Li Depletion Research Articles

Effects of Polymeric Layers on Li Depletion and Electrochemical Performance of Li-O2 Rechargeable Batteries

Li‒O2 batteries have received enormous attention as alternatives to current state-of-the-art rechargeable Li-ion batteries because of their high theoretical specific energy density. However, there are still substantial technical obstacles to developing a practical battery. One of the most significant challenges arise from reactivity of Li metal anode resulting in Li depletion such as solid electrolyte interphase (SEI) and Li dendrite formation. Most approaches to reduce Li depletion focus on adjusting electrolyte components, additives and mechanical barrier. On the other hand, extremely high capacity from a cathode in Li-O2 batteries needs much higher Li utilization of an anode. High Li utilization accelerates Li depletion seriously and consequently results in poor electrochemical performance including cycle stability. Therefore, it is recommended to study on Li depletion and its prevention in more detail for rechargeable Li-O2 batteries. In this study, effects of polymer coating layers on the cycle stability were investigated. Li metal adopting poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) highly and effectively increased the cycle stability of a Li-O2 battery. The introduction of this polymeric layer, which exhibited sufficient mechanical strength, suppressed the needle-like dendrite formation. This indicates that the coating may prevent shape changes of the metal during discharge and charge cycles. It was found that improved reversibility of Li redox was achieved by coating with PVdF-HFP polymer.

Scanning Probe Characterization of Memristors Based on a Li Intercalation Metal Oxide

Memristor devices are a promising technology to replace CMOS for neuromorphic computing applications. As an alternative to filament-type memristors that require ‘forming’ procedures and which typically exhibit binary ‘on/off’ switching, we are investigating memristors based on a Li ion intercalation oxide LixCoO2. Our devices are composed of simple structures consisting of LixCoO2 films on insulating substrates with top or bottom contacts of Au. The electronic conductivity of the LixCoO2 film strongly depends on the Li-ion concentration and can exhibit synaptic multilevel analog states. However, determining the precise physical mechanisms that give rise to resistive states within a working device remains a challenge. This challenge arises because bulk characterization techniques (i.e. electrochemical impedance spectroscopy (EIS)) can be insensitive to the details of the materials microstructure that are critical to the device behavior. Scanning probe microscopy offers an attractive route to overcome these limitations in order to better understand transport at interfaces and along nanometer length scales. Here, we have carried out in operando Kelvin probe force microscopy (KPFM) on active LixCoO2 memristor devices. Using KPFM, we have directly imaged the potential drops along the device and determined the resistance of the channel versus resistance at the electrode interfaces. By capturing the time evolution of the potential landscape, the ionic and electronic dynamics are separated and their interdependence is revealed. Localized changes in work function suggest regions of Li accumulation and depletion that are associated with particular resistive memory states. The insights we gain from these experiments will guide the fabrication of more complex memristor devices such as row-column addressable arrays.

Theoretical insight into charging process in a Li3PO4 (100)/LiFePO4 (010) coherent interface system

We have investigated the introduction of Li vacancy (VLi× in the Kröger–Vink notation) into a Li3PO4 (100)/LiFePO4 (010) coherent interface with the density functional theory in order to gain an insight into the initial stage of the charging process. The VLi× introduction results in the formation of a Li ion vacancy (VLi′) and hole (h). When one VLi× is introduced in each bulk LiFePO4 and Li3PO4 materials (both VLi′ and h are donated to the position in the proximity of the initial VLi× position), the formation energies of the Li vacancy (EV) are quite different between them. On the other hand, when introduced into the Li3PO4/LiFePO4 interface system, the values of EV in the LiFePO4 and Li3PO4 bulk regions of the interface become almost equal. This is because irrespective of the introduced VLi× position, the associated h is always donated to the LiFePO4 region while the Li3PO4 region keeps its insulating properties. Although the Li atoms near the interface have smaller EV than in the bulk regions, it is suggested that only a fraction of them may be extracted at the initial stage of charging which is not enough to lead to the Li depletion at the interface and as a result the effect of the space charge layer may be negligible in the Li3PO4/LiFePO4 interface.

Lithium evolution in metal-poor stars: from pre-main sequence to the Spite plateau

Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accretion. We show that $^7$Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by a tail of matter accretion which follows the Li depletion phase and that could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and microscopic diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass $m_0=0.62 - 0.80 M_{\odot}$, and the Li declining branch for lower mass dwarfs, e.g, $m_0=0.57 - 0.60 M_{\odot}$, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance $A({\rm Li}) =2.72$. This environmental Li evolution model also offers the possibility to interpret the decrease of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and the low Li abundance in planet hosting stars.

Lithium evolution from Pre-Main Sequence to the Spite plateau: an environmental solution to the cosmological lithium problem

AbstractLithium abundance derived in metal-poor main sequence stars is about three times lower than the primordial value of the standard Big Bang nucleosynthesis prediction. This disagreement is referred to as the lithium problem. We reconsider the stellar Li evolution from the pre-main sequence to the end of main sequence phase by introducing the effects of overshooting and residual mass accretion. We show that 7Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by residual accretion which follows the Li depletion phase and could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass m0=0.62–0.80 M⊙, and the Li declining branch for lower mass dwarfs, e.g, m0=0.57–0.60 M⊙, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance A(Li) = 2.72.

EMPIRICAL ISOCHRONES FOR LOW MASS STARS IN NEARBY YOUNG ASSOCIATIONS

Absolute ages of young stars are important for many issues in pre-main sequence stellar and circumstellar evolution but are long recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in HR diagrams for low-mass stars and brown dwarfs in the eta Cha, epsilon Cha, and TW Hya Associations and the beta Pic and Tuc-Hor Moving Groups. A successful theory of pre-main sequence evolution should match the shapes of the stellar loci for these groups of young stars. However, when comparing the combined empirical isochrones to isochrones predicted from evolutionary models, discrepancies lead to a spectral type (mass) dependence in stellar age estimates. Improved prescriptions for convection and boundary conditions in the latest models of pre-main sequence models lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncertainties or by model limitations. Independent of model predictions, linear fits to combined stellar loci of these regions provide a simple empirical method to order clusters by luminosity with a reduced dependence on spectral type. Age estimates calculated from various sets of modern models that reproduce Li depletion boundary ages of the beta Pic Moving Group also imply a ~4 Myr age for the low mass members of the Upper Sco OB Association, which is younger than the 11 Myr age that has been recently estimated for intermediate mass members.

Convective settling in main sequence stars: Li and Be depletion

The process of convective settling is based on the assumption that a small fraction of the low-entropy downflows sink from the photosphere down to the bottom of the star's envelope convection zone retaining a substantial entropy contrast. We have previously shown that this process could explain the slow Li depletion observed in the Sun. We construct a parametric model of convective settling to investigate the dependence of Li and Be depletion on stellar mass and age. Our model is generally in good agreement with the Li abundances measured in open clusters and solar twins, although it seems to underestimate the Li depletion in the first ~1 Gyr. The model is also compatible with the Be abundances measured in a sample of field stars.

Lithium Depletion and the Rechargeability of Li–O2 Batteries in Ether and Carbonate Electrolytes

AbstractLi metal is a highly promising candidate anode material because of its high energy density. However, Li depletion caused by the formation of a passivation layer and dendrites prevent the use of Li metal for rechargeable batteries. In this study, we investigate Li depletion in practical Li–O2 batteries by using two typical electrolytes, carbonate and ether, under high Li utilization. The ether‐based solvent tetraethylene glycol dimethyl ether (TEGDME) showed greatly increased levels of Li depletion through the formation of both solid electrolyte interphase (SEI) layers and dendrites than carbonated‐based solvents (ethylene carbonate/diethyl carbonate (EC/DEC)). Although TEGDME is known as a stable solvent for oxygen reduction species, it may be less appropriate as a solvent with respect to Li reactivity, which is very important for the cycle stability of Li–O2 battery systems. In contrast, although slight decomposition of EC‐DEC was observed, cells constructed with EC‐DEC were found to be more stable than those with TEGDME for Li–O2 batteries.

COMPLEX ORGANIC AND INORGANIC COMPOUNDS IN SHELLS OF LITHIUM-RICH K GIANT STARS

Hydrocarbon organic material, as found in the interstellar medium, exists in complex mixtures of aromatic and aliphatic forms. It is considered to be originated from carbon enriched giant stars during their final stages of evolution, when very strong mass loss occurs in a few thousand years on their way to become planetary nebulae. We show here that the same organic compounds appear to be formed in previous stages of the evolution of giant stars. More specifically, during the first ascending giant branch K-type stars. According to our model this happens only when these stars are being abruptly enriched with lithium together with the formation of a circumstellar shell with a strong mass loss during just a few thousand years. This sudden mass loss is, on an average, a thousand times larger than that of normal Li-poor K giant stars. This shell would later be detached, specially when the star stops its Li enrichment and a rapid photospheric Li depletion occurs. In order to gain extra carbon-based material to form the organic hydrocarbons, and also to explain the presence of complex inorganic compounds in these stars, we propose an interaction of these strong winds with remaining asteroidal/cometary disks that already existed around these stars since they were dwarf A-type stars. The mechanism of interaction presented here is successful to explain the presence of inorganic compounds, however it is unable to produce new carbon free atoms to form the organic hydrocarbon compounds. Finally, we discuss some suggestions and speculations that can eventually help solving the long-standing puzzle of Li-rich giants.

Trace element anomaly in fault rock induced by coseismic hydrothermal reactions reproduced in laboratory friction experiments

AbstractFriction experiments at high velocities (0.1 to 0.4 m/s) at room temperature under high pore fluid pressures (2 or 5 MPa) and trace element analyses of the run products were carried out on simulated fault gouge derived from the Chelungpu fault, Taiwan. The friction coefficient decreased to ~0.1 during sliding, and the slip surface temperature reached 300°C by 6 m of slip displacement. The slip caused a small, but distinct decrease of Li in the deformed gouge when the slip surface temperature exceeded 300°C. The observed Li depletion agreed with calculated results, indicating that it resulted from a hydrothermal reaction at a high temperature produced by short‐duration (up to 40 s) frictional heating. The geochemical data suggest a small fluid/rock ratio and low reaction temperature in the simulated fault, which is explained by higher normal stress or repeated earthquakes which elevated fluid‐rock ratios in the natural fault.

Comparative Study on Li Depletion for Li-O2 Batteries Using Carbonate and Ether Solvents

Recently, many researchers have interest on the Li-O2 rechargeable battery as a promising energy storage system because of its extremely large theoretical energy density. Due to its highly negative redox potential and an extremely large specific capacity, Li metal is essential for this system. However, Li metal has some drawbacks as an anode material for rechargeable batteries such as dendrite formation in charging process, surface passivation layer formation resulting in a loss of Li amount. Li loss by dendrites and SEI layers attribute depletion of energy sources, and therefore, significantly deteriorate cycleability of cells. In spite of its high importance, in previous studies, researches about Li metal are not studied in details especially in Li-O2 batteries. In this study, we investigate the Li depletion and its influence on cyclestability of cells depending on solvents including EC/DEC and TEGDME which is representative solvents in Li‒O2 batteries. Although ether based solvent is considered for good candidates as it has a fairly low vapor pressure with higher stability against oxidation, we confirmed serious dendrites with newly developed SEI layer of ROLi by XPS and ATR-FTIR analysis. This indicates increased Li depletion for TEGDME based cells and consequently influence on cycle stability. Figure 1

Impact of Electrochemical Charging on Fracture Toughness and Elastoplastic Properties of LiCoO2

Capacity fade and impedance growth of lithium ion battery (LIB) electrodes have been correlated with mechanical degradation of active particles through extended cycling. The design of fracture-resistant electrodes requires understanding of material mechanical properties such as elastic modulus E, hardness H, and fracture toughness K Ic over the entire range of compositions through which the active materials are cycled. In this work, we measured E, H, and K Ic of the prototypical layered material LiXCoO2 using instrumented nanoindentation, varying the composition, X, through varying durations of galvanostatic charging. We found that within a single charge cycle, E and H decreased by up to 60%, while K Ic decreased by up to 70% compared to the fully-lithiated state. X-ray diffraction, Raman spectroscopy, and optical and electron microscopy demonstrated that the drop in mechanical properties was correlated with extensive grain boundary fracture and attributable to Li depletion at the sample surfaces. Such differences in mechanical properties of Li-storage materials can impact the critical length scales (either grain size or particle size) that mark the boundary between fracture-resistant and fracture-prone electrode designs. This work demonstrates that when fracture toughness is used in battery design, it cannot be assumed to be constant over the course of charge cycling. This evidence of electrochemical-history-dependent fracture toughness is particularly important to the design of Li-storage compounds that undergo significant chemical expansion or phase changes during electrochemical cycling.

Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss

We searched for a correlation between the two anomalous properties of K giants: Li enhancement and IR excess from an unbiased survey of a large sample of RGB stars. A sample of 2000 low-mass K giants with accurate astrometry from the Hipparcos catalog was chosen for which Li abundances have been determined from low-resolution spectra. Far-infrared data were collected from the $WISE$ and $IRAS$ catalogs. To probe the correlation between the two anomalies, we supplemented 15 Li-rich K giants discovered from this sample with 25 known Li-rich K giants from other studies. Dust shell evolutionary models and spectral energy distributions were constructed using the code DUSTY to estimate different dust shell properties, such as dust evolutionary time scales, dust temperatures, and mass-loss rates. Among 2000 K giants, we found about two dozen K giants with detectable far-IR excess, and surprisingly, none of them are Li-rich. Similarly, the 15 new Li-rich K giants that were identified from the same sample show no evidence of IR excess. Of the total 40 Li-rich K giants, only 7 show IR excess. Important is that K giants with Li enhancement and/or IR excess begin to appear only at the bump on the RGB. Results show that K giants with IR excess are very rare, similar to K giants with Li enhancement. This may be due to the rapid differential evolution of dust shell and Li depletion compared to RGB evolutionary time scales. We also infer from the results that during the bump evolution, giants probably undergo some internal changes, which are perhaps the cause of mass-loss and Li-enhancement events. However, the available observational results do not ascertain that these properties are correlated. That a few Li-rich giants have IR excess seems to be pure coincidence.

On the age of the β Pictoris moving group

Jeffries & Binks (2014) and Malo et al. (2014) have recently reported Li depletion boundary (LDB) ages for the {\beta} Pictoris moving group (BPMG) which are twice as old as the oft-cited kinematic age of $\sim$12 Myr. In this study we present (1) a new evaluation of the internal kinematics of the BPMG using the revised Hipparcos astrometry and best available published radial velocities, and assess whether a useful kinematic age can be derived, and (2) derive an isochronal age based on the placement of the A-, F- and G-type stars in the colour-magnitude diagram (CMD). We explore the kinematics of the BPMG looking at velocity trends along Galactic axes, and conducting traceback analyses assuming linear trajectories, epicyclic orbit approximation, and orbit integration using a realistic gravitational potential. None of the methodologies yield a kinematic age with small uncertainties using modern velocity data. Expansion in the Galactic X and Y directions is significant only at the 1.7{\sigma} and 2.7{\sigma} levels, and together yields an overall kinematic age with a wide range (13-58 Myr; 95 per cent CL). The A-type members are all on the zero age-main-sequence, suggestive of an age of $>$20Myr, and the loci of the CMD positions for the late-F- and G-type pre-main-sequence BPMG members have a median isochronal age of 22 Myr ($\pm$ 3 Myr stat., $\pm$ 1 Myr sys.) when considering four sets of modern theoretical isochrones. The results from recent LDB and isochronal age analyses are now in agreement with a median BPMG age of 23 $\pm$ 3 Myr (overall 1{\sigma} uncertainty, including $\pm$2 Myr statistical and $\pm$2 Myr systematic uncertainties).

Variation of lithium isotope geochemistry during basalt weathering and secondary mineral transformations in Hawaii

Lithium isotopes are a potential tracer of silicate weathering but the relationship between lithium isotope compositions and weathering state still need to be established with precision. Here, we report Li concentrations and Li isotope compositions of soils developed along a 4 million year humid-environment chronosequence in the Hawaiian Islands. Li concentrations are variable with depth and age, ranging from 0.24 to 21.3ppm, and significant Li depletions (up to 92%) relative to parent basalts are systematically enhanced towards the surface. Our calculations show that the relative contribution from atmospheric deposits to the Li soil budget remains small, with a maximum contribution from dust Li of 20% at the oldest site. This is explained by the capacity of the weathering products to retain, within the profiles, the Li coming from basalt alteration, and allows us to explore more specifically the role of alteration processes on soil Li isotope signatures. The δ7Li values display a large range between −2.5‰ and +13.9‰. The youngest soils (0.3ka) display the same δ7Li value as fresh basalt, regardless of depth, despite ∼30% Li loss by leaching, indicating that there is little Li isotope fractionation during the incipient stage of weathering. δ7Li values for the older soils (⩾20ka) vary non-linearly as a function of time and can be explained by progressive mineral transformations starting with the synthesis of metastable short-range order (nano-crystalline) minerals and followed by their transformation into relatively inert secondary minerals. Results highlight significant Li isotope fractionation during secondary mineral formation and in particular during Li uptake by kaolinite. Finally, we suggest that the non-monotonous evolution of the regolith δ7Li value over the last 4Ma is consistent with climatic variations, where congruent release of Li isotopes occurs during warmer periods.

Effect of annealing temperature on the microstructure and mechanical properties of an as-rolled Mg-9wt.%Li-3wt.%Al-1wt.%Zn alloy sheet

This study investigated the effect of annealing temperature on the mechanical properties of an as-rolled Mg-9.26wt.%Li-3.03wt.%Al-1.10wt.%Zn (LAZ931) alloy sheet. The dual-phase (α + β) LAZ931 alloy plate of 3 mm in thickness were rolled (67% reduction) and then annealed at temperatures at 100°C–350°C. The alloy’s ductility showed a sharp concave downward tendency as a function of annealing temperature. The elongation of the LAZ931 alloy sheet increased with annealing temperature up to 150°C, followed by a sharp decrease of the alloy’s ductility as the annealing temperature higher than 150°C. The specimen exhibited an extremely low elongation (only ∼0.5%) at annealing temperature around 300°C. Formation of brittle AlLi particles on boundary resulted in Li depletion zone near by grain boundary, transforming the Li depletion zone into α (hcp) layer. The combined effects including brittle AlLi particles on boundary and the hcp α layer on boundary resulted in the brittlement of the high-temperature-annealing sample.

A TALE OF TWO ANOMALIES: DEPLETION, DISPERSION, AND THE CONNECTION BETWEEN THE STELLAR LITHIUM SPREAD AND INFLATED RADII ON THE PRE-MAIN SEQUENCE

We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed Teff is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

Crystallisation of magmatic topaz and implications for Nb–Ta–W mineralisation in F-rich silicic melts — The Ary-Bulak ongonite massif

Textural, mineralogical and geochemical data on F-rich rhyolite (ongonite) from the Ary-Bulak massif of eastern Transbaikalia help constrain the formation of magmatic topaz. In these rocks, topaz occurs as phenocrysts, thus providing compelling evidence for crystallisation at the orthomagmatic stage. Cathodoluminescence images of topaz and quartz reveal growth textures with multiple truncation events in single grains, indicative of a dynamic system that shifted from saturated to undersaturated conditions with respect to topaz and quartz. Electron microprobe and Raman analyses of topaz indicate near-pure F composition [Al2SiO4F2], with very limited OH replacement. Laser ablation ICP-MS traverses revealed the presence of a large number of trace elements present at sub-ppm to hundreds of ppm levels. The chemical zoning of topaz records trace element fluctuations in the coexisting melt. Concentrations of some trace elements (Li, Ga, Nb, Ta and W) are correlated with cathodoluminescence intensity, thus suggesting that some of these elements act as CL activators in topaz. The study of melt inclusions indicates that melts with different F contents were trapped at different stages during formation of quartz and topaz phenocrysts, respectively. Electron microprobe analyses of glass in subhedral quartz-hosted melt inclusions indicate F ≤ 1.2 wt.%, whereas irregular-shaped melt inclusions hosted in both topaz and quartz have F ≤ 9 wt.%. Cryolithionite [Na3Li3Al2F12] coexists with glass in irregular inclusions, implying high Li contents in the melt. The very high F contents would have increased the solubility of Nb, Ta and W in the melt, thus allowing progressive concentration of these elements during magma evolution. Crystallisation of Nb–Ta–W-oxides (W-ixiolite and tantalite–columbite) may have been triggered by separation of cryolithionite, which would have caused F and Li depletion and consequent drop in the solubility of these elements.

STATE-TO-STATE QUANTUM WAVE PACKET DYNAMICS OF THE LiH + H REACTION ON TWO AB INITIO POTENTIAL ENERGY SURFACES

The dynamics and kinetics of the LiH + H reaction have been studied by using an accurate quantum reactive time-dependent wave packet method on the ab initio ground electronic state potential energy surfaces (PES) developed earlier. Reaction probabilities for the two possible reaction channels, the LiH?+?H? H2?+?Li depletion process and the LiH + H?H + LiH hydrogen exchange reaction, have been calculated from 1?meV up to 1.0?eV collision energies for total angular momenta J from 0 to 80. State-to-state and total integral cross sections for the LiH-depletion and H-exchange channels of the reaction have been calculated over this collision energy range. It is found that the LiH-depletion channel is dominant in the whole range of collision energies for both PESs. Accurate total rate coefficients have been calculated on both surfaces from 100?K to 2000?K and are significantly larger than previous empirical estimates and previous J-shifting results. In addition, the present accurate calculations present noticeable differences with previous calculations using the centrifugal sudden approximation.

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

Context: A key science goal of the Gaia-ESO survey (GES) is to use the kinematics of low-mass stars in young clusters to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive W-R binary gamma^2 Velorum was one of the first GES targets. Aims: To empirically determine the radial velocity (RV) precision of GES data, construct a kinematically unbiased sample of cluster members and characterise their dynamical state. Methods: Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy used to derive RVs and assess membership from the strength of the Li6708A line. The RV distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries. Results: The GES RV precision is about 0.25km/s and sufficient to resolve velocity structure in the low-mass population around gamma^2 Vel. The structure is well fitted by two kinematic components with roughly equal numbers of stars; the first has an intrinsic dispersion of 0.34+/-0.16km/s, consistent with virial equilibrium. The second has a broader dispersion of 1.60+/-0.37km/s and is offset from the first by ~2km/s. The first population is older by 1-2Myr based on a greater level of Li depletion seen among its M-stars and is probably more centrally concentrated around gamma^2 Vel. Conclusions: We consider several formation scenarios, concluding that the two kinematic components are a bound remnant of the original, denser cluster that formed gamma^2 Vel, and a dispersed population from the wider Vela OB2 association, of which gamma^2 Vel is the most massive member. The apparent youth of gamma^2 Vel compared to the older (>=10Myr) low-mass population surrounding it suggests a scenario where the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars.[abridged]