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We, at Hitachi High-Tech, have realized an original "air protection system" for microstructure analysis of highly active lithium ion battery materials that easily react with the atmosphere. Sample processing by ion milling and SEM observations can be carried out with the bulk sample mounted on a special holder and shut off from the atmosphere. With this holder, you can process the sample into a thin film state by FIB-SEM while keeping the atmosphere shut off. In addition, STEM observations and analysis can be carried out by replacing with the air protection holder for mounting thin film samples. This system enables observation and analysis over a wide magnification range without bringing the sample into contact with the atmosphere.
Ultrahigh-Resolution Scanning Electron Microscope
This ultrahigh-resolution scanning electron microscope is indispensable for research and development of carbon materials and polymer materials used for lithium-ion rechargeable batteries. The high-brightness cold FE electron gun and detection signal control function, provide high contrast images with high resolution.
The SU8600 is equipped with an optical system automatic adjustment function and an optional function to support automation of data acquisition, which enables automatic acquisition of large volumes of data.
The automated sequential imaging of a separator was performed using the EM Flow Creator software which automatically executes the acquisition of the SEM image. 345 clear SEM images in total were able to be acquired including 5 images each in 3 hours and 36 minutes, while changing visual fields between 5,000, 30,000, and 80,000 magnifications. The distribution of the fibrous fields of a separator has been able to be confirmed at a magnification of 5,000, the fibrous structure and image of the alternately aligned pores of a separator at 30,000, and the microstructure on the surface of a separator at 80,000.
Ultrahigh-Resolution Schottky Scanning Electron Microscope
This ultrahigh-resolution scanning electron microscope is indispensable for research and development of carbon materials and polymer materials used for lithium-ion rechargeable batteries. The standardly equipped Schottky FE electron gun responds to an extensive range of analytical methods from the observation of ultra-low accelerating voltages to high-speed analysis which requires a high irradiation current.
The SU8700 is equipped with an optical system automatic adjustment function and an optional function to support automation of data acquisition, which enables automatic acquisition of large volumes of data.
Below are SEM images of LIB positive electrode material observed at an irradiation voltage of 10 V. In (a), the active material, conductive assistant, and the binder can be identified clearly by the shape and contrast. In (b) which is an observation of the magnified area enclosed in red in (a), the condition where the conductive assistant and active material are bonded via a binder, and the residual substance of the binder thinly adhered to the surface of the active material can be confirmed in detail. In the SU8700 which uses an electrostatic/electromagnetic field superposed objective lens, the outermost surface can also be observed easily by such ultra-low acceleration.
〈Surface analysis〉 Atomic force microscopes (AFM)
AFM5300E is an atomic force microscope that can scan a sample surface with a small probe, and observe three-dimensional shapes with high resolution. In addition to its shape, it is possible to map differences in mechanical properties such as viscoelasticity and absorptivity of the sample, and electromagnetic properties such as surface potential and conductivity.
This is an image obtained by superimposing an SSRM (scanning spread resistance microscope) image on an AFM image of the cathode surface of a lithium-ion battery measured by SIS (sampling intelligent scan). The AFM and SSRM images clearly show that the low-resistance conductive agent is surrounding the active materials such as the ternary active material Li (Ni-Mn-Co) O2.
Ion milling system
ArBlade 5000 is Hitachi High-Tech's most advanced model equipped with a hybrid ion milling function that supports cross-sectional milling and flat milling. This model is equipped with various functions for sample preparation required for evaluation of cathode and anode materials of lithium-ion batteries. The air protection cross-sectional milling holder was developed for lithium-ion battery materials whose shape changes significantly when they react with oxygen and moisture in the atmosphere. SEM observation can be carried out after ion milling without sample exposed to air. A cooling temperature control unit (optional) is provided for reducing damages by ion beam irradiation.
SEM image of anode material of lithium-ion battery with atmosphere shut-off (a), and SEM image after exposing a sample to the atmosphere for about 10 minutes (b). In (a), the layer structure of graphite is clearly confirmed, but in (b), precipitates are formed throughout the cross section of the anode material due to contact with moisture and oxygen in the atmosphere, and the effectiveness of the air protection milling holder can be confirmed.
The surface that was smoothed by performing ion milling cross-sectional and plane processing on the lithium-ion battery cathode electrode material was observed in a vacuum using a scanning spreading resistance microscope (SSRM). The figure is an image in which the color of the electrical resistance distribution given by SSRM is superimposed on the 3D image given by AFM. The surface shape and properties can be seen clearly.
Correlation analysis using SEM and AFM
Hitachi High-Tech's unique technology "SÆMic." enables correlation analysis using SEM and AFM. At the same observation point, it is possible to simultaneously analyze and evaluate the shape, composition, and elemental analysis, etc. by SEM (scanning electron microscope), 3D shape measurement by AFM (atomic force microscope), mechanical information, and electromagnetic property information. In addition, SÆMic. uses an air protection holder that completely shuts off the atmosphere, meaning that it can quickly analyze lithium-ion battery electrodes that are degraded by moisture or oxygen in the atmosphere.
This is a measurement example in which cross-sectional fabrication and plane finishing are performed using an atmosphere shut-off holder, and observation and evaluation are performed using SEM and AFM. When exposed to the atmosphere, the surface undergoes a chemical reaction and changes in quality due to the effects of moisture and oxygen in the atmosphere. Under the condition with atmosphere shut-off, there is no such effect, and clear SEM contrast and electric resistance distribution given by SSRM are obtained.
Focused ion and electron beam system
The Ethos NX5000 is a high-performance FIB-SEM composite system equipped with a world-class high-intensity cold-cathode field emission electron gun and a newly developed magnetic/electrostatic compound objective lens. The system incorporates in a single specimen chamber an FIB column for specimen processing and an SEM column for high-magnification observation to enable high-resolution analysis of fine structure and composition at specific locations on a specimen surface and inside the specimen.
Real-time 3D analytical FIB-SEM
NX9000 has unique orthogonal layout of SEM and FIB column for ideal 3D imaging and analysis. Due to this layout, it enables repeating sample milling and capturing images precisely. It delivers 3D fine structure of specimen in addition to 3D distribution of particles of electrode.
Typical extracted sample size is 10 μm (horizontal) × 3 μm (thickness) × 10 μm (height). All the process is carried out inside high vacuum specimen chamber with monitoring both SEM and FIB.
Air protection holder equips cylinder which slides to the end of holder tip in order to isolate specimen from outside. It maintains specimen under inert gas atmosphere or vacuum. In addition, LN2 cooled holder is also available. This reduces thermal damage during sample preparation.
Field emission transmission electron microscope
HF5000 is embodiment of Hitachi's art of skill through the development of TEM. STEM spatial resolution of 0.078 nm, high-angle sample tilt, and large solid angle EDS (energy dispersive X-ray analyzer) are realized in a single pole piece. Hitachi High-Tech offers sub-Å-level spatial resolution and high analytical capability with variety of observations and analysis technique for a wide range of users, including those in the field of development and manufacturing of lithium-ion batteries.
This is an ADF-STEM image and ABF-STEM image of LiCoO2 (LCO). Although the Co atomic column is clearly observed as bright contrast in the ADF-STEM image, the Li atom which is the light element cannot be observed. On the other hand, in the annular bright field (ABF) - STEM image which detects the electrons scattered at a low angle by an annular type detector, the Li atoms can also be observed with sufficient contrast, which indicates its effectiveness as a method to directly observe Li atoms in LCO crystals.