Additives For Lithium-ion Batteries Research Articles

First Identification of Toxic Cyclotriphosphazenes as New Pollutants Prevailing in Various Urban Environments: A Class of Widely Used Flame Retardant Electrolyte Additives in Lithium-Ion Batteries

First Identification of Toxic Cyclotriphosphazenes as New Pollutants Prevailing in Various Urban Environments: A Class of Widely Used Flame Retardant Electrolyte Additives in Lithium-Ion Batteries

Optimize Electrolytes and Additives for Lithium-Ion Batteries Using C/SiO2 Synthesized from Rice Husk As an Anode Material

Silicon-based anodes derived from agricultural waste, particularly rice husks, have recently been focused on replacing conventional graphite due to its abundance, low cost, fast charge ability, and remarkable theoretical capacity (~ 3600 mAh.g-1). SiO2 has several drawbacks, including low electrical conductivity and short cycling life associated with high-volume expansion (~ 300%) during the charge-discharge process. Hence, a hybrid composite C/SiO2 was an ideal solution to overcome these challenges.To strengthen the electrochemical properties of LIBs, the compatibility between electrodes and electrolytes plays a crucial role. Lithium hexafluorophosphate (LiPF6) and Lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) are promising candidates for investigation due to their effectiveness cost. Regarding LiPF6, widely used in LIBs, offers high solubility and stability, while LiTFSI provides enhanced ionic mobility. However, LiTFSI is corrosive to aluminum current collectors, and LiPF6 unexpectedly dissociates to form HF acid and PF5, leading to cycling degradation. To mitigate these issues, additives such as Fluoroethylene-carbonate (FEC) and Vinylene Carbonate (VC) are introduced to enhance battery performance. This study employed FEC and VC, adding in the optimal electrolyte to stabilize the SEI layer, prevent lithium loss during cycling due to the instability of the interfacial layer, as well as to enhance high-rate performance. In detail, FEC could effectively prevent SEI degradation by enhancing the F-based component of this layer, stabilizing the SEI layers, and protecting electrodes. Simultaneously, VC offers a synergistic effect on the interphase modulation by reinforcing the inorganic/organic components. Thus, we investigate various electrolyte systems to evaluate half-cell performance of C/SiO2 synthesized from rice husk as the anode. Then, the optimal-chosen electrolytes were used to assemble full-cell LFP||C/SiO2 and investigated at high-rate performance.According to the experimental sections, there are two main lithium-salts comprised of LiPF6 and LiTFSI, which dissolved in three solvent systems, including EC: DEC (1: 1-v/v); EC: DMC (1:1-v/v), and EC: DMC: DEC (1:1:1 – v/v/v). After optimizing the solvents, the system of EC: DEC (1: 1-v/v) shows the highest performance, which was chosen to investigate the impact of various ratios of FEC and VC additive. The 1M LiPF6 in EC: DEC (1:1-v/v) + 5 wt% FEC has the highest specific capacity compared to the LiPF6 samples, reaching the value of 220.0 mAh.g-1. Meanwhile, the 1M LiTFSI in EC: DEC (1:1-v/v) 2.5 wt% FEC + 2.5 wt% VC is the best electrolyte to offer a stable capacity of 223.4. mAh.g-1 after 50 cycles in comparison to LiTFSI samples. This phenomenon is plausible with the conductivity of 6.16 and 7.45 mS.cm-1, respectively. Furthermore, they undergo remarkable oxidation at 4.05 and 4.23 V at a current density of 0.002 mA, demonstrating they have a good stability potential window. Since there is no significant difference in half-cell performance, they were used to evaluate full-cell properties. According to battery performance, the full-cell LFP||C/SiO2 using LiPF6 + 5 wt% FEC shows that the initial capacity reaches 111.6 mAh.g-1 and is maintained 40% after 50 cycles with a stable CE above 96%. Full cell LiTFSI +2.5 wt% FEC + 2.5 wt% VC shows an initial discharge capacity of 159.9 mAh.g-1. However, this capacity value is significantly reduced to only 28.5 mAh.g-1 after 50 cycles and CE ~ 94%. Regarding rate capability results, full cell 1M LiPF6 in EC: DEC (1:1-v/v) + 5 wt% FEC illustrates better performance in all discharged rates than full cells using LiTFSI salt. Moreover, this full-cell shows a discharge capacity of ~ 50 mAh.g-1 at high-rate performance while full-cell using LiTFSI-based electrolyte displays a negligible capacity value. To explain, the total resistance of 25 Ohm is obtained for full cell LiPF6 + 5 wt%. FEC is three times lower than full-cell 1M LiTFSI + 2.5 wt% FEC + 2.5wt% VC. Furthermore, the HR-TEM ex-situ indicates that the stability of SEI layer formation is consistent in thickness but exhibits uneven distribution when using different electrolytes. Besides, the SEI components analyzed by XPS data indicate the presence of carbonate groups and LixPFyOz-based compounds due to the irreversible reactions on the SEI layer after the initial discharge cycle. This research brings some remarkable information to study the electrolyte compatibility for full-cell performance using C/SiO2 as an anode material. Figure 1

Boron based podand molecule as an anion receptor additive in Li-ion battery electrolytes: A combined density functional theory and molecular dynamics study

This article explores the potential of boron based molecules as electrolyte additives in lithium ion batteries (LIBs) to increase conductivity and solid electrolyte interface formation. Specifically, a new class of B-based podand molecule is introduced as an anion receptor additive in LIB electrolytes. The efficacy of this novel additive is studied using Density functional theory (DFT) and atomistic molecular dynamics (MD) simulation, and its performance is compared to a commonly used B-based additive, TPF, in different solvent environments. Results show that the designed additive is more efficient in binding PF6- ion, promoting the diffusion of Li+ and lowering viscosity under various conditions. Some calculated properties are validated with existing experimental data. This research holds promise for the development of more efficient and effective energy storage solutions.

Blending fiber-shaped long-range conductive additives for better battery performance: Mechanism study based on heterogeneous electrode model

Conductive additives in lithium-ion batteries are indispensable for constructing electronic conductive networks and enabling continuous electrochemical reactions. Fine carbon black powder, typically composed of small round particles with a diameter of tens of nanometers, is the most commonly used conductive additive. The experimental results in some literature indicate that blending fiber-shaped conductive additives can help boost battery performance. The heterogenous electrode model is employed in this study to explore the distribution of electronic current density within lithium-ions batteries, demonstrate the benefits of blending fiber-shaped long-range conductive additives, and shed light on its mechanism. Our findings show that the introduction of long-range conductive additives leads to reallocation of the electron flow: as the proportion/weight ratio of long-range conductive additives increases, the electronic current undertaken by all conductive additives increases, while that undertaken by the active particles decreases. Without changing the total wt.% of conductive additives in batteries, the ohmic resistance of the electrode and the whole cell can be significantly reduced due to more electrons passing through compositions with better conductivity. These results help researchers gain a better understanding on the correlation between conductive network geometry and electron transfer effectiveness.

Design Strategies of Flame-Retardant Additives for Lithium Ion Electrolyte

Abstract As the energy density of lithium-ion batteries continues to increase, battery safety issues characterized by thermal runaway have become increasingly severe. Battery safety issues have severely restricted the large-scale application of power batteries. Among them, the flammable liquid organic electrolyte is one of the main reasons for the safety hazards of battery thermal runaway. This article reviews the flame-retardant mechanism and research progress of phosphorus-based flame-retardant additives, nitrogen-based flame-retardant additives, and halogen-based flame-retardant additives. The design strategies of conventional flame-retardant additives and intelligent flame-retardant additives in lithium-ion batteries are summarized. Finally, a development direction and research prospects of flame-retardant additives in lithium-ion battery electrolytes are prospected.

Comprehensive Insight into the Probability of Cyclotriphosphazene Derivatives as the Functional Electrolyte Additives in Lithium-Ion Batteries: Which Is Better and Why?

Enhancing the flame retardancy of electrolytes and the quality of interface films is of great significance to improve the safety performance of lithium-ion batteries (LIBs). In this work, the effects of (ethoxy)pentafluorocyclotriphosphazene (PFPN), hexafluorocyclotriphosphazene (FPPN), and pentafluoro(phenoxy)cyclotriphosphazene (HFPN) as flame-retardant additives in the functional electrolyte on the performances of LiNi0.6Mn0.2Co0.2O2 (NCM622)/graphite pouch cells are comprehensively investigated. It is indicated that the contents of PFPN, FPPN, and HFPN, respectively, reach 5, 8, and 8% to achieve the purpose of flame retardancy in the 1 M LiPF6/EC + EMC (EC/EMC = 1:2 in weight) system. When the cells without and with PFPN, FPPN, and HFPN additives are, respectively, charge–discharged in the voltage range of 3.0–4.4 V at 1C, their capacity retentions are 36.1, 60.7, 74.7, and 73.8% after 150 cycles. The interface analysis and theoretical calculation show that PFPN, FPPN, and HFPN can facilitate the formation of stable interface films on two electrodes and subsequently improve the battery performance. The addition of cyclotriphosphazene flame retardant in the electrolyte ultimately improves the safety of NCM622/graphite pouch cells without sacrificing electrochemical performance. The as-prepared additive-containing electrolyte exhibits promising prospects in the application, and the evaluation method is also useful to develop the functional electrolyte with flame retardant and film-forming properties.

Thermal Effect and Mechanism Analysis of Flame-Retardant Modified Polymer Electrolyte for Lithium-Ion Battery.

In recent years, the prosperous electric vehicle industry has contributed to the rapid development of lithium-ion batteries. However, the increase in the energy density of lithium-ion batteries has also created more pressing safety concerns. The emergence of a new flame-retardant material with the additive ethoxy (pentafluoro) cyclotriphosphazene can ameliorate the performance of lithium-ion batteries while ensuring their safety. The present study proposes a new polymer composite flame-retardant electrolyte and adopts differential scanning calorimetry (DSC) and accelerating rate calorimetry to investigate its thermal effect. The study found that the heating rate is positively correlated with the onset temperature, peak temperature, and endset temperature of the endothermic peak. The flame-retardant modified polymer electrolyte for new lithium-ion batteries has better thermal stability than traditional lithium-ion battery electrolytes. Three non-isothermal methods (Kissinger; Kissinger–Akahira–Sunose; and Flynn–Wall–Ozawa) were also used to calculate the kinetic parameters based on the DSC experimental data. The apparent activation energy results of the three non-isothermal methods were averaged as 54.16 kJ/mol. The research results can provide valuable references for the selection and preparation of flame-retardant additives in lithium-ion batteries.

In Situ Measurement of Ionic and Electronic Conductivities of Conductive Polymers as a Function of Electrochemical Doping in Battery Electrolytes

Conductive polymers are being studied increasingly as additives in lithium-ion batteries, supercapacitors, and other electrochemical devices due to their ability to conduct electrons and ions and s...

Research progress of fluorine-containing electrolyte additives for lithium ion batteries

The construction of Solid Electrolyte Interface (SEI) film in Li-ion batteries with functional electrolyte additives is able to passivate the active material surface and inhibit the decomposition of the electrolyte continuously. In addition, safety issue is also an important factor restricting the large scale application of present lithium-ion batteries. Therefore, the additives for film-forming and safety enhancement are a class of cost-effective components that promote the application and development of batteries. Fluorine is a kind of “bipolar” element, which has strong electronegativity and weak polarity. Fluorine-containing electrolyte additives have excellent kinetic reactivity, which can preferentially generate stable SEI films and uniform Cathode-Electrolyte Interface (CEI) films to effectively improve the electrochemical performance of the batteries. Meanwhile, fluorine-containing electrolyte additives can also be used as flame-retardants to improve safety performance. In this review, we summarize the research status of fluorine-containing additives in recent years and elaborate its reaction mechanisms of improving battery performance. Finally, a personal perspective on the future of the development of fluorine-containing additives is presented.

Zwitterionic osmolyte-inspired additives as scavengers and low temperature performance enhancers for lithium ion batteries

Zwitterionic lithium-silica sulfobetaine silane (Li-SiSB) is fabricated and used as an additive together with hydroxyl–terminated poly(dimethylsiloxane) (PDMS-HT) for use as low temperature additives in lithium ion batteries (LIB). The additives dissolved in 1 M LiPF6 (ethylene carbonate/dimethyl carbonate = 1:1). The electrolyte containing Li-SiSB and PDMS-HT shows higher ionic conductivity (1.54 × 10-3 Scm−1 at −20 °C). Full cells show enhanced specific capacity at higher C-rates in the presents of additives due to anti–freezing and enhanced ionic conductivity. The also enhance early, stable and dense SEI which in turn leads to improved cycling stability. These results merit the use of both Li-SiSB and PDMS-HT as electrolyte additives for improved low temperature performance in lithium-ion batteries.

In-Situ EIS to Investigate Effect of C-Rate on Impedance Spectra of Positive Electrodes with Different Ratio of Conductive Additives in Lithium Ion Batteries

Active materials, conductive additives and binders are widely used for the fabrication of positive electrodes of lithium ion batteries (LIBs). The electrochemical performance of positive electrodes is affected by the addition rate of conductive additives on the electrode 1). It is important to investigate the effect of the addition rate of conductive additives on the electrode performance of the positive electrode during charge-discharge cycle in order to develop LIBs that can charge and discharge at high C-rate. In the present study, the in-situ EIS 2) was employed to investigate the effect of C-rate on impedance spectra of positive electrode with different additive rates of conductive additives.The positive electrode with different additive rates of acetylene black (AB) was fabricated by screen printing. The mixture of the slurry containing LiCoO2 powder, AB, polyvinylidene fluoride and N-methylpyrrolidone were screen-printed on the aluminum foil. In the present study, the positive electrode with different additive rates of AB was used for the impedance measurement. The spherical natural graphite fabricated on cupper foil was used as the negative electrode and a lithium wire was used as the reference electrode (RE). All measurements were carried out by the three-electrode cell (Toyo system co. ltd.) at room temperature in an argon atmosphere.The 3D impedance of positive electrode, negative electrode and full cell was measured by in-situ EIS during charge and discharge. In the 3D impedance of positive electrode, three loops were observed on the Nyquist plane during charge and discharge. As the diameter of loop in the low frequency range was decreased with the increase of the state of charge (SOC), this loop may be related to the time constant composed of the charge transfer resistance R ct and the electric double layer capacitance 2). In order to examine the effect of C-rate on impedance of positive electrode, the changes of R ct values during charge and discharge were estimated from the instantaneous impedance at arbitrary SOC on 3D impedance of positive electrode. The relationship between C-rate and additive rates of AB on the impedance of positive electrode was discussed.

Regulation of Cathode-Electrolyte Interphase via Electrolyte Additives in Lithium Ion Batteries.

As the power supply of the prosperous new energy products, advanced lithium ion batteries (LIBs) are widely applied to portable energy equipment and large-scale energy storage systems. To broaden the applicable range, considerable endeavours have been devoted towards improving the energy and power density of LIBs. However, the side reaction caused by the close contact between the electrode (particularly the cathode) and the electrolyte leads to capacity decay and structural degradation, which is a tricky problem to be solved. In order to overcome this obstacle, the researchers focused their attention on electrolyte additives. By adding additives to the electrolyte, the construction of a stable cathode-electrolyte interphase (CEI) between the cathode and the electrolyte has been proven to competently elevate the overall electrochemical performance of LIBs. However, how to choose electrolyte additives that match different cathode systems ideally to achieve stable CEI layer construction and high-performance LIBs is still in the stage of repeated experiments and exploration. This article specifically introduces the working mechanism of diverse electrolyte additives for forming a stable CEI layer and summarizes the latest research progress in the application of electrolyte additives for LIBs with diverse cathode materials. Finally, we tentatively set forth recommendations on the screening and customization of ideal additives required for the construction of robust CEI layer in LIBs. We believe this minireview will have a certain reference value for the design and construction of stable CEI layer to realize desirable performance of LIBs.

Asymmetric Imides as Electrolyte Additive for Lithium‐Ion Batteries with NCM111 Cathode

AbstractThe synthesis, spectroscopic and electrochemical characterization of Li[N(SiMe3)(SO2RF)] (RF=CF3, n‐C4F9) as well their behavior as electrolyte additive in lithium ion batteries (LIBs) is reported. The lithium salts were obtained by deprotonation of the corresponding acids HN(SiMe3)(SO2RF) with n‐butyllithium in n‐pentane. The electrochemical investigations suggested potential as additives for LIBs. Thus, NCM111/graphite cells (NCM111=Li[Ni0.33Co0.33Mn0.33]O2) with LP57 as electrolyte (LP57=1.0 M LiPF6 in EC/EMC 3 : 7) were built to test the performance. Cells with Li[N(SiMe3)(SO2RF)] as additives show coulombic efficiencies of over 99.6 %, less capacity fading over 55 cycles and a significantly lower cell impedance built up.

Preparation of BF3 Carbonates and their Electrochemical Investigation as Additives in Lithium Ion Batteries

This study reports the behavior of the compounds BF3·D (with D = dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate) as electrolyte additives in Li[Ni0.33Co0.33Mn0.33O2]/graphite cells with LiPF6 (1 M) in EC:EMC (3:7 wt%) as electrolyte. The adducts were prepared from gaseous BF3 with the corresponding carbonates in a simple Lewis acid base reaction and fully characterized (FT–IR and NMR spectroscopy, single crystal X-ray diffraction). The electrochemical behavior of the additives was examined at concentrations of 1 wt% and 0.25 wt% added to the electrolyte. Electrochemical impedance spectroscopy of cells with 1 wt% additive, display a significantly lower cell impedance than cells without additive, but also a slightly decreased capacity. To combine the high capacity retention with a low cell impedance the concentration of the additive was reduced. Thus, cell testing with 0.25 wt% additive incorporated with the electrolyte showed no difference in capacity retention after 55 cycles at 25 °C, but had lower cell impedance. The rate-performance test shows a higher capacity retention for cells with additive at high C–rates. The surface chemistry of the electrodes was studied by X-ray photoelectron spectroscopy and suggests that the additives react on both electrodes (Li[Ni0.33Co0.33Mn0.33O2] and graphite) and improve the electrode interphases.

New Insight on the Role of Electrolyte Additives in Rechargeable Lithium Ion Batteries

Solid electrolyte interphase (SEI)-forming agents such as vinylene carbonate, sulfone, and cyclic sulfate are commonly believed to be film-forming additives in lithium-ion batteries that help to en...

Hierarchical Carbon Nano Fibres for Flexible Zn-Air Batteries

Nanostructured functional materials, specifically carbon nanofibres/nanotubes, are attractive due to their chemical stability and electrochemical properties. Carbon based structures across different length scales have already been used in a range of energy applications including carbon papers for proton exchange membrane fuel cells, carbon nanofibers for supercapacitors and carbon nanotubes as conductive additives in lithium-ion batteries. The development of hierarchical, designed nanomaterials bridging length scales is required for next generation devices because each length scale of interest offers certain advantages, macro-scale fibres offering ease of fabrication and nano-scale tubes offering superior electrochemical performance. Functional carbon nanofibers with hierarchical architectures are essential components in advanced energy applications. Here, we present a simple approach to preparing highly engineered, hierarchical nanofibers and a simple heat treatment. This simple synthesis route has been successfully developed to prepare a 3D structure consisting of large backbone fibres decorated with hierarchical, small carbon nanotubes produced via in-situ growth during carbonisation. The carbon nanofiber with hierarchical structure can significantly enhance the nanoporous 3D carbon network by increasing the specific surface area and number of electron and ion pathways, resulting in a doubled power density when compared to the carbon nanofiber without hierarchical structure. When utilized as an air cathode in the solid-state zinc-air battery, the carbon nanofiber with hierarchical structure showed markedly better electrochemical performance, delivering a long cycle life while remaining highly flexible.

Holey graphenes as the conductive additives for LiFePO4 batteries with an excellent rate performance

Graphene has been investigated and widely used as the high performance conductive additives in lithium ion batteries. Unfortunately, the LiFePO4 batteries with graphene additives present quite a low rate performance because the graphene with planar structure blocks the Li ion transportation. Herein, a binary conductive additive containing only 1 wt% holey graphene (HG) and 1 wt% Carbon Black such as Super-P (SP) has been developed, which achieves excellent high-rate performance for the LiFePO4 battery that is comparable to that of the battery with 10 wt% SP. The HG with large amount of holes and large specific surface area substantially enhances the electronic conductivity of LiFePO4 electrode, but not compromises the high efficient ionic transportation. A small content of SP as the supplement of long-range conductive network formed by HG can contact the LiFePO4 sufficiently for achieving excellent conductivity in the whole LiFePO4 electrode. A balance of electronic conductivity and ionic diffusivity can be achieved using the HG and SP simultaneously. The HG and SP with low content can synergistically construct an excellent ionic and electronic conductive network in LiFePO4 electrode. This study may promote the commercial applications of HG additives for high performance LiFePO4 batteries.

Zwitterions for Organic/Perovskite Solar Cells, Light‐Emitting Devices, and Lithium Ion Batteries: Recent Progress and Perspectives

AbstractZwitterions, a class of materials that contain covalently bonded cations and anions, have been extensively studied in the past decades owing to their special features, such as excellent solubility in polar solvents, for solution processing and dipole formation for the transfer of carriers and ions. Recently, zwitterions have been developed as electrode modifiers for organic solar cells (OSCs), perovskite solar cells (PVSCs), and organic light‐emitting devices (OLEDs), as well as electrolyte additives for lithium ion batteries (LIBs). With the rapid advances of zwitterionic materials, high‐performance devices have been constructed with enhanced efficiencies by introducing them as interface layers and electrolyte additives. In this review, recent progress in OSCs, PVSCs, OLEDs, and LIBs by using zwitterions is highlighted. The authors also elaborate the role of various zwitterionic materials as interfacial layers and additives for highly efficient OSCs, PVSCs, OLEDs, and LIBs. This article presents an overview of device performance of zwitterionic materials. The structure–property relationship is also discussed. Finally, the prospects of zwitterion materials are also addressed.

Comparative Performance Evaluation of Flame Retardant Additives for Lithium Ion Batteries – I. Safety, Chemical and Electrochemical Stabilities

AbstractWithin this 1st part of a comparative study, flame retardant electrolyte additives (FRs), as candidates for lithium ion battery electrolytes, from four different phosphorous‐containing molecule classes, are investigated. The five FRs (tris(2,2,2‐trifluoroethyl)phosphate (TFP), tris(2,2,2‐trifluoroethyl)phosphite (TTFPi), bis(2,2,2 trifluoroethyl)methylphosphonate (TFMP), (ethoxy)pentafluorocyclotriphosphazene (PFPN) and (phenoxy)pentafluoro‐cyclotriphosphazene (FPPN)) are investigated in a comparative manner to conclude structure‐property relationships according to their self‐extinguishing time (SET), onset temperature of the thermal runaway, chemical and electrochemical stability. SET experiments using standard electrolyte (1 M LiPF6 in ethylene carbonate : dimethyl carbonate 1 : 1 wt%) confirm high reproducibility of the used SET device. The results reveal a strong dependency of the ignition time on the SET. Therefore it is suggested, to investigate the SET for various ignition times. All FR additives remain chemically stable for weeks after added to the standard electrolyte during storage (approved by nuclear magnetic resonance). Cyclophosphazenes show superior results concerning their first time of inflammation and thermal electrolyte stability (approved by adiabatic reaction calorimetry). All additives show partial electrolyte decomposition only during the first charge in voltammetric experiments.

Understanding Fluoroethylene Carbonate and Vinylene Carbonate Based Electrolytes for Si Anodes in Lithium Ion Batteries with NMR Spectroscopy.

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are widely used as electrolyte additives in lithium ion batteries. Here we analyze the solid electrolyte interphase (SEI) formed on binder-free silicon nanowire (SiNW) electrodes in pure FEC or VC electrolytes containing 1 M LiPF6 by solid-state NMR with and without dynamic nuclear polarization (DNP) enhancement. We find that the polymeric SEIs formed in pure FEC or VC electrolytes consist mainly of cross-linked poly(ethylene oxide) (PEO) and aliphatic chain functionalities along with additional carbonate and carboxylate species. The formation of branched fragments is further confirmed by 13C-13C correlation NMR experiments. The presence of cross-linked PEO-type polymers in FEC and VC correlates with good capacity retention and high Coulombic efficiencies of the SiNWs. Using 29Si DNP NMR, we are able to probe the interfacial region between SEI and the Si surface for the first time with NMR spectroscopy. Organosiloxanes form upon cycling, confirming that some of the organic SEI is covalently bonded to the Si surface. We suggest that both the polymeric structure of the SEI and the nature of its adhesion to the redox-active materials are important for electrochemical performance.