Lithium Loss Research Articles

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells.

Silicon (Si)‐based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re‐formation of the solid electrolyte interphase and consumption of active lithium. The pre‐lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si‐based LIB full‐cells and enable their practical implementation. Here, the use of lithium squarate (Li2C4O4) as low‐cost and air‐stable pre‐lithiation additive for a LiNi0.6Mn0.2Co0.2O2 (NMC622)‐based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full‐cells is reported, which grows linearly with the initial amount of Li2C4O4, due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre‐lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre‐lithiation additive.

Spatially Resolved Operando X-Ray Absorption Spectroscopy in NCA/Graphite to Quantify the Potential-Dependent Transition Metal Dissolution and Its Effect on Capacity Fading

Layered transition metal oxides like NCAs (LiNixCoyAlzO2, with x+y+z=1) and NCMs (LiNixCoyMnzO2, with x+y+z=1) are used as cathode active materials (CAMs) for high energy Li-ion batteries due to their high capacity. However, at high upper cut-off potentials, those CAMs suffer from structural instabilities, resulting in severe capacity fading and thus limiting the accessible capacity that can be obtained. Possible causes for the capacity fade at high cut-off potentials and high state-of-charge (SOC) include the (electro)chemical oxidation of the electrolyte oxidation and transition metal (TM) dissolution from the CAM surface.1 Furthermore, layered TM-oxides are known to release lattice oxygen from the near-surface region at high SOC (i.e., at ≈80% SOC when referenced to the total amount of lithium), resulting in reactive oxygen species that induce electrolyte oxidation and HF formation.2 This release of lattice oxygen results in a surface reconstruction from the pristine layered structure to a more resistive spinel- or rocksalt-like structure, thereby inducing an impedance build-up on the cathode. Diffusion of dissolved transition metals to the anode and their subsequent deposition on the anode active material particles can also have a severe effect on cell aging, as the accumulation of metal species on the graphite anode has shown to catalyze the degradation of the protective anode solid/electrolyte interphase (SEI), eventually resulting in the loss of active lithium and in an anode impedance growth. Since the dissolution of manganese is considered to have the most detrimental effect on the anode SEI compared to cobalt and nickel,3 manganese-free NCAs (e.g., LiNi0.8Co0.15Al0.05O2) might have an advantage over manganese-containing NCMs.In this study, we will examine the potential-dependent dissolution of Ni and Co in NCA/graphite cells using operando XAS, and compare it to the potential-dependent dissolution of Ni, Co, and Mn from LiNi0.6Co0.2Mn0.2O2 (NMC622) that we had determined previously by operando XAS.4 Owing to the specially designed geometry of the operando XAS cell,5 we can spectroscopically access and independently investigate the concentration and oxidation state of transition metals, both dissolved in the electrolyte and deposited within the graphite anode. This is illustrated for an NCA/graphite cell in Figure 1. We will also examine the effect of lattice oxygen release from NCA on the NCA/graphite full-cell performance by applying different techniques: We employ a three-electrode Swagelok® type T-cell with a gold wire micro reference electrode (µ-GWRE)6 to quantify the anode and the cathode impedance over the course of 100 cycles as a function of the upper cutoff voltage. In addition, on-line electrochemical mass spectrometry (OEMS)7 is applied to detect the onset SOC for the release of lattice oxygen. From these comparisons, we aim to get a detailed understanding about the influence of transition metal dissolution from NCA on capacity fade and cycle life.

Optimal Charging Protocols to Restrict Lithium-Ion Battery Degradation

Lithium-ion batteries degrade due to several mechanisms that occur during cell operation. These mechanisms can be parasitic reactions that lead to loss of lithium inventory or loss of active material. Some examples of these side reactions include the growth of the solid-electrolyte interphase (SEI) layer, transition metal dissolution and deposition, lithium plating, solvent oxidation, etc. Thermal effects and mechanical fatigue on the electrodes also lead to cell aging and capacity fade.For widespread implementation of lithium-ion batteries for electric vehicles, batteries should last approximately 10 years.1 Fast charging has also been heavily researched for accelerating this prevalent circumstance. However, charging at high currents can severely degrade the cell, affecting the cell’s lifetime. Algorithms that optimize charging can be effective to reduce cell aging. Physics-based battery models can be used to design these algorithms by restricting phenomena that occur in the cell that causes cell aging. For example, lithium plating can be prevented by restricting the overpotential of the reaction.In our previous work, we have shown optimal charging profiles where the intercalation induced stresses, lithium plating and the SEI layer growth was restricted using reformulated physics-based models using model-based control 2 - 3 In this talk, we show different optimal charging protocols for restricting different mechanisms, and analyze the interplay between them to predict optimal charging profiles. References M. T. Lawder, P. W. C. Northrop, and V. R. Subramanian, J. Electrochem. Soc., 161, A2099–A2108 (2014).B. Suthar, P. W. C. Northrop, R. D. Braatz, and V. R. Subramaniand, J. Electrochem. Soc., 161, F3144–F3155 (2014).M. Pathak, D. Sonawane, S. Santhanagopalan, R. D. Braatz, and V. R. Subramanian, ECS Trans., 75, 51–75 (2017).

An Improved Pre-Lithiation of Graphite Anodes Using through-Holed Cathode and Anode Electrodes in a Laminated Lithium Ion Battery

In order to actually compensate “an irreversible capacity (i.e., an active lithium loss) ˮ usually observed at the 1st charging/discharging cycle of lithium ion batteries (LIBs), e.g., caused by a solid-electrolyte interphase (SEI) formation, a so-called pre-lithiation was applied to the graphite anodes of the laminated cell composed of three graphite anodes and three LFP (lithium iron phosphate) cathodes which were through-holed with the hole diameter of 20, 100 or 200 μm like the squares of a “Go-board” (Fig. 1). The pre-lithiation was carried out (keeping an appropriate pre-lithiation charge amount) firstly by directly contacting the anodes with Li metal, which was previously introduced in the cell, to intercalate Li+ ions to them and then conducting the capacity balancing among the Li+-intercalated anodes by contacting them for a various period of time (Fig. 2). It was found that in the cell composed of the through-holed anodes and cathodes with a given hole diameter the irreversible capacity can be significantly reduced by appropriately choosing the pre-lithiation charge amount and the capacity balancing time. Typically, in the anodes (the hole diameter: 20 μm) with the total capacity of 35 mAh, when the pre-lithiation charge amount was 3 mAh and the capacity balancing time was 12 h, no irreversible capacity could be observed actually, i.e., the 1st charge capacity was close to 100% and the expected stable charge/discharge capacities were obtained with the capacity retention of almost 100% in the continuous charge/discharge cycle. The results obtained demonstrate that the pre-lithiation of LIBs can be significantly improved using through-holed anodes and cathodes. Figure 1

Direct Recycling of Cathode Active Materials from EV Li-Ion Batteries

Direct recycling of Li-ion batteries is a promising and low-cost recycling technology since the process recovers values of active materials directly without converting active materials into metal elements. However, the process is challenging from a separation perspective due to purity requirement. Herein, a new physical separation system was developed to recycle and produce ultra-high purity of cathode active materials from EV Li-ion batteries. Results showed that the recycled cathode active material product contained 99% purity of active materials with less than 500 ppm of aluminum and copper. Both the stoichimetry and structure of the recycled cathode active materials remained the same compared with those collected manually from electrode sheets. Results obtained from electrochemical testing showed that the capacity of the recycled materials was comparable to that of pristine cathode active materials, despite there was a lithium loss associated with battery charging and discharging. The present result demonstrates a viable direct recycling process for electric vehicle Li-ion batteries.

Thickness change and jelly roll deformation and its impact on the aging and lifetime of commercial 18650 cylindrical Li-ion cells with silicon containing anodes and nickel-rich cathodes

Two types of commercial cylindrical cells in the format 18650 both with NCA cathode and anodes containing different silicon materials were electrochemically long-term cycled. Two voltage windows and their influence on the aging of the cells were investigated. Multiple CT images after a pre-determined number of completed cycles reveal volume expansion and jelly roll deformation during the aging of the cells. With an optical micrometer, the reversible and irreversible thickness change was studied in operando. Furthermore the electrode expansion was investigated with an electrochemical dilatometer. Depending on the type of silicon active material used, differences in the aging behavior of the cells were observed. These findings were linked to the rest of the non-destructive, destructive and post-mortem analyses. With the help of differential voltage analysis, pulse tests and different evaluations using the generated CT data, the inhomogeneous thickness change of the cells especially at critical spots could thus be revealed and reasons for capacity degradation or resistance increase can be directly seen. Due to post-mortem analysis a much better understanding of the underlying aging mechanisms was generated. With SEM/EDX analysis, ICP-OES and TGA, the formation of passivation layers on the electrodes was observed. By comparing the results with new cells, individual causes of failure were revealed. It was found that the main aging mechanism is the loss of lithium from the cathode together with the volume change of the anode. Cells with pure Si instead of SiOx have exhibited a faster degradation because of the additionally higher thickness change during charging and discharging. Delamination of the electrode coating because of particle swelling, binder failure and jelly roll deformation is seen after unrolling the aged cells. Limiting the voltage range leads to longer lifetime, less resistance increase and overall less aging of silicon in all tested cells.

Lithium oxide loss of lithium niobate nanocrystals during high-energy ball-milling

Congruent lithium niobate (LiNbO 3 ) prepared by sintering was ground under wet conditions in a planetary mill in order to produce nanocrystals. By using gradually lower sizes of the balls in the mill, the final particle size of the crystals could be reduced to about 12–15 nm. The particle size achieved as well as the lithium oxide (Li 2 O) loss of the lithium niobate particles were followed as a function of the grinding time. Lithium oxide was found to be released throughout the entire milling procedure, even in the case when the particle size no longer changed upon the grinding with a particular ball size. About 12% and 20% Li 2 O loss was detected upon grinding with 3 mm and 0.5 mm balls, respectively. X-ray diffractometry revealed the formation of a lithium-deficient phase, LiNb 3 O 8 , the presence of which was confirmed by means of Raman spectroscopy. The LiNb 3 O 8 :LiNbO 3 volume ratio achieved for 70 nm particle size as calculated from both the diffractograms and the lithium oxide loss determined by coulometric titration was assessed to be 0.39 (± 0.03). Correlation was revealed between the composition change of the nanopowder and the total surface area of the particle assembly calculated from dynamic light scattering measurements. • Lithium niobate nanopowders were produced with the help of a planetary mill. • The loss of lithium oxide and formation of LiNb 3 O 8 were observed upon milling. • The lithium loss during the wet grinding process was quantitatively characterized. • Particle size determined by SEM and DLS were in good agreement. • The surface area increase of the particle assembly correlated with the Li 2 O release.

Effect of precursor structure transformation on synthesis and performance of LiNi0.5Co0.2Mn0.3O2 cathode material

The precursor has great influences on electrochemical performance of LiNi1-x-yCoxMnyO2 cathode materials. However, the effect of precursor structure transformation on the synthesis and electrochemical performance of LiNi1-x-yCoxMnyO2 is rarely mentioned. In this paper, Ni0.5Co0.2Mn0.3(OH)2 and different-temperature-preheated Ni0.5Co0.2Mn0.3(OH)2 were synthesized to prepare LiNi0.5Co0.2Mn0.3O2. The results show that Ni0.5Co0.2Mn0.3(OH)2 precursor transform into spinel-type solid solution (Ni0.5Co0.2Mn0.3)3O4 after preheating, and the contents of Ni3+, Co3+ and Mn4+ increase significantly. Comparative analyses reveal that the precursor structure change has no obvious effects on the crystal structure and surface morphology of the prepared LiNi0.5Co0.2Mn0.3O2. But the preheated precursors can reduce the undesirable lithium loss due to lithium volatilization in the high-temperature sintering process, leading to excess lithium ions enter into transition metal ions layer. Lithium excess can affect the amount of Ni3+, lattice parameters and residual lithium compounds on the particle surface, which in turn lead to different electrochemical behaviors of the prepared LiNi0.5Co0.2Mn0.3O2.

Production and Characterisation of Fibre-Reinforced All-Solid-State Electrodes and Separator for the Application in Structural Batteries

The electrification of the air transport sector demands for an energy storage that adds as little volume and weight to the overall system as possible. Regarding this so-called structural battery, composites enable the storage of electrical energy in commonly used load bearing fibre composite structures. A structural battery composite can store electrical energy while bearing mechanical loads, thus reducing parasitic mass and volume. In this study, structural cathodes were prepared by slurry coating carbon fibres with lithium iron phosphate (LFP), polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and carbon black. For the structural anodes, the carbon fibres were utilised as active material and slurry coated with PEO and LiTFSI. These structural electrodes as well as a structural separator were characterised by electrochemical cycling. With 139 mAhgAM−1, the structural cathodes demonstrated good utilisation of the active material. The carbon fibres used in the anode exhibited capacities of up to 92 mAhgAM−1. High irreversible lithium losses were observed, which are attributed to the poor electrolyte wetting behaviour of the carbon fibres. A structural battery demonstrator with a lithium metal anode was realised and reached a maximum specific energy of 64 Whkg−1 with respect to electrode and separator weight.

Effect of annealing on microstructure and thermal conductivity of Li2TiO3 and Li4SiO4

• The microstructure of Li 2 TiO 3 keeps stable during annealing. • The phase decomposition of Li 4 SiO 4 is observed during annealing. • Li 2 TiO 3 has stable thermal performance, however Li 4 SiO 4 degrades during long-term operation. Li 2 TiO 3 and Li 4 SiO 4 are considered as candidate tritium breeding materials due to its excellent physical, chemical and tritium release performance. Thermal conductivities of solid tritium breeding materials are determined by microstructure, sintering density and surface condition which will change during operation of fusion reactor. A comprehensive understanding of thermal performance of tritium breeding materials is essential due to the extreme operation condition in the fusion reactor. In this work, the microstructure and thermal conductivity was investigated for Li 2 TiO 3 and Li 4 SiO 4 annealed at the corresponding temperature of tritium breeding blanket. SEM (Scanning electron micrography) results presented the stable structure of Li 2 TiO 3 and instability of Li 4 SiO 4 . XRD (X-ray diffraction) and Raman indicated the disorder of the crystal structure. It can be attributed to lithium loss during annealing process. EPR (Electron paramagnetic resonance) showed that there were almost no defects related unpaired electron. It is due to defect recovery at higher temperature, as well as tiny H 2 amount in sweeping gas. There was no obvious change of thermal performance for Li 2 TiO 3 during different annealing time. It is indicated that Li 2 TiO 3 has a good thermal performance to resist heat load. But thermal performance of Li 4 SiO 4 decreased largely after annealing. It is resulted from variation of the structure during annealing process. Based on the present work, it is illustrated that Li 2 TiO 3 has stable thermal performance under annealing condition, however, the thermal performance of Li 4 SiO 4 is not so stable for long service time at higher temperature.

Quantifying lithium lost to plating and formation of the solid-electrolyte interphase in graphite and commercial battery components

A key degradation mechanism in lithium-ion batteries (LIBs) is the irreversible loss of cyclable lithium during cycling. At the graphite negative electrode, this loss occurs through the deposition of lithium-containing compounds in the solid-electrolyte interphase (SEI) and through plating of metallic lithium, resulting in so-called dead lithium. The separate quantification of SEI and dead lithium has so far been a challenge in post mortem analysis of commercial LIBs. Here we report a simple and fast 7Li nuclear magnetic resonance spectroscopy (NMR) protocol applied to solid-state samples derived from lab-built batteries to independently quantify these and other lithium species in graphite electrodes without the need for specialized cell design nor knowledge of prior charging history. The metallic lithium content is corroborated by electrochemical calculations; the total amount of lithium is also determined from 7Li liquid-state NMR and inductively coupled plasma optical emission spectroscopy (ICP-OES) in suitably digested samples. Factors influencing accuracy like the sample handling process, the radiofrequency skin effect, and re-intercalation losses are investigated. Measurements on samples from commercial cells aged under realistic conditions demonstrate quantification of dead lithium and remaining ionic species (SEI), and further reveal lithium dendrites entrained in the separator following cell disassembly. The method uses conventional and widely available NMR instrumentation and is applicable to samples from lab-scale test cells or commercial batteries, thereby presenting a vast improvement over prior post mortem methods.

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

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

New Insight into Effects of Higher Upper Cutoff Voltage on the Cycling Performance of Graphite‐SiOx/Li‐rich Layered Oxide Pouch‐Type Batteries

High‐energy‐density lithium‐ion batteries based on the graphite–SiOx anode and Li‐rich layered oxide (LLO) cathode are expected to solve the “range anxiety” of electric vehicles, but face undesired capacity degradation. Usually, the rise in upper cutoff voltage (UCV) can increase the capacity but reduce the cycle life. Herein, the effect of different UCVs (4.4, 4.5, 4.6 V) on graphite–SiOx/LLO pouch‐type battery capacity degradation is investigated. Unexpectedly, the batteries at 4.5 and 4.6 V UCVs exhibit the minimum and maximum capacity after 300 cycles, separately. The comprehensive analysis shows that after 300 cycles, a greater loss of anode active material for the battery at 4.5 V UCV occurs, and a larger reversible lithium loss at 4.4 V UCV appears. Nevertheless, for the battery at 4.6 V UCV, a more stable solid electrolyte interphase film generated on the anode slows down the capacity degradation.

Revealing the Impact of Fast Charge Cycling on the Thermal Safety of Lithium-Ion Batteries

The safety of the degraded lithium-ion batteries has an essential impact on second life application. This study systematically investigates the thermal safety changes of lithium-ion batteries after deep aging under the fast charge aging path and reveals the degradation mechanisms caused by fast charge cycling. Lithium plating is the primary degradation mechanism, which thickens the solid electrolyte interface film, causes the loss of active lithium and electrolyte, and leads to a significant increase in impedance and a dramatic decrease in capacity. Therefore, compared with the fresh cells, the heat generation rate increases, while the total heat generation is reduced for aged cells. Besides, the thickened solid electrolyte interface film has lower thermal stability, decreasing the self-heating temperature for aged cells. Furthermore, thermal runaway results of partial cells prove that fast charge cycling reduces the thermal stability of the anode, which further proves that the thermal runaway-triggering temperature decrease is the result of the combination of the anode–electrolyte and anode–cathode reactions. Moreover, fast charge cycling reduces the lithium plating potential upon overcharging, which leads to the occurrence of side reactions in advance, creating the ratio of side reaction heat increase of aged cells for thermal runaway triggering. In addition, the loss of active materials reduces the maximum temperature and maximum temperature rise rate of the aged cell. The findings can provide references for battery safety management system optimization and safer battery screening.

Achieving SEI preformed graphite in flow cell to mitigate initial lithium loss

The irreversible lithium loss due to the formation of solid electrolyte interphase (SEI) in the initial cycle on the graphite anode greatly reduces the overall cell energy density of lithium ion batteries, that is, the lost Li ions from forming SEI lead to the decrease of Li ions for the intercalation. The method of cathode prelithiation has been widely explored to compensate this lithium loss. However, these cathode additives with high lithium contents inevitably lower the loading of the cathode active materials. Here we report a novel approach to solve this challenge, a facile graphite prelithiation method by preforming SEI layers on the surface of graphite powders (Pre-SEI graphite) utilizing a specially designed flow cell. The Li accommodation in the graphite anode can be controlled by the operating time and current density in the flow cell for the electrochemical SEI formation. As a result, we demonstrate a 10% initial Columbic efficiency increase of the LiFePO4 electrode in a full cell configuration using the Pre-SEI graphite, compared with the pristine graphite anode. The electrochemical preformation of SEI on the graphite powders offers a complete solution to offset initial lithium loss without a sacrifice of active cathode material loading.

Comparative study on aging and thermal runaway of commercial LiFePO4/graphite battery undergoing slight overcharge cycling

Overcharging may occur due to the inconsistency of lithium-ion batteries (LIBs), which is likely to trigger battery failure or thermal runaway (TR). Herein, the aging mechanism and TR behavior of aged LiFePO4 batteries induced by different degrees of slight overcharge cycling are studied. First, the capacity degradation and aging mechanisms are studied qualitatively and quantitatively by conducting in-situ experiments. The results indicate that the high cut-off voltage (4.5 V) accelerates capacity fading, which is dominated by loss of lithium. However, capacity retention is benefited if the overcharge voltage is properly increased (4 and 4.2 V). Then, the TR behavior of cells is tested using the extended volume accelerating rate calorimeter (EV-ARC). The results indicate that the thermal stability of aged cells worsens because the internal short circuit is more likely to occur due to lithium plating on the anode experiencing overcharge cycling. Finally, the intrinsic interaction between the aging mechanism and TR features of slightly overcharged LIBs is revealed. Meanwhile, we also provide valuable information regarding the reusability of LIBs undergoing overcharge cycling. Therefore, this study is useful for battery safety design and early warning of TR.

Frontispiece: Prelithiation Reagents and Strategies on High Energy Lithium‐Ion Batteries

Prelithiation is an effective strategy for compensating irreversible lithium loss during the formation of an anode passivating layer in lithium-ion batteries, and so for improving the energy density. In their Review on page 5▪ff., Luo and Zhou et al. 10.1002/chem.202104282 briefly describe the various types of prelithiation methods with respect to the working mechanism, electrochemical performance, advantages, and potential challenges, with the aim of aiding the future design of prelithiation. In addition, the further developments of prelithiation to suit the real production environments are also discussed.

Influence of external pressure on silicon electrodes in lithium-ion cells

The influence of external pressure on lithium-ion cells containing a silicon anode is investigated. The performance of pouch-type full cells under rigid compression is compared to unconstrained cells, where the electrode stack is allowed to swell during cycling. The negative electrode contains only silicon as active material, while prelithiated lithium titanium oxide (LTO) is used as the positive electrode. The results show that the main failure mechanism in such cells is a continuous irreversible consumption of lithium ions, likely due to repeated solid electrolyte interphase breakage and reformation. At high pressures, the lithium depletion has a larger influence than at lower pressures. This effect is examined by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) as well as dilation measurements of flexibly-constrained cells and can be traced back to an increase of the ionic pore resistance being more pronounced under high pressure. A new approach is used to compensate the lithium loss, i.e. internal relithiation of the LTO electrode via a lithium reservoir. This not only proves the theory of irreversible lithium consumption being the main challenge in these cells, but also enables cycling for 1000 cycles at 1200 mAhgSi−1 without capacity fading.

Fast and Simple Ag/Cu Ion Exchange on Cu Foil for Anode-Free Lithium-Metal Batteries

Lithium-metal batteries with zero excess lithium on the anode side paired with a fully lithiated cathode are regarded as a form of the highest energy-density configuration. Unfortunately, the continuous lithium loss over cycling from a limited amount of the lithium reservoir significantly degrades the overall cell performance in the anode-free system. To mitigate the deterioration, modifying the current collector for enhanced lithium cycling is an indispensable route. Here, we apply a Ag/Cu ion exchange to precipitate micro-sized Ag particles on the Cu current collector to enhance the lithium reversibility via a (de)alloying process. We show a smoother morphology of lithium upon alloying, which leads to a lowered nucleation potential as well as increased average Coulombic efficiency in Li||Cu cells regardless of electrolyte formulation. The preferred lithium adsorption on Ag and AgLi over Cu is demonstrated using density functional theory calculations, which supports that Li forms a gamma-phase alloy in the last stage rather than being deposited beneath the alloy. Lastly, this simple Cu foil modification enhances lithium reversibility and reduces its nucleation barrier, thus mitigating the capacity fade of Cu||LiFePO4 with reduced polarization.

Pre-Lithiation Strategies and Energy Density Theory of Lithium-Ion and Beyond Lithium-Ion Batteries

Pre-lithiation is the most effective method to overcome the initial capacity loss of high-capacity electrodes and has the potential to be used in beyond-conventional lithium-ion batteries. In this article we focus on two types of pre-lithiation: the first type can be applied to batteries in which the cathode has been fully lithiated but the anode has a large initial capacity loss, such as batteries made with lithium metal oxide cathode and silicon-carbon anode. The second type can be applied to batteries in which both electrodes are initially lithium-free and suffer a loss of lithium during the initial cycles, such as batteries made with sulfurized-polyacrylonitrile cathode and silicon-carbon anode. We describe the pre-lithiation procedures and electrode potential profiles during pre-lithiation corresponding to different pre-lithiation sources for both types of pre-lithiation. We also derive formulas for the theoretical specific energy and energy density that are based entirely on measurable parameters such as specific capacities, porosities, mass densities of two electrodes and extra lithium source, Coulombic efficiencies of electrodes, and the voltage of the cell. These formulas can be applied to different pre-lithiation sources to predict the specific energy of conventional and beyond-conventional lithium-ion batteries as a function of the type of pre-lithiation.