Applications of advanced metrology for understanding the effects of drying temperature in the lithium-ion battery electrode manufacturing process

The performance of lithium-ion batteries is determined by the architecture and properties of electrodes formed during manufacturing, particularly in the drying process when solvent is removed and the electrode structure is formed. Temperature is one of the most dominant parameters that in ﬂ uences the process, and therefore a comparison of temperature e ﬀ ects on both NMC622-based cathodes (PVDF-based binder) and graphite-based anodes (water-based binder) dried at RT, 60, 80, 100 and 120 (cid:1) C has been undertaken. X-ray computed tomography showed that NMC622 particles concentrated at the surface of the cathode coating except when dried at 60 (cid:1) C. However, anodes showed similar graphite distributions at all temperatures. The discharge capacities for the cathodes dried at 60, 80, 100 and 120 (cid:1) C displayed the following trend: 60 (cid:1) C < 80 (cid:1) C < 100 (cid:1) C < 120 (cid:1) C as C-rate was increased which was consistent with the trends found in adhesion testing between 60 and 120 (cid:1) C. Focused-ion beam scanning electrode microscopy and energy-dispersive X-ray spectroscopy suggested that the F-rich binder distribution was largely insensitive to temperature for cathodes. In contrast, conductivity enhancing ﬁ ne carbon agglomerated on the upper surface of the active NMC particles in the cathode as temperature increased. The cathode dried at RT had the highest adhesion force of 0.015 N mm (cid:3) 1 and the best electrochemical rate performance. Conversely, drying temperature had no signi ﬁ cant e ﬀ ect on the electrochemical performance of the anode, which was consistent with only a relatively small change in the adhesion, related to the use of lower adhesion water-based binders. adhesion the graphite


Introduction
Lithium-ion batteries (LIBs) have been widely applied in portable electronic devices and state-of-the-art electric vehicles due to their high energy and power density. 1 To maintain consistency within cell electrodes, a homogeneous and defectfree electrode coating is required to enable uniform current densities and to facilitate lithium-ion transport between electrodes, reducing degradation and failures rates. 2 The porous electrode structure, and physical, mechanical and electrochemical properties of the electrode coatings are extremely important in maintaining good consistency in LIBs. The electrode physico-chemical properties are controlled by the mixing, coating and, most importantly, the drying and subsequent calendering processes, which in turn relate to the various parameters/variables during the drying process (DP). [3][4][5] The three-stage drying mechanism is illustrated in Fig. 1.
Temperature is known to play an important role in the DP as a key parameter that inuences drying rate. For example, high temperatures lead to binder migration (typically to the upper free surface), reducing the adhesive strength between the coating layer and the current collector (CC). This can result in the delamination of the coating from the CC, electrode shrinkage and coating component segregation; 7-10 which in turn increases the internal resistance of the electrode through poor adhesion and cohesion properties 7,11 and decreases cell capacity. 12 Recent modelling work by Lombardo et al. 13 applied a physics-based three-dimensional model to mimic additive migration during drying; this simulated the effect of drying rate on the nal electrode mesostructure and the dynamics of additive migration. Tsotsas and Mujumdar 14 described different types of modelling: continuum-level models based on volumeaveraging, pore-network models, continuous thermomechanical models and computational uid dynamics. Defraeye et al. 15 considered convective heat and mass transfer modelling at airporous material interfaces. Iqbal et al. 16 used a coupled electrochemical-mechanical and cohesive-zone nite-element model to study mechanical failure at the interface between graphite particles and polyvinylidene uoride (PVDF) binder in LIBs. Tirumkudulu et al. 17 and Yow et al. 18,19 studied the critical stress of cracking in drying latex lms.
Although modelling studies have led to new insights into electrode DP, experimental investigations are required for denitive analysis and to validate such models. Zhang et al. 2 recently reviewed the most up-to-date metrologies which have been applied, or have the potential to be applied, to study the DP of LIBs. For example, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (SEM-EDS) has become a powerful technique to investigate the binder migration behaviour of LIB electrodes occurring during the DP. Jaiser et al. 20 not only investigated microstructure formation in LIB electrodes during drying, but also component gradients for anode coating cross-sections at different stages of drying using EDS under cryogenic conditions. The liquid phase binder and solvent diffusion were both implicated in the binder gradients of dried electrodes by "dragging" the binder to the surface with capillary forces. 20 Westphal et al. 3 used SEM-EDS to detect uorine concentration to indicate binder distribution inside an electrode coating. EDS was used to map the uorine distribution through the electrode coating layer, showing that the binder was more concentrated at the top layer of the electrode coating. The binder distribution was also investigated within an electrode made with water-based binders, such as styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC). Sodium is the typical element in CMC which is used to map these binder distributions by EDS. 21,22 To investigate the porosity and pore size distribution (PSD) of the electrode microstructures futher, multi-scale X-ray computed tomography (CT) has been applied to characterize the electrodes. [23][24][25][26][27][28] Westhoff et al. created a framework for stochastic 3D modelling of the microstructure of electrodes and the structures were validated by 3D tomography. 23 Danner et al. 24 employed synchrotron X-ray tomography to create 3D microstructure models of electrodes for battery performance. Ebner et al. 28 used synchrotron X-ray tomographic microscopy to statistically characterize the microstructure of transition metal oxide-based electrodes. The authors introduced their segmentation algorithm to be able to identify each of the particles and evaluate the PSD; the calculated PSD was consistent with the PSD obtained by experimental work by laser diffraction. Rahe et al. 26 used nanoscale X-ray CT to investigate the structural change in aged automotive LIB cells; the CT images showed the morphology of the electrodes in terms of their internal porous structure. The porosity of aged anodes was reduced due to organic residues and depositions that were quantied and visualized by CT imaging and analysis. Mapping the 3D microstructure of electrodes, rather than 2D crosssections only, is recognized as increasingly important for understanding any structural heterogeneity and its corresponding effects on battery performance. X-ray CT has also been applied in situ to determine microstructure evolution during battery degradation. 4,[29][30][31] Overall, the drying of wet electrode lms is complex and known to critically inuence nal physico-chemical performance, but the drying dynamics are poorly understood. To better manipulate electrode structure and properties in the DP, it is useful to correlate and/or integrate multiple drying analysis methodologies to understand better the effect of each parameter. In this paper we undertake a comprehensive study of the effect of temperature on the drying of LIB electrodes (both NMC622-based cathodes with PVDF-based binder and graphitebased anodes with water-based binder, which are both commonly used in LIBs). The investigation involves several advanced characterization methods, including X-ray CT for analysing electrode active material (AM) distributions; adhesion testing of the electrode coating on CC using the axial capability of a rheometer; a focused-ion beam/scanning electrode microscopy with energy-dispersive X-ray spectroscopy (FIB-SEM-EDS) to study binder distribution in electrodes; and electrochemical analysis of electrodes dried at different temperatures. The ndings provide a deeper understanding of the temperature effects during the DP of LIB electrodes, which will hopefully benet and shorten process optimization for LIB manufacturing.

Materials
The recipes for both cathodes and anodes in this work are industrially relevant formulations. 32 The cathode slurry consisted of 96 wt% LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622, BASF), 2 wt% PVDF (Solvay) and 2 wt% C 65 (Imerys). The anode slurry consisted of 95.25 wt% articial graphite (S360 E3 Articial Graphite, BTR), 1.5 wt% CMC (BVH8, Ashland), 2.25 wt% SBR (BM451-B, Zeon), and 1 wt% C 45 (Imerys). All powders were dried at 120 C in a vacuum oven over 12 h to remove moisture. Details of the procedure for making the electrode slurries and coatings have been reported previously. 32 A THINKY mixer (ARE-20, Intertronics) was used to mix the cathode binder solution (PVDF and N-methyl pyrrolidone, NMP) at 2000 rpm for 15 min until the solution became homogenous. Then, NMC622 and C 65 were added slowly to the binder solution to form a slurry with a solid content $60 wt%. The slurry was then mixed again at 2000 rpm for two periods of 15 min, 5 min apart, to cool down the slurry. The homogenous slurry was degassed in the THINKY mixer at a speed of 2000 rpm for 2 min. To prepare the anode slurry, CMC was rstly pre-dissolved in water to make a 1.5% solution. The weighed graphite, C 45 , the 1.5% CMC solution and SBR were added into a THINKY pot to form a slurry with 44 wt% solid content. The mixing procedure was the same as that used for the cathode slurry preparation. The cathode slurry was then coated onto a piece of aluminium foil with thickness $16 mm (PI-KEM) using a doctor blade thin-lm applicator (calibrated with a metal shim), resulting in a wet electrode of $280 mm thickness. The anode slurry was coated on a copper foil with thickness $9 mm (Phi-Chem) using a similar procedure, resulting in $300 mm thick slurry coating. The slurry cast coatings were subsequently dried on a pre-heated hotplate (Nickel-Electro Clion HP1-2D) with digital control and an aluminium plate (457w Â 305d mm) at room temperature (RT), 60, 80, 100 and 120 C. The drying process was conducted inside of a fumehood with temperature and moisture control.

X-ray computed tomography
An A Series/Compact Laser Micromachining System (Oxford Lasers, Oxford, UK) with an embedded Class 4, 532 nm wavelength laser was used to prepare samples for X-ray CT characterization. All cathodes were cut into 2 mm discs and anodes were cut into 500 mm discs. All X-ray CT imaging was performed using a Zeiss Xradia 520 Versa (Carl Zeiss Microscopy Inc., Pleasanton, US) micro-CT instrument. X-ray CT scans were carried out with an X-ray source tube voltage of 60 kV with an exposure time of 15 s per projection image for cathodes and 60 s for anodes. A total of 901 projection images were collected per scan with a 20Â lens for cathodes and 1201 projections were collected for anodes. Reconstruction of the radiographic data was achieved using a cone-beam ltered back-projection algorithm implemented in Zeiss Scout and Scan soware resulting in a reconstructed voxel size of $0.33 mm. Post-processing of the reconstructed CT data was conducted using Avizo 9.4 (Thermo Fisher Scientic, UK) and ilastik (machine-learning-based, open-source segmentation soware 33 ) for evaluation of AM particle distributions.

Adhesion testing
Adhesion testing was performed using a Netzsch Kinexus Pro+ Rheometer following a 180-degree peel method devised inhouse. A 25 mm-wide piece of double-sided tape was attached to a section of coating, and the free end of the coating and the tape attached to the upper and lower rheometer geometry, respectively. These were driven apart at 10 mm s À1 to enact a 180-degree peel (fully removing the coating from the substrate) with axial force measurement from the rheometer. The force was recorded in a region where the axial force measurement was stable and peeling was visually consistent. 34 This was repeated on six samples for each coating to take an average and normalized by the width of the tape to give the force per unit length required to peel the coating from the substrate.

Focused-ion beam/scanning electrode microscopy with energy-dispersive X-ray spectroscopy
The equipment used for microscopic observation, crosssectioning, and elemental mapping was a Thermo Scientic™ Helios™ G4 PFIB CXe DualBeam™ FIB/SEM combined with EDS (Oxford EDS, Ultim max 170 SDD detector). The electrodes were dried at various temperatures and then glued onto sample holders with Acheson silver dag (Agar Scientic, UK). A 5 mmthick Pt layer was deposited on the area of interest. The primary beam was a Xe + plasma source at 30 keV, incident on the surface of the electrode and operated with a range of currents from 15 nA to 0.2 mA for sectioning and milling with reduced beam damage. For elemental mapping of the fabricated cross-sections, EDS was used. An electron beam was perpendicular to the cross-section for imaging and for exciting the characteristic X-rays of the elements in the area of interest. All the secondary electron images and EDS maps were collected at 10 kV, 1.6 nA. Aztec soware (Oxford Instruments, AZtec 4.1 SP1) was used to analyze the mapping results.

Electrochemical performance test
The electrodes were cut into 15 mm discs for coin cells. A Celgard separator was cut into 19 mm discs to avoid short circuits. All the coin cell components, namely the cut electrodes, separators, and other coin cell parts (spacer thickness was 1 mm) were dried overnight in a vacuum oven at 80 C to remove any moisture before assembly. 70 mL of electrolyte (Solvionic, 1 mol L À1 lithium hexauorophosphate in (1 : 1 vol%) ethylene carbonate : dimethyl carbonate with 2 wt% vinylene carbonate -99.9%) was lled in each of cell. Aer the assembly of the coin cells, a formation step composed of two CC-CV chargedischarge cycles at a C-rate of C/20 (C/50 cut-off) was conducted within a voltage window of 2.5 to 4.2 V vs. Li/Li + for cathode halfcells and 0 to 2.5 V vs. Li/Li + for anode half-cells, where the half cells contained a lithium metal counter electrode. Electrochemical testing was carried out using a BCS-805 Biologic battery cycler (Biologic, France). The cells were then charged at a constant current C/10 and corresponding to discharged Crates of C/10, C/5, C/3, C, 2C and 3C.

Results and discussion
3.1 Effects of drying temperature on active material particle distribution within electrodes Reconstructed 2D orthoslices and 3D volume renderings of the cathodes dried at RT, 60, 80, 100 and 120 C are shown in Fig. 2. The NMC622 particles are clearly visible in Fig. 2(a), (c), (e), (g) and (i), where NMC 622 particles appear as round, light grey shapes, and the pores and binder occupy the gaps between particles. A cubic volume rendering, with 200 mm dimensions, of the segmented AM particles for each cathode sample is shown in Fig. 2(b), (d), (f), and (h), illustrating the internal structure of the cathode coatings. Fig. 2(h) is a bespoke 3D printed holder for rapid, multiple-recipe X-ray micro-CT imaging with Versa CT as used in a previous study. 35 The Xray attenuation coefficient is much greater for the NMC622 particles than either the pore or the carbon binder domain (CBD) and thus the particles can be clearly identied according to their higher grayscale values, allowing for ready segmentation and further AM distribution analysis. It should be noted that it has been reported that the application of X-ray CT for characterizing LIB electrodes (at this length scale) comes with limitations for identifying the CBD, in which the pore and CBD of the electrode are observed as a single phase. 36,37 Therefore, this work uses X-ray CT as a powerful tool to analyse only the AM distribution through the coating layer.
Areal fraction plots as a function of distance from the CC to the surface of the coating illustrating through-plane inhomogeneity for cathodes dried at different temperatures are shown in Fig. 3(a), (c), (e), (g) and (i). Each electrode was scanned three times for three different samples to improve the statistical robustness of the results, displaying similar AM distributions across the repeated scans. Corresponding volume renderings of the segmented electrode active particles dried at different temperatures are shown in Fig. 3(b), (d), (f), (h) and (j). The different colours of the round particles indicate the size of the particles. The particle size distribution is dominated by the NMC622 particles which will not be affected by the drying process. The average areal fractions of AM as a function of distance from the CC for cathodes dried at different temperatures are also plotted, as shown in Fig. 3(k). In Fig. 3(a), (c), (e), (g) and (i), the results show the different behavior of AM distributions for cathodes dried at different temperatures. For all samples except 60 C, more NMC622 particles accumulated at the coating surface, as shown in Fig. 3(a), (e), (g) and (i). However, in Fig. 3(a), (c) and (e), there is an accumulation of NMC622 particle fractions near the CC for cathodes dried at RT, 60 and 80 C. Conversely, in Fig. 3(g) and (i), there is a relatively even NMC622 particle distribution near the CC for cathode dried at 100 and 120 C.
Reconstructed 2D orthoslices and 3D volume renderings of the anodes dried at RT, 60, 80, 100 and 120 C are shown in Fig. 4(a), (c), (e), (g) and (i). The graphite particles are clearly visible, where their irregular shape is light grey, and the pores and binder occupy the gaps between graphite particles. Cubic volume renderings of each anode are shown in Fig. 4(b), (d), (f), (h) and (j), illustrating the 3D structure of the anode coatings. As with the cathodes, the graphite particles (AM) were readily segmented versus the background due to higher X-ray attenuation versus pore space and CBD.
As with the triplicate results for cathodes shown in Fig. 3, the AM distribution derived from X-ray CT scans of the cathodes showed high repeatability. The areal fraction of anode AM (graphite) as a function of distance from the CC for anodes dried at different temperatures is plotted in Fig. 4(k). The results show similar behavior for graphite distributions for anode dried at RT, 60, 80, 100 and 120 C, with no signicant difference in AM distributions as a function of temperature. The graphite distribution apparently undulates slightly through the coating, which may due to be the irregular shape of the graphite particles. The results correlate with the electrochemical performance of the anode half-cells, as shown in Fig. 8, with no signicant change in capacity. This nding is supported by Li and Wang 38 who investigated binder concentration distributions in dried water-based and organic-based (PVDF-based) binder LiCoO 2 electrode sheets and the physical, electrical and electrochemical properties of the electrodes. They showed the organic-based binder electrode had a non-uniform distribution of the electrode components, with greater heterogeneity than water-based binder electrode, which may arise because the 'time-for-segregation' for the anode is shorter than cathode drying. 38 The anodes in this work were prepared with a waterbased binder and the cathode was prepared with organicbased binder using NMP as the solvent. NMP has a much higher boiling point (202 C) than water such that it takes a longer time to be fully removed by evaporation. Consequently, the reduced drying time for anodes leads to a reduced time-forsegregation, thus providing an even distribution of graphite at all investigated temperatures.

Effects of drying temperature on adhesion force and binder distribution of the electrode
Adhesion testing for both cathodes and anodes dried at RT, 60, 80, 100 and 120 C was performed using a Netzsch Kinexus Pro+ rheometer following a 180-degree peel method devised inhouse. The electrode dried at each temperature was tested six times to probe the repeatability of the experiments. Adhesion forces for each sample, average adhesion force for each electrode, standard deviation of adhesion force for each electrode, average adhesion force per millimeter and standard deviation of adhesion force per millimeter are shown in Table S1 in the ESI. † A plot of the average adhesion force per millimeter for cathodes dried at different temperatures is shown in Fig. 5(a), and for anodes in Fig. 5(b). For cathodes, there is no signicant difference in the adhesion force for those dried from 60 to 120 C, which is further supported by uorine mapping by FIB-SEM-EDS in Fig. 6(k)-(o). FIB-SEM micrographs of cathodes dried at RT, 60, 80, 100 and 120 C are presented in Fig. 6 (a) RT, (b) 60, (c) 80, (d) 100 and (e) 120 C, respectively. The EDS mapping of uorine distributions from CC toward the surface of coatings for cathodes dried at different temperatures are shown in Fig. 6 (k) RT, (l) 60, (m) 80, (n) 100 and (o) 120 C, respectively. The results show no signicant differences in uorine distribution for cathodes dried at different temperatures, implying that all cathodes have a near-homogeneous distribution of binder. Although there is no obvious difference in uorine distribution, the EDS mapping of carbon distributions for cathodes dried at different temperatures was performed in a different way. These maps are shown in Fig. 6 (f) RT, (g) 60, (h) 80, (i) 100 and (j) 120 C, which show there is a qualitative impression that the carbon (yellow squares) accumulates more towards the top of the NMC622 particles as the temperature increases, correspondingly there is a tendency for less carbon on the underside of the NMC622 particles (blue squares), although further investigation and a more quantitative approach is required to conrm this impression. Westphal et al., 7 who also investigated the inuence of temperature on electrode component segregation, similarly found higher drying temperatures led to greater segregation of inactive materials. Recalling that RT gave the highest adhesion force per millimetre in cathodes, as shown in Fig. 5(a), these effects combine such that in the C-rate discharge capacity tests (Fig. 7), the cathode dried at RT has the highest specic capacity.
The anodes dried at 80 and 100 C gave only slightly higher adhesion force per millimeter compared with anodes dried at other temperatures. This is again consistent with Westphal et al., 3 who reported that adhesion strength is independent of mass loading at a relatively low temperature ($80 C) as the driving force for solvent evaporation is small. However, high temperatures have been reported to potentially lead to greater binder migration (as seen for the NMC cathodes earlier), which can cause anode delamination and result in high resistance. 7-10 Electrode adhesion is strongly dependent upon the drying temperature and higher temperatures result in lower adhesion strength between the copper CC and the coating layer. 7,8,39 However, the thickness of the coatings also needs to be considered, and in the case of graphite, [13] the adhesion strength can also decrease as the drying temperature increases from 80 to 110 C with mass loadings up to 8.1 g cm À2 . In these cases, the temperature played a minor role in electrode adhesion, which was more sensitive to thickness and mass loading. The adhesion results are consistent with the EDS mapping of elemental sodium across the electrode cross-sections, as shown in Fig. 6(u)-(y), which are proxy elements for the binder. Sodium is distributed comparatively evenly across the anodes, regardless of drying temperature. This may be explained by a shorter time-to-xation, which is indicative of faster polymer entanglement, and subsequently, there is less time for binder segregation. It cannot be ignored that the binder concentration in anodes is very low which leads to less concentrated sodium maps, possibly requiring further investigation. Although higher temperatures will cause faster convection currents towards the surface as solvent is removed, the polymer matrix will also become more rapidly entangled as solvent is lost, resisting this motion, and the two competing effects approximately cancel.
Comparing the adhesion forces for both cathodes and anodes, it is obvious that the adhesion forces in cathodes are much higher than in anodes; for example, the average adhesion forces per millimetre for cathodes and anodes dried at 80 C are 0.0034 and 0.0024 N mm À1 , respectively. This nding is consistent with the literature that states that organic-based binders provide higher adhesion force than water-based binders. 32,38 The inferior wetting of aqueous slurries on the CC leads to higher surface tension and lower adhesion strength, potentially reducing the cycle life of the cell. [40][41][42] Moreover,  electrodes made from water-based solvents can lead to more cracking without optimum drying protocols. [42][43][44][45] 3.3 Effects of drying temperature on the electrochemical performance of electrodes Electrochemical properties were tested in coin cells with different C-rates of C/10, C/5, C/3, C, 2C and 3C at discharge state, and specic capacity plots for cathodes and anodes are shown in Fig. 7 and 8, respectively. Charge and discharge parameters are shown in Tables S3 and S4 in the ESI. † As expected, the specic capacity of the electrodes (cathodes and anodes) is highest at the lowest C-rate of C/10 for both cathodes and anodes, regardless of drying temperature. Comparing the specic capacity for electrodes dried at different temperatures, the cathodes dried at RT have the highest specic capacity at all C-rates. Conversely, drying temperature does not play a dominant role in dictating the electrochemical performance of the anodes.
In Fig. 7, and Table S3 in ESI, † the discharge performance of the cathode dried at RT has the highest specic capacity of 150.06 mA h g À1 at C/10. There are similar ndings at other Crates: cathodes dried at RT have the highest specic discharge capacities at all C-rates, compared with cathodes dried at 60, 80, 100 and 120 C. The relatively slow drying rate at RT tends to promote a more homogeneous CBD distribution, which will enhance the electrochemical performance of the electrode. The assumption is supported by the EDS mapping of carbon and uorine, as shown in Fig. 6 (f, k) RT, (g, l) 60, (h, m) 80, (i, n) 100 and (j, o) 120 C, where the uorine distribution is not signicantly affected by drying temperature. While carbon tends to accumulate more on the top of the AM particles as the temperature increases (yellow circles), this segregation is more localised in length-scale, and needs rmer quantication. While there was no signicant difference in cathode binder distribution according to EDS at the different temperatures, as shown in Fig. 6(k)-(o), adhesion is affected: the cathode dried at RT has the highest capacity and the highest adhesion of 0.015 N mm À1 . The increased adhesion is benecial both when assembling the cells (less likely to crack/delaminate and incur failure), and also less likely to delaminate during cycling causing poor cycle life.
As shown in Fig. 7, cathodes dried at RT showed consistently higher discharge capacities as a function of C-rate, and the discharge capacity for the cathode dried at 60, 80, 100 and 120 C presented a trend of 60 C < 80 C < 100 C < 120 C as Crate increases. The results are consistent with the adhesion test results (Fig. 5(a)), in that the adhesion force for cathodes dried at 60, 80, 100 and 120 C display a similar trend of 60 C < 80 C < 100 C < 120 C. As shown in Fig. 8, the specic capacity of the anodes dried at different temperatures do not display a clear trend or major difference. The results are consistent with the adhesion force test as shown in Fig. 5(b) that the adhesion forces for anodes dried at different temperatures are similar. The results are also supported by the similar distribution of AM, as plotted in Fig. 4(h), although it may be harder to identify differences in anode adhesion due to the generally much smaller values.

Conclusion
Drying temperature effects on LIB electrodes have been investigated using a variety of characterization methods, and the inter-related aspects of active materials distribution, electrode adhesion and carbon-binder distribution elucidated. The electrochemical performance of NMC622-based cathodes and graphite-based anodes dried at different temperatures ranging from RT to 120 C has also been studied. The ndings are given below: X-ray CT results show diverse behavior of AM distributions for cathodes dried at different temperatures, with active NMC622 particles tending to concentrate more at the free surface of the electrode coating as drying temperature increases. Meanwhile, NMC622 particles also concentrated near the current collector when dried at relatively low temperatures of RT, 60 or 80 C. Conversely, there is an even NMC622 particle distribution near the CC for cathode dried at 100 and 120 C. This correlates well with the electrochemical results obtained, in that at low C-rates there is not much difference, but as C-rate increases there is a trend of 60 C < 80 C < 100 C < 120 C for discharge capacity which is consistent with the trend in adhesion force between 60 to 120 C. X-ray CT shows similar graphite distributions for anodes dried at each temperature, with no signicant trend apparent in areal fraction as a function of distance from the CC.
Although there was no obvious difference in binder distribution obtained by FIB-SEM-EDS uorine mapping, the EDS mapping of carbon distributions for cathodes dried at different temperatures were performed in a different way showing that carbon accumulated more on the top of the AM particles as the temperature increased.
This work also showed that cathodes dried at RT had the highest adhesion force of 0.015 N mm À1 , and that the specic capacity for these cathodes were higher than those dried at higher temperatures for all C-rates.
Comparing the specic capacity for the electrode (cathode and anodes) at different C-rates, the results show that the specic discharge capacity was highest at the lowest C-rate of C/ 10 for both cathodes and anodes, regardless of the drying temperature.
Comparing the specic capacity for the electrode (cathodes and anodes) dried at different temperatures, the cathode dried at RT had the highest specic capacity at all C-rates.
Conversely, the anode drying temperature did not play a dominant role in determining the electrochemical performance of the anodes, such that the specic capacity of the anodes dried at different temperatures presented no clear trend. These results corresponded well with the adhesion force testing and the distribution of graphite particles.