An in-situ battery device for soft X-ray microscopy imaging

Abstract

The present invention relates to an in-situ battery device for soft X-ray microscopy imaging, comprising: an upper silicon nitride wafer and a lower silicon nitride wafer; one upper observation window and one lower observation window are respectively opened on the upper and lower silicon nitride wafers; one liquid injection / extraction port is opened on each side of the upper observation window; at least one groove is opened on the other two sides of the upper observation window, and at least one flow channel is etched between the liquid injection / extraction port and the groove; a liquid cell is opened on the lower silicon nitride wafer; two electrodes are fabricated on the lower silicon nitride wafer such that one end of the two electrodes is relatively placed in the liquid cell with a certain gap therebetween; the electrode region where the liquid cell overlaps with the groove is used to store bulk electrode particles, and a single layer of electrode particles is left in the remaining electrode region in the liquid cell; at least one upper through hole and one lower through hole are respectively opened at corresponding positions around the upper and lower observation windows. The in-situ battery device provided by the present invention uses a single layer of electrode particles, and there is a large distance between the electrode particles under soft X-rays, enabling accurate high-resolution soft X-ray imaging of single electrode particles.

Description

Technical Field

[0001] The invention relates to the field of synchrotron radiation CT imaging and in-situ devices, and in particular to an in-situ battery device for soft X-ray microscopic imaging. Background Art

[0002] In the field of energy materials, with the explosive growth of portable devices and electric vehicles, the need to develop a new generation of batteries with excellent performance and high safety is becoming more and more urgent. The development of such advanced batteries requires the optimization of existing materials, as well as the discovery and utilization of new battery materials with better electrochemical properties. At present, most commonly used battery materials are micron-sized particles. When characterizing them, the average information of multiple particles is obtained at the same time, and it is impossible to accurately characterize a single particle. In order to clarify the reaction and degradation mechanism of battery materials, it is important to achieve imaging of single electrode particles and conduct correlation analysis between material morphology and function.

[0003] Although ex situ imaging techniques can provide a lot of valuable information about battery materials, the test results are not necessarily completely accurate because they cannot be tested in a real reaction environment. For example, during the charge and discharge cycle, the non-equilibrium and transient processes of the reaction, that is, the intermediate phase and possible metastable phase, are difficult to observe. And because the ex situ characterization of a single particle requires disassembly of the battery, it is technically very difficult to track the same particle through repeated charge and discharge cycles. In addition, due to the high sensitivity of some electrode materials to oxygen and moisture, they may be contaminated and irreversibly changed when handling and transferring samples, and these results may mislead the understanding of the reaction and degradation mechanisms.

[0004] When performing in-situ imaging of single electrode particles and the surrounding electrolyte, electron microscopes have poor penetration (about 100nm) and will cause significant radiation damage to the material. Although hard X-rays have strong penetration, they have poor imaging contrast for light elements (such as graphite electrodes in batteries) and cannot produce high-quality imaging results. Therefore, these two imaging methods are difficult to conduct in-situ research on full batteries containing electrolytes. Soft X-ray imaging technology is a high-resolution, highly penetrating nondestructive testing technology with a penetration ability between electron microscopes and hard X-ray microscopes. It is a powerful means of characterizing micron-sized particles.

[0005] At present, the in-situ imaging technology based on soft X-rays is still in its infancy and faces great challenges in its implementation. First of all, due to the limitations of soft X-ray imaging conditions (short working distance, ultra-high vacuum, soft X-ray penetration ability, etc.), it is necessary to strictly control the width of the designed imaging chip, the particle size of the electrode particles, and the thickness of the electrolyte. However, the strict particle thickness makes the electrode thickness of the battery smaller, which greatly limits the capacity of the in-situ battery, which will have a certain impact on the electrochemical performance of the battery. How to increase the battery capacity as much as possible without increasing the thickness, and then realize the charging and discharging function of the in-situ battery under soft X-ray imaging conditions is an urgent problem to be solved. At present, only Lim et al. from Stanford University have designed an in-situ battery device for STXM (scanning transmission X-ray microscope), but the overall device structure is complex; and the processing requirements for microfluidic chips and battery devices are high, and the price is also relatively expensive. Therefore, it is necessary to design a cost-effective in-situ battery device suitable for soft X-ray imaging. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an in-situ battery device for soft X-ray microscopy imaging.

[0007] The in-situ imaging study of the battery is to image and characterize the electrode particles and the solid-liquid interface between the electrode particles and the electrolyte. Due to the limitation of the penetration ability of soft X-rays, the distance between the two imaging windows needs to be strictly controlled. The linear absorption coefficients of different materials in the system are not much different. The thickness of the electrode and the window are both in the nm level, while the thickness of the electrode particles and the electrolyte are in the μm level, which are the main factors affecting the soft X-ray penetration rate. To ensure the imaging quality, a penetration rate of 20% is the minimum requirement for imaging. Under different electrolyte thicknesses, the penetration rate of soft X-rays (taking 850eV as an example) on the graphite particles of the in-situ battery and the penetration rate of the electrolyte on the surface of the graphite particles are as follows: Figure 1A and Figure 1B As shown, it can be seen that when the electrolyte thickness is 1.8μm, the penetration rate of soft X-rays to graphite particles is 20%, and the penetration rate to the electrolyte is higher than 20%, that is, the electrolyte thickness needs to be strictly controlled to be less than 1.8μm. However, strict thickness restrictions will result in too few electrode particles, that is, the battery capacity is too small, and the battery cannot work normally. To solve this problem, the embodiments of the present invention provide the following device and method.

[0008] The technical solution of the present invention is: an in-situ battery device for soft X-ray microscopy, characterized in that it includes: an upper silicon nitride wafer 1 and a lower silicon nitride wafer 2; an upper observation window 11 and a lower observation window 21 are respectively opened on the upper silicon nitride wafer 1 and the lower silicon nitride wafer 2; a liquid extraction port 12 is opened on both sides of the upper observation window 11; at least one groove 13 is opened on the other two sides of the upper observation window 11, and at least one flow channel 14 is etched between the liquid extraction port 12 and the groove 13; a liquid pool 22 is formed by etching or using a photoresist 23 as a fence on the lower silicon nitride wafer 2, and the width of the liquid pool 22 is greater than the distance between the two liquid extraction ports 12; on the lower silicon nitride wafer 2 Two electrodes 24 are made on the top, so that one ends of the two electrodes 24 are respectively placed opposite to each other in the liquid pool 22 and separated by a certain gap, and the gap is located in the area covered by the field of vision of the upper observation window 11 and the lower observation window 21; the electrode area 25 where the liquid pool 22 overlaps with the groove 13 is used to store large blocks of electrode particles, and the remaining electrode areas in the liquid pool 22 are left with a single layer of electrode particles 26; at least one upper through hole 15 and a lower through hole 27 are respectively opened at corresponding positions around the upper observation window 11 and the lower observation window 21.

[0009] Compared with the prior art, the present invention has the following advantages:

[0010] 1. The present invention discloses an in-situ battery device for soft X-ray microscopic imaging. The imaging method has a wide applicability. For both TXM (full-field transmission imaging) and STXM (scanning transmission imaging), the electrochemical chip assembled by the chip structure and the corresponding assembly method can be used for in-situ imaging. After reducing the depth of the liquid pool, this method can also be used to make an in-situ battery device for TEM (transmission electron microscope) and SEM (scanning electron microscope) in-situ imaging.

[0011] 2. Since the thickness of the positive electrode material of lithium-ion batteries is mostly in the micron level, soft X-rays have a high imaging contrast for electrode particles with a thickness of about 1 to 2 microns. The particle placement method disclosed in the present invention can ensure that only a single layer of particles is left on the electrode, that is, the thickness of the liquid pool is controlled within 1.8 microns, and there is a large distance between the electrode particles in the window area under soft X-rays, which can achieve accurate high-resolution soft X-ray imaging of single electrode particles.

[0012] 3. The present invention has a groove outside the imaging window to increase the capacity of the battery material, which can increase the battery capacity without increasing the thickness of the liquid pool, thereby ensuring the normal charging and discharging function of the in-situ battery and realizing high-resolution soft X-ray imaging, thus solving the contradiction between insufficient battery capacity and weak soft X-ray penetration ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1AThis is a graph showing the penetration rate of soft X-rays into graphite particles of an in-situ battery in an embodiment of the present invention;

[0014] Figure 1B This is a diagram of the penetration rate of soft X-rays on the electrolyte on the surface of graphite particles of an in-situ battery in an embodiment of the present invention;

[0015] Figure 2 This is a schematic diagram of an in-situ battery device for soft X-ray microscopy imaging in an embodiment of the present invention;

[0016] Figure 3 This is a schematic diagram of the structure of the upper silicon nitride wafer in an embodiment of the present invention;

[0017] Figure 4 Schematic diagram of the structure of the lower silicon nitride wafer in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention provides an in-situ battery device for soft X-ray microscopic imaging, and the imaging method has wide applicability; a single-layer electrode particle is used, and the electrode particles have a large distance under soft X-rays, so that accurate high-resolution soft X-ray imaging of the single electrode particle can be achieved; at the same time, a groove structure is used to increase the capacity of the battery without affecting the electrolyte thickness at the imaging window, so as to solve the contradiction between insufficient battery capacity and weak soft X-ray penetration ability.

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below through specific implementations and in conjunction with the accompanying drawings.

[0020] Embodiment 1

[0021] An embodiment of the present invention provides an in-situ battery device for soft X-ray microscopy imaging, comprising:

[0022] An upper silicon nitride wafer 1 and a lower silicon nitride wafer 2; an upper observation window 11 and a lower observation window 21 are respectively opened on the upper silicon nitride wafer 1 and the lower silicon nitride wafer 2; a liquid extraction port 12 is respectively opened on both sides of the upper observation window 11; at least one groove 13 is opened on the other two sides of the upper observation window 11, and at least one flow channel 14 is etched between the liquid extraction port 12 and the groove 13; a liquid pool 22 is formed by etching or using a photoresist 23 as a fence on the lower silicon nitride wafer 2, and the width of the liquid pool 22 is greater than 2 The distance between the liquid extraction ports 12 is made; two electrodes 24 are made on the lower silicon nitride wafer 2, so that one ends of the two electrodes 24 are respectively placed in the liquid pool 22 opposite to each other and separated by a certain gap, and the gap is located in the area covered by the field of vision of the upper observation window 11 and the lower observation window 21; the electrode area 25 where the liquid pool 22 overlaps with the groove 13 is used to store large blocks of electrode particles, and a single layer of electrode particles 26 is left in the remaining electrode area in the liquid pool 22; at least one upper through hole 15 and a lower through hole 27 are respectively opened at corresponding positions around the upper observation window 11 and the lower observation window 21.

[0023] In the embodiment of the present invention, Figure 2 As shown, the in-situ battery consists of two opposite upper silicon nitride wafers 1 and lower silicon nitride wafers 2, and the size of the upper silicon nitride wafer 1 can be smaller than, larger than or equal to the size of the lower silicon nitride wafer 2. Figure 3 and Figure 4 As shown, an upper observation window 11 and a lower observation window 21 are opened at corresponding positions of the upper silicon nitride wafer 1 and the lower silicon nitride wafer 2, so that there is an overlapping portion between the lower observation window 21 and the upper observation window 11, and both the upper observation window 11 and the lower observation window 21 are made of silicon nitride film so that the soft X-ray beam can penetrate the upper observation window 11 and the lower observation window 21.

[0024] like Figure 3 As shown, a liquid extraction port 12 is provided on each side of the upper observation window 11 for adding or extracting electrolyte. At least one groove 13 is provided on the other two sides of the upper observation window 11 for covering large electrode particles to increase the overall capacity of the in-situ battery. At least one flow channel 14 is etched between the liquid extraction port 12 and the groove 13 to ensure that the groove 13 can be filled with electrolyte when the liquid is extracted.

[0025] like Figure 4As shown, a liquid pool 22 is formed on the lower silicon nitride wafer 2 by etching or photoresist 23 fence, and the liquid pool 22 is used to store electrolyte and ensure that soft X-rays have a high penetration ability for the electrolyte at this depth. The width of the liquid pool 22 is greater than the distance between the two liquid extraction ports 12 of the upper silicon nitride wafer 1, so that the electrolyte in the liquid pool 22 can be added or extracted through the liquid extraction ports 12; two electrodes 24 are made on the lower silicon nitride wafer 2, so that one end of the two electrodes 24 is respectively placed in the liquid pool 22 opposite to each other and separated by a certain gap, and the gap is located at the upper observation window 11 The area overlapping with the field of view of the lower observation window 21; the electrode area 25 in the liquid pool 22 overlapping with the groove 13 is used to store large blocks of electrode particles. After the electrode 24 area in the liquid pool 22 is printed or cleaned by the PDMS block, it is ensured that a single layer of electrode particles 26 is left in the remaining electrode area in the liquid pool 22, and the electrode particle conditions of the two electrodes 24 can be observed through the overlapping part of the upper observation window 11 and the lower observation window 21; the other ends of the two electrodes 24 extend out of the liquid pool 22 respectively; four upper through holes 15 and four lower through holes 27 are respectively opened at corresponding positions around the upper observation window 11 and the lower observation window 21. When the upper observation window 11 and the lower observation window 21 are aligned, the four upper through holes 13 and the four lower through holes 27 overlap, which are used for soft X-ray imaging to collect background images so as to achieve normalization of imaging data.

[0026] Before covering the bulk electrode particles, a photoresist fence is made in the electrode area in the liquid pool corresponding to the groove of the upper silicon nitride wafer to control the position of the bulk electrode particles and ensure that the thickness of the liquid pool will not increase due to the bulk electrode particles. After the bulk electrode particles are made, the fence is cleaned with acetone.

[0027] Before dropping a single layer of particles, a photoresist fence is made along the edge of the electrode in the liquid pool to control the electrode particles to stay only on the electrode area and control the placement of the electrode particles so that the electrode particles will not flow out of the electrode surface to prevent micro short circuits caused by contact between positive and negative electrode particles. After making a single layer of positive and negative electrode particles, the fence is cleaned with acetone.

[0028] The present invention provides an in-situ battery performance device for soft X-ray microscopy imaging, which is no longer applicable to the traditional method of transferring electrode particles only by dripping / spin coating. The reasons are: first, due to the small electrode area, it is impossible to accurately control the electrode particles to be placed on the edge of the electrode; second, the dripping / spin coating method will inevitably cause particle aggregation, which will affect the thickness of the overall liquid pool and further affect the soft X-ray penetration ability, making it impossible to achieve soft X-ray imaging research. Therefore, the present invention uses a groove structure to place a large number of particles and increase the battery capacity, and designs a photoresist structure on the electrode to control the position of the particle placement. After the particles are placed on the electrode, a PDMS (polydimethylsiloxane) block is used to gently and repeatedly imprint / clean the electrode area filled with electrode particles to remove the aggregated particles to ensure that only a single layer of particles is left.

[0029] The present invention discloses an in-situ battery device for soft X-ray microscopic imaging. The imaging method has wide applicability. For both TXM (full-field transmission imaging) and STXM (scanning transmission imaging), the electrochemical chip assembled by the chip structure and the corresponding assembly method can be used for in-situ imaging. After reducing the depth of the liquid pool, the in-situ battery device can also be manufactured by this method for in-situ imaging of TEM (transmission electron microscope) and SEM (scanning electron microscope).

[0030] Since the thickness of the positive electrode materials of lithium-ion batteries is mostly in the micron level, soft X-rays have a high imaging contrast for electrode particles with a thickness of about 1 to 2 microns. The particle placement method disclosed in the present invention can ensure that only a single layer of particles is left on the electrode, that is, the thickness of the liquid pool is controlled within 1.8 microns, and there is a large distance between the electrode particles in the window area under soft X-rays, so that accurate high-resolution soft X-ray imaging of single electrode particles can be achieved.

[0031] The present invention has a groove outside the imaging window for increasing the capacity of the battery material, which can increase the battery capacity without increasing the thickness of the liquid pool, thereby ensuring the normal charging and discharging function of the in-situ battery and realizing high-resolution soft X-ray imaging, thus solving the contradiction between insufficient battery capacity and weak soft X-ray penetration ability.

[0032] Embodiment 2

[0033] Since the addition of electrolyte in the embodiment of the present invention needs to be carried out in a glove box, and the window size is small and difficult to align, the traditional method of first dripping electrolyte and then aligning the two chips to seal is no longer applicable. In order to facilitate operation and prevent the silicon nitride wafer from moving, it is necessary to align the upper and lower silicon nitride wafers under a microscope and first use ultraviolet glue to fix the edge of the connection between the two chips, then remove the silicon nitride wafer from the microscope, and use epoxy resin to completely seal the gap between the two silicon wafers. In the glove box, drip electrolyte at the injection port, completely cover the liquid extraction port with a flat-headed syringe with a hose, and slowly pull the core rod upward. It can be seen that the droplets at the injection port slowly become smaller and stop when the droplets are about to disappear. At the liquid extraction port, pull the syringe core rod after dripping the electrolyte, and repeat dripping and pulling until the electrolyte overflows the liquid extraction port. This ensures that the entire liquid pool is filled with liquid, and avoids the observation window rupture in an ultra-high vacuum environment due to the presence of a small amount of gas inside the liquid pool after sealing.

[0034] An embodiment of the present invention provides an in-situ battery manufacturing method for a soft X-ray CT system, comprising the following steps:

[0035] Step S1: using photoresist to construct a fence in the electrode area where the liquid pool and the upper silicon nitride wafer groove overlap, the fence size is equal to or smaller than the size of the upper silicon nitride wafer groove; adding concentrated solutions containing positive and negative electrode particles respectively to the fence so that large pieces of electrode particles are present in the fence; cleaning the fence, specifically comprising:

[0036] A fence is constructed by using photoresist in the electrode area where the liquid pool and the groove of the upper silicon nitride wafer overlap, and the fence size is equal to or smaller than the groove size of the upper silicon nitride wafer; a concentrated solution containing positive and negative electrode particles at a concentration of more than 10 mg / mL is added to the fence by using a pipette gun, wherein the embodiment of the present invention uses but is not limited to isopropanol as the concentrated solution; so that large pieces of electrode particles are stored in the fence, and at the same time, the groove of the upper silicon nitride wafer can completely cover the large pieces of electrode particles of the lower silicon nitride wafer; finally, the fence is washed off with a cleaning solvent, wherein the cleaning solvent uses but is not limited to acetone;

[0037] This step can ensure that a large number of particles are covered on the electrode without increasing the thickness of the liquid pool, that is, without affecting the imaging penetration rate and quality, thereby increasing the battery capacity, which not only ensures the normal charging and discharging function of the in-situ battery, but also realizes high-resolution soft X-ray imaging, thus solving the contradiction between insufficient battery capacity and weak soft X-ray penetration ability.

[0038] Step S2: In a liquid pool, a fence is constructed at the edge of the positive and negative electrodes using photoresist, and a dilute solution containing positive and negative electrode particles is added to the electrodes so that the positive and negative electrode particles completely cover the electrodes, and the fence is washed away; under a microscope, the area where the positive and negative electrode particles are gathered except for the large electrode particles in step S1 is found and cleaned until only a dispersed single layer of positive and negative electrode particles is left, specifically including:

[0039] In a liquid pool, a fence is constructed at the edge of the positive and negative electrodes using photoresist, and a dilute solution containing positive and negative electrode particles at a concentration of 0.1 mg / mL to 1 mg / mL is dripped onto the electrodes using a pipette gun, so that the positive and negative electrode particles completely cover the electrodes, wherein the embodiment of the present invention uses but is not limited to isopropanol as the dilute solution, and the dilute solution is ultrasonically dispersed for 30 minutes before dripping; the fence is washed away, wherein the washing solvent is used but is not limited to acetone; under a reflective optical microscope, the area where the positive and negative electrode particles are gathered except for the large block electrode particles in step S1 is found, and a PDMS block is used to repeatedly and gently stamp or sweep until only a dispersed single layer of positive and negative electrode particles is left;

[0040] This step can ensure that only a single layer of particles is left on the electrode, that is, the thickness of the liquid pool is controlled within 1.8 microns, and there is a large distance between the electrode particles in the window area under soft X-rays, so that accurate high-resolution soft X-ray imaging of the single layer of electrode particles can be achieved;

[0041] Step S3: aligning the upper and lower silicon nitride wafers and sealing the gap between the upper and lower silicon nitride wafers, specifically comprising:

[0042] Align the upper and lower silicon nitride wafers under a reflective optical microscope, fix the edges with UV glue, remove them from the sample stage of the reflective optical microscope, and use epoxy resin to completely seal the gap between the upper and lower silicon nitride wafers;

[0043] Step S4: transferring the sealed upper and lower silicon nitride wafers to a glove box, dripping electrolyte at the liquid injection port, and extracting liquid at the liquid extraction port. After the liquid pool is filled with electrolyte, the liquid injection port and the liquid extraction port are sealed to prepare an in-situ battery, which specifically includes:

[0044] After standing for one hour, transfer the sealed upper and lower silicon nitride wafers to the glove box, add 1-2μL of electrolyte to the injection port, completely cover the withdrawal port with a flat-mouth syringe with a hose, and slowly pull up the core rod until the droplet is about to disappear, stop, repeat 2-3 times, and use epoxy resin to seal the injection port and withdrawal port.

[0045] After the in-situ battery is made, the electrode extending from the lower silicon nitride sheet is connected to the sample rod through a lead, and the sample rod is connected to the electrochemical workstation outside the vacuum chamber used for imaging through a vacuum wire, a flange, and the vacuum chamber. The electrochemical workstation is used to power the in-situ battery device, and a soft X-ray microscope is used to characterize the electrochemical reaction process in the liquid pool in situ.

[0046] The above embodiments are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the present invention should all be included within the scope of the present invention.

Claims

1. A method for making an in-situ battery device for soft X-ray microscopy, It is characterized in that The in-situ battery device comprises: an upper silicon nitride wafer (1) and a lower silicon nitride wafer (2); an upper observation window (11) and a lower observation window (21) are respectively provided on the upper silicon nitride wafer (1) and the lower silicon nitride wafer (2); a liquid extraction port (12) is respectively provided on both sides of the upper observation window (11); at least one groove (13) is provided on the other two sides of the upper observation window (11); at least one flow channel (14) is etched between the liquid extraction port (12) and the groove (13); a liquid pool (22) is formed on the lower silicon nitride wafer (2) by etching or using a photoresist (23) as a fence, and the width of the liquid pool (22) is greater than the width of the two liquid extraction ports (12); two electrodes (24) are fabricated on the lower silicon nitride wafer (2), so that one end of the two electrodes (24) are respectively placed in the liquid pool (22) opposite to each other and separated by a certain gap, and the gap is located in the area covered by the visual field of the upper observation window (11) and the lower observation window (21); the electrode area (25) where the liquid pool (22) overlaps with the groove (13) is used to store large blocks of electrode particles, and the remaining electrode area in the liquid pool (22) has a single layer of electrode particles (26); at least one upper through hole (15) and a lower through hole (27) are respectively opened at corresponding positions around the upper observation window (11) and the lower observation window (21); The production method comprises the following steps: Step S1: using photoresist to construct a fence in the electrode area where the liquid pool and the upper silicon nitride wafer groove overlap, the fence size is equal to or smaller than the size of the upper silicon nitride wafer groove; adding concentrated solutions containing positive and negative electrode particles respectively into the fence, so that large pieces of electrode particles are stored in the fence; washing the fence; Step S2: In a liquid pool, a fence is constructed at the edge of the positive and negative electrodes using photoresist, and a dilute solution containing positive and negative electrode particles is added to the electrodes so that the positive and negative electrode particles completely cover the electrodes, and the fence is washed away; under a microscope, the area where the positive and negative electrode particles are gathered except for the large electrode particles in step S1 is found and cleaned until only a dispersed single layer of positive and negative electrode particles is left; Step S3: aligning the upper and lower silicon nitride wafers and sealing the gap between the upper and lower silicon nitride wafers; Step S4: Transfer the sealed upper and lower silicon nitride wafers to a glove box, drip electrolyte into the liquid injection port, and draw liquid out through the liquid extraction port. After the liquid pool is filled with electrolyte, seal the liquid injection port and the liquid extraction port to prepare an in-situ battery.

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