Too large or too small interlayer spacing of electrode materials will lead to the increase of diffusion resistance of Li⁺, which is not conducive to the rapid diffusion of Li⁺. Therefore, the rate capability of LIBs can be improved by properly adjusting the interlayer spacing of electrode materials. Xu et al. Prepared new recycled graphite (N-RG) from acid-treated waste graphite by one-step vapor exfoliation and nitrogen doping^[16]. The interlayer spacing of N-RG is enlarged from 0.337 nm to 0.348 nm (Figure 1A). The enlarged layer spacing can provide a wider channel for the transmission of Li⁺, thus improving the fast charging performance of LIBs. Meanwhile, the nitrogen configuration and content of N-RG are 42.28% pyridine nitrogen, 54.37% pyrrole nitrogen and 3.35% graphite nitrogen. Pyridine nitrogen and pyrrole nitrogen are mainly located at the defect sites or edges of the graphene plane (Figure 1B), which are very active for the adsorption of Li⁺ and help to improve the Li⁺storage capacity of the material. The LiFePO₄/N-RG full cell has a capacity of 111.3 mAh·g⁻¹ at 4 C (Figure 1C). In addition, Kim et al. Prepared expanded graphite with expanded interlayer spacing (0.3359 nm increased to 0.3390 nm) under mild conditions^[17]. Enlarging the interlayer spacing is to improve the diffusion kinetics of ions by widening the transport space of Li⁺. The activation energy of Li⁺ intercalation is significantly reduced due to the introduction of a variety of functional groups into the expanded graphite, which can form hydrogen bonds with carbonate solvent molecules in the electrolyte. Therefore, the capacity of the half-cell using expanded graphite as the negative electrode is 243 mAh·g⁻¹ at 50 C, while the pristine graphite is only 66 mAh·g⁻¹. Jiang et al. Synthesized a selenium disulfide/graphene/selenium disulfide （SnS₂/rGO/SnS₂） composite by a simple one-step hydrothermal method, which expanded the interlayer spacing of SnS₂ to ~ 8.2323 Å^[18]. The enlarged interlayer spacing and the uniform distribution of a large number of ultrafine SnS₂ nanoparticles on the surface of the graphene sheet can promote the rapid intercalation/deintercalation of Li⁺, thereby accelerating the transport kinetics. Therefore, SnS₂/rGO/SnS₂ exhibits an excellent rate capability (capacity of 844 mAh·g⁻¹） at a current density of 10 A·g⁻¹.

To sum up, too small interlayer spacing will lead to slow intercalation of Li⁺, while too large interlayer spacing will lead to too much electrolyte immersion, resulting in the formation of a thick SEI layer, thus limiting the transmission of Li⁺. Therefore, by adjusting the optimal interlayer spacing of the electrode material, the Li⁺ can diffuse in the electrode material at the fastest speed to realize the fast charging of LIBs.

The small particle size brought by nanostructure can shorten the diffusion distance of Li⁺, improve the intercalation and deintercalation kinetics of Li⁺ in electrode materials, and increase the electron transfer speed to some extent^[19]. At the same time, the contact area between the electrode material and the electrolyte increases due to the nanocrystallization, which is beneficial to the rapid diffusion of Li⁺ at the electrode/electrolyte interface^[20]. Therefore, the nano-structure design of materials is one of the effective ways to improve the rate capability of electrode materials.

The nanostructure of electrode materials can be divided into zero-dimensional nanostructure, one-dimensional nanostructure and two-dimensional nanostructure according to the dimensionality of the material. Zero-dimensional nanostructures have a large specific surface area, but they usually exhibit low thermal and electrochemical stability. The specific surface area and porosity of one-dimensional nanostructures are difficult to adjust in a wide range. However, two-dimensional nanostructures usually have large specific surface area and unique sheet-like structure. Due to the sheet-like nature of 2D nanostructures, it is much easier to design their structure and porosity. Therefore, the specific surface area and porosity of two-dimensional nanostructures can be adjusted in different ways. Therefore, compared with zero-dimensional nanostructures and one-dimensional nanostructures, two-dimensional nanostructures with high stability, short Li⁺ diffusion distance and large specific surface area are more suitable for fast-filling LIBs^[21,22]. Wang et al. Prepared ultrathin mesoporous Li₄Ti₅O₁₂ nanosheets by combining a simple solvothermal reaction with a calcination process^[23]. First, the ultrathin nanosheet with an average thickness of about 1 nm shortens the transport path of Li⁺ and electrons in the direction perpendicular to the surface of the nanosheet. Secondly, the uniform mesoporous structure can make the electrolyte penetrate into the active material, reduce the concentration polarization and improve the rate performance of LIBs. Finally, Li₄Ti₅O₁₂ with a large specific surface area （181.7 m²·g⁻¹） can provide more effective active sites for Li⁺ storage, thereby improving the specific capacity and rate capability. Therefore, the Li₄Ti₅O₁₂ nanosheets exhibit excellent cycling stability (95% capacity retention after 2500 cycles at 20 C) and remarkable rate capability (145 mAh·g⁻¹） capacity at 50 C). In addition to the nanostructure mechanism mentioned above, there is a special statement in LiFePO₄. The Li⁺ in the LiFePO₄ can only diffuse along the [010] direction. Therefore, Zhao et al. Shortened the diffusion distance of Li⁺ and increased the specific surface area of the active material by preparing LiFePO₄ nanosheets with nanometer thickness in the [010] direction (Figure 2A)^[24]. The LiFePO₄ nanosheets have a capacity of 55 mAh·g⁻¹ at 30 C (Figure 2B).

Nanostructures have undeniable advantages in improving rate capability, but nanostructured materials usually have low tap density, which leads to a sharp decline in the volume energy density of electrode materials. Chen et al. Prepared a layered microsphere electrode material based on Li₄Ti₅O₁₂ nanosheets (U-LTO-NHMS) that can simultaneously achieve high tap density （1.32 g·cm⁻³） and high rate performance^[25]. U-LTO-NHMS was prepared by a simple solvothermal reaction followed by a brief thermal annealing treatment. The tap density can be controlled by changing the solvothermal reaction temperature, thereby changing the size of the secondary particle. As shown in Figure 2C, the solvothermal reaction has the largest secondary particle size at 160 ° C (U-LTO-NHMS-160), resulting in a higher tap density. Meanwhile, U-LTO-NHM S-160 also has moderate specific surface area （67.03 m²·g⁻¹） and uniform mesoporous structure. The moderate specific surface area can provide more effective active sites for Li⁺storage, and the uniform mesoporous structure can reduce the concentration polarization. Therefore, U-LTO-NHMS-160 can improve the cycling performance (99.5% capacity retention after 2000 cycles at 50 C) and rate capability (155 mAh·g⁻¹ capacity at 50 C) of LIBs.

Coating the surface of electrode materials is a commonly used method to construct artificial interface films (SEI and CEI)^[26]. The introduction of an artificial interfacial film can physically separate the electrolyte and the electrode material to protect the electrode and provide ideal ionic conductivity. Therefore, the coating layer on the electrode surface can promote the diffusion of Li⁺.

Carbon materials are often used to coat the surface of electrode materials because of their good conductivity and structural stability^[27]. Coating carbon materials on the surface of electrode materials can increase the conductivity of electrode materials and provide rapid Li⁺ diffusion channels^[28]. In addition, as a protective layer, it can prevent the side reaction between the electrode material and the electrolyte^[29]. Lyu et al. Synthesized titanium-niobium oxide （TiNb₂O₇,TNO）@C materials with different thickness of carbon coating using glucose as carbon source^[30]. The TNO with carbon coating exhibited better rate performance than the pristine TNO, but the materials with 2 wt% and 3 wt% carbon coating exhibited worse rate performance than the 1 wt% carbon coating material. This indicates that the carbon coating can effectively improve the electronic conductivity of TNO materials, but if the coating is too thick, it will hinder the diffusion of Li⁺. The 1 wt% carbon-coated TNO material with the best rate capability has a capacity of 240 and 211 mAh·g⁻¹ at 5 and 10 C, respectively. Guan et al. Prepared three-dimensional LiFePO₄@C/ graphene composite by solvothermal reaction of LiFePO₄@C and graphene oxide with glucose as carbon source^[31]. The LiFePO₄@C particles are uniformly embedded in the three-dimensional graphene framework, which hinders the stacking phenomenon that graphene oxide is prone to occur during the reduction process. The excellent conductivity of graphene and the sufficient and effective contact between LiFePO₄@C and graphene facilitate the rapid transfer of electrons of Li⁺. Therefore, the composite shows excellent rate capability (capacity of 112.4 and 96.7 mAh·g⁻¹） at 30 and 50 C, respectively.

The addition of inorganic compounds, polymers, and organic/inorganic hybrids other than carbon materials to coat the electrode materials can also suppress the interfacial reaction between the electrode materials and the electrolyte, resulting in thinner and more stable SEI or CEI. Kim et al. Demonstrated that coating graphite with amorphous Al₂O₃ is one of the effective ways to improve the fast charging ability of LIBs graphite anode materials (Fig. 3A, B)^[32]. The introduction of amorphous Al₂O₃ improves the electrolyte wettability of graphite electrode, which can improve the kinetics of Li⁺ intercalation. The electrode material has a capacity of 337.1 mAh·g⁻¹ at a current density of 4 A·g⁻¹, corresponding to 97.2% of the capacity at a current density of 100 mA·g⁻¹ (Figure 3C). Ran et al. Successfully prepared the LiNi_0.6Co_0.2Mn_0.2O_2−x(PO₄)_x@Li₃PO₄-PANI cathode material by combining the doping PO₄³⁻ and double conductive layer （Li₃PO₄-PANI） methods (Fig. 3D)^[33]. Firstly, the introduction of the double conductive layer can reduce the amount of residual lithium salt on the surface of the LiNi_0.6Co_0.2Mn_0.2O₂ cathode, thus inhibiting the side reaction at the electrode/electrolyte interface to some extent. In addition, the double conductive layer can also improve the ionic conductivity of the cathode material. Compared with the original LiNi_0.6Co_0.2Mn_0.2O₂（1.53×10⁻⁵S·cm⁻¹）, the ionic conductivity of the LiNi_0.6Co_0.2Mn_0.2O₂ with the double conductive layer is improved to a 4.7×10⁻⁴S·cm⁻¹. Secondly, gradient doping can replace the original O²⁻ with PO₄³⁻（ Fig. 3 e). Due to the strong covalent P-O bond and excellent structural stability, the gradient-doped PO₄³⁻ can achieve the stability of the positive oxygen layer, thereby improving the lattice stability, resulting in better cycling stability of LiNi_0.6Co_0.2Mn_0.2O_2−x(PO₄)_x@Li₃PO₄-PANI (capacity retention of 76.6% after 100 cycles) as well as excellent rate capability (capacity of 130 mAh·g⁻¹） at 5 C).

Porous structure can be formed by etching the electrode material. At present, the main pore-forming methods include oxidation etching, thermal stripping, laser etching and so on. The porous structure can significantly increase the number of active sites for Li⁺ intercalation/deintercalation and reduce the diffusion distance of Li⁺ inside the electrode material, thus promoting the rapid diffusion of Li⁺. Cheng et al. Constructed a graphite with porous structure (Figure 4A) by using KOH to etch the graphite surface, which can increase the number of sites for Li⁺ intercalation/deintercalation and reduce the diffusion distance of Li^+[34]. The capacity retention of KOH-etched graphite and as-received graphite at 3 C is 93% and 85%, respectively. In addition, the capacity retention of KOH-etched graphite at 6 C is still 74%. Kim et al. Modified the original graphite by acid and alkali respectively (Fig. 4B)^[35]. Sulfuric acid/nitric acid can oxidize graphite, thus exfoliating the bulk graphite layer into thin exfoliated graphite. The chemical oxidation process also transforms the hydrophobic original graphite into hydrophilic graphite by introducing — OH groups into the carbon structure, which helps the electrolyte to diffuse into the electrode, thus increasing the rapid transport of Li⁺ between the graphite layers. The surface of the graphite layer etched by KOH will form a large number of pores, which will promote the diffusion of Li⁺ and increase the number of Li⁺ intercalation sites in the graphite layer. The capacity of acid and alkali treated graphite at a current density of 1.5 A·g⁻¹ (95 and 93 mAh·g⁻¹） is better than that of pristine graphite （50 mAh·g⁻¹）. Chen et al. Created a large number of micropores on the surface of graphite negative electrode by laser etching technology to help the rapid diffusion of Li⁺ in the thick electrode (Fig. 4C)^[36]. Making a large number of micropores on the surface of the negative electrode can effectively accelerate the diffusion of Li⁺ in the electrode, reduce the polarization of the negative electrode during charging, and avoid lithium precipitation from the negative electrode, thus significantly improving the cycle life under fast charging. The capacity retention of the laser-etched graphite anode is 93% and 56% after 100 and 600 cycles at 6 C, respectively, which is much higher than that of the pristine graphite anode.

In addition to improving the internal ion transport by adjusting the electrode material structure, the external ion transport can also be enhanced by the structural design of the counter electrode. The vertical array structure can control the orientation of the electrode in a specific direction and reduce the tortuosity of the diffusion path of Li⁺ inside the electrode, thus effectively accelerating the diffusion of Li⁺ in the electrode. Billaud et al. Regulated the orientation of graphite by applying a magnetic field formed by an external current to make it grow vertically on the current collector^[37]. This method reduces the tortuosity of the graphite electrode and shortens the diffusion path of Li⁺ on the electrode, resulting in excellent rate performance under ultra-high loading of （10 mg·cm⁻²）. Guo et al. Used the freeze-coating technique to study the microstructure and electrochemical performance of LiFePO₄ electrodes at different solid contents and freezing rates^[38]. The electrode fabricated by the freeze-coating technique can improve the electron transfer and Li⁺ diffusion rate of the LiFePO₄ electrode due to the vertically interconnected solid network (Figure 5A). The LiFePO₄ electrode fabricated when the solid content is 30 wt% and the freezing time is 5℃·min⁻¹ has the highest Li⁺ diffusion coefficient （1.32×10⁻¹²cm⁻²·s⁻¹） and the highest conductivity （3.1×10⁻³S·cm⁻¹）. Therefore, the capacity of the LiFePO₄ electrode fabricated by the freeze-coating technique is 40.7 mAh·g⁻¹ at 15 C, while the capacity of the LiFePO₄ electrode fabricated by the conventional coating technique decays to a negligible level at 15 C (Figure 5B). Tu et al. Proposed an electrode structure consisting of a large-scale monolayer of particles with vertically aligned carrier transport channels^[39]. Monolayer particle electrodes have continuous, short and straight ion and electron transport paths (fig. 5C), high electrode density, and low electrolyte intake (fig. 5d, e) compared to conventional particle electrodes. In addition, the contact resistance of the monolayer particle electrode in the direction of ion transport is smaller, so its overpotential is smaller. Therefore, the monolayer particle electrode has a unique advantage for LIBs to achieve fast charging.

Doping generally improves the electron conductivity by controlling the non-stoichiometric ratio to create new electrons or holes^[40]. Therefore, the diffusion rate of Li⁺ can be improved by doping atoms or ions in the electrode materials. Dopant atoms in electrode materials can introduce more defects and active sites for the intercalation of Li⁺, thereby improving the storage capacity of Li⁺. For example, the incorporation of nitrogen atoms in the carbon structure can introduce more active sites and facilitate charge transfer, thereby significantly improving the storage capacity of Li^+[41]. In addition, doping atoms can also improve the conductivity of electrode materials, thus promoting the transfer of electrons and ions. Wang et al. Used tricresyl phosphate as a phosphorus source, oligomeric phenolic resin as a carbon source, and triblock copolymer F127 as a soft template to induce the co-assembly of ternary components on the polyurethane sponge skeleton through solvent evaporation to prepare large-pore phosphorus-doped mesoporous carbon^[42]. Phosphorus doping can improve the electronic conductivity and enlarge the interlayer spacing of mesoporous carbon, which is beneficial to the rapid transfer of electrons and the intercalation/deintercalation of Li⁺. In addition, phosphorus doping can also introduce more defects in the carbon skeleton to provide more active sites for the storage of Li⁺. The large-pore phosphorus-doped mesoporous carbon can not only maintain the capacity of 236 mAh·g⁻¹ at 8 C, but also provide long-term cycling stability.

Doping ions in electrode materials can adjust the electronic structure and optimize the electronic conductivity of electrode materials by narrowing the band gap and creating local defects. In addition, the doping ions can also create more active sites for the intercalation of Li⁺. Tu et al. Improved the fast charging performance of Ti₂Nb₁₀O₂₉（TNO） by combining doping ions and spiral array structure^[43]. Firstly, a novel porous vertical graphene @ TiC-C array (VGTC) framework was designed as a conductive matrix. VGTC has excellent mechanical stability and high ionic/electronic conduction properties. Then, the spiral growth of Cr³⁺ doped TNO nanoparticles (Cr-TNO) was realized on the VGTC framework, forming Cr-TNO @ VGTC arrays (Figure 6A). By density functional theory calculations, Li⁺ presents an energy barrier of 0.8 eV in Cr-TNO (3.6 eV in TNO and 1.6 eV in nanosized TNO), indicating the faster reaction kinetics of Cr³⁺ doped TNO. In addition, the conductivity of Cr-TNO is significantly enhanced due to the presence of an impurity level between the valence and conduction bands. Density functional theory calculations proved the improvement of both conductivity and ion transfer of Cr³⁺ doped TNO. Therefore, the Cr-TNO @ VGTC array has a capacity of 220 mAh·g⁻¹ at 40 C. Wu et al. Synthesized Li_0.99K_0.01V_0.995Zr_0.005PO₄F/C composite （K1Zr_0.5 by double ion doping of K⁺ and Zr⁴⁺ on lithium vanadium fluorophosphate （LiVPO₄F） materials^[44]; Fig. 6 B). The Hall effect shows that Zr⁴⁺ doping changes the conductivity type of LiVPO₄F materials from P-type semiconductor to N-type semiconductor, and the conductivity increases by 104 times, thus making the conductivity reach the 1.2×10⁻²S·cm⁻¹. The ionic radii of K⁺ and Zr⁴⁺ are larger than those of Li⁺ and V³⁺,Therefore, the doping of Zr⁴⁺ and K⁺ will expand the unit cell volume of LiVPO₄F.It leads to the expansion of the diffusion path of Li⁺, which promotes the diffusion coefficient （9.83×10⁻¹³cm⁻²·s⁻¹） of Li⁺. The capacity of the K1Zr_0.5 at 60 C can still reach the 105.7 mAh·g⁻¹. Meanwhile, the capacity retention after 2000 cycles at 10 C was 80% (Fig. 6 C).

Generally speaking, the index to quantify the transport ability of Li⁺ in electrolyte is the ionic conductivity of electrolyte^[46]. The low ionic conductivity of the electrolyte will cause the transport of Li⁺ in the electrolyte to be hindered, thus affecting the fast charging performance. The most effective way to improve the ionic conductivity of the electrolyte is to replace all or part of the main solvent with a solvent with low viscosity and high dielectric constant. For example, butyronitrile solvent can fully dissolve lithium salt due to its high dielectric constant, so it can improve the ionic conductivity of the electrolyte as the main solvent of the electrolyte^[47]. In addition, Logan et al. Prepared lithium hexafluorophosphate （LiPF₆） an ester-based electrolyte dissolved in methyl acetate (MA), which was greatly improved in ion transport^[48]. MA has a low viscosity and a higher dielectric constant than traditional carbonate-based solvents, which greatly improves the transport characteristics of the electrolyte. At a salt concentration of 2 mol·kg⁻¹, the ionic conductivity of MA/LiPF₆ is 25 mS·cm⁻¹, which is twice the ionic conductivity of the ethylene carbonate (EC)/dimethyl carbonate （DMC）/LiPF₆ electrolyte system. Therefore, at this salt concentration, the capacity retention of MA/LiPF₆ electrolyte at 4 C is 65%, while that of EC/DMC/LiPF₆ electrolyte is only 20%. Gao et al. Solved the problem of short cycle life of LIBs under extreme fast charge conditions by designing a novel ester-based electrolyte （1 M LiPF₆ dissolved in methyl propionate (MP) + 10% fluoroacetate (FEC) (M9F1))^[49]. First, the lower viscosity of the MP solvent enables the M9F1 electrolyte to increase the ionic conductivity to 12.1 mS·cm⁻¹（ Fig. 7A) and also increase the ionic transference number to 0.46. Secondly, the interface thickness formed by M9F1 electrolyte after 1000 cycles is thinner than that of conventional electrolyte (Fig. 7B). In addition, the SEI formed in M9F1 exhibited a higher LiF/Li_xPF_y ratio, indicating the formation of a stable SEI rich in LiF. A lower ROCO₂Li/Li₂CO₃ ratio was also found in M9F1, which is generally considered to be more favorable for Li⁺ diffusion in the SEI. Finally, the activation energy for desolvation of M9F1 electrolyte is about 5 kcal·mol⁻¹, while that of conventional electrolyte exceeds 7 kcal·mol⁻¹. The lower activation energy of M9F1 electrolyte is more favorable for charge transfer. As a result, the battery using M9F1 showed 88.2% and 77.9% capacity retention after 500 and 1000 cycles at 4 C charge (Figure 7 C), compared to 54.1% and 12.4% for the battery using EC/ethyl methyl carbonate (EMC) electrolyte (Figure 7 d).

The interfacial films (SEI and CEI) that meet the requirements of fast charging should have high ionic conductivity, suitable thickness, extremely high uniformity, ideal mechanical strength, and outstanding chemical/structural stability^[50]. The interfacial film derived from conventional electrolyte is mainly composed of organic oligomers generated by EC reduction. The interface film has fewer grain boundaries than interface films mainly composed of inorganic components such as lithium nitride （Li₃N）, lithium fluoride (LiF), lithium oxide （Li₂O）, and the like. The energy barrier of Li⁺ diffusion through grain boundary is lower and the migration speed is faster^[51]. Therefore, the transport of Li⁺ through the organic-dominated interfacial film can be hindered at high current, resulting in a significant increase in the interfacial resistance. Moreover, this interfacial film is sensitive to temperature. Compared with normal rate charging, fast charging leads to an increase in internal temperature, which accelerates electrolyte decomposition and increases the thickness of the interfacial film, which increases the energy barrier for Li⁺ to cross the interfacial film. The electrolyte film forming additive has a lower reduction potential than EC, and can be reduced and decomposed before EC to form an interfacial film. Therefore, by selecting a small proportion of electrolyte film-forming additives, the interface film mainly composed of organic matter can be changed into an interface film mainly composed of inorganic matter, thus improving the fast charging performance of lithium-ion batteries. Shi et al. Dissolved 1 mol·L⁻¹LiPF₆ in EC and DMC and added fluorosulfonyl isocyanate (FI) to improve the fast charging performance of LIBs^[52]. Compared with EC and DMC, FI has a lower lowest unoccupied molecular orbital, which can make FI reduce before EC and DMC. FI forms SEI on the graphite surface, which is mainly composed of inorganic components, which can make the impedance at the graphite/electrolyte interface lower, thus promoting the rapid diffusion of Li⁺.

The diffusion rate of Li⁺ in the CEI on the cathode surface also affects the fast charging performance of LIBs. Cheng et al. added lithium bisoxalatoborate (LiBOB) and dopamine (DA) to the traditional carbonate-based electrolyte to form an organic/inorganic composite CEI on the surface of the cathode (Figure 8 a)^[53]. The internal cracks of the LiNi_0.8Co_0.1Mn_0.1O₂ will cause the continuous penetration of the electrolyte, and the reaction between the electrolyte and the new interface will lead to a sharp decline in capacity. However, the electrolyte containing LiBOB and DA can well improve this problem, which will form a uniform and stable CEI on the surface of the positive electrode, and there will be no obvious cracks in the LiNi_0.8Co_0.1Mn_0.1O₂ during cycling. In addition, nitrogen-rich LiBOB and DA-derived CEI have lower impedance. Because nitrogen has a high affinity for Li⁺, it can promote the diffusion of Li⁺. LiBOB and DA-derived CEI can not only improve the cycle stability of LIBs, but also improve the rate capability. The capacity of the Li||LiNi_0.8Co_0.1Mn_0.1O₂ cell using this electrolyte was 96 and 51 mAh·g⁻¹（ at 10 and 20 C, respectively Fig. 8 B). Wang et al. Reported the ester-based electrolyte （1 mol·L⁻¹LiPF₆FEC/EMC-LiBF₄（2%）-LiNO₃（2%）） with lithium tetrafluoroborate （LiBF₄） and lithium nitrate （LiNO₃） as additives^[54]. The electrolyte can not only form a stable SEI on the negative electrode, but also enhance the reversibility of Li⁺ intercalation/deintercalation. At the same time, the thin and strong CEI formed by the electrolyte can avoid the continuous side reaction from the electrolyte and maintain the structural integrity of the LiNi_0.8Co_0.1Mn_0.1O₂. In addition, LiBF₄ can promote the dissolution of LiNO₃ in traditional carbonate solvents through its unique steric structure and Lewis acidity. The introduction of LiNO₃ additive makes both SEI and CEI rich in lithium nitride compounds with fast ion transport characteristics, thus promoting the transport of Li⁺ at the interface between the positive and negative electrodes. The electrolyte based on this design enables the Li||LiNi_0.8Co_0.1Mn_0.1O₂ cell to have a 185.6 mAh·g⁻¹ capacity at 5 C.

Salt concentration is a key factor in determining the solvation structure of Li⁺. As the salt concentration increases, fewer solvent molecules are available to occupy the solvation sheath due to the decrease in solvent molecules, allowing anions to enter the solvation sheath to interact with the Li^+[55]. The solvated structure also changes from the original coordination of Li⁺ and solvent molecules to contact ion pairs (CIPs) with one anion coordinated to one Li⁺ or aggregates (AGGs) with one anion coordinated to two Li⁺; Fig. 9 a)^[56].

Aggregation of anions in the solvated structure of Li⁺ can form an anion-derived SEI. The decomposition of anions can produce inorganic components such as LiF, Li₃N, lithium sulfide （Li₂S）, Li₂O^[57]. These inorganic components usually have smaller band gaps and higher mechanical hardness, which can lead to excellent performance of inorganic-rich SEI^[58,59]. LiF-rich SEI has high chemical/electrochemical stability, which can simultaneously inhibit the continuous decomposition of electrolyte and the growth of lithium dendrite^[60]. Secondly, Li₃N is considered to be a favorable SEI component for passivating the interface and accelerating the interfacial dynamics because of its high ionic conductivity （~10⁻³S·cm⁻¹）^[61]. Synergistic effect of these characteristics, the anion-derived SEI has higher interfacial stability and faster interfacial dynamics at relatively thin thickness. The inorganic component makes the SEI have the beneficial characteristics mentioned above, but the rich inorganic component reduces the organic component in the SEI, and the organic component can buffer the volume change of the electrode material to maintain the integrity of the interface. Therefore, excessive inorganic components can make the SEI unable to adapt to the volume change of electrode materials, resulting in the continuous growth of SEI and the reduction of reversible capacity^[62]. Based on a systematic analysis of the interfacial dynamics in the model system, it was found that the solvated structure composed of an anion with Li⁺ has a lower activation energy for desolvation, and the inorganic-rich anion-derived SEI formed from this solvated structure has a lower activation energy for Li⁺ diffusion in the SEI (Fig. 9 B)^[63]. In addition, the reduction of SEI thickness also contributes to accelerating the kinetics of interfacial transport. The favorable characteristics of the solvated structure composed of anions and Li⁺ fundamentally ensure the fast charging performance and cycling stability of LIBs.