Dual-graphite Batteries Research Articles

High energy density potassium-based dual graphite battery with high concentration carbonate electrolyte

Dual ion batteries (DIBs) differ from traditional lithium-ion and sodium-ion batteries in that the electrolyte acts as a significant source of active materials in DIBs, directly influencing the specific capacity, charge-discharge efficiency, and cycle life. Traditional potassium (K)-based dual ion batteries use electrolytes with concentrations below 1 m (mol kg−1), which exhibit a comparatively low oxidation potential of ∼4.4 V versus K/K+. This limits the operational longevity and energy density of the batteries. To enhance the electrochemical stability of the electrolyte and improve the capacity and reversibility of anions/cations intercalating into graphite electrodes, this study introduces a 10.0 m potassium bis(fluorosulfonyl)imide (KFSI) in carbonate ester electrolytes. The results show that increasing the electrolyte concentration effectively raises the oxidation potential to 6.1 V vs. K/K+. A K-dual graphite dual ion battery (K-DGDIB) is assembled using 10.0 m KFSI/ethylene carbonate (EC):dimethyl carbonate (DMC) electrolyte and incorporates both a graphite cathode and a graphite anode. This battery provides a discharge capacity of 94.2 mAh g−1 at 100 mA g−1, a discharge medium voltage of ∼4.24 V, and an energy density of ∼5.8 Wh kg−1 considering the total mass of all added electrolyte and the total mass of the active materials.

LiNi0.5Mn1.5O4 Addition to Anion-Storing Graphite Cathode Yields Multifaceted Benefits to Dual Graphite Batteries

Dual graphite batteries (DGBs) yield an output voltage of ∼4.5 V vs Li+/Li by functioning on the “scissor-cutting” type dual-ion storing mechanism. However, they lack capacity, suffer from poor cycling efficiency, and exhibit insufficient cycle life. The improvement strategies reported in the literature ameliorate only the targeted parameter but downgrade the rest. Herein, the approach of blending LiNi0.5Mn1.5O4 (LNMO) spinel oxide with graphite at cathode is demonstrated as a multifunctional remedy. LNMO represents an additional lithium reservoir that replenishes the depleted lithium at anode during cycling, thereby boosting cycling efficiency. It acts as a sacrificial salt that compensates for the irreversibly consumed Li+ from its stock during parasitic reactions, thus reducing the self-discharge rate of dual-graphite full cell. Further, the Ni4+/2+ redox couple at ∼4.75 V vs Li+/Li in LNMO enhances capacity, upshifts average discharge voltage, and increases the energy output of the full cell. The interaction between de/intercalating Li+ and PF6− during the “cooperated scissor-cutting mechanism” functional at blended cathode decreases charge transfer resistance. The presence of LNMO enriches the interfacial composition in inorganic components that benefit long-term cycling. Moreover, the physical properties like tap density, durability, and pore structure are reinforced in graphite/ LNMO blended cathode.

Mechanistic insights into the solvent assisted thermal regeneration of spent graphite and its upcycling into dual graphite batteries

The spent lithium-ion battery is upcycled into a dual-graphite battery via a solvent assisted thermal treatment.

Perspectives on emerging dual carbon fiber batteries: advantages, challenges and prospects.

This perspective article describes a new dual carbon fiber battery, where both the cathode and anode are made of carbon fiber. The dual carbon fiber battery combines the advantages of carbon fiber and dual graphite batteries, including a higher working potential compared to lithium-ion batteries, a high areal capacity, and easy access due to the mature manufacturing technology of carbon fibers. In this article, we discuss the mechanism, current status and potential application areas of dual carbon fiber batteries. Additionally, we highlight the challenges and prospects of these batteries.

Modeling Diffusion-Induced Mechanical Degradation in Dual-Graphite Battery Cathodes: Application to Intercalation

In this work, we propose a finite element framework to analyze the diffusion-induced mechanical degradation in graphite active particles (APs) due to bulky anion intercalation in dual-graphite batteries (DGBs). Finite strain formulation is considered to account for the large volume expansion that typically occurs in graphite cathodes. The proposed model considers chemo-mechanical coupling, including the effect of the particle volume changes due to the penetration of ions and its eventual fracture, modeled using a phase-field fracture approach. To account for the stochastic nature of graphitic microstructures, the mechanical properties are described by means of a Weibull distribution function. Our model is able to reproduce realistic cracking patterns that take place during the charging and discharging processes in APs. Finally, we use the model to simulate different galvanostatic charging rates and particle sizes to provide insight into the mechanical degradation of graphite APs during intercalation. We use this information to provide design rules for improved graphite cathodes or better operation strategies in DGBs.

Differing Electrolyte Implication on Anion and Cation Intercalation into Graphite.

Emerging dual-graphite batteries (DGBs) capture extensive interest for their high output voltage and exceptional cost-effectiveness. Yet, developing electrolytes compatible with both the cathode and anode stands to be a tremendous challenge, and how electrolyte impacts anion and cation intercalation into graphite remains inexplicit or controversial. Herein, we have evaluated the performance of graphite anode and cathode in typical ethyl methyl carbonate (EMC) based electrolytes and unveiled their electrode-electrolyte interphase using Cryogenic transmission electron microscopy (Cryo-TEM). The addition of fluoroethylene carbonate (FEC) brings substantial improvement in cycle stability and Coulombic efficiency for both the graphite cathode and anode, but its implication on cation and anion intercalation differs. FEC is involved in anodic side reactions to produce a LiF-embedded solid-electrolyte interphase layer. It is much thinner and more uniform than that formed in the electrolyte without FEC, which is correlated with less graphite exfoliation and enhanced stability. As for the graphite cathode, both basal and edge planes are largely bare, and only few scattered byproducts are found. In addition, we also reveal layer bending and local lattice disordering of the graphite cathode based on multiple Cryo-TEM images, which are speculated to be caused by high lattice strain induced by anion intercalation and local oxidation under high voltage. The absence of cathode-electrolyte interphase (CEI) layers overturns the paradigm of attributing cathodic performance to CEI features and is regarded as a fundamental reason for severe self-discharge of graphite cathode. FEC helps to alleviate graphite exfoliation issues and enhance cycle stability, and we ascribe it to weakened solvation, which means reduced probability of solvent co-intercalation during charging, rather than compositional changes of cathodic byproducts.

Differences between cation and anion storage electrochemistry of graphite and its impact on dual graphite battery

The redox-amphoteric nature of graphite is tactically utilized to store cations and anions simultaneously in a dual graphite battery (DGB). The major differences between cation and anion storage electrochemistry of graphite are identified here and their impacts on the electrochemical performances of DGBs are analyzed. All the differences are found to originate primarily from ionic size mismatch (76 p.m. of Li+vs. 254 p.m. of PF6−) that further induces kinetic and thermodynamic limitations upon intercalation. The electrochemical studies reveal that the anion intercalation lags behind the cation because of a higher energy barrier for the interconversion among (PF6)Cx stages, the occurrence of a valley-type region in the discharge profile that delays deintercalation by 500 mV, dynamic changes in organic-rich cathode electrolyte interphase, and sluggish diffusion inside graphite bulk. In contrast, cation intercalation affects DGBs' performance negatively due to higher desolvation barriers and lithium plating on the anode surface at higher current densities. Therefore, the cathode limits the capacity and cycling efficiency, whereas the anode restricts cycle life and power density. This work also explores the strategies to mitigate the degradation pathways by electrolyte modification.

Promise of dual carbon batteries with graphene-like graphite as both electrodes

Graphene-like graphite (GLG) exhibits a higher capacity for intercalation/deintercalation of lithium ions and anions compared to graphite, making it a promising candidate for both electrodes for dual carbon batteries, also known as dual-ion batteries (DIBs). In this study, we constructed DIB full cells with GLG electrodes to address specific issues related to the full cell while optimizing the cell configuration and charge-discharge conditions to improve its performance. With 3 mol dm−3 LiPF6/ethyl methyl carbonate (EMC) electrolyte solution, the reversible capacity was very small, suggesting that this was due to a cross-talk reaction where decomposition products generated at the cathode migrated to the anode and were reductively decomposed. Conversely, the use of 3 mol dm−3 lithium bis(fluorosulfonyl)amide (LiFSA)/EMC suppressed the cross-talk reaction, resulting in improved charge-discharge performance. In addition, the pre-cycling of the anode to form solid electrolyte interphase significantly suppressed the cross-talk reaction to greatly increase the reversible capacity. Consequently, we achieved a relatively high capacity of 66 mAh g−1 for the GLG cathode, even with a low cutoff voltage at 4.6 V, surpassing the capacity of a dual graphite battery under the same conditions. This outcome clearly demonstrates the promise of GLG as active materials for DIBs.

Solvation Structure Modulation Of High-Voltage Electrolyte For High-Performance K-Based Dual-Graphite Battery.

Due to the advantages of dual-ion batteries (DIBs) and abundant resources, potassium-based dual-carbon batteries (K-DCBs) have wide application prospects. However, conventional carbonate ester-based electrolyte systems have obvious drawbacks such as poor oxidation resistance and difficulty in sustaining the anion intercalation process at high voltages, which seriously affect the capacity and cycle performance of K-DCBs. Therefore, a rational design of more efficient novel electrolyte systems is urgently required to realize high-performance K-DCBs. Herein, we report a solvation structure modulation strategy for the K-DCB electrolyte systems. Consequently, substantial K+ ion storage improvement at the graphite anode and enhanced FSI- intercalation capacity at the graphite cathode are successfully realized simultaneously. As a proof-of-concept, the assembled K-DCB exhibited a discharge capacity of 103.4 mAh g-1 , and after 400 cycles, approximately 90% capacity retention was observed. Moreover, the energy density of the K-DCB full cell reached 157.6Wh kg-1 , which is the best performance in reported K-DCBs till date. This study demonstrates the effectiveness of solvation modulation in improving the performance of K-DCBs. This article is protected by copyright. All rights reserved.

Study on ionic liquid-based gel polymer electrolytes for dual-graphite battery systems

Study on ionic liquid-based gel polymer electrolytes for dual-graphite battery systems

A high-concentrated and nonflammable electrolyte for potassium ion-based dual-graphite batteries

A high-concentrated and nonflammable electrolyte for potassium ion-based dual-graphite batteries

In‐situ Sacrificial Positive Additive Strategy for the Construction of a Stable Negative Interface in Dual Graphite Batteries

AbstractDue to their merits of affordability, safety, and environmental friendliness, dual graphite batteries (DGBs) have drawn widespread interest as novel energy storage devices. Nevertheless, the development of DGBs is plagued by inferior cyclic stability that arise from the irreversible loss of cations and the anion‐cation crosstalk during the formation of an negative interface. We proposed an in‐situ sacrificial positive additive strategy to enhance the electrochemical performances, based on the decomposability of potassium oxalate monohydrate (K2C2O4⋅H2O). The experimental and computational results show that the positive additive can add cations to support a stable negative interface and suppress the anion‐cation crosstalk. The as‐constructed DGBs with K2C2O4⋅H2O deliver high‐rate capability (31.8 mAh g−1 at 3.0 C) and excellent cyclic stability (∼84.1 % capacity retention after 180 cycles). This work provides a new opportunity of negative interface construction for propelling the commercial evolution of the advanced DGBs.

Emerging dual carbon fiber batteries

Dual graphite battery emerges as a promising renewable energy storage system with merits of a high working voltage, low cost and environment-friendliness. However, energy density is limited because of a low packing density of graphite. We propose for the first time dual carbon fiber batteries (DCFBs) in which carbon fiber functions as both cathode and anode. With a graphite mass loading of ∼30 mg cm−2 at pitch-based carbon fiber (PCF) cloth, the reversible discharge capacity of PCF-PCF type DCFBs (with PCF cloth cathodes/anodes) can reach 72 mAh g−1 at 0.1 C (1 C corresponding to 80 mAh g−1), resulting in an unprecedentedly high areal capacity of ∼2.2 mAh cm−2. Unlike the general applicability of commercialized carbon fiber as DCFBs anode, only PCF out of five kinds of commercialized carbon fibers can function as DCFBs cathode. Meanwhile, PCF-PCF type DCFB enables investigation into distinct electrochemical behaviors of Li+/PF6−intercalation/deintercalation in PCF. Morphological difference of PCF brought about by Li+/PF6− ions, as found out by ex-situ X-ray diffraction (XRD) and ex-situ scanning electronic microscopy/energy dispersive spectroscopy (SEM/EDS) characterizations, facilitates comprehensive understanding of electrochemical behavior of graphite. This work lays good foundations for future exploration into a new arena of dual ion batteries.

A flexible [(DMPI+)(AlCl4−)]/PVDF-HFP polymer gel electrolyte and its electrochemical performance for dual-graphite batteries

Recently, dual-graphite batteries (DGBs) receive growing attention for their advantages of high working voltage, environmental friendliness and inexpensive. However, the conventional liquid organic electrolytes used in DGBs still possess issues of safety and electrolyte leakage that might limit their further development. Herein, a non-flammable [(DMPI+)(AlCl4−)] ionic liquid (DAIL) is embedded into a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) matrix to prepare a [(DMPI+)(AlCl4−)] polymer gel electrolyte (DAPGE) for solving these conventional issues. The DAPGE, as both the electrolyte and separator, is characterized and electrochemically tested in DGB, which shows favourable ionic conductivity of 2.28 × 10−3 S cm−1. The DGB using a DAPGE shows a specific capacity of 80 mAh g−1 at a current density of 100 mA g−1. Moreover, the DGB pouch cell with DAPGE can work well under bending, critical temperature and even exposure to air. Besides, DAPGE decreases the utilization (around 40%) of liquid IL electrolyte as compared to that of conventional glass fibre separators does. Consequently, the application of DAPGE in DGBs shows promise for achieving higher energy density and better robustness.

Advanced Dual-Ion Batteries with High-Capacity Negative Electrodes Incorporating Black Phosphorus.

Dual‐graphite batteries (DGBs), being an all‐graphite‐electrode variation of dual‐ion batteries (DIBs), have attracted great attention in recent years as a possible low‐cost technology for stationary energy storage due to the utilization of inexpensive graphite as a positive electrode (cathode) material. However, DGBs suffer from a low specific energy limited by the capacity of both electrode materials. In this work, a composite of black phosphorus with carbon (BP‐C) is introduced as negative electrode (anode) material for DIB full‐cells for the first time. The electrochemical behavior of the graphite || BP‐C DIB cells is then discussed in the context of DGBs and DIBs using alloying anodes. Mechanistic studies confirm the staging behavior for anion storage in the graphite positive electrode and the formation of lithiated phosphorus alloys in the negative electrode. BP‐C containing full‐cells demonstrate promising electrochemical performance with specific energies of up to 319 Wh kg–1 (related to masses of both electrode active materials) or 155 Wh kg–1 (related to masses of electrode active materials and active salt), and high Coulombic efficiency. This work provides highly relevant insights for the development of advanced high‐energy and safe DIBs incorporating BP‐C and other high‐capacity alloying materials in their anodes.

19F MAS NMR study on anion intercalation into graphite positive electrodes from binary-mixed highly concentrated electrolytes

Dual-graphite batteries (DGBs), which are based on anion intercalation into graphite positive electrodes, exhibit great potential for stationary energy storage due to use of more sustainable and low-cost electrode materials and processing routes. Binary-mixed highly concentrated electrolytes (HCEs) appeal highly suitable for the high operating voltages of DGBs, although the lack of sufficient insights into the formation of graphite intercalation compounds (GICs) limits the cell performance in terms of specific capacity and lifetime so far. Herein, anion intercalation from single-salt HCEs (LiPF 6 and LiBF 4 ) and an equimolar binary mixture of LiPF 6 /LiBF 4 are studied in graphite || Li metal cells, revealing an improved performance in terms of specific capacity and Coulombic efficiency in the order LiPF 6 > LiPF 6 /LiBF 4 > LiBF 4 . LiBF 4 -based cells exhibit an increased onset potential for anion intercalation and higher area specific impedance, suggesting an ineffective interphase formation at graphite. X-ray diffraction reveals GIC formation, while a lower stage number is achieved for the LiBF 4 -based HCE. 19 F MAS NMR spectroscopy analysis at various states-of-charge confirms no significant charge transfer between the intercalated anions and the graphite host and suggest preferred intercalation of PF 6 - compared to BF 4 - as well as a high translational and/or rotational mobility of the intercalated anions. • Anion intercalation into graphite from binary-mixed BF 4 ˉ/PF 6 - electrolytes. • Electrochemical performance: LiPF 6 /DMC > LiPF 6 /LiBF 4 /DMC > LiBF 4 /DMC. • 19 F MAS NMR spectroscopy is a powerful method to analyze BF 4 ˉ/PF 6 - intercalation. • Molar ratios of intercalated anions verify preferred PF 6 - intercalation. • High translational and/or rotational mobility of the intercalated anions.

The mechanism of bulky imidazolium cation storage in dual graphite batteries: a spectroscopic and theoretical investigation

The insights into cation storage in the shallow surface of the bulk GE provided by in situ XRD and in situ Raman spectroscopy is the combination of intercalation and intercalation pseudocapacitance and is dominated by the latter.

Editors’ Choice—Mechanistic Elucidation of Anion Intercalation into Graphite from Binary-Mixed Highly Concentrated Electrolytes via Complementary 19F MAS NMR and XRD Studies

Dual-graphite batteries have emerged as promising candidate for sustainable energy storage due to their potentially low costs and absence of toxic materials. However, the mechanism of anion intercalation and the structures of the resulting graphite intercalation compounds (GICs) are still not well understood. Here, we systematically evaluate the anion intercalation characteristics into graphite for three highly concentrated electrolytes containing LiPF6, LiTFSI and their equimolar binary mixture. The binary mixture exhibits a significantly enhanced capacity retention and improved intercalation kinetics compared to the single-salt electrolytes in graphite ∣∣ Li metal cells. In situ X-ray diffraction studies prove the formation of stage 1-GICs and a homogeneous distribution of anions within graphite. From ex situ solid-state 19F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) measurements, GICs can be identified at various states-of-charge (SOCs). The 19F chemical shifts of intercalated anions indicate no significant charge transfer between anion and graphite. The observed narrow 19F linewidths of the GIC-signals are most likely caused by a high translational and/or rotational mobility of the intercalates. Furthermore, the 19F MAS NMR studies allow the identification of the molar ratios for PF6− and TFSI− anions intercalated into graphite, suggesting a preferred intercalation of PF6− anions, especially at lower SOCs.

(Invited) Exploiting New Electrolytes and Mechanistic Solvation Kinetics for Extreme Low Temperature Batteries

Improving the extremely low temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of high-rate discharge are in short supply. Herein, we demonstrate the holistic design of dual-graphite batteries, which circumvent the sluggish ion desolvation process found in typical lithium-ion batteries during discharge. These batteries were enabled by a novel electrolyte, which simultaneously provided high electrochemical stability and ionic conductivity at low temperature. The dual-graphite cells, when compared to industry-type graphite || LiCoO2 full-cells demonstrated an 11 times increased capacity retention at -60 oC for a 10 C discharge rate, indicative of the superior kinetics of the “dual-ion” storage mechanism. These trends are further supported by GITT and EIS measurements at reduced temperature. This work provides a new design strategy for extreme low-temperature batteries. In addition, the electrolytes developed for dual-ion cells have also been extended to search for other high-capacity, high-rate electrodes, which leads to further improved energy density and stability for both high and extremely low temperatures.

Designing a hybrid electrode toward high energy density with a staged Li+ and PF6 - deintercalation/intercalation mechanism.

Existing lithium-ion battery technology is struggling to meet our increasing requirements for high energy density, long lifetime, and low-cost energy storage. Here, a hybrid electrode design is developed by a straightforward reengineering of commercial electrode materials, which has revolutionized the "rocking chair" mechanism by unlocking the role of anions in the electrolyte. Our proof-of-concept hybrid LiFePO4 (LFP)/graphite electrode works with a staged deintercalation/intercalation mechanism of Li+ cations and PF6 - anions in a broadened voltage range, which was thoroughly studied by ex situ X-ray diffraction, ex situ Raman spectroscopy, and operando neutron powder diffraction. Introducing graphite into the hybrid electrode accelerates its conductivity, facilitating the rapid extraction/insertion of Li+ from/into the LFP phase in 2.5 to 4.0 V. This charge/discharge process, in turn, triggers the in situ formation of the cathode/electrolyte interphase (CEI) layer, reinforcing the structural integrity of the whole electrode at high voltage. Consequently, this hybrid LFP/graphite-20% electrode displays a high capacity and long-term cycling stability over 3,500 cycles at 10 C, superior to LFP and graphite cathodes. Importantly, the broadened voltage range and high capacity of the hybrid electrode enhance its energy density, which is leveraged further in a full-cell configuration.