Suppressed Internal Intrinsic Stress Engineering in High‐Performance Ni‐Rich Cathode Via Multilayered In Situ Coating Structure

LiNixCoyAlzO2(NCA) cathode materials are drawing widespread attention, but the huge gap between the ideal and present cyclic stability still hinders their further commercial application, especially for the Ni‐rich LiNixCoyAlzO2 (x > 0.8, x + y + z = 1) cathode material, which is owing to the structural degradation and particles' intrinsic fracture. To tackle the problems, Li0.5La2Al0.5O4 in situ coated and Mn compensating doped multilayer LiNi0.82Co0.14Al0.04O2 was prepared. XRD refinement indicates that La–Mn co‐modifying could realize appropriate Li/Ni disorder degree. Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain. AFM further improves as NCA‐LM2 has superior mechanical property. The SEM, TEM, XPS tests indicate that the cycled cathode with LLAO–Mn modification displays a more complete morphology and less side reaction with electrolyte. DEMS was used to further investigate cathode–electrolyte interface which was reflected by gas evolution. NCA‐LM2 releases less CO2 than NCA‐P indexing on a more stable surface. The modified material presents outstanding capacity retention of 96.2% after 100 cycles in the voltage range of 3.0–4.4 V at 1C, 13% higher than that of the pristine and 80.8% at 1 C after 300 cycles. This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li0.5La2Al0.5O4 (LLAO) could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion. We believe that it can be a useful strategy for the modification of Ni‐rich cathode material and other advanced functional material.

LiNi x Co y Al z O 2 (NCA) cathode materials are drawing widespread attention, but the huge gap between the ideal and present cyclic stability still hinders their further commercial application, especially for the Ni-rich LiNi x Co y Al z O 2 (x > 0.8, x + y + z = 1) cathode material, which is owing to the structural degradation and particles' intrinsic fracture.To tackle the problems, Li 0.5 La 2 Al 0.5 O 4 in situ coated and Mn compensating doped multilayer LiNi 0.82 Co 0.14 Al 0.04 O 2 was prepared.XRD refinement indicates that La-Mn comodifying could realize appropriate Li/Ni disorder degree.Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain.AFM further improves as NCA-LM2 has superior mechanical property.The SEM, TEM, XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte.DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution.NCA-LM2 releases less CO 2 than NCA-P indexing on a more stable surface.The modified material presents outstanding capacity retention of 96.2% after 100 cycles in the voltage range of 3.0-4.4V at 1C, 13% higher than that of the pristine and 80.8% at 1 C after 300 cycles.This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li 0.5 La 2 Al 0.5 O 4 (LLAO) could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion.We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.always overlooked.In fact, a strategy to strengthen its mechanical performances should be paid more attention.Here, a coating layer with appropriate Young's modulus should to be established.As for conventional coating method, there are always lattice mismatch because of the different volume effects with incompatible Young's modulus.Thus, after cycling, the coating layer might squeeze with bulk material and fall off from the surface.Among many coating strategies, the in situ coating method always has better performances, which has less lattice mismatch.29][30] Thus, it is crucial to select the appropriate reactions and products, which determine the preparing condition and the stability of the surface, respectively.Hence, how to economically improve cycle life is the key issue to realize the wider range of applications.Because the system of La-Li-Al-O will form Li 0.5 La 2 Al 0.5 O 4 (LLAO) from the reaction among La 2 O 3 , Li 2 O, and Al 2 O 3 at 800 °C. [31]Meanwhile, Li 0.5 La 2 Al 0.5 O 4 is not only chemically stable but also a kind of fast ionic conductor with K 2 NiF 4 structure.Moreover, the LLAO has excellent mechanical properties.To avoid the failure of realizing the ideal performances by single modification strategy, the dual-modification method is put forward to achieve great comprehensive properties.
Here, we take advantage of this to bring in an in situ coating layer of Li 0.5 La 2 Al 0.5 O 4 .But the mentioned reaction will consume some Al atoms in the superficial phase of secondary particles, which leads to the lattice distortion.Thus, the stoichiometric Mn atoms are doped into the Al-deficient layer to form the LiNi 0.82 Co 0.14 Al 0.04-x Mn x O 2 (LNCAM), which becomes a transition layer suppressing the lattice mismatch on the interface.In general, we prepared a series of materials with different La and Mn contents and were inspired by the special molar ratio of 4:1.Later, the TEM and XPS analyses show that the prepared material includes three layers which are the amorphous Li 0.5 La 2 Al 0.5 O 4 in situ coating layer, the LNCAM transition layer, and the pristine LiNi 0.82- Co 0.14 Al 0.04 O 2 (LNCA) phase from the surface to the inside, respectively.Computational result and AFM test demonstrate that LLAO possesses better mechanical properties.As a kind of Li + -conductor, LLAO layer could also enhance the transport of Li + along grain boundary.Compared with the pristine LiNi 0.82 Co 0.14 Al 0.04 O 2 material, the modified material shows a much better electrochemical performance.

Results and Discussion
The prepared multilayer coating structure on NCA-LM2 is demonstrated in Figure 1a.The details of synthesis and parallel samples are clarified in the experimental section.The SEM images of NCA-P and NCA-LM2 are clarified in Figure S1a,b, Supporting Information, where La-Mn comodification makes the primary gain of particles smaller and denser, which is attributed to the coating layer.The AFM images in Figure S1c,d, Supporting Information, further reveal that NCA-LM2 has more smooth topography compared with NCA-P because of the uniformly LLAO coating layer.TEM and HRTEM testing are employed in Figure 1 and specific areas are selected to do Fast Fourier Transform (FFT).Figure 1c-I, c-II are selected in bulk and surface of NCA-P respectively, where both interplanar spacings are measured to be 0.203 nm, typically for the (104) planes of α-NaFeO 2 with R-3 m space, proving that the NCA-P has the consistent phase in both bulk and surface.In comparison, there is an amorphous coating layer on NCA-LM2 with a thickness of ~2.5 nm, which involves the LLAO layer.As shown in Figure 1e-II, the lattice fringe of the intraparticle is observed to be 0.203 nm, which is identical with the (104) plane indicating the same bulk structure with NCM-P.To investigate the multilayer structure, one area next to the coating layer is selected.According to the FFT image in Figure 1e-I, the (104) plane distance shifts to 0.204 nm, demonstrating that there is a new phase between surface and bulk, denoted as a middle layer.Coincidentally, high-performance quaternary Li(Ni0.89Co0.05Mn0.05Al0.01)O2(NCMA) cathode was reported by Sun. [36]In their research, the lattice values of NCMA are calculated as a hex = 2.87239 Å, c hex = 14.20136Å by Rietveld refinement and the interplanar distance of (104) plane is calculated to be ~0.2037nm using the formula (1).The observed value of the middle layer is consistent to the reported results well.It is reasonable to consider the relationship of the reported NCMA cathode and the middle layer because of the same (104) distance of both materials.Moreover, the similar interplanar spacing could suppress the lattice mismatch between the in situ coating layer and bulk material effectively.
XRD curves shown in Figure 1f indicate that both NCA-P and NCA-LM2 are indexed to the well-defined layered α-NaFeO 2 structure.But noticeably, three characteristic peaks of Li 0.5 La 2 Al 0.5 O 4 appear at 2θ of 31.7°,24.6°, and 33.6°, which is more convincing evidence for the formation of Li 0.5 La 2 Al 0.5 O 4 coating layer.Rietveld refinement is employed (Figure 1g,h) to investigate the lattice parameters as given in Table 1 with the wRp value of <4%.The a hex has little change among NCA-P, NCA-L2, and NCA-LM2 due to the fact that the doped atoms have no effect on lattice parameter along a-axis, while the value of c hex increases after La modification and decreases after La-Mn comodification.Li/Ni mixing degree is obviously suppressed by introduced La atoms from 8.65% to 2.81%.On the contrary, the NCA-LM2 has larger Li/Ni disorder value than NCA-L2 (Figure S2, Supporting Information), which could be attributed to the introduction of Mn 4+ .In our previous works, Mn 4+ could lead to compensation for valence balance in transition metals sites, inducing Ni 3+ to convert to Ni 2+ , which results in more Li/Ni disorder. [7] La-doping enlarges the transition metal interslab because of the introduction of La 3+ with big radius (1.032 Å).Meanwhile, Mn-doping shrinks S (MO2) and increases I(LiO2) compared with NCA-L2.Thus, Ni-rich cathodes have modest thickness of Li and transition metal slab after La-Mn co-modifying.
To figure out the valence state on the surface and the depth distribution of La, Mn, X-ray photoelectron spectroscopy (XPS) testing and depth analysis are employed as shown in Figure 2. As for Figure 2a, it could be observed that the Al2p peaks of NCA-P and NCA-LM2 have little difference, which means that La-Mn co-modifying has little influence with the chemical state of Al on the surface.As seen in the fitting results of the Ni2p 3/2 peak at ~855 eV in Figure 2b, the higher Ni 2+ ratio of NCA-P hints the more serious degree of Li/Ni mixing than NCA-LM2.The peaks at ~289 eV of C1s and ~531 eV of O1s are always related to Li 2 CO 3 , which reduce by 8.3% and 10.8%, Energy Environ.Mater.2024, 7, e12574 2 of 9 respectively.Residual lithium compounds on the surface will aggravate the interface between electrolyte and cathode material.Thus, fewer residual lithium compounds of NCA-LM2 means more excellent performances.As presented in Figure 2e, the intensity of La 3d has the highest value on the surface at ~855.1 eV and gradually decreases with the binding energy reduction.It is proved that La mainly distributes on the surface, where the binding energy is higher due to the La-O band.In Figure 2f, the intensity of the Mn2p peak on the surface is weaker than that in the 5 nm-depth interior and gradually decreases with the etching deepened, reflecting that Mn compensates into Al-vacancies.The To explore the best proportions of La and Mn, the samples with different contents were characterized by two-step condition experiments at the voltage range of 3.0-4.4V under a constant current of 1C with a room temperature (25 °C) environment.Figure S3a, Supporting Information, shows the capacity fading of the samples with La contents of 0, 0.2%, 0.4%, and 0.6%.The La-modified samples yield similar initial discharge capacities about 181 mAh g −1 at 1 C.Meanwhile, NCA-P experienced a capacity decay of 16.8% after 100 cycles, with the initial discharge of 181.3 mAh g −1 as shown in Figure 3d.NCA-L2 exhibits the lowest cycling decay with a capacity retention of 92.5%.The other samples such as NCA-L1 and NCA-L3 also show more cyclic stability than NCA-P in different degree.[41][42] Therefore, NCA-L2 is chosen as the basal sample to further explore the effect of La-Mn co-modified with Mn content of 0.05%, 0.1%, 0.2%, 0.3%, and 0.4%, respectively.As Figure S3b, Supporting Information, represents, NCA-L2 benefits from the modification of manganese.The capacity retentions of NCA-LM (1-5) after 100 cycles are 92.8%,96.2%, 95.3%, 95.6%, and 95.4%, respectively.The initial capacity of most samples is close besides NCA-LM5, which is lower than others by around 1.3 mAh g −1 .Figure 3a reveals that NCA-LM2 presents the best cyclic performance with the capacity retention ratio of 96.2%, where the molar ratio of La and Mn is 4:1.It is worth mentioning that the molar ratio of La and Al is also 4:1 in Li 0.5 La 2 Al 0.5 O 4 , which implies the relevance between the excellent cycling ability and the formation of Li 0.5 La 2 Al 0.5 O 4 .In Figure 3c, the capacity retention of NCA-LM2 after 300 cycles gets up to 80.8%, while NCA-P just exhibits that of 61.7% after 200 cycles with the serious capacity drop.Moreover, there is a turning point of NCA-P around 60 cycles as noted with red circle, which is related to the formation of intergranular cracks caused by H2 → H3 phase transition. [11]However, NCA-LM2 has no inflection point with mechanical stability benefited from LLAO coating layer.At the 8C rate as in Figure 3e, the capacity retention of NCA-LM2 reached 95.0% after 100 cycles with an initial capacity of 159.6 mAh g −1 .However, NCA-LM2 drops to 92.1% of the initial capacity (150.1 mAh g −1 ) after 100 cycles.This high rate performances ability may be attributed to the LLAO coating layer which is a K 2 NiF 4 -type Li + conductor.Figure 3b presents the dQ/dV curves of NCA-P and NCA-LM2 measured after every 100 cycles interval.The main peak deviation of NCA-P is 0.109 V, while that of NCA-LM2 is only 0.062 V. Compared with NCA-P, the dQ/dV curves of NCA-LM2 are more concentrated, which indicates that the NCA-LM2 is less affected by electrochemical polarization and side reactions during cycling and has better cyclic performance.Table S1, Supporting Information, lists the impedance of EIS plots in Figure 3f-h.There are few differences among all samples with the R f (surface film impendence) value of 8-20 Ω.But compared with NCA-P, the R ct (charge transfer resistance) of NCA-LM2 is reduced obviously whatever at 1C (121.9Ω vs 52.4 Ω) or 8C (152 Ω vs 95.6 Ω), proving that the La-Mn comodification can effectively reduce the charge transfer impedance.The multilayered modified strategy is helpful for charge transfer.
The LLAO coating layer is identified as advantageous to the cyclic life according to the mentioned results.To further investigate the mechanical properties, the structural stability of NCA-P and LLAO are studied by calculating the values of stress changes with the strain.According to the operando XRD analysis as shown in Figure 4a,b, the (003) plane of NCA-P shifts from 18.75°to maximum 19.32°.Moreover, c-axis is perpendicular to (003) plane, which shows that the altered (003) peak in operando XRD analysis could indicate the strain along c-axis by Bragg's Law (2dsinθ = nλ, n = 1,2. ..).Thus, the values of average interlayer spaces of (003) plane before and after cycling are calculated as d 1 = nλ/2sin18.75°andd 2 = nλ/2sin19.32°,respectively.Li + is under an obvious misplacement over 2% tensile strain, which means that the particles of NCA-P tend to crush at a charged state.The highest estimated tensile strain ε = (d 2 -d 1 )/d 1 is 2.84%. The illustration of maximal c-axis is presented in Figure 4a-i, b-i, where NCA-LM2 displays a smaller lattice parameter of c-axis.Correspondingly, the stress-strain curve of LLAO coating layer is computed in Figure 4d, which shows exponential behavior at a large-scale strain without fracture.The charged state NCA-P (Li 0.5 Ni 0.82- Co 0.14 Al 0.04 O 2 ) and LLAO were chosen to explore because the halfcharged state undergo the maximum anisotropy of crystal structure as demonstrated in Figure 4.In Figure 4c,d, c-axis of NCA-P has the highest range of variation in different strain states among a,b,c-axes particularly under the compressive strain, and there are little differences in Energy Environ.Mater.2024, 7, e12574 lattice along a and b directions.The stress of c-axis decreases exponentially with the reducing of compressive strain and the linear relationship between stress and strain is absent over 2% tensile strain.According to the computational results (Figure 4c,d), LLAO has 5% larger Young's modulus (6.2 GPa) than that of NCA-P (5.9 GPa), and will not break under greater stress compared with NCA-P.Thus, the NCA-P primary particles suffer from inelastic deformation at charged state which may cause fracture and intra-and inter-granular cracks.
Table S2, Supporting Information, lists the stress values in a(b),c directions in different strain states.LLAO shows a great stress isotropy in tensile strain, in which the curve of stress along a(b),c directions is practically identical.LLAO presents a uniformly linear behavior until 17.5% tensile strain, indicating that there are no cracks upon cycling with LLAO coating layer.As for operando XRD as in Figure 4a,b, the maximum strain is calculated as 1.2% via formula (4).The strain is suppressed by the LLAO coating effectively.Otherwise, for NCA-LM2, the total 2θ angular shifts of ( 003) and ( 104) peak are 0.66°and 0.80°respectively, smaller than those of 0.83°and 0.82°, which demonstrates less lattice expansion along the c-axis after the in situ LLAO coating.
To further verify the enhancement of mechanical properties, quantitative nanoscale mechanical characterization (QNM) of AFM was used to measure the Young's modulus of the surface.The average Young's modulus of NCA-LM2 is much more than that of NCA-P.Therefore, it can be concluded that the high strength LLAO coating layer has been successfully coated on the surface.The side reaction in cathode-electrolyte intersurface is closely related to gas evolution, such as O 2 and CO 2 , especially in carbonate-based electrolyte.Thus, operando differential electrochemical mass spectrometry (DEMS) results are shown in Figure 5e,f.The evolution of O 2 and CO 2 is monitored upon charging to 4.5 V. NCA-P releases CO 2 obviously as highlighted by the red circle in Figure 5e.On the contrary, as for NCA-LM2, no obvious gaseous products (CO 2 ,O 2 ) are detected, which demonstrates the La-Mn dual-modification could enhance cathode-electrolyte intersurface and inhibit the decomposition of electrolyte effectively.The morphology and surface phase of cycled cathodes has a great relationship with electrochemical performances.Therefore, the SEM, TEM, and XPS tests are carried out as shown in Figure 6.In SEM images (Figure 6b,d), the secondary particles of NCA-P are observed to break and pulverize upon long cycling, and the schematic illustration was plotted in Figure 6a.Moreover, the impurity phase such as rock salt phase generates on the surface (Figure 6c).Otherwise, NCA-LM2 maintains the morphology of secondary particles well, of which the crack is effectively suppressed by LLAO coating, and meanwhile the FFT as shown in Figure 6d reflects that it remains a layered structure with the hexagonal system after cycling.XPS for cycled electrode also reflects in Figure 6e-h.For O 1s spectrum of NCA-LM2 (Figure 6f), the peaks located at 531.79 eV, 529.2 eV refer to residual lithium species (Li 2 CO 3 /LiOH) and lattice O, respectively. [45]However, there is no lattice O in NCA-P indicating a thick layer of oxide on the surface.In the C 1s spectrum of Figure 6g  Energy Environ.Mater.2024, 7, e12574 687.9 eV refers to Li x PO y F z .The peak at 685.1 eV is attributed to LiF, which is regarded as the degradation from LiPF 6 due to the serious decomposition of electrolyte. [46]In Figure S4, Supporting Information, the XRD curves of cycled NCA-P and NCA-LM2 are tested.It can be concluded that after 100 cycles, the NCA-P underwent a drastic phase transformation reaction.The value of (003)/(104) is greatly reduced with the layered structure to spinel structure.However, the layered structure of NCA-LM2 still maintains good crystallinity with a great  Energy Environ.Mater.2024, 7, e12574 ratio of (003)/(104).The overall diffraction intensity of NCA-P is lower than that of NCA-LM2, indicating that NCA-LM2 possesses good crystallinity upon cycling.Overall, the particles of NCA-P undergo a high tensile strain state to crash and expose more surface, which leads to more drastic side reaction with electrolyte, generating residual lithium compounds and rock salt NiO phase.It is proved that LLAO coating layer could improve the reversible capacity by means of restraining the grains breakage and side reaction on the surface.

Conclusions
To stabilize the electrolyte interface, an in situ Li 0.5 La 2 Al 0.5 O 4 layer is coated.And manganese atoms compensate into Al-vacancies which form during the synthesis of Li 0.5 La 2 Al 0.5 O 4 according to the results of XPS, TEM, and XRD.The formed NCMA middle layer suppresses the lattice mismatch and distortion.A novel multilayered modified strategy is put forward.After La-Mn co-modifying, NCA-LM2 shows excellent performances.The capacity retention of NCA-LM2 after 300 cycles gets up to 80.8%, far better than NCA-P.By operando XRD analysis, the strain in c direction was relieved.The computational result shows that the LLAO layer exhibits a better mechanical behavior than NCM-P.The LLAO coating could restrain the strain in Ni-rich cathode.The XPS, TEM, and DEMS results of cycled cathode demonstrate that the NCA-LM2 has a weaker side reaction without fracture.AFM test demonstrates that the La-Mn co-modifying could strengthen the Young's modulus, thereby the fragmentation of particles upon cycling was suppressed effectively.Herein, an effective strategy is provided to enhance the electrochemical performances of Ni-rich layered oxides to relieve the break and pulverize.
Material characterization: XRD (Rigaku D/max-2500 diffraction, Cu Kα) method was used to study the structure, and at the scan speed of 2°/min.The scanning electron microscope (SEM/EDS, JEOL JSM-6360LV, Japan) was used to characterize the morphology of the surface.The oxidation states of elements were acquired by X-ray photoelectron spectroscopy (XPS, VG Multilab, 2000).Transmission electron microscopy (TEM) was measured by JEM 2100 and FEI Talos F200S.The atomic force microscopy (AFM) was tested by Bruker Dimension Icon instrument.
Density functional theory (DFT) as implemented in Vienna Ab Initio Simulation Package (VASP) was used to calculate the deformation of Li 0.5 La 2 Al 0.5 O 4 and NCA along the c-axis. [32] These calculations were started with a cell parameters and geometry optimization of these two structures.For structural optimization, a kinetic energy cutoff of 520 eV was used, the Brillouin zone integration was sampled with 6 × 6 × 1 Monkhorst-Pack K point mesh grid. [35]After optimization of lattice structure, six different deformed structure with the cell parameter along the c-axis changed from −15% to 17.5% were generated.The atoms in their structures were also relaxed to stable positions and the final energies of these deformed structures were obtained.
Electrochemical test: The sintered active cathode material was mixed with polyvinylidene fluoride (PVDF) and acetylene black at the mass ratio of 8:1:1.The emulsion was made up by dispersing the mixture in N-methyl-2-pyrrolidone (NMP) and then pasted onto the Al foil.After baking at 90 °C for 4 h, the Al foil was punched into several discs with a diameter of 14 mm as the positive electrode.The metallic lithium was used as the negative electrode.The mixture of EMC (33%), EC (33%), and DMC (33%) dissolved in 1 M LiPF 6 was taken as the electrolyte.The CR2016-type coin half-cells were assembled in the nitrogen gas atmosphere glove box.
To explore the reversibility during the charge/discharge process, Land Test System was used to test assembled half-cells at different rates (1 C = 180 mAh g −1 ) in the range of 3.0-4.4V.The scan rate was set as 0.1 mV s −1 .The electrochemical impedance spectroscopy (EIS) was tested over the frequency range of 0.01 Hz-100 kHz.The amplitude of the AC signal was set as AE5 mV.The scan speed of multicycle cyclic voltammetry (CV) was set as 0.1 mV s −1 over the range of 3.0-4.4V. CV and EIS are both tested in VersaSTAT MC electrochemical workstation made by Princeton.

Figure 1 .
Figure 1.a) Schematic illustration of the synthesis method and La-Mn co-modification effect.TEM, HRTEM, and homologous FFT figures b, c) NCA-P and d, e) NCA-LM2.XRD patterns of f) NCA-P and NCA-LM2 with g, h) corresponding XRD refinement results.

Figure 3 .
Figure 3. a) The electrochemical performances of NCA-P, NCA-L2, and NCA-LM2.The cyclic performances and Coulomb efficiency of NCA-P, NCA-L2, and NCA-LM2.b) dQ dV −1 curves for NCA-P and NCA-LM2 at specific cycles.c) Cyclic performances of 300 cycles at 1 C. d) The initial charge and discharge curves of NCA-P, NCA-L2, and NCA-LM2.e) 8 C rate performances of NCA-P and NCA-LM2; the Nyquist plots of impedance measured after 100 cycles at f) 1 C and g) 8 C. h) EIS curves of NCA-P and NCA-LM2 after 200 cycles.
, the characteristic peaks centered at 290.8, 285.8, and 284.8 eV belong to Li 2 CO 3 , C-O, and C-C/C-H, respectively.The Li 2 CO 3 proportion of NCA-LM2 is less than that of NCA-P by 3.9%, indicating a similar result of O1s spectrum.In Figure 6h, F 1s consists of two compounds.The peak observed at

Figure 4 .
Figure 4. Charge and discharge curve and operando XRD analysis of a) NCA-P and b) NCA-LM2.a-i, b-i) The homologous schematic illustrations for the states of largest interlayer space.c, d) Computational result of strain versus stress in charged NCA-P and LLAO.

Figure 6 .
Figure 6.a) The schematic illustrations of the pulverized and broken particles of NCA-P.SEM and homologous TEM images of a, c) NCA-P after 200 cycles and b, d) NCA-LM2 after 300 cycles.The XPS analyses of cycled cathodes for e) survey spectrum f) O1s, g) C1s, and h) F1s.The XPS spectra are revised versus the C 1s peak of hydrocarbon species at 284.8 eV.

Table 1 .
Calculated values of lattice parameters from Rietveld refinement.