiO2@graphite electrodes were used in medium with tap water or 10 mmol L-1 NaCl. DOX treatments at concentrations of 1.25-5 mg L-1 were carried out in a voltage source with 1.5-5 V. The cathode used was the platinum electrode. The treatment of DOX 1.25 mg L-1 with 10 mmol L-1 NaCl electrolyte using the AuO-TiO2@graphite electrode at 5 V and 1 mA was the best methodology to promote its degradation. Also, the modified electrode was efficient to DOX degradation after 17 cycles of reuse. An energy expenditure of 1.11 and 0.2 kWh m-3 were obtained for 3 and 50 mL of treatment, respectively. Fish embryo acute toxicity test with zebrafish (Danio rerio) were performed before and after treatment by EO using NaCl. This treatment caused no effect on embryo-larval development, however it induced significant damage in the DNA of the zebrafish larvae after 96 h of exposure, which emphasizes the importance of a depth ecotoxicological evaluation during the development of EO methodologies.

Graphite as a Long-Life Ca2+-Intercalation Anode and its Implementation for Rocking-Chair Type Calcium-Ion Batteries.

Herein, graphite is proposed as a reliable Ca2+-intercalation anode in tetraglyme (G4). When charged (reduced), graphite accommodates solvated Ca2+-ions (Ca-G4) and delivers a reversible capacity of 62 mAh g-1 that signifies the formation of a ternary intercalation compound, Ca-G4·C72. Mass/volume changes during Ca-G4 intercalation and the evolution of in operando X-ray diffraction studies both suggest that Ca-G4 intercalation results in the formation of an intermediate phase between stage-III and stage-II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca-G4 has a planar structure with Ca2+ surrounded by G4, which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g-1 at 1.0 A g-1 s vs 62 mAh g-1 at 0.05 A g-1) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca2+-shuttling calcium-ion batteries with a graphite anode, a full-cell is constructed by coupling with an organic cathode and its electrochemical performance is presented.

Multistage Mechanism of Lithium Intercalation into Graphite Anodes in the Presence of the Solid Electrolyte Interface.

A so-called solid electrolyte interface (SEI) in a lithium-ion battery largely determines the performance of the whole system. However, it is one of the least understood objects in these types of batteries. SEIs are formed during the initial charge-discharge cycles, prevent the organic electrolytes from further decomposition, and at the same time govern lithium intercalation into the graphite anodes. In this work, we use electrochemical impedance spectroscopy and atomic force microscopy to investigate the properties of a SEI film and an electrified "graphite/SEI/electrolyte interface". We reveal a multistage mechanism of lithium intercalation and de-intercalation in the case of graphite anodes covered by SEI. On the basis of this mechanism, we propose a relatively simple model, which perfectly explains the impedance response of the "graphite/SEI/electrolyte" interface at different temperatures and states of charge. From the whole data obtained in this work, it is suggested that not only Li+ but also negatively charged species, such as anions from the electrolyte or functional groups of the SEI, likely interact with the surface of the graphite anode.