Tuning Cation Disorder in LiNi₀.₅Mn₁.₅O₄ via Room Temperature Continuous Flow Co-precipitation and Controlled Heat Treatment

Tuning Cation Disorder in LiNi₀.₅Mn₁.₅O₄ via Room Temperature Continuous Flow Co-precipitation and Controlled Heat Treatment | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 18 March 2026 V1 Latest version Share on Tuning Cation Disorder in LiNi₀.₅Mn₁.₅O₄ via Room Temperature Continuous Flow Co-precipitation and Controlled Heat Treatment Authors : Bangxun Yin 0009-0001-0863-0790 , Jack Quayle , Jiacheng Wang , David Wilde , Ivan Parkin , and Jawwad Darr [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.177386264.47597397/v1 176 views 92 downloads Contents Abstract Introduction Results and Discussion Conclusion Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract A room temperature continuous co-precipitation process incorporating in-line dynamic mixing was employed for the synthesis of a precursor (production rates up to 0.42 kg·h⁻¹) to the high-voltage lithium-ion cathode material LiNi₀.₅Mn₁.₅O₄ (LNMO). The co-precipitate was initially lithiated in a tube furnace in air via a two-step heat treatment (500 °C/5 h and 850 °C/12 h). After cooling, a third and final heat treatment at either 650, 700, or 750 °C was used to tune the degree of cation disorder in the final LNMO sample. X-ray Photoelectron Spectroscopy revealed a clear temperature-dependent trend for the surface of the final LNMO sample heat-treated at 650 °C (surface disorder ca. 38%), whilst those heat-treated at 700 and 750 °C showed ca. 46 and 53% surface disorder, respectively. Electrochemical testing of the three final LNMO samples demonstrated the latter material (final 750 °C sample) delivered discharge capacities of 124, 116 and 81 mAh·g⁻¹ at 0.1, 1, and 5C, respectively. Furthermore, incorporation of 2.5 wt % multi-walled carbon nanotubes (MWCNTs) into the electrode formulation significantly enhanced the rate capability, yielding 98 mAh·g⁻¹ at 5 C and 91 mAh·g⁻¹ at 10 C, together with improved cycling stability (up to 98.4 % retention after 100 cycles at 1 C). Overall, the use of a flow process for precursor synthesis provided a scalable and energy-efficient route to spinel-phase LNMO, offering both high performance and tuneable surface cation disorder. Introduction Compared with other rechargeable battery systems, such as lead–acid, nickel–cadmium, lithium–sulphur, and sodium–aluminium ion batteries, lithium-ion batteries (LIBs) are among the most widely adopted technologies owing to their high energy density, long cycle life, and excellent power performance [1–3] . These advantages have enabled LIBs to support a broad range of applications, including portable electronic devices and electric vehicles, for more than two decades [4–8] . LiNi₀.₅Mn₁.₅O₄ (LNMO) was first proposed as a high-voltage cathode material in 1997 by T. Ohzuku and colleagues, who reported its spinel structure possessed excellent cycling stability and high voltage characteristics [9] . Subsequent studies further optimized electrochemical performance through chemical substitution and surface engineering [10,11] . The rapid growth of the electric vehicle and energy storage markets has increased the demand for high-performance LIBs. Therefore, cathodes with ever-increasing capacity and stability are required [1,2,12] . LNMO has a high operational voltage (4.7 V vs Li/Li + ), demonstrates excellent cycling performance and has also shown potential in all-solid-state lithium batteries, where combining it with solid state electrolytes can enhance energy density and safety [13,14] . Typical synthesis methods for preparing LNMO include solid-state synthesis from transition-metal oxides or carbonates [15] , co-precipitation [16,17] and hydrothermal synthesis [18–20] . The solid-state method often results in impurities from milling and irregular particle shapes, while the hydrothermal method, though providing better control over particle morphology, struggles to be readily scalable [19,21] . Semi-continuous Stirred Tank Reactors (CSTRs) have successfully been implemented in industry for the manufacture of battery cathode materials; however, there are challenges with increased waste and in optimizing parameters such as the pH, temperature, duration, and atmosphere, often requiring extended times to obtain a suitable cathode precursor [22,23] . For future syntheses of cathode precursors (pre-lithiation), fully continuous, rapid and energy efficient methods to prepare precursors that eventually lead to phase pure lithiated cathodes are needed [24] . In this work, a scalable continuous co-precipitation route was employed to synthesise the LNMO precursor [25–27] . The flow co-precipitation process operates at ambient temperature and pressure and employs an in-line dynamic mixer to homogenise reagent feeds, yielding precursors that can be eventually converted to a LNMO cathode after solid state lithiation. Indeed, post-lithiation of the precursor, a further and final heat-treatment was conducted to control the cation-disorder, which affected the final electrochemical performance of LNMO materials. Experimental Section 2.1. Synthesis of LNMO The LNMO (LiNi₀.₅Mn₁.₅O₄) cathode precursors were synthesized via an Ambient Continuous Turbulent In-line Mixing (ACTIM) co-precipitation system as shown in Figure 1 [27] . First, aqueous solutions of Ni(NO₃)₂·6H₂O (≥ 97.0 %, Sigma-Aldrich, Cat. No. 72253) and Mn(NO₃)₂·4H₂O (≥ 97.0 %) were each prepared in deionized water at concentrations in the range 1 to 2 M as the metal precursor feeds. Meanwhile, a KOH solution (from KOH pellets, ≥ 85 %, Sigma-Aldrich, Cat. No. P1767) was prepared at concentrations in the range 2 to 4 M to serve as the precipitating reagent. The metal salt and base solutions were then fed via independent high-pressure pumps (Milton Roy PK100H8M260/ST.9.VV2) at flow rates in the range 80 and 160 mL·min⁻¹. Prior to entering the high-shear mixing chamber operating at 12,000 rpm (Silverson Verso-UHS-HV), the streams converged through a low-volume T-junction and entered the high-shear mixer, prompting uniform precipitation of the slurry. Under the conditions of 1 M metal salt and 2 M KOH solutions at 160 mL·min⁻¹, the slurry measured downstream exhibited an initial pH of ~10.6; under 2 M metal salt and 4 M KOH solutions at the same flow rate, the downstream slurry pH was ~11.5. The samples in this study that were synthesised using 1 M and 2 M metal stock concentrations are labelled as 1M-LNMO (0.21 kg·h -1 ) and 2M-LNMO (0.42 kg·h -1 ), with corresponding KOH concentrations of 2 and 4 M, respectively. A plot of pH of the output slurry using ACTIM against the input KOH concentration is provided in Supplementary Figure S1. The freshly formed suspension was collected in a 50 L stirred tank and aged overnight. To clean the slurry, 500 mL aliquots were subjected to repeated centrifugation at 4500 rpm for 10 minutes per cycle. After each cycle, the supernatant in each aliquot was removed and replaced with deionized water with shaking until the supernatant exhibited a conductivity below 50 ppm. The washed product was reduced to a thick sludge and then frozen to -40 °C before being freeze-dried for 24 hours (Virtis Genesis 35 XL, USA) under a vacuum of 200 Torr, and the resulting dry solid was finely ground by hand using a mortar and pestle for 10 minutes. Lithiation was achieved by first dispersing the dried precursor in the required amount of 5 M LiOH solution with homogenisation (IKA ULTRA-TURRAX T18) at 6000 rpm for 30 minutes. The mixture (Li content was added at a Li:(Ni + Mn) molar ratio of 0.5:1, with an additional 5 wt% excess) was again frozen to -40 °C and then freeze-dried (24 hours) under a vacuum of 200 Torr, to obtain a dark-brown powder. To control the degree of cation disorder in the final LNMO materials, a multi-step heat-treatment protocol was employed. Systematic optimisation studies were conducted prior to finalising the thermal conditions (see Supplementary Information, Text S1 and Figures S2–S7 for more information), as the extent of cation ordering in LNMO has been widely reported to significantly influence electrochemical performance [28–31] . Upon addition of a Li source to the co-precipitate, the heat-treatment was 500 °C for 5 h (denoted herein as HTS-1) to promote lithium diffusion with a subsequent treatment step at 850°C for 12 hours, with a heating rate of 5 °C min⁻¹ (denoted herein as HTS-2). To investigate whether the extent of ordering could be further controlled, a portion of the 2M LNMO sample (production rate 0.42 kg·h -1 ) were given a third heat-treatment (denoted herein as HTS-3) in air at either 650 °C, 700 °C, or 750 °C (with a heating rate of 5 °C min⁻¹). These samples are denoted herein as 2M-LNMO-650, 2M-LNMO-700, and 2M-LNMO-750, respectively. The 2M-LNMO sample was selected for further optimisation due to increased production rate. 2.2. Electrode Fabrication and Electrochemical Characterisation Cathode electrodes for cell testing were prepared by blending the final LNMO powder, conductive additives, and polyvinylidene fluoride (PVDF, PI-KEM, Staffordshire, UK) binder in a mass ratio of 80:10:10. The conductive additives consisted of either carbon black alone or a mixture of carbon black and Multi-Walled Carbon Nanotubes (MWCNTs). To prepare the slurry, 0.8 g of LNMO was mixed with 0.1 g of conductive additives, 2.0 g of a 5 wt% PVDF solution in N-methyl-2-pyrrolidone (NMP, ≥ 99.5 %, Sigma-Aldrich, Dorset, UK) and 0.2 g of additional NMP. The mixture was processed in a planetary centrifugal mixer (THINKY ARE-250, Thinky Corporation, Tokyo, Japan) together with eight 3 mm zirconia milling beads and subjected to a three-step mixing program: 1000 rpm for 10 min, 1500 rpm for 5 min and 2000 rpm for 5 min, yielding a homogeneous slurry. The slurry was coated onto 20 µm-thick aluminium foil (battery-grade current collector, PI-KEM, Staffordshire, UK) using a doctor blade with a wet thickness of ca. 60 µm at a coating speed of 0.75 m·min⁻¹. The coated electrodes were dried on a hotplate at 75 °C for 10 min and then vacuum-dried overnight at 60 °C in a vacuum oven under low pressure to remove residual solvent and moisture before further processing. Circular electrodes (15 mm diameter) were punched from the dried films for coin-cell fabrication. In selected electrode formulations, MWCNTs were introduced as partial replacements for Super P® conductive carbon black (Alfa Aesar / Sigma-Aldrich, Heysham, UK) at 2.5, 5.0, 7.5, and 10.0 wt% of the total electrode mass (the total carbon mass was always maintained at 10 wt% of overall mass). The MWCNTs were a commercial dispersion (ORGACYL™ NMP0413, Nanocyl S.A., Belgium), containing 4 wt% NC7000™ MWCNTs dispersed in NMP with < 2 wt% polymeric dispersants. The Super P® had a specific surface area of ~62 m²·g⁻¹ and extremely low metallic impurities (< 1 ppm Ni and < 5 ppm Fe). Coin cells (CR2032 type, MSE PRO, MSE Supplies, UK) were assembled in an argon-filled glovebox (O₂ < 0.1 ppm, H₂O < 0.5 ppm) using lithium metal foil (15.6 mm diameter, 0.45 mm thick, PI-KEM, UK) as the counter/reference electrode. The electrolyte consisted of 1 M LiPF₆ dissolved in a 1:1 (w/w) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (BASF, Ludwigshafen, Germany). Electrochemical testing was conducted at 25 °C on an Arbin battery testing system (Arbin Instruments, College Station, USA) over the voltage range of 3.5 to 4.9 V vs. Li⁺/Li, with cycling at a fixed theoretical capacity of 200 mAh·g⁻¹. Electrochemical impedance spectroscopy (EIS) measurements were carried out using a Gamry Interface 1000 potentiostat/galvanostat (SciMed, Cheshire, UK) over the frequency range of 100 kHz to 0.01 Hz with a 10 mV AC perturbation. 2.3. Materials Characterization Powder X-ray diffraction (PXRD) was conducted in the 2θ range of 2–40° using Mo Kα radiation (λ = 0.7107 Å). The step time was set to 10 s and the step size was set to 0.5°. PXRD patterns were collected using a STOE StadiP diffractometer, and peak identification was done by comparing the data with references from the Inorganic Crystal Structural Database (ICSD). Raman spectroscopy was performed using a Bruker Senterra II Raman Microscope with a laser wavelength of 532 nm. Scans were collected over the range 100 to 1600 cm⁻¹ with a step size of 1 cm⁻¹. Bulk elemental composition was investigated using X-Ray Fluorescence (XRF) spectroscopy (Epsilon 4, Malvern Panalytical, Malvern, UK). The powders were transferred into 30 mm XRF cups and covered with a Mylar® film (Precut Circles, 3.6µm, Ø 63,5mm). A 20.00 kV beam voltage and a 0.100 mA beam current were used to collect data for 15 minutes for each sample. The analysis of the data was performed with Epsilon 3 Software. X-ray Photoelectron Spectroscopy (XPS) was performed with a Thermo Scientific K-alpha™ Spectrometer using Al Kα radiation (1486.6 eV). High-resolution scans for elements were performed at 50 eV. Analysis and peak fitting were performed using CasaXPS TM software (version 2.3.16), with the C1s peak calibrated to 284.8 eV. Powder samples were affixed onto double-sided carbon tape and vacuumed to a chamber pressure below 1 × 10⁻⁸ Torr. Scanning Electron Microscopy (SEM) was carried out using a JEOL JSM-6701F high-resolution Field Emission Scanning Electron Microscope (FESEM) to analyse the particle shape, size, and uniformity. Samples were pre-coated using an Agar Scientific Automatic Gold Coater. Energy-Dispersive X-ray Spectroscopy (EDS) was performed on the materials using the JEOL JSM-6701F with an Oxford Instruments detector. 2.4. Energy consumption of ACTIM co-precipitation process The energy consumption of the ACTIM co-precipitation process was calculated and compared to that for other methods including Continuous Hydrothermal Flow Synthesis (CHFS) used by some of the authors and a conventional batch co-precipitation route (see Supplementary Table S1 for a comparison of ACTIM co-precipitation and batch co-precipitation methods). Previous work by the authors has demonstrated the effectiveness of CHFS in producing cathode precursor materials [32,33] , however, CHFS requires high temperatures and pressures which is not the case for the ACTIM flow process (thus ACTIM co-precipitation consumes less energy). The conventional batch co-precipitation route operates at moderate temperatures but necessitates prolonged reaction and post-synthesis thermal treatment, leading to increased overall energy consumption, as shown below. The ACTIM co-precipitation process included two continuous steps: precursor solution mixing and ambient flow co-precipitation. For 1 kg of LNMO precursor, mixing at ~0.7 kW for 30 min consumed 0.35 kWh, and co-precipitation (2 M metal salts, 4 M KOH) at the estimated batch co-precipitation process using a CSTRs involved mixing (0.7 kW, 30 min, 0.35 kWh), reactor heating (2 kW, 30 min, 1.0 kWh), pH stabilization (1.5 kW, 20 min, 0.5 kWh), and co-precipitation (0.3 kW, 4 h, 1.2 kWh), totalling ~3.05 kWh per 1 kg batch [34–37] . Based on experimental data and estimation, the energy consumption during the co-precipitation step was 1.85 kWh for ACTIM co-precipitation and was 3.05 kWh for batch co-precipitation, indicating that ACTIM co-precipitation saves approximately 39 % of the energy compared to the batch process. Subsequent steps for LNMO are centrifugation (2.3 kW, 40 min, 1.53 kWh), freeze-drying (0.35 kW, 24 h, 8.4 kWh), lithiation (1.0 kW, 30 min, 0.5 kWh), and a second freeze-drying (0.35 kW, 24 h, 8.4 kWh), which resulted in total consumptions of ~20.0 kWh·kg⁻¹ for ACTIM co-precipitation and ~21.5 kWh·kg⁻¹ for batch co-precipitation. Industrial production benefits from economies of scale, with the Argonne model estimating ~5.6 kWh kg⁻¹ for spinel LMO via co-precipitation, including electrical and thermal energy [38] . Similarly, process studies on co-precipitation synthesis of NMC111 precursors have reported electricity consumption of approximately 4 kWh·kg⁻¹ and water usage of about 15 L·kg⁻¹ [35] . Under pilot-scale conditions, smaller batch sizes and higher fixed losses raise specific energy use. For instance, a 100 kg-per-batch NMC811 pilot study by the Indonesian National Battery Research Institute reported 2.18 GWh for 36 tons in a year, equivalent to ~60 kWh·kg⁻¹ [34] . This indicates that scale effects are significant, with industrial-scale operation achieving markedly lower energy consumption per kilogram compared to pilot-scale systems. As a result, further improvements in energy efficiency can reasonably be anticipated for the ACTIM process upon scale-up. Results and Discussion Lithiated Lithium Nickel Manganese Oxide (LNMO) samples were synthesized using the ACTIM flow co-precipitation process followed by lithium source addition and three heat-treatment steps. Prior to the development of the optimum conditions discussed below (see Supplementary text S1, Figure S2-S7), some exploratory experiments were conducted to understand control over the degree of disorder in the final LNMO materials which had been shown to be related to performance [28–31] . After this investigation, the final details of the heat-treatment were as follows; two co-precipitate samples (comparing the use of both 1M and 2M metal salt solutions in the ACTIM co-precipitation step, denoted as 1M-LNMO and 2M-LNMO) after lithiation were treated at 500 °C for 5 h (HTS-1) to promote lithium diffusion and then subsequently treated at 850 °C for 12 h (HTS-2). To investigate whether the extent of ordering could be further controlled, the 2M-LNMO sample (made at the highest production rate) was carried forward and given a third heat-treatment (HTS-3) in air at either 650 °C, 700 °C, or 750 °C (denoted as 2M-LNMO-650, 2M-LNMO-700, and 2M-LNMO-750). In comparison to the very long heat treatment times given here, the authors previously investigated synthesis of layered cathode materials using ultra-short heating methods to develop low defect controlled lithiated NCA cathode materials [32] . Powder X-ray diffraction patterns of the 2M-LNMO materials herein after HTS-3 (PXRD) are given in Figure 2a, with the corresponding Raman spectra in Figure 2b. PXRD analysis of the 1M-LNMO and 2M-LNMO samples after HTS-1 and HTS-2 (Figure S7) showed a dominant spinel phase (Fd3̅m/P4₃32) [39–41] . A weak additional reflection near 2θ associated with partial Ni/Mn cation ordering in the LNMO spinel structure [31,39,41] . The disappearance of this weak superlattice reflection after HTS-3, suggests increased cation disorder in the spinel lattice, resulting from a more random distribution of Ni and Mn over the octahedral sites and suppression of long-range cation ordering [30,31,42] . Raman spectroscopy was used to gain structural insights into the cathodes due to its increased sensitivity towards crystal symmetry [39,43] . The Raman spectra (Figure 2b) exhibited characteristic spinel LNMO vibrational modes at ~165 cm⁻¹ (T ₂g , sensitive to Ni/Mn cation ordering), (T ₂g , Mn–O and Ni/Mn–O vibrations), and range as a fingerprint peak highly sensitive to crystal symmetry [40,41] . The relative intensity of the Raman band at disorder, with a reduced intensity corresponding to an increased degree of disorder within the spinel lattice [44,45] . Mechanistically, increased cation disorder is associated with a higher Mn³⁺ content, which introduces local Jahn–Teller distortion of MnO₆ octahedra, softening the lattice and attenuating the intensity of collective low-frequency lattice vibrations [46,47] . In previous literature reports, the extent of cation disorder in LNMO materials was demonstrated to correlate to the specific capacity, where the Mn 3+ /Mn 4+ redox contributed towards the performance up to an optimal capacity for LNMO materials possessing ca. 50 % extent of surface disorder, where a larger amount of Mn 3+ (a larger amount of disorder) present in the structure (above ca. 50 %) resulted in lattice expansion and structural instability due to Jahn–Teller effects [46,47] . The influence of cation ordering on the Raman response is further evidenced by peak splitting arising from the reduced crystallographic symmetry of the ordered P4₃32 phase relative to the disordered Fd3̅m phase [40,48] . In the ordered phase, periodic Ni/Mn ordering in the P4₃32 structures reduce site equivalence within the octahedral sublattice, lifting the degeneracy of Raman-active phonon modes [41,48] . As a result, the characteristic Raman band in the range ~580 to 590 cm⁻¹ region splits into two distinct peaks in the ordered phase, whereas it appears as a single peak in the Fd\(\overline{3}\)m structure [40,41,48] . This can be seen clearly in Figure 2b, where 2M-LNMO-650 demonstrates peak splitting, while sample 2M-LNMO-700 has visibly less, and 2M-LNMO-750 has only a single peak in the range of 580 to 590 cm⁻¹. This trend suggests that the samples containing the greatest extent of ordering were achieved at lower HTS-3 temperatures. Additionally, the Raman peak at ca. 165 cm⁻¹ was largest for sample 2M-LNMO-650 (i.e. HTS-3 at 650 °C), indicating that this peak is correlated with the extent of ordering. The X-ray Photoelectron Spectroscopy (XPS) fits for the Mn 2p region are shown in Figure 3a–c. The surface Mn³⁺ at% (relative to Mn⁴⁺) for the samples where HTS-3 was conducted at 650, 700 and 750 °C was 38, 46, and 53%, respectively. This showed that 2M-LNMO-650 possesses the lowest degree of surface disorder, while 2M-LNMO-750 exhibits the highest. These findings were consistent with Raman spectroscopy in Figure 2b and lattice parameters in Table 1(Figure 2c-d), which indicated a larger extent of disorder, and that the lattice parameter and unit cell volume increased with increased HTS-3 temperature. Specifically, the lattice parameter a increased from 8.1769 Å for 2M-LNMO-650 to 8.1965 Å for 2M-LNMO-750, corresponding to an expansion of the unit cell volume from 546.9 to 550.2 ų. The progressive increase suggested a gradual transition from a more ordered to a more disordered spinel structure, as reported in previous studies [49] . By contrast, the XPS spectra of the 2M-LNMO sample (Figure S8) without HTS-3 exhibited a high Mn³⁺ content of 55.4 %, indicating a more cation-disordered spinel structure and highlighting the effectiveness of the low-temperature HTS-3 step in promoting Ni/Mn ordering and suppressing secondary-phase formation. Scanning Electron Microscopy (SEM) images depicting the morphology of 2M-LNMO-650, 2M-LNMO-700, and 2M-LNMO-750 samples are presented in Figure 4a–f. SEM images of 2M-LNMO (without HTS-3) are presented in Figure S9. The micrographs revealed distinct particle aggregation and growth behaviour with increasing heat-treatment temperature. Specifically, the 2M-LNMO-750 sample (Figure 4c and 4f) exhibited well-defined polyhedral crystallites with a relatively uniform size distribution compared with samples where HTS3 was conducted at 650 or 700 °C. The LNMO samples exhibited mean secondary particle sizes of 5 ± 1.6 μm, 7 ± 2.1 μm, and 8 ± 2.4 μm (standard deviations calculated from 200 agglomerates) for samples 2M-LNMO-650, 2M-LNMO-700, and 2M-LNMO-750, respectively. The corresponding primary particle sizes were estimated to fall within the ranges of 0.3–0.9 μm, 0.3–1.1 μm, and 0.3–1.0 μm based on measurements of 200 particles (Figure S10). Energy-Dispersive X-ray Spectroscopy (EDS) elemental maps confirmed a homogeneous distribution of oxygen (O), manganese (Mn) and nickel (Ni) across all samples, indicating effective elemental mixing (are shown in Figure 4g–i). The quantified atomic ratios obtained from EDS (Table S2) were consistent across the series, with Mn:Ni atomic ratios matching the target 3:1 stoichiometry (e.g., sample 2M-LNMO-700: Mn 33.4 at%, Ni 10.5 at%), and oxygen content estimated in the range 54–56 at%. The SEM-EDS values are in good agreement with XRF measurements (Table S3), which reported Ni atomic percentages of 25.8 and 26.7 at%, (73.0 and 73.9 at% for Mn) for production rates of 0.21 and 0.42 kg·h -1 , respectively. A previous study has demonstrated that homogeneity in morphology and elemental distribution is related to superior long-cycle stability [50] . The consistency between input composition, XRF output, and EDS analysis supports the reliability of the ACTIM method in producing stoichiometrically consistent LNMO materials with uniform elemental distribution. Figure 5a illustrates the rate capability of coin half cells made from LNMO cathodes with the 2M-LNMO-750 cell delivering the highest specific discharge capacities across various C-rates. Rate capability tests as shown in Figure 5a revealed that sample 2M-LNMO-750 achieved a specific capacity of 124.1 mAh·g −1 at a 0.1C (current rate 14.7 mA·g -1 ) and 81 mAh·g −1 at a 5C (current rate 735 mA·g -1 ). In contrast, the reference 1M-LNMO and 2M-LNMO samples without the HTS-3 heat-treatment (Figure S11) exhibited virtually no discharge capacity after 5C, highlighting that the HTS-3 heat-treatment was critical for enabling encouraging high-rate performance through controlling disorder in the structure. Electrochemical testing of the half cells showed that at the lowest rate of 0.1C, the specific discharge capacities of all HTS-3 samples were comparable in the range 121.4 to 124.1 mAh·g⁻¹, with the 2M-LNMO-750 significantly outperforming others at elevated C-rates. This was attributed to its higher Mn 3+ content and lower charge-transfer resistance, which facilitated faster charge/discharge kinetics. Figure 5b–c shows the cycling stability of the HTS-3 heat-treated LNMO cathodes at 1 C. Discharge capacities of 115.6 mAh·g⁻¹ (2M-LNMO-650), 113.1 mAh·g⁻¹ (2M-LNMO-700), and 120.7 mAh·g⁻¹ (2M-LNMO-750) were obtained at the 6th cycle for samples treated at progressively higher temperatures. All electrodes exhibited stable cycling behaviour over 100 cycles (Figure 5b). Among them, 2M-LNMO-650 delivered the highest capacity retention of 91.3% after 100 cycles, followed by 2M-LNMO-750 (89.1%) and 2M-LNMO-700 (85.8%). The retention values were calculated from the 6th cycle, after five formation cycles at 0.05 C. To improve cycling performance through the introduction of conductive additives, MWCNTs were added into the electrode formulation (replacing C black) of the champion performing sample 2M-LNMO-750 (Figures 5b and 5d). Electrodes containing 2.5, 5.0 and 7.5 wt% of MWCNTs were prepared whilst always maintaining a conductive additive amount (MWCNTs and CB) as 10 wt% in an 80:10:10 wt% ratio of active material, binder, and total carbon. The rate performance is plotted in Figure 5b, where at a low C-rate of 0.1 C, all MWCNT-containing electrodes delivered ca.128 mAh·g −1 , while the electrode containing 2.5 wt% MWCNTs achieved the highest capacity of 129.7 mAh·g⁻¹. At higher C-rates the electrode with 2.5 wt% MWCNTs delivered 123.3 mAh·g −1 at 0.5 C, 119.6 mAh·g −1 at 1 C, and 98.3 at 5 C and 90.9 mAh·g −1 at 10 C, demonstrating excellent high-rate capability. The 5 wt% MWCNTs electrodes delivered a capacity at 0.2 C (125.7 mAh·g −1 ) but marginally lower capacities than the 2.5 wt% MWCNTs case at the highest C rates. The electrode with 7.5 wt% MWCNTs showed high initial capacity (129.5 mAh·g −1 at 0.1 C), but its performance declined (71.8 mAh·g −1 at 10C). Figure 5d highlights the improvements in cycling stability achieved by introducing MWCNTs into the 2M-LNMO-750 cathode. All LNMO electrodes incorporating 2.5 wt% MWCNTs exhibited higher capacities and better capacity retention over extended cycling compared with their counterparts that used only carbon black without additional additives. For example, at 1C over 100 cycles, the discharge capacity of the 2M-LNMO-750 electrode increased from 107.3 with no MWCNTs to 128.2 mAh·g −1 with 2.5 wt% MWCNTs, with the 100-cycle capacity retention improving from 89.1% to 98.4 %. Over 500 continuous cycles (Figure 5d), the 2M-LNMO-650 electrode (with 2.5 wt% MWCNTs) retained 95.6 % of its initial capacity. This was closely followed by the 2M-LNMO-750 (2.5 wt% MWCNTs) electrode at 92.3 % retention, whereas the 2M-LNMO-700 (2.5 wt% MWCNTs) electrode showed a significantly lower retention of 90.4 %. As summarised in Figure S12, the electrochemical performance of the optimised 2M-LNMO-750 sample compares favourably with literature reports for LNMO cathodes with partially disordered spinel structures. Previous studies typically report initial discharge capacities of ~118–134 mAh·g⁻¹ with capacity retentions of ~86–95 % after 100 cycles, depending on the synthesis method and degree of Ni/Mn cation disorder [14,20,47,51–67] . The performance achieved in this work therefore lies within the upper range of reported electrochemical behaviour for disordered spinel LNMO cathodes. Broad reviews of LNMO and thick-electrode designs noted that low MWCNTs loadings near the percolation threshold ( ~ 1–3 wt% in many cathode formulations) can maximize conductivity without displacing active mass; beyond percolation, extra carbon yields diminishing returns and can even depress areal capacity, which is consistent with the finding herein [68] . All of these electrochemical tests indicated that the optimal sample was 2M-LNMO-750, which gave the largest discharge capacities at each cycle and C-rate, both with and without MWCNTs in the electrode formulation. Galvanostatic voltage profiles for 2M-LNMO samples subjected to HTS-3 (Figure 6a–d) showed a distinct plateau at ~ 4.0–4.1 V charge/discharge that is most pronounced for 2M-LNMO-750, weaker for 2M-LNMO-700, and nearly absent for 2M-LNMO-650. This feature was attributed to the Mn³⁺/Mn⁴⁺ redox couple and became more visible with increasing cation disorder (higher Mn³⁺ content), whereas the ~ 4.7 V plateaux arose from Ni²⁺/Ni³⁺/Ni⁴⁺ processes [44,69,70] . The trend in plateau prominence in the galvanostatic voltage profiles mirrored the Raman/XPS conclusions regarding the extent of disorder increasing with increasing HTS-3 temperature (Figure 2b and Figure 3), further indicating that the disordered Fd\(\overline{3}\)m spinel domains contributed appreciably to low-rate capacity. Overall, the sequence of plateau sizes at ~ 4.0–4.1 V (2M-LNMO-750 > 2M-LNMO-700 > 2M-LNMO-650) was consistent with a higher fraction of disordered domains at higher HTS-3 heat-treatment temperatures. Nyquist plots are provided in Figure 7a for 2M-LNMO samples subjected to HTS-3. The plots in Figure 7a revealed that 2M-LNMO-750 exhibited the lowest charge-transfer resistance (R ct = 91.3 Ω) among the three samples, indicating superior interfacial charge-transfer kinetics compared with 2M-LNMO-700 (226.4 Ω) and 2M-LNMO-650 (124.7 Ω). After 100 cycles, all samples demonstrated an increase in R ct due to interfacial degradation, yet 2M-LNMO-750 maintained a rise to the smallest R ct (to 173.7 Ω), reflecting superior surface stability. Nyquist plots are shown for coin half cells of 2M-LNMO-750 electrodes containing varied amounts of MWCNTs in Figure 7b. Varying the MWCNT content in 2M-LNMO-750 electrodes reduced R ct with the 2.5 wt% formulation exhibiting the lowest resistance (76.8 Ω, R² = 0.979), presumably due to the optimal 3D conductive network. Although MWCNT content ≥ 7.5 wt% led to higher R ct (154.5 Ω) for 2M-LNMO-750, the electrode still maintained good electrochemical stability. Consistent with prior LNMO literature reports [71,72] , CNT-based percolation networks <3wt% CNT lowered R ct and enhanced high-rate performance at low loadings. Herein, specifically, at ca. 2.5 wt% MWCNT the minimum R ct (Figure 7b) and best rate capability (Figure 5b) were obtained, whereas higher MWCNT contents produced diminishing returns (Figures 5b and 7b). Figure 7c and d present the Cyclic Voltammetry (CV) curves of 2M-LNMO-650 and 2M-LNMO-750 recorded over five cycles at 0.05 mV s⁻¹ in the voltage range 3.5 to 4.9 V. In the first cycle, the larger oxidation current indicated an irreversible activation related to structural rearrangement and electrolyte decomposition. From the second cycle onward, the peaks stabilized, suggesting a reversible Ni/Mn redox process. Compared to sample 2M-LNMO-650, sample 2M-LNMO-750 showed sharper, more symmetric Ni²⁺/Ni⁴⁺ peaks and a stronger Mn³⁺/Mn⁴⁺ response, consistent with its lower polarization and smaller charge-transfer resistance observed in EIS results. Conclusion In this work, single-phase LNMO cathode materials were produced via a continuous co-precipitation flow process at atmospheric pressure and room temperature that incorporated an inline dynamic mixer (the ACTIM process) that facilitated a mass production rate of up to 0.42 kg·h⁻¹ for the co-precipitate. The use of a two stage lithiation process followed by an additional third heat-treatment was used to deliberately tune cation disorder, the latter of which directly correlated to electrochemical performance in the final cathode. The ACTIM co-precipitation process offers several distinct advantages, including a high degree of automation and minimal operator intervention once steady-state operation is established. This contrasts with conventional batch stirred tank reactors or batch syntheses commonly used in academia and industry, which typically require continuous monitoring and real-time adjustment of process parameters. In addition, based on experimental measurements and life cycle energy-consumption estimates, the ACTIM process exhibits lower energy demand during the co-precipitation step, an advantage that is expected to become increasingly significant under scaled or industrial implementation. After the initial heat-treatment regime (solid state lithiation during HTS-1 and HTS-2), the 2M-LNMO materials were subjected to HTS-3 at either 650, 700, or 750 °C (for 10 h in air) which facilitated control of ordering in the LNMO spinel. Raman, XPS and galvanostatic charge-discharge voltage curves all indicated that the 2M-LNMO sample produced with HTS-3 step at 750 °C possessed the greatest degree of surface disorder in the spinel phase, at ca. 53 % (as suggested from Mn 3+ content derived from XPS results). Electrochemical testing showed that this sample delivered discharge capacities of approximately 124, 116, and 81 mAh·g⁻¹ at 0.1, 1, and 5 C, respectively, and maintained 89.1% capacity retention after 100 cycles at 1 C. Overall, electrochemical performance improved as the degree of disordered spinel phase in the LNMO increased. The high-rate cell cycling performance was significantly enhanced through the optimum addition of 2.5 wt% MWCNTs into the electrode formulation, achieving a discharge capacity of 91 mAh·g⁻¹ at 10C and 92.3% capacity retention after 500 cycles at 1C. Future work will be undertaken towards engineering LNMO cathodes using less heat treatment steps or shorter heat-treatments to reduce energy inputs and also to investigate the cathode cells at larger active masses in the electrode formulation while preserving or enhancing the rate performance and stability. Acknowledgements JAD, IPP, DW, JW and JQ thank InnovateUK, the UK Research and Innovation (UKRI) under the UK governments Horizon Europe funding guarantee and the European Union’s Horizon Europe programme for funding this work (AM4BAT: Gen. 4b Solid State Li-ion battery by additive manufacturing, grant agreement No 101069756, HORIZON-CL5-2021-D2-01). Author Contributions Bangxun Yin: Investigation, Methodology, Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Jack J. Quayle: Investigation, Validation, Writing – review & editing. Jiacheng Wang: Investigation, Methodology, Formal analysis, Writing – review & editing. 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From Rietveld refinement, the lattice parameters, unit cell volume and R wp goodness of fit values are provided for the 2M-LNMO-650 , 2M-LNMO-700 and 2M-LNMO-750 samples. 2M-LNMO-650 8.1769 8.1769 546.9 14.11 2M-LNMO-700 8.1836 8.1836 548.5 13.19 2M-LNMO-750 8.1965 8.1965 550.2 14.38 Information & Authors Information Version history V1 Version 1 18 March 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords cation disorder continuous synthesis lini0.5mn1.5o4 lithium-ion batteries scale-up Authors Affiliations Bangxun Yin 0009-0001-0863-0790 University College London View all articles by this author Jack Quayle University College London View all articles by this author Jiacheng Wang University College London View all articles by this author David Wilde Leitat Technological Center View all articles by this author Ivan Parkin University College London View all articles by this author Jawwad Darr [email protected] University College London View all articles by this author Metrics & Citations Metrics Article Usage 176 views 92 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Bangxun Yin, Jack Quayle, Jiacheng Wang, et al. Tuning Cation Disorder in LiNi₀.₅Mn₁.₅O₄ via Room Temperature Continuous Flow Co-precipitation and Controlled Heat Treatment. Authorea . 18 March 2026. 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