Effect of LMFP / NCM Blending on Resistivity, Compaction and Mechanical Behavior of Cathode Powders

Powder Resistivity & Compaction Density Case

Updated on 2025/08/22

1. Preface

With the rapid growth of the new energy vehicle market, the demand for high-performance lithium-ion batteries continues to increase. Automotive batteries require high energy density, long cycle life, enhanced safety, and competitive cost. Common cathode materials such as lithium cobalt oxide (LCO) and nickel-cobalt-manganese (NCM) offer high energy density but face challenges in cost and safety. In contrast, lithium iron phosphate (LFP) provides excellent stability and safety, though its energy density is nearing practical limits.

Lithium manganese iron phosphate (LMFP) has emerged as a promising alternative, combining the safety of LFP with higher energy density. Manganese doping increases the charge voltage to around 4.1V, boosting theoretical energy density by 15–20% compared to conventional LFP. However, LMFP cathode materials still face issues such as voltage hysteresis, low electronic conductivity, and limited rate capability.

In order to utilize the advantages of the above materials and also to meet different market demands, the strategy of hybrid cathode electrode has emerged ^[1,2]. By physically and mechanically mixing two (or more) cathode materials with complementary properties, and utilizing the advantages of other component materials to make up for their disadvantages while giving full play to the advantages of one component material, a lithium battery with good performance and moderate price can be prepared to meet the balanced requirements of cycle performance, range and safety. For example, H.S. Kim et al ^[2]. mixed NCM cathode and LCO cathode in different ratios and found that the reversible specific capacity and cycle stability of the battery improved significantly as the proportion of NCM in the components increased, but its multiplicity performance decreased sequentially. When the mixing ratio was 1:1, the multiplicity and cycle performance reached the dynamic optimum.

Different cathode materials have different operating voltages, so the synergistic effect between materials needs to be considered when mixing multiple active particles within a certain operating voltage range.The LMFP and NCM materials have similar discharge voltage windows, i.e., the electrochemical properties of both materials can be well utilized under the same voltage window. Therefore, the mixing of these two materials may have a better synergistic effect.

In this paper, the resistivity, compaction density, and stress-strain curves of anode materials mixed with different ratios of LMFP and NCM under different pressures were investigated by using the Powder Resistivity & Compaction Density Meter (PRCD3100, IEST) and the differences in the electrical and mechanical performances of the anode materials with different mixing ratios were further analyzed.

2. Experimental methods

2.1 Equipment

All tests were performed on the Powder Resistivity & Compaction Density Tester (PRCD3100, IEST), shown in Figure 1, which simultaneously records four-probe resistivity, conductivity and thickness while applying controlled uniaxial pressures up to 5 T. The instrument enables synchronized acquisition of electrical and mechanical data required to derive compaction and stress–strain behavior.

Figure 1. Schematic diagram of the Powder Resistivity & Compaction Density Meter (PRCD3100, IEST) and the two testing principles of powder resistivity.

2.2 Sample preparation & test plan

Six powder compositions were prepared (mass basis):

100% LMFP
80% LMFP / 20% NCM
60% LMFP / 40% NCM
40% LMFP / 60% NCM
20% LMFP / 80% NCM
100% NCM

Measurement procedure:

Stepwise pressurization from 10 MPa to 350 MPa with 20 MPa increments; record resistivity and thickness to obtain resistivity vs. pressure and compaction density vs. pressure curves.
After reaching 350 MPa, stepwise depressurization back to 10 MPa to capture full stress–strain loops and quantify reversible vs. irreversible deformation.

3. Results & analysis

3.1 Resistivity and conductivity trends

Figure 2(a) shows resistivity vs. pressure for the six compositions. Key observations:

Resistivity decreases with increasing pressure for all samples, reflecting improved particle–particle contact and reduced contact resistance under compaction.
100% LMFP exhibits the highest resistivity across the pressure range, confirming LMFP’s relatively poor intrinsic electronic conductivity.
Adding NCM progressively lowers resistivity: hybrid cathodes with higher NCM fractions approach the conductivity of pure NCM. This demonstrates that blending can mitigate the lmfp cathode’s conductivity limitation by providing better electronic percolation paths.

Mechanistically, mixed-particle systems benefit when smaller particles fill voids between larger ones and conductive NCM particles help form electron conduction networks. Note that conductive additive content and binder also affect electrode sheet conductivity; here the active-material mix itself produced clear conductivity differences.

3.2 Compaction density behavior

Figure 2(b) presents compaction density versus pressure:

Pure LMFP has the lowest compaction density, while increasing NCM content yields higher packing densities.
Improved compaction arises from particle size distribution and mechanical deformability: NCM addition allows better particle packing and reduced void fraction at a given pressure.
Higher compaction density generally benefits volumetric energy density for assembled electrodes but must be balanced against electrolyte infiltration and rate performance.

In summary, the addition of NCM materials to LMFP cathode materials can effectively improve the electron transportation capacity and compaction density of LMFP materials. However, it is worth noting that, although in this study, the improvement effect of these two parameters shows a monotonically better trend with the continuous addition of NCM, it does not mean that the more NCM materials are mixed in, the better the performance of the hybrid anode is, which also needs to comprehensively evaluate the cycle performance, multiplication performance, safety performance, and cost advantage of the hybrid anode after it is prepared into a battery, and finally determine the optimal mixing ratio X.X. Zhao et al ^[3] prepared NCM and LMFP mixtures and assembled 18650 full batteries with NCM-LMFP mixtures as cathodes, and the overall performance of the batteries was better than that of single-material NCM or LMFP batteries, including superior multiplicity performance, good cycling stability, and high and low temperature performance.

Figure 2. (a) Resistivity variation curves and (b) compaction density variation curves with pressure for six different ratios of LMFP and NCM hybrid cathode materials.

Figure 3. (a) Shows the stress-strain curves of six mixed positive electrodes with different ratios during pressurization and depressurization. (b) demonstrates the maximum deformation, irreversible deformation, and reversible deformation of the six hybrid anodes with the NCM addition ratio.

In addition, T. Liebmann et al ^[4] also conducted a systematic study on how the electrochemical properties of the components affect the behavior of hybrid electrodes for several mainstream cathode materials, i.e., olivine LFP, layered NCM, and spinel LMO. The results show that the basic electrochemical properties of the hybrid electrodes obey the physical mixture model and can be predicted accordingly based on the properties of the components with different mass fractions, including the thermodynamic properties, such as the equilibrium potential versus specific capacity curves, entropy distributions, and derived properties.

3.3 Stress–strain characteristics and rebound

Stress–strain measurements (Figure 3) reveal:

All samples show some irreversible (plastic) deformation after unloading; the thickness does not fully recover to the initial value.
The maximum, reversible and irreversible deformations follow a U-shaped dependence on composition, with the lowest overall deformation at ~40% LMFP / 60% NCM. This composition exhibited minimal thickness rebound and the smallest irreversible deformation among the tested mixes.
Pure LMFP and pure NCM display larger deformations, suggesting that a tailored blend can optimize mechanical stability during calendering and handling.

Process implication: minimizing thickness rebound is important for consistent electrode coating thickness and quality control. The 40%/60% LMFP/NCM blend showed favorable mechanical feedback for electrode manufacturing.

4. Discussion

Electrical trade-offs: Although NCM addition improves electronic conductivity of an LMFP-rich cathode, the optimal blend must also consider electrochemical cycle life, high-rate performance and cost. Excessive NCM can raise cost and potentially compromise safety benefits associated with LMFP.
Microstructure matters: Conductivity and mechanical behavior are strongly tied to particle morphology, size distribution and contact networks. Homogeneous mixing and controlled particle size engineering can further improve percolation and packing.
Process tuning: Different blends require distinct calendering pressures and drying/infiltration parameters. The stress–strain profiles from PRCD3100 help define pressure windows that minimize irreversible deformation while achieving target compaction.
Literature context: Prior studies (e.g., X.X. Zhao et al.) show that LMFP/NCM blends can improve overall full-cell performance compared with single-material cathodes when composition and processing are optimized.

5. Summary

Using PRCD3100, we characterized resistivity, compaction density and mechanical deformation of LMFP/NCM hybrid cathodes across six compositions. Principal findings:

LMFP alone shows the highest resistivity and lowest compaction density; incremental NCM addition steadily improves conductivity and packing.
A 40% LMFP / 60% NCM blend minimized deformation under pressure and exhibited the smallest irreversible thickness rebound, indicating favorable mechanical stability for electrode processing.
While hybridization clearly improves electronic transport and densification of LMFP-based cathodes, the final choice of blend must weigh electrochemical performance, safety, and cost to determine the optimal lmfp cathode composition for specific applications.

Future work should validate these powder-level findings in full-cell tests (cycle life, rate capability, thermal stability) and explore particle-size engineering or surface coating to further boost LMFP conductivity without large increases in NCM content.