Lithium Desorption Research Articles

Regeneration of graphite from spent lithium‐ion batteries as anode materials through stepwise purification and mild temperature restoration

AbstractGraphite is one of the most widely used anode materials in lithium‐ion batteries (LIBs). The recycling of spent graphite (SG) from spent LIBs has attracted less attention due to its limited value, complicated contaminations, and unrestored structure. In this study, a remediation and regeneration process with combined hydrothermal calcination was proposed to remove different impurities as value‐added resources from SG. This study focuses on the application of different removal methods for different impurity metals by hydrothermal and acid leaching under different conditions for the removal of Cu, Li, Co, Mn, and Ni from SG. Then, mild‐tempreture calcination of SG was performed to remove residual organic compounds. The regenerated graphite (RG) was found to have a better morphology structure and increased pore volume, which is more favorable for the embedding and desorption of lithium (Li) in graphite. In terms of electrochemical performance, the first discharge‐specific capacity of RG at 0.5 C is 359.40 mAh/g, with a retention of 353.49 mAh/g after 100 cycles (retention rate of 98.36%). This study can be a green and efficient candidate for the regeneration of graphite from spent lithium‐ion batteries as anode material by reduced restoration temperature, with different metal resources as by‐products.

Preparation of PVC-LMZO membrane and its lithium adsorption performance from brine

The forming technology of lithium ion sieves is of great significance for their industrial production and application in brine. A PVC-LMZO lithium ion sieve precursor membrane was prepared by blending the zirconium-coated lithium ion sieve precursor LMZO with PVC, PMMA and PVPk30. The adsorption and cyclic performance of the PVC-LMZO membrane obtained after treatment with HCl were studied. The results showed that the optimal condition for membrane preparation is to add 10 wt% PVC, 20 wt% LMZO, 6 wt% PMMA and 2 wt% PVPk30. After treatment with 0.1 mol·L−1 HCl for 2 h, the lithium desorption reached equilibrium, and the manganese loss rate was approximately 0.332 %. After 15 cycles of adsorption and desorption in brine, the Li+ adsorption capacity was lost by only 5.8 % (from 18.33 mg/g to 17.27 mg/g). The PVC-LMZO membrane had high selectivity for Li+ in brine containing a variety of complex ions such as K+, Ca2+, Na+ and Mg2+. The PVC-LMZO membrane has a stable structure and excellent recycling performance, which is conducive to its industrial application. The PVC-LMZO membrane accords with the Langmuir adsorption isotherm model and pseudo-second-order kinetics model, indicating a monolayer chemisorption. The PVC-LMZO membrane has great development potential for extracting lithium from liquid lithium resources such as salt lake brine.

Experimental and density functional theory study of the Li+ desorption in spinel/layered lithium manganese oxide nanocomposites using HCl

The increasing demand for portable electronic devices and batteries has led to a growing interest in Li compounds. Lithium manganese oxides (LMO) are the most popular lithium-ion sieves (LIS) precursor materials due to their high lithium adsorption capacity and selectivity. The key step in forming LIS is the lithium desorption process from the crystalline lattice of the LMO. However, this process has been less researched than its counterpart, the lithium adsorption process. In this line, there are some studies describing the process of lithium desorption in acid media from spinel-type LMO. Nevertheless, there is no evidence of the lithium desorption process of layered-type lithium-rich LMO in acidic media. In the present work, we investigated the lithium desorption behavior of different LMO nanocomposites in HCl. LMOs with different Li/Mn ratios were synthesized by promoting the lithium-rich layered phase (Li2MnO3). The morphology, size, crystallinity, chemical composition, and surface properties of LMO nanocomposites and delithiated products were studied. In addition, density functional theory (DFT) calculations were carried out to understand the differential lithium desorption behavior, confirming its dependence on the Li/Mn ratio of the LMO nanocomposites. Herein, we demonstrate that the lithium diffusion energy barrier plays a major role during lithium desorption from LMO nanocomposites. Our results suggest that an exhaustive characterization of lithium precursor materials (LMO) is necessary to select a suitable desorption process.

Novel composite materials of modified roasted date pits using ferrocyanides for the recovery of lithium ions from seawater reverse osmosis brine

In this paper, novel composite materials from modified roasted date pits using ferrocyanides were developed and investigated for the recovery of lithium ions (Li+) from seawater reverse osmosis (RO) brine. Two composite materials were prepared from roasted date pits (RDP) as supporting material, namely potassium copper hexacyanoferrate-date pits composite (RDP-FC-Cu), and potassium nickel hexacyanoferrate-date pits composite (RDP-FC-Ni). The physiochemical characterization of the RO brine revealed that it contained a variety of metals and salts such as strontium, zinc, lithium, and sodium chlorides. RDP-FC-Cu and RDP-FC-Ni exhibited enhanced chemical and physical characteristics than RDP. The optimum pH, which attained the highest adsorption removal (%) for all adsorbents, was at pH 6. In addition, the highest adsorption capacities for the adsorbents were observed at the initial lithium concentration of 100 mg/L. The BET surface area analysis confirmed the increase in the total surface area of the prepared composites from 2.518 m2/g for RDP to 4.758 m2/g for RDP-FC-Cu and 5.262 m2/g for RDP-FC-Ni. A strong sharp infrared peak appeared for the RDP-FC-Cu and RDP-FC-Ni at 2078 cm−1. This peak corresponds to the C≡N bond, which indicates the presence of potassium hexacyanoferrate, K4[Fe(CN)6]. The adsorption removal of lithium at a variety of pH ranges was the highest for RDP-FC-Cu followed by RDP-FC-Ni and RDP. The continuous increase in the adsorption capacity for lithium with increasing initial lithium concentrations was also observed. This could be mainly attributed to enhance and increased lithium mass transfer onto the available adsorption active sites on the adsorbents’ surface. The differences in the adsorption in terms of percent adsorption removal were clear and significant between the three adsorbents (P value < 0.05). All adsorbents in the study showed a high lithium desorption percentage as high as 99%. Both composites achieved full recoveries of lithium from the RO brine sample despite the presence of various other competing ions.

LiCl Photodissociation on Graphene: A Photochemical Approach to Lithium Intercalation.

The interest in the research of the structural and electronic properties between graphene and lithium has bloomed since it has been proven that the use of graphene as an anode material in lithium-ion batteries ameliorates their performance and stability. Here, we investigate an alternative route to intercalate lithium underneath epitaxially grown graphene on iridium by means of photon irradiation. We grow thin films of LiCl on top of graphene on Ir(111) and irradiate the system with soft X-ray photons, which leads to a cascade of physicochemical reactions. Upon LiCl photodissociation, we find fast chlorine desorption and a complex sequence of lithium intercalation processes. First, it intercalates, forming a disordered structure between graphene and iridium. On increasing the irradiation time, an ordered Li(1 × 1) surface structure forms, which evolves upon extensive photon irradiation. For sufficiently long exposure times, lithium diffusion within the metal substrate is observed. Thermal annealing allows for efficient lithium desorption and full recovery of the pristine G/Ir(111) system. We follow in detail the photochemical processes using a multitechnique approach, which allows us to correlate the structural, chemical, and electronic properties for every step of the intercalation process of lithium underneath graphene.

Lithium recovery from hydraulic fracturing flowback and produced water using a selective ion exchange sorbent

Increased demand for lithium products for use in lithium-ion batteries has led to a search for new lithium resources in recent years to meet projected future consumption. One potential lithium resource is low lithium bearing brines that are discharged from hydraulically fractured oil and gas wells as flowback and produced water (FPW). In this way, hydraulic fracturing presents an opportunity to turn what is normally considered wastewater into a lithium resource. In this research, two manganese-based lithium-selective adsorbents were prepared using a co-precipitation method and were employed for lithium recovery from FPW. At optimized conditions, lithium uptake reached 18 mg g−1, with a > 80% lithium recovery within 30 min. The recovered lithium was isolated and concentrated to 15 mM in an acidic final product. The degree of sorbent loss during acid desorption of lithium was significantly higher for sorbents used in the FPW as compared to recovery from a synthetic lithium-bearing brine (4.5% versus 0.8%). Thus, we propose that organic molecules present in the FPW reduce manganese in the sorbent structure during lithium sorption, leading to increased sorbent loss through reductive dissolution. Systematic characterization including wet chemical manganese valence measurements, along with EXAFS, XPS, and TEM-EELS show that exposure to FPW causes tetravalent manganese in the bulk sorbent structure to be reduced during lithium sorption, which subsequently dissolves during acid desorption. Partial removal of these organic molecules by nanofiltration leads to decreased sorbent dissolution in acid. In this way, we show that dissolved organic molecules represent a critical control on the reductive dissolution of manganese-based lithium ion exchange sorbents. This research provides promising results on the use of manganese-based lithium sorbents in FPW.

Evaluation of Effect of Volume Expansion on Cell Performance of All-Solid-State Batteries with 1D Simulation

The development of an all-solid-state lithium-ion battery (ASSB) as a next-generation storage battery is being promoted from the viewpoints of higher energy density and safety, but higher power density is an issue. One of the factors is that the interface resistance is high. At present, research is being actively conducted to reduce interface resistance by applying external stress. However, it is not clear how the volume change accompanying the lithium desorption and insertion of the active material particles affects the interface resistance. Therefore, in this research, we constructed an analysis model incorporating these effects and examined the effects on battery performance.The electrode layer is a three-phase uniform porous media including an active material (AM), a solid electrolyte (SE), and void space. There was no temperature distribution inside the battery, and the concentration distribution of lithium ions in the electrolyte was uniformly constant. In this research, based on the porous electrode theory [1], the effects of expansion and contraction of the active material were incorporated. The change in the thickness of the electrode layer was calculated from the balance between the local strain and the force of the entire cell. Assuming that the active material is a rigid body and the solid electrolyte is an elastic body, the reaction interface area was calculated by incorporating a geometric model that changes depending on the lithium concentration of the active material into the Random capillary model [2]. The change in tortuosity was calculated assuming that the change was a function of the volume fraction of each phase. The external stress dependence of the contact interface is given by equation of Tian et al [3]. The positive electrode active material is LiCoO2 (LCO), the negative electrode active material is graphite, and the high expansion negative electrode assumed to be 3 times the capacity of Si (virtual Si whose expansion volume at full charge is 3 times the volume before charging). As the solid electrolyte, Li10GeP2S12 was used. The volume fraction of the active material was set to 0.4, the porosity was set to 0.3, and the solid electrolyte ratio was set to 0.3. In the case of a Si negative electrode, a rise in surface pressure from the inside of the cell to the outside due to expansion of the Si active material upon charging has been reported [4]. In this study, this internal pressure is assumed to be proportional to the lithium intercalation rate of the negative electrode active material in the local area of the electrode layer. And it is treated as the force applied to the electrode-solid electrolyte interface together with the cell fastening pressure. The initial stress was 1 to 100 MPa, and the thickness of the positive electrode, negative electrode, and SE layer was 60 µm, 60 µm, and 20 µm. The Li ion conductivity of the solid electrolyte was set to 1.2 × 10-2 S/cm [5]. Figure 1 shows the charging curves of negative electrode graphite (a) and Si (b) at an external stress of 1 to 100 MPa. Comparing the two charging curves with the same external stress, it can be confirmed that the charging voltage of Si is lower than that of graphite and the charging rate (SOC) is higher. This is because the increase in internal pressure due to lithium insertion is large due to a large expansion rate, and the effective contact interface is increased due to an increase in stress applied to the interface. This reduced the reaction overpotential and led to an increase in the active material used. Figure 2 shows the SOC distribution at the external stress of 50 MPa. In the case of graphite having a low expansion rate, an effective contact interface is insufficient, and distribution occurs in the thickness direction. In general, expansion should be reduced to improve battery performance, but this research suggests that in order to form an effective solid-solid contact interface, expansion may be effective depending on the design of the expandable battery and fastening conditions.AcknowledgmentThis research was supported by Grants-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices” MEXT, Japan FY2019-2023.

Light-induced atomic desorption of lithium.

We demonstrate loading of a Li magneto-optical trap using light-induced atomic desorption. The magnetooptical trap confines up to approximately 4 × 104 7Li atoms with loading rates up to approximately 4 × 103 atoms per second. We study the Li desorption rate as a function of the desorption wavelength and power. The extracted wavelength threshold for desorption of Li from fused silica is approximately 470 nm. In addition to desorption of lithium, we observe light-induced desorption of background gas molecules. The vacuum pressure increase due to the desorbed background molecules is ≲ 50 % and the vacuum pressure decreases back to its base value with characteristic timescales on the order of seconds when we extinguish the desorption light. By examining both the loading and decay curves of the magneto-optical trap, we are able to disentangle the trap decay rates due to background gases and desorbed lithium. Our results show that light-induced atomic desorption can be a viable Li vapor source for compact devices and sensors.

Adsorption of Lithium from Shale Gas Produced Water Using Titanium Based Adsorbent

Lithium is a valuable metal that has been recovered from synthetic shale gas produced water using the titanium-based adsorbent H2TiO3 in this study. The maximum adsorptive capacity of lithium obtained was 2.58 mmol/g after adsorption–desorption tests, and the recovery rate of Li+ was much higher than those of the other cations in the produced water when used with a pH buffer. To enhance the adsorptive capacity and selectivity of lithium, the precipitation process using sodium carbonate was applied prior to adsorption. More than 96% of the divalent cations such as barium, calcium, and strontium were precipitated. From the precipitation–adsorption–desorption test, the lithium desorption capacity obtained for the produced water was 3.61 mmol/g, with a higher selectivity compared to the other cations. Thus, adsorption using a titanium-based adsorbent might be a promising method for lithium recovery from shale gas produced water, when used in conjunction with precipitation.

Reaction-diffusion-stress coupling model for Li-ion batteries: The role of surface effects on electrochemical performance

Recent years, nanostructured design for battery electrodes has emerged as a promising solution to improve rate capability and reliability of the high-capacity electrodes. However, the surface effects arising from small feature size may affect the multi-physical features of electrodes subject to non-equilibrium electrochemical cycles. In this study, a reaction-diffusion-stress coupling model is developed with the contribution of surface effects, which can capture the interactions between surface electrode reaction, diffusion and solid deformation in a nanoparticle of an electrode under non-equilibrium cyclic charge and discharge. Numerical results show that compressive stress at the surface of an electrode particle during insertion inhibits lithium absorption, while tensile stress at the surface of an electrode particle due to ion extraction suppresses lithium desorption with regard to surface electrochemical reactions. When surface mechanics is taken account into nanoscale electrode study, surface tension is found to be responsible for the increase in mechanical stability, as well as the significant reduction in charge capacity during both the galvanostatic and potentiostatic operation in the meantime. By further introducing tunable surface modulus effects, it is shown that the positive surface modulus aggravates charge capacity loss, whereas the negative surface modulus remedies it for a given potential. The results of the study provide a new idea for nano-surface engineering to optimize the design of electrode to meet required durability and electrochemical performance.

Modelling of column lithium desorption from Li+-loaded adsorbent obtained by adsorption from salt brine

Desorption technology is important to fabricate the economical process for Li+ recovery from brine by adsorption method, but there have been no systematic studies on the column Li+ desorption. The purpose of this paper is to find the elution conditions to have the eluate with high Li+ concentration in a short time, from which Li2CO3 can be precipitated without pre-concentration. The promising conditions of column Li+ desorption could be proposed on the bases of column desorption experiments and model calculations.The natural salt brine (pH6.8) containing 0.21M (1M=1moldm−3) Li+, 2.7M Na+, 0.51M K+, 1.3M Mg2+, 5.4M Cl−, and 0.25M SO42− was used for the Li+ adsorption. The granulated adsorbent sieved to 0.42–0.71 or 0.71–1.0mm was prepared with colloidal silica as a binder. The Li+-loaded adsorbents were prepared by treating the granulated adsorbent with the NaHCO3 added brine by a batch method. The column elution experiments were carried out by passing HCl or H2SO4 solutions with different concentrations through the Li+-loaded adsorbents at different flow rates.A model consisting of Li+ migration in the solid phase and of surface H+/Li+ exchange was proposed for the analysis of desorption behavior. The calculated elution curves well approximated the experimental ones when the effective acid concentration and the elution delay were considered. These approximations may be caused by the influence of the other metal ions co-adsorbed from brine. The calculation showed that the elution by passing a 2M acid solution at a space velocity of 10/h up to 2 bed volume produces the eluate of high Li+ concentration (1.15M) with high Li+ recovery (87%). This process has the advantages of eliminating the step of pre-concentration of eluate for precipitation and reducing the acid consumption.

Effect of Temperature on the Desorption of Lithium from Molybdenum(110) Surfaces: Implications for Fusion Reactor First Wall Materials.

Determining the strength of Li binding to Mo is critical to assessing the survivability of Li as a potential first wall material in fusion reactors. We present the results of a joint experimental and theoretical investigation into how Li desorbs from Mo(110) surfaces, based on what can be deduced from temperature-programmed desorption measurements and density functional theory (DFT). Li desorption peaks measured at temperatures ranging from 711 K (1 monolayer, ML) to 1030 K (0.04 ML), with corresponding desorption onsets from 489 to 878 K, follow a trend similar to predicted Gibbs free energies for Li adsorption. Bader charge analysis of DFT densities reveals that repulsive forces between neighboring positively charged Li atoms increase with coverage and thus reduce the bond strength between Mo and Li, thereby lowering the desorption temperature as the coverage increases. Additionally, DFT predicts that Li desorbs at higher temperatures from a surface with vacancies than from a perfect surface, offering an explanation for the anomalously high desorption temperatures for the last Li to desorb from Mo(110). Analysis of simulated local densities of states indicates that the stronger binding to the defective surface is correlated with enhanced interaction between Li and Mo, involving the Li 2s electrons and not only the Mo 4d electrons as in the case of the pristine surface, but also the Mo 5s electrons in the case with surface vacancies. We suggest that steps and kinks present on the Mo(110) surface behave similarly and contribute to the high desorption temperatures. These findings imply that roughened Mo surfaces may strengthen Li film adhesion at higher temperatures.

Spreading of lithium on a stainless steel surface at room temperature

Lithium conditioned plasma facing surfaces have lowered recycling and enhanced plasma performance on many fusion devices and liquid lithium plasma facing components are under consideration for future machines. A key factor in the performance of liquid lithium components is the wetting by lithium of its container. We have observed the surface spreading of lithium from a mm-scale particle to adjacent stainless steel surfaces using a scanning Auger microprobe that has elemental discrimination. The spreading of lithium occurred at room temperature (when lithium is a solid) from one location at a speed of 0.62 μm/day under ultrahigh vacuum conditions. Separate experiments using temperature programmed desorption (TPD) investigated bonding energetics between monolayer-scale films of lithium and stainless steel. While multilayer lithium desorption from stainless steel begins to occur just above 500 K (Edes = 1.54 eV), sub-monolayer Li desorption occurred in a TPD peak at 942 K (Edes = 2.52 eV) indicating more energetically favorable lithium-stainless steel bonding (in the absence of an oxidation layer) than lithium–lithium bonding.

Comparison Study of PVDF-HMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4 &lt;/sub&gt; and PES-HMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Membrane-Type Adsorbents for Lithium Adsorption/Desorption

Much attention has been paid to membrane-type lithium adsorbents to overcome the shortages of the leakage of powder, poor permeability and difficult recycle for powder lithium adsorbents. In this work, a series of membrane-type adsorbents of spinel-type manganese oxides were converted from lithium manganese oxide precursor membranes by acid treatment. Precursor membranes were prepared by solvent exchange method using polyvinylidene fluoride (PVDF) and Polyether sulphone (PES) respectively as binders, powder LiMn2O4 as the precursor and N,N-dimethyl acetamide (DMAc) as the solvent. The preparation conditions were investigated by changing the binder and the concentration of powder LiMn2O4. The surfaces and morphology of membrane-type adsorbents were observated by scanning electron microscope. The comparation of the capacities of lithium desorption from precursor and adsorption for membrane-type adsorbents based on different binders shows that PVDF is more suitable to be the binder than PES with liquid film thickness of 0.25mm, and the proper concentration of PVDF and powered LiMn2O4 are respectively 12% and 60%.

Magnesium-Doped Manganese Oxide with Lithium Ion-Sieve Property: Lithium Adsorption from Salt Lake Brine

Abstract Magnesium-doped lithium manganese oxides LimMgxMnIIIyMnIVzO4 (0 &amp;lt; x ≤ 0.5) with cubic spinel structure were synthesized by a coprecipitation method followed by calcination at 450 °C in air. Protonated samples were obtained after treatment with HCl solution. Chemical stability is very important for lithium uptake in industry. We used 0.5 M HCl for desorption of lithium, then dissolution of Mn decreased from 5.8 wt % for a sample without Mg to 1.0 wt % for a Mg-doped sample (Mg/Mn = 0.33). Raw brine was collected from the Salars de Uyuni, Bolivia. The effects of magnesium-doping on lithium adsorptive properties of the protonated samples in NaHCO3 containing brine were studied by a batch method. The results showed that lithium adsorptive capacity and chemical stability of the protonated samples increased with increase in Mg/Mn ratio. The regeneration of the sample with Mg/Mn = 0.33 up to 10 cycles showed good performance with lithium adsorptive capacity of 23–25 mg g−1 at pH 6.6, and the dissolution of manganese ca. 0.25 wt % Mn.

Inorganic adsorbent containing polymeric membrane reservoir for the recovery of lithium from seawater

Polymeric membrane reservoir system which contains inorganic ion-exchange adsorbent inside is suggested for the recovery of lithium from natural seawater. Manganese oxide particles having high selectivity toward lithium adsorption was used as inorganic ion-exchange adsorbent. Polymeric membrane reservoir was prepared from non-woven fabric, polysulfone (PSf) membrane, PSf/non-woven fabric composite membrane, and Kimtex ®. Leakage of the inorganic particles and morphology of the membrane were investigated and availability as membrane reservoir for the lithium recovery was evaluated by the lithium desorption from Li 1.33Mn 1.67O 4 in the membrane reservoir. From this study, ease of water diffusion to the reservoir was the most important factor for the reservoir system to be applied to lithium recovery from seawater and membrane reservoir prepared by Kimtex ® showed the best result. The proposed system has the advantage of direct application in the sea without using pressurized flow system.

Isotope effect in electron-stimulated desorption: Li+ emission from LiF on Si(100)

A strong isotope effect has been found for 6Li+ and 7Li+ emission from the LiF/Si(100) system. 6Li+ ions are emitted with the efficiency 1.52 greater than that observed for 7Li+ ions. From the analysis of the kinetic energy distribution of the 6Li+ and 7Li+ ions the desorption quenching parameters are estimated. The changes found in survival probabilities indicate that at least two paths in the lithium desorption were present. It is suggested that the ions registered with energies below 0.6eV originated from the emission and de-excitation of Li∗∗ (1s2s2) atoms. The possibility of final-state potential curve estimation for the emitted particles is also discussed.

Influence of temperature on the yield of ions desorbed as a result of electron transitions: Relaxation model

A relaxation model of electron-stimulated desorption is used to investigate the influence of temperature on the yield of desorbed ions and to calculate the corresponding temperature coefficient. Experimental data on the electron-stimulated desorption of lithium and sodium ions from a tungsten surface coated with a silicon monolayer are interpreted on the basis of the theoretical results.

Study of Li + adsorption onto polymeric aluminium (III) hydroxide for application in the treatment of geothermal waters

Li + adsorption onto aluminium hydroxide has been investigated at various temperatures. Experiments were made on two high-salinity geothermal-type fluids in which the lithium concentration reaches values greater than 30 and 50 mmol −1 respectively, in order to study the recovery of lithium from the fluids. Aluminium hydroxide was produced by adding AICl 3·6H 2O salt and KOH solution to the two reconstituted fluids. Experiments were performed at various pH values, temperatures (20, 50 and 80°C) and AI contents. The results indicate high Li + adsorption rates for both fluids at 80°C, even under conditions where small amounts of Al salt were added to the fluids. Under certain conditions, the chemical composition of the geothermal fluids had an influence on the Li + adsorption rate. The presence of certain ions in solution, such as borate, which prevent Li + adsorption, is therefore discussed. Experiments on the desorption of lithium from aluminium hydroxide using dilute solutions of hydrofluoric and sulphuric acid gave good results for the hydrofluoric acid.

Simultaneous laser-induced fluorescence and quadrupole-mass-spectroscopy studies of electron-stimulated desorption of ground-state lithium atoms from lithium fluoride crystals.

Under certain experimental circumstances, a number of authors have observed an unexpected increase in the yield of desorbed lithium atoms (a ``delayed maximum'') following the cessation of electron bombardment. The origin of this delayed maximum remains uncertain and continues to be a subject of active study. In all previous experiments that monitored delayed emission, a quadrupole mass spectrometer (QMS), which is relatively insensitive to the kinetic energy of the desorbing particles, was used for the detection of the desorbed lithium atoms. An important question is whether the delayed maximum arises from lithium atoms rather than dimers (which would appear as atoms following the ionization state of the QMS), and whether their velocity distribution is thermal as is the case for alkali-metal atoms desorbed during electron bombardment. To address these issues, we performed simultaneous laser-induced fluorescence (which is sensitive to the velocity of the desorbed atoms) and quadrupole-mass-spectrometry experiments, under experimental conditions where a delayed maximum could be observed. Our results prove that the occurrence of the delayed maximum is caused by the desorption of lithium monomers, not dimers, and indicate that the velocity distribution of the lithium atoms contributing to the delayed maximum does not appear to correspond to a Maxwell-Boltzmann velocity distribution. In addition, we observed an unexpected shift of the velocity distribution of the emitted atoms during bombardment as measured by laser-induced fluorescence that cannot be explained by any reasonable change in the surface temperature of the crystal during electron impact. Further, our data show that the substrate temperature dependence of the lithium desorption yield is the same for both experimental measurement techniques.