A high-voltage LiNi based on heterostructure 0.5 Mn 1.5 O4 cathode material and its preparation method

Abstract

The application relates to the technical field of lithium ion battery positive electrode materials, and discloses a high-voltage LiNi0.5Mn1.5O4 positive electrode material based on a hetero-interface structure and a preparation method thereof. 0.5 Mn 1.5 O4 powder and LiNbO3 coating layer preparation, Co-doped LNMO powder is prepared through a sol-gel method combined with microwave assistance, and different mass fractions of LiNbO3 are coated on the surface of the Co-doped LNMO powder through a liquid-phase mixing calcination method; the positive electrode material is a core-shell structure formed by coating LiNbO3 on the surface of a Co-doped LiNi 0.5 Mn 1.5 O4 core body, and a c-LNMCO|c-LiNbO3 hetero-interface is constructed; through a synergistic modification strategy of Co doping and LiNbO3 coating, the electrochemical reaction of the LNMO is changed from a two-phase reaction to a solid solution reaction, the unit cell volume change is significantly reduced, transition metal dissolution and interface side reactions are inhibited, the high-voltage cycle stability, the rate performance and the high-temperature electrochemical performance of the material are improved, and the material has a good application prospect in the field of lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials technology, and in particular to a high-voltage LiNi based on a heterostructure interface. 0.5 Mn 1.5 O4 cathode material and its preparation method. Background Technology

[0002] In recent years, environmental pressures have continued to intensify, and the exploitable reserves of non-renewable resources have been declining. To address the dual challenges of energy supply and ecological security, accelerating the development and utilization of renewable energy has become an urgent priority. Due to their long cycle life and high energy density, lithium-ion batteries (LIBs) have become the dominant energy storage technology for portable electronic devices and have shown broad application prospects in electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, the energy density of existing commercial systems still falls short of rapidly growing demand, becoming a major bottleneck for further development. Effective strategies to improve the energy density of LIBs include increasing the specific capacity of cathode materials or raising their operating voltage. Over the past few decades, researchers have continuously explored cathode materials with higher resource sustainability, higher energy density, and better electrochemical stability. LiNi 0.5 Mn 1.5 O4 (LNMO) is valued for its high operating voltage (4.7V vs. Li / Li). + High energy density (650Wh kg) -1 ) and fast three-dimensional Li + Diffusion channels are considered a promising cathode material. However, the practical application of LNMO still faces several key challenges: (1) The low degree of Ni / Mn disorder limits the Li + (1) The transmission of the material can easily trigger a significant two-phase transformation, leading to stress accumulation and microcrack formation, which ultimately weakens its long-term cycling stability under high voltage operation; (2) As the charging voltage increases, spinel-type LNMO is prone to severe interfacial side reactions, such as electrolyte oxidation / decomposition, HF-induced interfacial corrosion, and transition metal dissolution. These processes will further trigger surface reconstruction and defect accumulation, weakening structural stability and accelerating cycle decay. Summary of the Invention

[0003] This invention aims to provide a high-voltage LiNi based on a heterostructure interface. 0.5 Mn 1.5 O4 cathode material and its preparation method: Through the synergistic modification of Co doping and LiNbO3 coating, a stable c-LNMCO│c-LiNbO3 heterostructure interface is constructed, while the bulk structure and interfacial properties of the material are optimized, significantly improving its electrochemical performance.

[0004] Therefore, the technical solution adopted in this invention is: a high-voltage LiNi based on a heterogeneous interface. 0.5 Mn 1.5 The preparation method of O4 cathode material includes the following steps:

[0005] S1: Preparation of Co-doped LiNi 0.5 Mn 1.5 O4 powder was weighed, and lithium source LiCH3COO, nickel source NiC4H6O4·4H2O, manganese source MnC4H6O4·H2O, and cobalt source (CH3CO2)2Co were dissolved in deionized water to obtain a mixed metal salt solution. Citric acid was added to the mixed metal salt solution as a complexing agent, and the solution was stirred until completely dissolved. The resulting solution was transferred to a microwave reactor and magnetically stirred at 100-110℃ until the solvent was completely evaporated to obtain a wet gel. The wet gel was dried, and then calcined successively at 500℃ and 900℃. After cooling, it was ground to obtain Co-doped LiNi. 0.5 Mn 1.5 O4 powder, i.e., LNMCO;

[0006] S2: Prepare LNMCO@LiNbO3 coated material. Weigh Nb2O5, ultrasonically disperse it in ethanol, add the LNMCO powder obtained in S1, mix evenly, and stir continuously at 60-70℃ until the solvent is completely evaporated. Dry the obtained solid, grind it thoroughly, calcine it at 500℃ in an oxygen atmosphere, and obtain the product after cooling.

[0007] As a preferred embodiment of the above scheme, in S1, the molar ratio of lithium source LiCH3COO, nickel source NiC4H6O4·4H2O, manganese source MnC4H6O4·H2O and cobalt source (CH3CO2)2Co is 1.05:0.5:1.47:0.03, and the molar ratio of metal ions to citric acid is 1:1.

[0008] More preferably, the purity of LiCH3COO in S1 is ≥99.9%, the purity of NiC4H6O4·4H2O is ≥99.9%, the purity of MnC4H6O4·H2O is ≥99.0%, and the purity of citric acid is ≥99.5%.

[0009] More preferably, the purity of Nb2O5 in S2 is ≥99.99%.

[0010] More preferably, the mass percentage of the Nb2O5 is 1-7%.

[0011] More preferably, the mass percentage of the Nb2O5 is 5%.

[0012] More preferably, the wet gel in S1 is dried at 75-80°C for 10-12 hours, and then calcined at 500°C for 4-5 hours and then calcined at 900°C for 9-10 hours.

[0013] A further preferred embodiment is that the solid obtained in S2 is dried at 110-120°C for 10-12 hours, thoroughly ground, and then calcined at 500°C for 4-5 hours in an oxygen atmosphere.

[0014] A high-voltage LiNi based on heterostructure 0.5 Mn 1.5 O4 cathode material, wherein the cathode material has a core-shell structure, and the core is Co-doped LiNi. 0.5 Mn 1.5 O4, with a shell of LiNbO3, and a c-LNMCO│c-LiNbO3 heterogeneous interface is formed between the core and the shell.

[0015] More preferably, the average particle size of the cathode material is 5-10 μm, and the thickness of the LiNbO3 shell is 3-5 nm; the cathode material has a cubic spinel structure with space group Fd-3m, and the main phase is LiNi with space group Fd-3m. 0.5 Mn 1.5 O4 has a crystalline LiNbO3 phase on its surface.

[0016] The beneficial effects of this invention are as follows: Co doping into the spinel lattice of LNMO enhances the disorder of Ni-Mn sites and improves electronic conductivity. At the same time, it transforms the electrochemical reaction of LNMO during lithium extraction / intercalation from a two-phase reaction to a solid solution reaction. The cell volume change during charge and discharge is reduced from 33.71 ų to 18.77 ų, which significantly alleviates lattice mismatch and mechanical stress accumulation, avoids microcrack formation, and improves the structural stability of the material.

[0017] The LiNbO3 shell coating on the LNMCO surface forms a c-LNMCO│c-LiNbO3 heterogeneous interface with the core. This interface is in close contact, which reduces the risk of coating peeling and effectively isolates the electrode from direct contact with the electrolyte, inhibiting electrolyte oxidative decomposition, HF-induced interfacial corrosion, and transition metal dissolution. Compared with pure LNMO, after immersing LNMCO-5wt% in electrolyte at 60℃ for 7 days, the dissolved concentrations of Ni and Mn decreased by 70.88% and 69.14%, respectively, and the interfacial side reactions were significantly suppressed.

[0018] The charge transfer resistance (Rct) of the LNMCO-5wt% cathode material is significantly reduced, the Li⁺ diffusion coefficient is increased to 2.52×10⁻¹¹, the polarization degree is greatly reduced, and the redox peak potential difference (ΔE) in the cyclic voltammetry test is as low as 0.147V, which is much lower than the 0.227V of pure LNMO, effectively promoting the transport and diffusion of Li⁺.

[0019] Under high rate conditions, the discharge specific capacity of the material is significantly improved. At a rate of 20C, the discharge specific capacity of pure LNMO is only 64.46 mAh g⁻¹, while the discharge specific capacity of LNMCO-5wt% reaches 112.93 mAh g⁻¹, showing a significant improvement in rate performance.

[0020] At 25℃ and 1C, the LNMCO-5wt% half-cell retained 81.44% capacity and 79.79% energy density after 500 cycles, with an average coulombic efficiency of 98.8%, while the pure LNMO retained only 58.48% capacity and 56.62% energy density. The LNMCO-5wt% graphite full-cell retained 78.11% capacity after 100 cycles at 1C, significantly better than the 57.58% of pure LNMO.

[0021] At 60℃ and 1C, the LNMCO-5wt% half-cell retained 71.29% of its capacity and had an average coulombic efficiency of 90.88% after 150 cycles, while pure LNMO entered a rapid capacity decay phase after 75 cycles. After high-temperature cycling, LNMCO-5wt% still maintained a dense and intact structure with no obvious surface corrosion, while pure LNMO showed severe surface corrosion and structural damage.

[0022] The LiNbO3 coating effectively improves the high-temperature decomposition threshold of LNMO, resulting in a higher decomposition initiation temperature and smaller total weight loss for LNMCO-5wt%. It can prevent lattice oxygen escape and transition metal reduction, providing a structural basis for excellent electrochemical performance at high temperatures.

[0023] Co-doped LNMO powder was prepared by a sol-gel method combined with microwave-assisted synthesis, and LiNbO3 coating was prepared by liquid-phase mixing and calcination. The process steps are simple, the reaction conditions are mild, the raw materials are readily available, and the LiNbO3 coating amount can be precisely controlled, making it suitable for large-scale production. Attached Figure Description

[0024] Figure 1 The structural characterization diagrams of LNMO, LNMCO and samples with different LiNbO3 coating amounts are shown below; (a) is the XRD pattern; (b) is the magnified image of the (012 / 104) peak; (c) is the magnified image of the (111) peak; (d) is the FT-IR spectrum; and (e) is the Raman spectrum.

[0025] Figure 2 The images show the morphology and elemental distribution of LNMO and LNMCO-5wt%; (a) is the SEM image of LNMO; (b) is the SEM image of LNMCO-5wt%; (c) is the HR-TEM image and FFT pattern of LNMCO-5wt%; (d) is the SAED pattern of LNMCO-5wt%; (e) is the EDS distribution map of LNMCO-5wt%; (f) is the FIB-SEM and FIB-EDS images of LNMCO-5wt%; and (g) is the line scan result of (f).

[0026] Figure 3 Comparison of XPS spectra and oxidation states of LNMO, LNMCO, and samples with different LiNbO3 coating amounts; (a) Mn 2p XPS spectrum; (b) Ni 2p XPS spectrum; (c) O 1s XPS spectrum; (d) Mn 4 (e) Comparison of Ni³⁺ / Ni²⁺; (f) Comparison of Ni³⁺ / Ni²⁺; (f) Changes in adsorbed oxygen content.

[0027] Figure 4 The following are the electrochemical performance graphs of the samples: (a) is the CV curve; (b) is the rate performance; (c) is the initial charge-discharge curve at 0.2C; (d) is the 1C cycle performance; (e) is the 1C cycle energy density; (f) is the constant current charge-discharge curve of LNMO; (g) is the constant current charge-discharge curve of LNMCO-5wt%; (h) is the full cell cycle performance; (i) is the full cell charge-discharge curve of LNMO; (j) is the full cell charge-discharge curve of LNMCO-5wt%; and (k) is the full cell rate performance.

[0028] Figure 5 (a) Electrochemical kinetics and high-temperature performance of the samples; (b) EIS Nyquist plot; (c) GITT curve and Li⁺ diffusion coefficient; (d) Comparison of Li⁺ diffusion coefficient; (e) High-temperature cycling performance at 60℃; (f) SEM image of LNMO after high-temperature cycling; (g) SEM image of LNMCO-5wt% after high-temperature cycling; (h) F 1s XPS spectrum of LNMO after high-temperature cycling; (i) F 1s XPS spectrum of LNMCO-5wt% after high-temperature cycling; (j) TG and DTG curves.

[0029] Figure 6The following are in-situ XRD characterization diagrams of LNMO and LNMCO-5wt%. (a) is the in-situ XRD pattern of LNMO; (b) is a magnified view of the Bragg peak of LNMO; (c) is the cell volume change of LNMO; (d) is the in-situ XRD pattern of LNMCO-5wt%; (e) is a magnified view of the Bragg peak of LNMCO-5wt%; (f) is the cell volume change of LNMCO-5wt%.

[0030] Figure 7 The images show the characterization of the samples after 500 1C cycles: (a) EIS Nyquist plot, (b) CV curve, (c) XRD pattern, (d) Raman spectrum, (e) F 1s XPS spectrum of LNMO, (f) F 1s XPS spectrum of LNMCO-5wt%, (g) SEM image of LNMO after cycling, and (h) SEM image of LNMCO-5wt% after cycling. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] The first step is to prepare Co-doped LiNi 0.5 Mn 1.5 O4 (LNMO) powder. LiCH3COO (purity ≥99.9%), NiC4H6O4·4H2O (purity ≥99.9%), MnC4H6O4·4H2O (purity ≥99.0%), and (CH3CO2)2Co were weighed in a molar ratio of 1.05:0.5:1.47:0.03 (5% excess lithium source) and dissolved in deionized water. Citric acid (purity ≥99.5%) was then added to the solution as a complexing agent, and the metal ions (Ni... 2+ Mn 4+ Co 3+ The molar ratio of the total amount of solvent (total solvent) to citric acid was 1:1. The solution was then transferred to a microwave reactor and magnetically stirred at 100-110 °C until the solvent was completely evaporated, yielding a wet gel. The resulting gel was dried at 80 °C for 12 h, and then calcined successively at 500 °C for 5 h and 900 °C for 10 h to finally obtain Co-doped LNMO powder (LNMCO).

[0034] The second step involved preparing the LNMCO@LiNbO3 coating material. Nb2O5 (purity ≥99.99%) was ultrasonically dispersed in ethanol and mixed with LNMCO. The mixture was stirred continuously at 60 °C until the solvent evaporated. It was then dried at 120 °C for 12 h and thoroughly ground. Finally, it was calcined at 500 °C for 5 h in an oxygen atmosphere to obtain the LNMCO@LiNbO3 coating material. Different mass fractions (1, 3, 5, and 7 wt%) of Nb2O5 were introduced using the same method, and the resulting samples were designated as LNMCO-1 wt%, LNMCO-3 wt%, LNMCO-5 wt%, and LNMCO-7 wt%, respectively.

[0035] The positive electrode material consists of 80 wt.% active material, 10 wt.% polyvinylidene fluoride (PVDF, dissolved in N-methylpyrrolidone NMP as a binder), and 10 wt.% conductive agent Super-P. The slurry was uniformly coated onto aluminum foil and dried in a vacuum oven at 120 °C for 12 h. Subsequently, a circular electrode sheet with a diameter of 12 mm and a charge loading of approximately 2 mg·cm⁻¹ was obtained by punching. -2 Polypropylene was used as the separator, and lithium metal was used as the negative electrode. The electrolyte was 1.2 M LiPF6 (0.3 mL), dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). CR2032 coin cells were assembled in a glove box filled with argon gas and with H2O and O2 contents both below 5 ppm.

[0036] XRD analysis was performed using a Rigaku Ultima IV X-ray diffractometer (Japan) at a working voltage of 40 kV. A Cu target (λ = 1.5406 Å) was used as the radiation source, and measurements were conducted at a scan rate of 10° / min within a 2θ range of 10°–80°. Rietveld refinement was performed using GSAS II software to calculate the lattice constant and cell volume of each sample. The range was 400–700 cm⁻¹. -1 Within this range, the structural characteristics of the material were investigated using Fourier transform infrared spectroscopy (FT-IR, Nicolet iS 5, USA). Raman spectra were acquired using a Horiba LabRAM HR Evolution Raman spectrometer (Horiba Corporation, Japan), with an excitation source of 532 nm and a measurement range of 100–800 cm⁻¹. -1The morphological changes of the cathode particles and electrodes before and after cycling were observed using field emission scanning electron microscopy (FE-SEM, ZEISS GeminiSEM 360, USA). The surface structure of LNMO crystals was analyzed using transmission electron microscopy (TEM, Thermo Fisher Talos F200X, USA). The cross-sectional morphology and elemental distribution of the samples were characterized using focused ion beam scanning electron microscopy (FIB-SEM, Crossbeam 350, Germany). The chemical bond state and elemental composition of the samples were analyzed using X-ray photoelectron spectroscopy (XPS, Thermo K-Alpha, USA). Al Kα rays (hv = 1486.68 eV) were used at an X-ray power of 150 W and a vacuum of 5 × 10⁻⁶. -9 mbar. The mass change of the cathode powder due to oxygen release during heating from 30 °C to 900 °C was measured using thermogravimetric analysis (TGA, NETZSCH TG 209F3, Germany) under a nitrogen atmosphere. The solubility of transition metal Ni / Mn was quantitatively analyzed using inductively coupled plasma atomic emission spectrometry (ICP-OES, Agilent 730, USA).

[0037] The electrochemical performance of the coin cells was characterized using a Neware battery testing system (CT-4008 5 V 20 mA-164, Shenzhen, China). The electrochemical performance was assessed at 3.5–4.9 V (vs. Li / Li). + Cyclic testing was conducted within the voltage range, starting with three activation cycles at 0.1C, followed by cycles at 1C (1C = 147 mAh g). -1 The cells underwent 500 cycles. Both the LNMO||Li half-cell and the LNMO||graphite full cell were tested within a voltage window of 3.5–4.9 V. Rate performance was evaluated at different rates from 0.2C to 20C. High-temperature long-cycle performance testing was conducted in a constant temperature chamber (60 °C, 1C, 150 cycles). Cyclic voltammetry (CV) tests were performed on an electrochemical workstation (Ivium-N-Stat, Ivium Technologies, Netherlands) at a scan rate of 0.1 mV·s. -1 The voltage range was 3.5–4.9 V. Electrochemical impedance spectroscopy (EIS) measurements were performed on the same workstation, with AC impedance frequencies ranging from 0.01 Hz to 100 kHz.

[0038] like Figure 1 As shown:

[0039] The crystal structures of LNMO and LNMCO samples with different LiNbO3 contents (x wt%) are shown below. Figure 1As shown in Figure a, the X-ray diffraction (XRD) patterns indicate that all samples exhibit a cubic spinel structure with space group Fd-3m (JCPDS No. 80-2162). For all compositions, the diffraction peaks corresponding to the (111) crystal plane are sharp and have extremely narrow full width at half maximum (FWHM), indicating that the samples have high crystallinity and also proving that the LiNbO3 heterostructure coating has minimal influence on the intrinsic crystal structure of LNMO. In addition, besides the characteristic diffraction peaks of LNMO, obvious LiNbO3 diffraction peaks (JCPDS No. 20-0613) also appeared, and they gradually increased with the increase of coating content, such as... Figure 1 As shown in b, this indicates that the surface LiNbO3 layer crystallized during the heat treatment process and exists as a stable phase on the LNMO surface. Simultaneously, a shift of the main LNMO diffraction peak towards lower angles was observed. Figure 1 (c). To further verify whether the crystal structure remained unchanged after coating, FT-IR and Raman analyses were performed on the sample, and the results are as follows. Figure 1 As shown in d and e, the LNMO structure can be divided into a disordered Fd-3m phase and an ordered P4332 phase. LNMOs in the P4332 space group have a structure in the 400-700 cm⁻¹ range. -1 It exhibits 8 infrared absorption peaks within the range, while the Fd-3m space group shows only 5 absorption peaks. From the FT-IR spectrum ( Figure 1 As can be seen from d), all samples were at 622, 581, 554, 503, and 470 cm⁻¹. -1 Five infrared absorption peaks were observed at each location, and at 622 cm⁻¹ -1 The peak at that location is higher than 581 cm. -1 The results indicate that the six samples primarily crystallize in the Fd-3m space group. The results also suggest that an increase in the oxygen vacancy concentration on the material surface induces stronger Ni-Mn site disorder, thereby improving electronic conductivity. In the Raman spectra, at 634 cm⁻¹... -1 The peak at 496 cm⁻¹ belongs to the Mn-O symmetric stretching vibration in the MnO₆ octahedron, while the peak at 496 cm⁻¹ belongs to the Mn-O symmetric stretching vibration in the MnO₆ octahedron. -1 The characteristic peaks at these locations correspond to the stretching vibrations of the Ni-O bond. Both of these characteristic peaks are consistent with the Fd-3m space group, further proving that the LiNbO3 coating does not change the crystal structure of LNMO.

[0040] The particle sizes of LNMO, LNMCO, and LNMCO-x wt% (x=1, 3, 5, and 7) are shown in Table 1.

[0041] Table 1: Particle sizes of LNMO, LNMCO, and LNMCO-x wt% (x=1, 3, 5, and 7).

[0042]

[0043] like Figure 2 As shown:

[0044] Figure 2 Tables a and b show SEM images of LNMO and LNMCO-5 wt% samples, as well as EDS mapping data for Ni, Mn, O, Co, and Nb. All prepared samples exhibited octahedral shapes, forming particles similar to uncoated LNMO, indicating that the coating did not alter the overall morphology. Compared to the smooth surface of uncoated LNMO, the surface roughness of LNMCO-5 wt% was significantly increased, which is attributed to the LiNbO3 coating layer. Table 1 compares the particle sizes of all prepared LNMO samples, with average particle sizes (D50) ranging from 5 to 10 μm, gradually decreasing with increasing coating weight. EDS mapping images confirmed that all elements (Ni, Mn, O, Co, and Nb) were uniformly distributed on the cathode material. To further investigate the coating structure of LNMCO-5 wt%, HRTEM characterization was performed, with details shown in the figures below. Figure 2 As shown in c and d. The bulk lattice fringes of LNMCO-5 wt% are 2.52 Å, corresponding to the (311) interplanar spacing of a highly crystalline spinel structure. At the boundary of the LNMCO-5 wt% material ( Figure 2 A distinct lattice stripe (2.58 Å) was found in the area within the red box (c), corresponding to the (110) crystal plane of LiNbO3 (PDF#20-0631), confirming the presence of a LiNbO3 shell layer approximately 4 nm thick on the surface of the LNMCO-5wt% material. Figure 2 The diffraction spots in d are highly matched with the atomic arrangement of LNMO in its space group. For example... Figure 2 As shown in the elemental distribution diagram, Ni, Mn, Co, and Nb are regularly distributed, further confirming that the LiNbO3 protective layer has been successfully formed on the LNMCO surface, creating a heterogeneous interface. Figure 2 As shown in f and g, the results of focused ion beam scanning electron microscopy (FIB-SEM) combined with focused ion beam-energy dispersive X-ray spectroscopy (FIB-EDS) indicate that a stable c-LNMCO│c-LiNbO3 heterointerface was successfully constructed on the surface of LNMCO-5 wt% particles, and Co 3+ It is uniformly distributed in the bulk phase. Figure 2The SEM, cross-sectional FIB-SEM, and FIB-EDS images of 5 wt% LNMCO particles show that the FIB cross-section reveals a dense and continuous interior within the particles with no obvious cracks, indicating that the coating does not damage the spinel structure, providing an excellent basic condition for interface regulation. In the EDS cross-sectional distribution, Mn is uniformly distributed within the particles. In contrast, Nb is significantly enriched at the edges with extremely weak internal signals, further confirming the "core-shell" structure of LiNbO3 / LNMCO. Additionally, Figure 2 The line scan results shown in g indicate that Co 3+ exists in the bulk phase of LNMO and is uniformly distributed. In contrast, Nb is mainly enriched at the edges. Due to the different compositions between the Nb-rich outer layer and the bulk LNMCO, significant hetero-phase contact appears, indicating the successful formation of the c-LNMCO│c-LiNbO3 hetero-interface. This tight hetero-contact not only reduces the risk of coating detachment but also provides a structural basis for suppressing interface side reactions and improving the high-voltage cycling stability.

[0045] As Figure 3 shown:

[0046] XPS was used to further confirm the coating materials and detailed element distribution on the cathode surface. All XPS data were calibrated based on the C 1s peak position of 284.80 eV. The Mn 2p spectrum shows the splitting of the electronic orbits of two peaks, Mn 2p3 / 2 (642.1 eV) and Mn 2p1 / 2 (653.9 eV), indicating the presence of Mn 3+ and Mn 4 + mixed chemical bond states on the upper surface of the prepared cathode, as shown in Figure 3 a. The relative content of Mn 3+ increases with the increase in the LNO content, Figure 3 d, LNMO(47.67%) < LNMCO (50.7%) < LNMCO-1 wt% (51.97%) < LNMCO-3 wt% (54.57%)<LNMCO-5 wt% (59.33%) LNMCO-5 wt% (63.86%). An appropriate amount of Mn 3+ can enhance the degree of cation disorder, promote the migration of Li + , and further improve the electrochemical performance of LNMO, which corresponds to the FT-IR and Roman results. Similarly, the Ni 2p spectrum shows the splitting of the electronic orbits of two peaks, Ni 2p3 / 2 (854.5 eV) and Ni 2p1 / 2 (872.1 eV), indicating the presence of Ni 2+ and Ni 3+ in the cathode, as shown in Figure 3b, e. With the increase of coating, Ni 3+ The contents were 30.21%, 31.87%, 33.79%, 36.58%, 39.15%, and 40.47% respectively. Ni at the interface... 2+ To Ni 3+ Transformation and combination of Mn 4+ To Mn 3+ The transformation process jointly achieves charge balance at the interface, realizing charge redistribution and enhancing the stability of the interface layer. O1s spectral analysis shows that the two peaks OL and Oabs at 529.2 and 532.6 eV, respectively, correspond to lattice oxygen bonded to the transition metal and surface adsorbed oxygen in LNMO. Figure 3 c. The adsorbed O ratio for each sample was calculated. LNMCO-xwt% showed a higher O adsorption ratio than LNMO. As the LiNbO3 coating amount increased, the Oabs component in the O1s spectrum gradually increased, such as... Figure 3 The interfacial phase effectively isolates LNMCO from direct contact with the electrolyte, inhibiting electrolyte decomposition and Mn dissolution. Furthermore, the polar Oabs component improves electrolyte wetting and Li... + Migration behavior reduces interfacial impedance. Therefore, the gradual increase in Oabs can be seen as a positive signal of heterogeneous interface optimization of the electrode / electrolyte interface.

[0047] The potential difference between the anodic peak (φA) and the cathode peak (φB) of each material is shown in Table 2:

[0048] Table 2: Potential difference between the anode peak (φA) and the cathode peak (φB).

[0049]

[0050] like Figure 4 As shown:

[0051] Half-cells were assembled in the voltage range of 3.5–4.9 V to evaluate the electrochemical performance of LNMO and LNMCO-xwt%. Figure 4 Figure a shows the cyclic voltammograms (CVs) for all samples in the range of 3.5–4.9 V. The results show that the redox peak near 4.0 V corresponds to Mn. 3+ / Mn 4+ Ni redox peak near 4.7 V 2+ / Ni 3+ and Ni 3+ / Ni 4+This further confirmed the Fd-3m structure of LNMO. The difference ΔE between the oxidation and reduction peaks indicates the degree of polarization during the oxidation and reduction processes. The ΔE values ​​for LNMO, LNMCO, LNMCO-1 wt%, LNMCO-3 wt%, LNMCO-5 wt%, and LNMCO-7 wt% were 0.227, 0.181, 0.172, 0.169, 0.147, and 0.17 V, respectively (Table 2). LNMCO-5 wt% had the lowest ΔE (0.147 V), indicating that LNMCO-5 wt% exhibited the lowest degree of polarization during charge and discharge. Figure 4 As shown in b, the rate performance of the modified sample is significantly improved compared to pure LNMO. At 20C, the discharge specific capacity of pure LNMO is only 64.46 mAh g⁻¹. −1 The discharge specific capacity of LNMCO-5 wt% is 112.93 mAhg. −1 . Figure 4 Figure c shows the initial discharge curves of all samples, with LNMCO-5 wt% exhibiting the highest initial discharge capacity (132.28 mAh g). −1 The discharge specific capacity of pure LNMO is 124.49 mAh g⁻¹. −1 The capacity retention, average coulombic efficiency, and energy density retention of all cathode materials were compared, such as... Figure 4 After 500 consecutive charge-discharge cycles, pure LNMO retained only 56.62% of its energy density. Among the optimized samples, LNMCO-5 wt% led in cycling performance with an energy density retention of 79.79%. Furthermore, LNMCO-5 wt% exhibited the highest average coulombic efficiency (98.8%). In terms of capacity retention, LNMCO-5 wt% achieved a remarkable 81.44%, significantly outperforming pure LNMO, which retained only 58.48%.

[0052] Co 3+ The doping process improves the structure of LNMO, effectively suppressing phase transitions and enhancing its electronic conductivity. Furthermore, LNMO forms a cathode-electrolyte interface (CEI) layer on the electrode surface during cycling, but the CEI has extremely poor conductivity. The early formation of the CEI layer in LNMO restricts Li-ion insertion and extraction, thus reducing cycling performance. In LNMCO with a LiNbO3 coating, the coating acts as a substitute for the CEI layer, effectively suppressing the formation of the insulating layer and reducing lithium-ion loss. To further elucidate the effect of the LiNbO3 coating on voltage stability during cycling, the charge-discharge voltage curves before and after 500 cycles were compared. Figure 4After 500 cycles, the voltage plateau of pure LNMO became noticeably tilted and shifted downwards, indicating significant voltage decay and increased polarization. In contrast, LNMCO-5 wt% exhibited a smaller voltage shift and better retention of the original flat voltage plateau. This improvement can be attributed to the role of the LiNbO3 coating in stabilizing the crystal structure and suppressing transition metal migration.

[0053] To further evaluate the practical application feasibility of the optimized cathode material, LNMO was subjected to voltage ranges of 3.5–4.7 V. The electrochemical performance of the graphite full-cell system was tested. After 100 cycles, the capacity retention, capacity, and average coulombic efficiency of LNCMO-5wt% were 78.11% and 87.04 mAh g⁻¹, respectively. -1 And 98.52%, while LNMO was only 57.58%, 59.4 mAhg -1 and 97.82%, such as Figure 4 The cycling stability of LNMO is better than that of LNCMO-5wt%, indicating that Co doping combined with interface engineering can also suppress capacity decay and improve cycling reversibility in full cells. Figure 4 Figures i and j show the charge-discharge curves of LNMO and LNCMO-5wt% samples at different cycle numbers. The voltage plateau of the LNMO sample tilts significantly with cycling, exhibiting significant voltage decay and polarization, while the LNCMO-5wt% sample maintains its initial high voltage plateau, indicating that its structure and interface are more stable during long cycling. Figure k in Figure 4 shows that the rate performance of LNCMO-5wt% is better than that of LNMO. It should be noted that when the current density recovers from 20 C to 1 C, its discharge specific capacity decreases significantly compared to the initial value. This is because the reversible lithium storage in the full cell is limited, and at high rates, it is easier to induce side reactions on the graphite anode surface and local lithium dendrite deposition, leading to structural degradation of the electrode / interface and exhibiting low recovery rate.

[0054] like Figure 5 As shown:

[0055] Electrochemical impedance spectroscopy (EIS) is used to characterize and compare the impedance of different samples, such as... Figure 5 As shown in Figure a, the LNMCO-5wt% sample exhibits the lowest Rct (charge transfer resistance). This indicates that the LiNbO3 coating effectively stabilizes the crystal structure, protects LNMO from electrolyte corrosion, and suppresses interfacial side reactions. In contrast, the LNMO sample underwent drastic structural changes and severe interfacial side reactions, resulting in a higher Rct. Intermittent galvanostatic titration (GITT) was used to analyze the Li content of each sample during the charge-discharge process. +The diffusion coefficient is shown in Figure 5b. Compared to LNMO, LNCMO-5wt% exhibits the highest Li diffusion coefficient. + Diffusion coefficient (2.52×10) -11 ),like Figure 5 c. This indicates that LNCMO-5wt% provides the most suitable coating, promoting better lithium-ion transport and diffusion into the electrode, and providing more stable Li. + The cycling performance of LNCMO-5wt% at 60°C is significantly improved, with a capacity retention of 71.29% and an average coulombic efficiency of 90.88% after 150 cycles at 1°C. Figure 5 Due to electrolyte oxidation at high temperatures, HF-induced dissolution of transition metals, and continuous interface reconstruction, lithium reserves are rapidly depleted and impedance rises sharply. Consequently, LNMO enters a rapid capacity decay phase after 75 cycles, with an average coulombic efficiency of only 81.99%.

[0056] After 150 high-temperature cycles, the surface morphology of the cathode was observed using a scanning electron microscope (SEM). Figure 5 The e and f samples of LNMO particles exhibited severe surface corrosion and lost their intact spinel structure, which was the main reason for the rapid capacity decay. In stark contrast, the cycled cathode LNCMO-5wt% exhibited a relatively dense and intact structure under the same conditions, with no obvious surface corrosion. This indicates that the continuous heterogeneous interface effectively prevented electrolyte corrosion and significantly suppressed interfacial side reactions. The XPS spectra of F1s of the two samples after high-temperature cycling were analyzed, as shown in the figure. Figure 5 The F1s of LNMO are dominated by LiF₂ with a relative content as high as 65.78%, indicating that electrolyte decomposition under high temperature and high voltage leads to continuous surface side reactions. In contrast, the LiF₂ content of LNCMO-5wt% is significantly reduced to 47.79%, further demonstrating that the erosion of the electrode surface by the electrolyte is effectively suppressed, which is consistent with the higher average coulombic efficiency and capacity retention during high-temperature cycling. The changes in Ni and Mn concentrations after immersing the electrode material in an electrolyte at 60℃ for 7 days are shown in the figure. Figure 5 As shown in g. Compared to LNMO, the solubility concentrations of Ni and Mn in LNMCO-5wt% decreased by 70.88% and 69.14%, respectively. This is consistent with the results of high-temperature experiments, further confirming the excellent electrochemical performance of the LNMCO-5wt% sample at high temperatures. Figure 5As shown in Figure j, the TG and DTG curves of both LNMO and LNMCO-5wt% samples exhibit typical multi-stage weight loss behavior. The low-temperature region (<150℃) corresponds to the removal of adsorbed water and residual solvent, while the mid-temperature region (150-600℃) remains relatively stable, indicating no significant structural changes within this range. The main weight loss stage occurs between 700-850℃, attributed to the release of lattice oxygen and partial decomposition of the spinel structure. The TG curve of the LNMCO-5wt% sample shows a higher decomposition onset temperature and a smaller total weight loss, indicating that the LiNbO3 coating significantly improves high-temperature stability. Furthermore, compared to the uncoated sample, the main weight loss process of LNMCO-5wt% shifts to the right, indicating that the LiNbO3 coating effectively increases the high-temperature decomposition threshold. These results demonstrate that the LiNbO3 coating prevents lattice oxygen escape and transition metal reduction at high temperatures, significantly improving the thermal stability of LNMO and providing a structural basis for its excellent high-temperature electrochemical performance.

[0057] like Figure 6 As shown:

[0058] In-situ XRD characterization of LNMO and LNMCO-5 wt% was performed to reveal the regulatory effect of modification on the crystal structure evolution and phase transition behavior of LNMO during lithium deintercalation / intercalation. The focus was on the peak position migration and peak shape evolution of the (111), (311), and (400) characteristic diffraction peaks during charge-discharge processes. The study shows that the phase transition reaction of LNMO during cycling mainly involves the reaction between LiNi and Ni. 0.5 Mn 1.5 O4 generates Li 1-x Ni 0.5 Mn 1.5 The solid solution reaction of O4 and the reaction of Li 1-x Ni 0.5 Mn 1.5 O4 generates Ni 0.5 Mn 1.5 Two-phase reaction of O4. For example Figure 6 As shown in Figure a, pure LNMO undergoes a two-phase reaction. During the initial charging phase, pure LNMO is converted from Li1Ni... 0.5 Mn 1.5 O4 and Li 0.5 Ni 0.5 Mn 1.5 O4 composition. As delithiation progresses, Ni appears. 0.5 Mn 1.5 O4 gradually increases. At the end of delithiation, pure LNMO consists only of Li. 0.5 Ni 0.5 Mn 1.5 O4 and Ni 0.5 Mn 1.5The composition is O4. During charge and discharge, pure LNMO undergoes a two-phase reaction, resulting in lattice mismatch and mechanical stress, which is detrimental to the structural stability of LNMO. Conversely, LNMCO-5 wt% does not exhibit obvious two-phase behavior but instead undergoes a solid solution reaction. Figure 6 The solid solution reaction avoids lattice mismatch at the two-phase interface, alleviating stress accumulation and thus helping to maintain particle structure integrity and improve LNMO cycling performance. With increasing delithiation depth, the Bragg peak shifts to the right due to lattice contraction; conversely, during lithiation insertion, the Bragg peak shifts to the left. Figure 6 The b and e values ​​show different Bragg angle shift trends on the (111), (311), and (400) crystal planes of pure LNMO and LNMCO-5 wt%. Compared to pure LNMO, LNMCO-5 wt% undergoes a smoother phase transition during discharge lithium intercalation. The solid solution reaction provides a smoother lithium delithiation / lithiation process for LNMCO-5 wt% during charging and discharging. This mitigates damage caused by lattice stress accumulation and extends the cycle life of LNMO. Figure 6 As shown in figures c and f, the cell volume changes of pure LNMO and LNMCO-5 wt% during cycling were investigated. During charging, lithium extraction causes cell shrinkage, while during discharging, lithium insertion causes cell expansion. The cell volume change of LNMO during charge-discharge was 33.71 ų, while that of LNMCO-5 wt% was only 18.77 ų. These results indicate that solid solution reaction can significantly reduce the cell volume change of LNMO. Therefore, LNMCO-5 wt% exhibits higher structural stability, which plays a crucial role in improving the electrochemical performance of LNMO.

[0059] like Figure 7 As shown:

[0060] The cycled LNMO cathode was characterized and analyzed to gain a comprehensive understanding of the causes and extent of battery failure. Figure 7 Figure a shows the Nyquist plots of the batteries containing LNMO and LNMCO-5 wt% after 500 cycles at 1C. The Rct value decreased for both samples after cycling; a decrease in Rct typically reflects gradual electrode activation and improved interfacial reaction kinetics. After 500 cycles, the electrolyte wetted the electrode pores and particle surfaces more effectively, increasing the effective reaction area. The Rct value of LNMCO-5 wt% was lower than that of LNMO, which is attributed to the excellent ionic conductivity of the LNO layer. The CV curves after 500 cycles were used to evaluate the activity and redox state of the cathode, and the results are shown below. Figure 7As shown in b. Due to increased polarization and voltage decay during cycling, the redox peaks of Mn and Ni shift further to the right compared to before the cycling test, resulting in a decrease in capacity. Comparing the ΔE values ​​before and after cycling, LNMO increased from 0.227V to 0.286V, an increase of 0.059, while LNMCO-5 wt% increased from 0.147V to 0.158, an increase of only 0.011. This indicates that the LNO coating effectively suppressed the increase in overvoltage. Figure 7 The XRD patterns of LNMO and LNMO-2 wt% after cycling were compared. Due to structural collapse and interfacial side reactions after cycling, other impurity peaks besides LNMO appeared. Compared to LNMO, LNMO-2 wt% exhibited more complete peaks and better crystallinity. After 500 cycles, the Raman spectra of LNMO and LNMCO-5 wt% still retained the characteristic vibrational bands of the spinel framework, indicating that the main structure did not completely collapse. Figure 7 d. Figure 7 e and f are XPS spectra of surface F1s of LNMO and LNMCO-5 wt% after cycling, respectively. Compared to LNMO, the surface F content of LNMCO-5 wt% is only 37.43%. The LNO layer stabilizes the high-pressure interface, suppresses HF-induced continuous side reactions and metal dissolution, and reduces the deposition of fluorine-containing decomposition products; therefore, LNMCO-5 wt% has a lower surface F content. To more intuitively observe the changes on the LNMO grain surface, SEM images after cycling were used for characterization, such as... Figure 7 The g and h values ​​of both samples showed that they retained sharp edges, indicating that the main structure of LNMO did not collapse after cycling. Compared to LNMO, the surface of LNMCO-5 wt% was smoother, indicating that the interfacial HF corrosion of LNMO was more severe, resulting in more LiF, which is consistent with the previous results on the surface F content after cycling.

[0061] Using a LiNbO3 protective layer combined with Co 3+ Doping was employed as a synergistic modification strategy to suppress significant phase transition behavior, transition metal dissolution, and interfacial side reactions. In-situ XRD revealed that Co... 3+ Doping facilitates a more continuous lattice evolution during the (de)lithiation process, transforming the reaction pathway of bare LNMO from a two-phase reaction to a solid solution-like process. This transformation reduces unit cell volume changes and mitigates internal stress accumulation, thereby stabilizing the crystal structure of LNMO. Furthermore, Co... 3+Doping enhances charge transfer kinetics and improves electron transport in the cathode. The c-LNMCO│c-LiNbO3 heterointerface not only suppresses transition metal dissolution but also weakens HF adsorption / interaction on the surface, thereby improving the stability of the electrode / electrolyte interface. For the LNMCO-5wt%||Li half-cell, a 112.93 mAh g⁻¹ was achieved at 20 C. -1 The high-rate discharge capacity was achieved. After 500 consecutive cycles at 1C and 25°C, the capacity retention reached 81.44%. Similarly, after 150 cycles at 1C and 60°C, the capacity retention was 71.29%. Notably, the LNMCO-5wt%||graphite full cell retained 78.11% of its capacity relative to the first cycle discharge capacity after 100 cycles at 1C. This novel synergistic strategy combines heterogeneous interface engineering with Co... 3+ Doping combinations offer a promising pathway for the practical application of durable high-voltage LNMO cathodes and high-energy-density lithium-ion batteries.

[0062] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A high-voltage LiNi based on heterogeneous interface construction 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... Includes the following steps: S1: Preparation of Co-doped LiNi 0.5 Mn 1.5 O4 powder was weighed, and lithium source LiCH3COO, nickel source NiC4H6O4·4H2O, manganese source MnC4H6O4·H2O, and cobalt source (CH3CO2)2Co were dissolved in deionized water to obtain a mixed metal salt solution. Citric acid was added to the mixed metal salt solution as a complexing agent, and the solution was stirred until completely dissolved. The resulting solution was transferred to a microwave reactor and magnetically stirred at 100-110℃ until the solvent was completely evaporated to obtain a wet gel. The wet gel was dried, and then calcined successively at 500℃ and 900℃. After cooling, it was ground to obtain Co-doped LiNi. 0.5 Mn 1.5 O4 powder, i.e., LNMCO; S2: Prepare LNMCO@LiNbO3 coated material. Weigh Nb2O5, ultrasonically disperse it in ethanol, add the LNMCO powder obtained in S1, mix evenly, and stir continuously at 60-70℃ until the solvent is completely evaporated. Dry the obtained solid, grind it thoroughly, calcine it at 500℃ in an oxygen atmosphere, and obtain the product after cooling.

2. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... In S1, the molar ratio of lithium source LiCH3COO, nickel source NiC4H6O4·4H2O, manganese source MnC4H6O4·H2O, and cobalt source (CH3CO2)2Co is 1.05:0.5:1.47:0.03, and the molar ratio of metal ions to citric acid is 1:

1.

3. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by: The purity of LiCH3COO in S1 is ≥99.9%, the purity of NiC4H6O4·4H2O is ≥99.9%, the purity of MnC4H6O4·H2O is ≥99.0%, and the purity of citric acid is ≥99.5%.

4. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by: The purity of Nb2O5 in S2 is ≥99.99%.

5. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... The mass percentage of Nb2O5 is 1-7%.

6. The high-voltage LiNi based on heterogeneous interface construction according to claim 5 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... The mass percentage of Nb2O5 is 5%.

7. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... The wet gel described in S1 is dried at 75-80℃ for 10-12 hours, and then calcined at 500℃ for 4-5 hours and then calcined at 900℃ for 9-10 hours.

8. The high-voltage LiNi based on heterogeneous interface construction according to claim 1 0.5 Mn 1.5 The method for preparing O4 cathode material is characterized by... The solid obtained in S2 is dried at 110-120℃ for 10-12 hours, thoroughly ground, and then calcined at 500℃ for 4-5 hours in an oxygen atmosphere.

9. A high-voltage LiNi based on a heterostructure interface as described in any one of claims 1-8 0.5 Mn 1.5 High-voltage LiNi cathode material prepared using a heterostructure-based method based on O4 cathode material fabrication. 0.5 Mn 1.5 O4 cathode material, characterized in that: The cathode material has a core-shell structure, with the core being Co-doped LiNi. 0.5 Mn 1.5 O4, with a shell of LiNbO3, and a c-LNMCO│c-LiNbO3 heterogeneous interface is formed between the core and the shell.

10. A high-voltage LiNi based on a heterogeneous interface as described in claim 9 0.5 Mn 1.5 O4 cathode material, characterized in that: The cathode material has an average particle size of 5-10 μm and a LiNbO3 shell thickness of 3-5 nm. The cathode material has a cubic spinel structure with space group Fd-3m, and the main phase is LiNi with space group Fd-3m. 0.5 Mn 1.5 O4 has a crystalline LiNbO3 phase on its surface.

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