Amorphous Li2O Research Articles

Single‐Atom Catalyst Induced Amorphous Li2O2 Layer Enduring Lithium–Oxygen Batteries with High Capacity

AbstractAprotic lithium–oxygen batteries (LOBs) may deliver exceptionally high energy density but struggle to attain rapid reversibility and substantial capacity simultaneously, due to typical surface or solution‐formed insulating solid Li2O2. Tuning the structure of Li2O2 to create a large‐area amorphous layer on the cathode is predicted to overcome the multiperformance limitations. Here, an isolated nickel single atom to nitrogen‐doped graphene as a cathode catalyst (Ni─NG SAC) for LOBs is presented via a green click‐trapping strategy. Derived from the maximized exposure of atomic active sites of the cathode, the formation/decomposition mechanisms of Li2O2 are tailored, and a large area of thin Li2O2 amorphous film is achieved. The structure and functions of Ni─NG SAC are explored by theoretical computation and synchrotron radiational investigation. Consequently, the abundant Ni─N4 sites enhance redox kinetics and stand out to deliver an impressive specific discharge/charge capacity of 24 248/17 656 mAh g−1 at 200 mA g−1, together with a long cycle life of over 500 cycles. This study contributes helpful insights to achieve high‐capacity LOBs with long lifespans, by constructing unique single‐atom catalysts to optimize the formation of amorphous discharge Li2O2 products.

Al–Ta dual-substituted Li7La3Zr2O12 ceramic electrolytes with two-step sintering for Stable All-solid-state Lithium Batteries

Cubic phase Li7La3Zr2O12 (LLZO) is a promising electrolyte material for all-solid-state rechargeable lithium-ion batteries. The homogeneous densification of the garnet solid electrolyte ceramic material is crucial for enhancing its ionic conductivity performance. Herein, an Al/Ta co-doped strategy is employed to stabilize the cubic phase structure of LLZO and is combined with a two-step sintering method to enhance densification, in order to investigate its effect on microstructure, ionic conductivity, and electrochemical properties. During the formation process, amorphous Li2O reacts with doped Al2O3 to create a Li–Al–O liquid phase at the grain boundaries. Combined with two-step sintering to ensure that the desired material transformation is achieved, resulting in a dense microstructure and better mechanical properties. The solid electrolyte Li6.4Al0.1La3Zr1.7Ta0.3O12 under two-step sintering (LLZATO-2) is successfully synthesized, delivering an ionic conductivity up to 7.33 × 10−4 S cm−1 at room temperature and an activation energy of 0.22 eV. This work also highlights the critical role of co-doping combined with two-step sintering in preparing well-performing solid-state electrolytes and all-solid-state lithium-ion batteries.

Scalable wet-slurry fabrication of sheet-type electrodes for sulfide all-solid-state batteries and performance enhancement via optimization of Ni-rich cathode coating layer

All-solid-state Li or Li-ion batteries (ASSLBs) have attracted much attention due to their potential high energy density, high safety, and low manufacturing costs compared to commercial liquid electrolyte Li-ion batteries. However, the rate capacity and cycling performance could not satisfy the practical application. Here, an island-like amorphous Li2O–ZrO2 (LZO) was coated on the surface of LiNi0.88Co0.10Al0.02 (NCA) via a sol-gel method and low-temperature sintering. The electrochemical performance and density functional theory calculation results demonstrate that the LZO coating layer significantly boosts Li-ions transfer. Targeting large-scale production, a sheet-type cathode was prepared by a wet-slurry process with PVDF-HFP as a binder, which exhibits an initial specific capacity of 181.91 mAh·g−1 at 0.13C and 25 °C. Remarkably, the wet-slurry cathode with a high NCA loading of 20 mg cm−2 delivers an initial areal capacity of 2.936 mAh·cm−2 and capacity retention of 69.93% after 1000 cycles at a rate of 0.64C. By employing X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy, we reveal that the LZO coating layer and PVDF-HFP binder inhibited the decomposition of sulfide electrolyte and detrimental structure evolution of NCA active material. This work would guide designing high-performance ASSLBs for practical application and commercialization.

Complementary lithium aluminum borate coating of Ni-rich cathode by synergetic boric acid and aluminum hydroxide for lithium-ion batteries

Substituting Ni for Co in high-Ni layered oxide cathodes is highly effective in enhancing the range of delithiation and reducing production costs, but the reactive Ni3+ and unavoidable residual surface impurities critically limit the cycleability of lithium-ion batteries (LIBs). Although the wet-coating method is one solution suitable for widespread industrial production, wet-coating of high-Ni layered oxides is complicated due to chemical delithiation, corrosion, and the inhomogeneous coating caused by their instability. Herein, we applied wet-coating chemistry to coat LiNi0.88Co0.06Mn0.06O2 (NCM88) with a thin boron–aluminum oxide layer using eco-friendly aqueous solutions. Under acidic H3BO3 conditions, Al(OH)3 is critical in preserving the fragile surface of Ni-rich layered oxides and forming a homogeneous coating. Furthermore, structural characterization reveals the formation of an amorphous Li2O–LiAlO2–LiBO2 (LABO) coating layer. A highly homogeneous LABO-coated NCM88 exhibits significantly improved cyclability, retaining 75.5% of its capacity after 250 cycles of charging/discharging. This is a much higher capacity retention rate than those of bare NCM88 (7%) and NCM88 coated with Al(OH)3 (64.4%) or H3BO3 (65.2%). The LABO-coated layer also demonstrates improved rate capability with charge voltages of 4.25 and 4.5 V.

Edge-Site-Free and Topological-Defect-Rich Carbon Cathode for High-Performance Lithium-Oxygen Batteries.

The rational design of a stable and catalytic carbon cathode is crucial for the development of rechargeable lithium-oxygen (LiO2 ) batteries. An edge-site-free and topological-defect-rich graphene-based material is proposed as a pure carbon cathode that drastically improves LiO2 battery performance, even in the absence of extra catalysts and mediators. The proposed graphene-based material is synthesized using the advanced template technique coupled with high-temperature annealing at 1800°C. The material possesses an edge-site-free framework and mesoporosity, which is crucial to achieve excellent electrochemical stability and an ultra-large capacity (>6700 mAh g-1 ). Moreover, both experimental and theoretical structural characterization demonstrates the presence of a significant number of topological defects, which are non-hexagonal carbon rings in the graphene framework. In situ isotopic electrochemical mass spectrometry and theoretical calculations reveal the unique catalysis of topological defects in the formation of amorphous Li2 O2 , which may be decomposed at low potential (∼ 3.6V versus Li/Li+ ) and leads to improved cycle performance. Furthermore, a flexible electrode sheet that excludes organic binders exhibits an extremely long lifetime of up to 307 cycles (>1535h), in the absence of solid or soluble catalysts. These findings may be used to design robust carbon cathodes for LiO2 batteries.

Garnet/polymer solid electrolytes for high-performance solid-state lithium metal batteries: The role of amorphous Li2O2

Solid-state electrolytes have been widely investigated for lithium batteries since they provide a high degree of safety. However, their low ionic conductivity and substantial growth of lithium dendrites hamper their commercial applications. Garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is one of the most promising active fillers to advance the performance of the solid polymer electrolyte. Nevertheless, their performance is still limited due to their large interfacial resistance. Herein, we embedded the amorphous Li2O2 (LO) into LLZTO particles via the quenching process and successfully achieved an interfacial layer of Li2O2 around LLZTO particles (LLZTO@LO). Amorphous Li2O2 acts as a binder and showed an excellent affinity for Li+ ions which promotes their fast transference. Moreover, the stable and dense interfacial Li2O2 layer enhances interfacial contact and suppresses the lithium dendrite growth during the long operation cycling process. The PEO/10LLZTO@2LO solid composite polymer electrolyte (SCPE) showed the highest ionic conductivity of 3.2 × 10-4 S cm−1 at 40 °C as compared to pristine LLZTO-based SCPE. Moreover, the Li│(PEO/10LLZTO@2LO) │Li symmetric cell showed a stable and smooth long lifespan up to 1100 h at 40 °C. Furthermore, the LiFePO4//Li full battery with PEO/10LLZTO@2LO SCPE demonstrated stable cycling performance for 400 cycles. These results constitute a significant step toward the practical application of solid-state lithium metal batteries (SS-LMBs).

The free-standing N-CoO matrix towards optimizing dual-electrodes for high-performance Li-O2 batteries

Lithium-oxygen batteries (LOBs) have been developed because of their high theoretical energy density. However, both the dendrite/passivation problem of the anode and the sluggish ORR/OER kinetics of the cathode impede the improvement of batteries. Herein, N-doped CoO nanoarrays grown on carbon cloth (N-CoO/CC) are developed as a free-standing matrix for both improved anode and cathode of LOBs. The superior lithiophilicity and unique three-dimensional structure of the lithium-infused N-CoO/CC composite anode (Li@N-CoO/CC) can regulate Li plating/stripping behavior and suppress lithium dendrite, achieving a cycle lifespan of more than 2500 h in a symmetrical Li metal battery (1 mA cm−2, 1 mAh cm−2). In addition, the Li@N-CoO/CC anode alleviates it from corrosion of water/oxygen to some extent in Li-O2 batteries due to the Li2CO3-riched SEI formed after cycling. Moreover, N-doped CoO nanoarrays can catalyze the formation/decomposition of amorphous Li2O2, featuring a decreased overpotential. Based on the optimized dual electrodes, the resultant Li-O2 battery can maintain 200 cycles at 0.1 mA cm−2 within 0.25 mAh cm−2.

Conformal Lithium Peroxide Growth Kinetically Driven by MoS2/MoN Heterostructures Towards High‐Performance Li−O2 Batteries

AbstractThe morphological control and spatial accommodation of Li2O2 discharge products on the oxygen cathode are crucial to bolstering both the Coulombic and round‐trip efficiencies of Li−O2 batteries. Herein, MoS2/MoN heterostructures are constructed on carbon cloth to serve as the freestanding and binder‐free oxygen cathode for Li−O2 batteries, lending a low charge/discharge polarization of 0.79 V, a large specific capacity of 9.04 mAh cm−2, and a superb cycling stability beyond 800 h. Through comprehensive microscopic, electroanalytical and density function theory analyses, the superb electrochemical performance is attributed to the formation of a conformal and amorphous Li2O2 layer, which is kinetically driven in virtue of the higher electric conductivity of MoN and stronger LiO2 intermediate adsorption on the heterostructures. This work advocates the merits of interfacial engineering to enhance the performance of Li−O2 batteries by manipulating the discharge product formation.

Oxygen Vacancy-Mediated Growth of Amorphous Discharge Products toward an Ultrawide Band Light-Assisted Li-O2 Batteries.

Photoassisted electrochemical reaction is regarded as an effective approach to reduce the overpotential of lithium-oxygen (Li-O2 ) batteries. However, the achievement of both broadband absorption and long term battery cycling stability are still a formidable challenge. Herein, an oxygen vacancy-mediated fast kinetics for a photoassisted Li-O2 system is developed with a silver/bismuth molybdate (Ag/Bi2 MoO6 ) hybrid cathode. The cathode can offer both double advantages for light absorption covering UV to visible region and excellent electrochemical activity for O2 . Upon discharging, the photoexcited electrons from Ag nanoplate based on the localized surface plasmon resonance (LSPR) are injected into the oxygen vacancy in Bi2 MoO6 . The fast oxygen reaction kinetics generate the amorphous Li2 O2 , and the discharge plateau is improved to 3.05V. Upon charging, the photoexcited holes are capable to decompose amorphous Li2 O2 promptly, yielding a very low charge plateau of 3.25V. A first cycle round-trip efficiency is 93.8% and retention of 70% over 500 h, which is the longest cycle life ever reported in photoassisted Li-O2 batteries. This work offers a general and reliable strategy for boosting the electrochemical kinetics by tailoring the crystalline of Li2 O2 with wide-band light.

Electron-redistributed Ni–Co oxide nanoarrays as an ORR/OER bifunctional catalyst for low overpotential and long lifespan Li–O2 batteries

N-doped NiCoO2/CoO nanoarrays with an optimized electronic structure facilitate the formation/decomposition of flake-like amorphous Li2O2 synergistically in lithium–oxygen batteries.

Induced construction of large-area amorphous Li2O2 film via elemental co-doping and spatial confinement to achieve high-performance Li-O2 batteries

In aprotic lithium-oxygen batteries (LOBs), it is hard to simultaneously achieve both high specific capacity and good reversibility with the insulating solid Li2O2 formed via traditional surface or solution route. Tuning the structure of Li2O2 to construct a large-area amorphous film on the surfaces of catalysts is expected to break the above performance limitation. In this work, nitrogen and sulfur co-doped carbon nanotube (CNT) arrays grown on the three-dimensional graphene (NS-CNTA/3DG) was developed as the efficient catalysts for LOBs. Large-area thin amorphous Li2O2 film is induced through the synergistic effect between doping engineering and spatial confinement on CNT arrays, confirmed by theoretical calculation and in-situ Raman examination. Consequently, the NS-CNTA/3DG cathode delivers both high specific capacity (23778 mAh g−1 at 200 mA g−1) and a high round-trip coulombic efficiency (∼87.8%) in the first deep discharge-charge process. This work contributes a new approach to optimize the formation of Li2O2 film, which will inspire the design and fabrication of new catalysts for high-performance LOBs.

Adjusting the d-band center of metallic sites in NiFe-based Bimetal-organic frameworks via tensile strain to achieve High-performance oxygen electrode catalysts for Lithium-oxygen batteries

Developing effective electrocatalyst and fundamentally understanding the corresponding working mechanism are both urgently desired to overcome the current challenges facing lithium-oxygen batteries (LOBs). Herein, a series of NiFe-based bimetal-organic frameworks (NiFe-MOFs) with certain internal tensile strain are fabricated via a simple organic linker scission strategy, and served as cathode catalysts for LOBs. The introduced tensile strain broadens the inherent interatomic distances, leading to an upshifted d-band center of metallic sites and thus the enhancement of the adsorption strength of catalysts surface towards intermediates, which is contributed to rationally regulate the crystallinity of discharge product Li2O2. As a result, the uniformly distributed amorphous film-like Li2O2 tightly deposits on the surface of strain-regulated MOF, resulting in excellent electrochemical performance of LOBs, including a large discharge capacity of 12317.4 mAh g−1 at 100 mA g−1 and extended long-term cyclability of 357 cycles. This work presents a novel insight in adjusting the adsorption strength of cathode catalysts towards intermediates via introducing tensile strain in catalysts, which is a pragmatic strategy for improving the performance of LOBs.

Polaronic conduction and switching phenomena of amorphous Li2O–CuO–P2O5

This study investigates electrical conductivity of bulk phosphate glasses containing Li2O and CuO, prepared by standard melt quenching technique. Furthermore, static current–voltage characteristic curves at high fields for memory switching behavior were examined. X-ray diffraction patterns for the studied materials revealed the amorphicity of the prepared films. It was observed that the activation energy of the samples lies in the range of 0.53–0.98 eV, depending on composition. The electrical conductivity at room temperature showed a minimum at a certain ratio of Li2O/CuO. Conduction mechanism and observed minimum were explained by small polaron hopping and interaction between polarons and ions. Current–voltage characteristics at high electric field showed memory switching. The mean value of the threshold voltage was found to be dependent on composition which decreased with increase in CuO content. Values of the threshold voltage and activation energy were obtained for the investigated compositions. The observed switching phenomenon was explained by thermal model. • Phosphate glasses with Li2O and CuO were prepared. • Electrical conductivity at room temperature was showed a minimum at a certain ratio of Li2O/CuO. • Current–voltage characteristic of the samples was showed memory switching at high electric field.

Electrochemical reduction of CO2 in ionic liquid: Mechanistic study of Li–CO2 batteries via in situ ambient pressure X-ray photoelectron spectroscopy

In-depth mechanistic understanding of CO 2 reduction reaction (CRR) and CO 2 evolution reaction (CER) is the prerequisite to develop stable and efficient Li–CO 2 batteries. In this study, we investigate the redox reaction of CO 2 on the porous carbon surface in ionic liquid electrolyte via synchrotron-based in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) technique. We used ionic liquid to facilitate CO 2 capture and stabilize CRR intermediate anions owing to its strong solvation for Li + . We demonstrate that pure CO 2 reduction is not electrochemically active at room temperature on porous carbon electrode and its kinetics can be remarkably improved by H 2 O, which could be responsible for the discrepancy on CRR kinetics in the literature. However, in the presence of H 2 O, the formed LiOH gradually converted to Li 2 CO 3 leading to severe electrolyte degradation in charging reaction. With the assistance of O 2 in the ionic liquid -based electrolyte, we show, for the first time, CRR yields a low-valence amorphous carbon and Li 2 O 2 /Li 2 O in the Li–CO 2 batteries. The formed amorphous carbon, Li 2 O 2 and Li 2 O exhibit higher rechargeability and faster kinetics compared with Li 2 CO 3 -oxidation. These new findings provide direct evidence of CRR mechanism and insights in resolving the discrepancy on CRR kinetics in Li–CO 2 batteries. • Synchrotron-based in-situ APXPS is developed to probe the Li–CO 2 reaction chemistry in ionic liquid electrolyte. • Pure CO 2 reduction is not electrochemically active at room temperature and its kinetics can be significantly improved by H 2 O. • CO 2 reduction in ionic liquid yields amorphous carbon and Li 2 O 2 /Li 2 O which are more reversible than Li 2 CO 3 .

Tuning the structure and morphology of Li2O2 by controlling the crystallinity of catalysts for Li-O2 batteries

Large overpotential in oxygen reduction and evolution reactions is the intractable obstruction of Li-O2 batteries, causing inferior round-trip efficiency and diminished cycle life. Modulating the reaction mechanism of Li2O2 is of crucial importance for a high-performance Li-O2 battery. Herein, we report a composite of amorphous RuO2 nanoparticles decorated carbon nanotubes (A-RuO2@CNT) as an efficient catalyst for Li-O2 batteries. The amorphous catalyst contains abundant defects and vacancies as well as distorted atom arrangements, which provide sufficient active sites for reactions and enhance the affinity for LiO2 intermediates. As a result, the formation/decomposition mechanisms of Li2O2 are reasonably regulated. An amorphous film-like Li2O2 product forms and uniformly deposits on the surface of A-RuO2@CNT, thus achieving faster redox kinetics and smaller overpotential. When used in Li-O2 batteries, the amorphous catalyst affords remarkably decreased charge overpotential and enhanced cyclic stability, which is superior to its crystalline counterpart.

Modeling the Interface between Lithium Metal and Its Native Oxide.

Owing to their high theoretical capacities, batteries that employ lithium (Li) metal as the negative electrode are attractive technologies for next-generation energy storage. However, the successful implementation of lithium metal batteries is limited by several factors, many of which can be traced to an incomplete understanding of surface phenomena involving the Li anode. Here, first-principles calculations are used to characterize the native oxide layer on Li, including several properties associated with the Li/lithium oxide (Li2O) interface. Multiple interface models are examined; the models account for differing interface (chemical) terminations and degrees of atomic ordering (i.e., crystalline vs amorphous). The interfacial energy, formation energy, and strain energies are predicted for these models. The amorphous interface yields the lowest interfacial formation energy, suggesting that it is the most probable model under equilibrium conditions. The work of adhesion is evaluated for the crystalline interfaces, and it is found that the O-terminated interface exhibits a work of adhesion more than 30 times larger than that of the Li-terminated model, implying that Li will strongly wet an oxygen-rich Li2O surface. The electronic structure of the interfaces is characterized using Voronoi charge analysis and shifts in the Li 1s binding energies. The width of the Li/Li2O interface, as determined by deviations from bulklike charges and binding energies, extends beyond the region exhibiting interfacial structural distortions. Finally, the transport of Li ions through the amorphous oxide is quantified using ab initio molecular dynamics. Facile transport of Li+ through the native oxide is observed. Thus, increasing the percentage of amorphous Li2O in the solid electrolyte interphase may be beneficial for battery performance. In total, the phenomena quantified here will aid in the optimization of batteries that employ high-capacity Li metal anodes.

Origin of Intergranular Li Metal Propagation in Garnet-Based Solid Electrolyte By Direct Electronic Structure Analysis and Performance Improvement By Bandgap Engineering

Garnet-structured oxide electrolyte (Li7La3Zr2O12, LLZO) has the significant advantage of being chemically and electrochemically stable against Li metal, which allows the implementation of Li metal batteries. However, a short-circuit failure by Li penetration through the LLZO electrolyte has remained a crucial issue for safety and is a major hurdle for Li-based batteries to overcome. Here, we investigate the mechanism of Li dendrite formation for the crystalline Ta-doped LLZO (LLZTO) by examining their energy band structures and defect states using reflection electron energy loss spectroscopy (REELS), scanning photoelectron microscopy (SPEM), and nanoscale charge-based deep level transient spectroscopy (Nano Q-DLTS) techniques. The experimental results reveal that the Schottky barrier height (SBH) was lowered by 0.5 eV due to the defect states localized in grain boundaries and the metallic Li propagation along the grain boundaries is caused by the SBH reduction. Based on the analytical results, the laser annealing of LLZTO was performed as a bandgap engineering method to suppress the Li dendrite formation by forming a mixed surface layer of amorphous LLZTO and Li2O, which has a wide bandgap to block the electron injection into the grain boundaries. The electrochemical measurements for the laser treated LLZTO demonstrate that the stability and cycling performance are significantly improved. This study sheds light on the importance of electronic structure, in particular, defect states to develop high performance oxide solid electrolytes for Li metal batteries and the practicality of surface modification by laser treatment.

Real-time and direct observation of lithiation of ultra-small tin oxide nanoparticles

Understanding of the lithiation process of ultra-small nanoparticles is crucial for the development of lithium-ion battery electrodes with high-rate charging capability, but remains quite limited. In this work, we successfully investigate the lithiation process of ultra-small SnO2 nanoparticles using in situ transmission electron microscopy (TEM). For the first time, lithiation stripes are observed in the lithiation of SnO2 nanoparticles. Interestingly, rather than a composite structure with LixSn particles dispersed in matrix-like amorphous Li2O reported for SnO2 nanowires, a novel acorn-shaped configuration forms after lithiation of the nanoparticles, in which Sn/Li13Sn5 acts as the shell and Li2O as the core. The lithiation mechanism of the nanoparticles is clearly revealed as two stages – an intercalation process which generates a volume expansion of <33%, and a conversion-alloying reaction which finally results in a volume expansion of ~100%. The total time for full lithiation of a nanoparticle scales linearly with the particle size, indicating that the lithiation process is reaction-controlled. The in situ TEM observations indicate that the ultra-small particles possess an ultrahigh rate-capability (>1000 C). This study strengthens the understanding of lithiation of nanoparticulate electrodes and provides guidance for the design of high-rate capable electrodes.

Li+-clipping for edge S-vacancy MoS2 quantum dots as an efficient bifunctional electrocatalyst enabling discharge growth of amorphous Li2O2 film

Molybdenum disulfide (MoS2), as an extremely intriguing two-dimensional (2D) material with excellent electrocatalyst, has attracted more and more attentions in recent years. However, the lack of precisely engineered rich-edge S-vacancy MoS2 constitutes a major obstacle for in-depth studying of structure-activity relationship of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, based on Lewis acid-base theory, we prepared rich-edge S-vacancy MoS2 quantum dots (MoS2 QDs) via top-down strategy using lithium bis(trifluoromethylsulphonyl)imide as a stripper and clipper. It is demonstrated for the first time that the rich-edge S-vacancy MoS2 QDs exhibit an extraordinary ORR/OER catalytic performance in Li-O2 batteries system by a joint experimental and theoretical study. Importantly, the rich-edge S-vacancy MoS2 QDs can run more than 230 cycles at high current density, which was almost 9 times longer than the cycle stability of bulk MoS2. The excellent activity arises primarily due to that the MoS2 QDs facilitate conformal growth of amorphous Li2O2 film on the cathode, originating from the significant differences of adsorption energies between Li+ and O2, which could significantly enhanced Li2O2 formation/decomposition kinetics. This work provides a novel way for controllable synthesis of rich-edge S-vacancy MoS2 QDs, establishes the underlying mechanisms for the high OER/ORR activity, and suggests high translatability to apply other TMDs.

Defect Chemistry in Discharge Products of Li–O2 Batteries

AbstractLi–O2 batteries, possessing the highest theoretical specific energy density among all known Li‐ion‐based batteries, demonstrate great potential as energy storage devices for powering electric vehicles. However, their battery performance is significantly limited by the insulating nature of the discharge product Li2O2, which has a wide bandgap (4–5 eV), resulting in high charge overpotential. Defect engineering of the discharge product emerges as a very promising strategy to improve the electrical conductivity and hence reduce the charge overpotential. The aim of this review is to highlight recent advances and progress in understanding and controlling the defect chemistry of discharge products in Li–O2 batteries. First, the theoretical perspectives of defects in Li2O2 are reviewed, with particular emphasis on defect design and engineering strategies to significantly improve the charge transport properties of Li2O2. Then intermediate defects in Li2O2 formed during the discharge and charge processes and materials with induced defects, including Li2− x O2, doped Li2O2, Li2O2 with surface/grain boundaries, and amorphous Li2O2, which are tailored by engineered catalysts and electrolyte additives are discussed. Finally, other alternative energy carriers for new energy storage chemistry of Li–O2 batteries, such as lithium superoxide, lithium hydroxide, and lithium carbonate, will also be discussed.