Medium-energy in-situ X-ray absorption spectroscopy test system and test method

Abstract

The invention discloses a moderate-energy in-situ X-ray absorption spectroscopy test system and a test method. The system comprises a vacuum cavity which is internally provided with a double crystal monochromator, a front ionization chamber, a sample cavity and a detector; wherein the sample cavity is used for placing a sample to be detected; the computer unit is used for sending an instruction to the QXAFS electronic control double-optical-flat monochromator to continuously rotate, continuously outputting synchrotron radiation light incident on the double-optical-flat monochromator into the sample cavity, and exciting a sample to generate a fluorescence signal and Auger electrons; the front ionization chamber is used for collecting X-rays and sending the X-rays to the current amplifier; the current amplifier amplifies the incident light intensity signal I0 and inputs the amplified incident light intensity signal I0 to the low-pass filter; the detector collects fluorescence signals and sends the fluorescence signals to the weak galvanometer; the weak galvanometer collects Auger electrons to obtain a full-electron yield signal It and a fluorescence yield signal If of the sample and sends the signals to the low-pass filter; the low-pass filter carries out high-frequency noise filtering on the input signal and then inputs the input signal into electronics to form an X-ray absorption spectrum of a sample.

Description

Technical Field

[0001] The invention belongs to the technical field of spectroscopy and relates to a medium-energy in-situ X-ray absorption spectroscopy test system and a test method. Background Art

[0002] With the rapid growth of global energy consumption, how to efficiently utilize renewable resources has become a global hot issue. High-performance and low-cost rechargeable batteries are one of the important ways to solve this problem. Government departments in many countries have formulated research plans to increase the energy density of rechargeable batteries (or secondary batteries) to 350-500W·h / kg. However, filling more active energy storage materials in the limited battery space and further reducing the proportion of inactive materials has reached a bottleneck from a technical perspective. In order to achieve this goal, it is necessary to rely on the development of a new generation of battery systems with high energy density. Among many battery systems, lithium-sulfur batteries are one of the key technical routes to achieve a battery cell energy density of 500W·h / kg. It uses elemental sulfur (1675mA·h / g) and metallic lithium (3860mA·h / g) as positive and negative electrode materials, respectively. These two electrode materials are the positive and negative electrode materials with the highest unit mass capacity, respectively, and are the key to achieving high energy density batteries.

[0003] When the lithium-sulfur battery is discharged, the elemental sulfur (S8) in the positive electrode is gradually reduced to form lithium polysulfide (Li2S n , 4≤n≤8), lithium sulfide (Li2S); during the charging process, the lithium sulfide needs to be completely oxidized into sulfur to complete an electrochemical cycle. Each S8 molecule can transfer 16 electrons when it is reduced to lithium sulfide. This is a multi-electron redox reaction and is the core of lithium-sulfur batteries to achieve high energy density. However, there are many factors that hinder the electrochemical reaction of sulfur, resulting in the comprehensive performance of lithium-sulfur batteries being far from expectations. Among them, the difficulty of electrochemical conversion between sulfur and lithium sulfide and lithium polysulfide is the key to limiting the energy density, power density and cycle stability / life of the battery, and the electrocatalytic conversion mechanism between them is still unclear and controversial.

[0004] In-situ X-ray absorption spectroscopy (XAS) measurement changes the sample environment through external equipment and dynamically tests the sample, thereby revealing the dynamic structural evolution of the sample and then correlating it with the sample performance. This places certain requirements on the time resolution of the XAS acquisition method, which needs to correspond to the time of sample change. Conventional XAS measurement is completed by waiting for the electronic acquisition signal every time the double crystal monochromator (DCM) rotates an angle, and then continues to rotate to the next angle. The acquisition time of a single spectrum generally takes about twelve minutes. At this time scale, this measurement method cannot capture the continuous changes of the sample in a short period of time during the in-situ process, and due to changes in the properties of the sample, the measured XAS spectrum will be inaccurate.

[0005] In-situ measurement technology with element and time resolution is a necessary means to overcome the above difficulties and reveal the electrocatalytic reaction process of sulfur. At present, the time-resolved XAS method is widely used in the hard X-ray energy region, but for the medium energy region where sulfur is located, there are few related test methods. Therefore, it is very important to develop corresponding time-resolved XAS, such as fast scanning X-ray absorption spectroscopy (QXAFS), to characterize systems such as lithium-sulfur batteries. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a medium-energy in-situ X-ray absorption spectroscopy testing system and testing method.

[0007] In the in-situ XAS test, since medium-energy X-rays are easily affected by air scattering, the sample to be tested needs to be placed in a vacuum chamber, and the vacuum environment or pure helium environment test is selected as appropriate. Then, the external equipment is connected to the sample through the wire connected to the outside in the vacuum chamber to monitor and apply in-situ conditions. Since the system is independent of the sample environment in the vacuum chamber, this method is not limited to in-situ tests related to lithium-sulfur batteries, but can be extended to various in-situ characterizations of elements in the medium-energy region.

[0008] The technical solution of the present invention is:

[0009] A medium energy in-situ X-ray absorption spectroscopy test system, characterized in that it comprises a computer unit, QXAFS electronics, a driver, a current amplifier, a low-pass filter, a weak current meter and a vacuum chamber, wherein the vacuum chamber is provided with a double flat crystal monochromator, a front ionization chamber, a sample chamber and a detector; wherein,

[0010] The sample cavity is used to place the medium energy zone sample to be tested;

[0011] The computer unit is used to send instructions to the QXAFS electronics to control the driver to drive the double flat crystal monochromator to rotate continuously, and continuously output the synchrotron radiation incident on the double flat crystal monochromator to the sample cavity to excite the sample to generate fluorescence signals and Auger electrons;

[0012] The front ionization chamber is used to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier;

[0013] The current amplifier is used to amplify the incident light intensity signal I0 of the X-ray incident into the sample cavity and then input it into the low-pass filter;

[0014] The detector is used to collect the fluorescence signal and convert it into an electrical signal and then send it to the weak current meter;

[0015] The weak current meter is used to connect to the sample chamber to collect the Auger electrons and obtain the total electron yield signal I of the sample. t and sent to the low-pass filter, connected to the detector to obtain the fluorescence yield signal I of the sample f and sent to the low-pass filter;

[0016] The low-pass filter is used to filter the high-frequency noise of the input signal before inputting it into the QXAFS electronics;

[0017] The QXAFS electronics processes the input signal to generate XAFS under the total electron yield or XAFS under the fluorescence yield of the sample and inputs the signal into the computer unit to form the X-ray absorption spectrum of the sample.

[0018] Furthermore, the computer unit is connected to the double-flat-crystal monochromator via an encoder for monitoring the position of the double-flat-crystal monochromator.

[0019] Furthermore, the sample chamber is a metal frame, the weak current meter is connected to the metal frame through a wire, and the Auger electrons are collected to obtain the total electron yield signal I of the sample. t .

[0020] Furthermore, the detector is a silicon diode.

[0021] Furthermore, the low-pass filter is a SR640 dual-channel low-pass filter, which converts I0, I t and I f Take I0 / I t or I0 / I f The two-by-two combinations are input to the SR640 dual-channel low-pass filter to filter high-frequency noise.

[0022] A medium energy in-situ X-ray absorption spectroscopy testing method, the steps of which include:

[0023] 1) Place the medium energy zone sample to be tested into the sample chamber;

[0024] 2) The computer unit sends instructions to the QXAFS electronics control driver to drive the double-flat crystal monochromator to rotate continuously, and continuously outputs the synchrotron radiation incident on the double-flat crystal monochromator into the sample cavity to excite the sample to generate fluorescence signals and Auger electrons;

[0025] 3) using the front ionization chamber to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier;

[0026] 4) the current amplifier amplifies the incident light intensity signal I0 of the X-ray incident into the sample cavity and then inputs the amplified signal into the low-pass filter;

[0027] 5) When performing a full electron yield test, the weak current meter is connected to the sample chamber to collect the Auger electrons to obtain the full electron yield signal I of the sample. t When the fluorescence yield test is performed, the weak current meter is connected to the detector, the detector is used to collect the fluorescence signal and convert it into an electrical signal and then sent to the weak current meter to obtain the fluorescence yield signal I of the sample. f and sent to the low-pass filter;

[0028] 6) The low-pass filter filters the high-frequency noise of the input signal and then inputs it into the QXAFS electronics;

[0029] 7) The QXAFS electronics processes the input signal to generate the XAFS under the full electron yield or the XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample;

[0030] Wherein, the double flat crystal monochromator, the front ionization chamber, the sample cavity and the detector are located in a vacuum environment.

[0031] A medium energy in-situ X-ray absorption spectroscopy test system, characterized in that it comprises a computer unit, QXAFS electronics, a driver, a current amplifier, a low-pass filter, a weak current meter, an in-situ test system and a vacuum chamber, wherein the vacuum chamber is provided with a double flat crystal monochromator, a front ionization chamber, a sample chamber and a detector; wherein,

[0032] The sample cavity is used to place the medium energy zone sample to be tested; the sample cavity is filled with helium and the air is discharged to keep the air pressure in the sample cavity constant;

[0033] The computer unit is used to send instructions to the QXAFS electronics to control the driver to drive the double flat crystal monochromator to rotate continuously, and continuously output the synchrotron radiation incident on the double flat crystal monochromator to the sample cavity to excite the sample to generate fluorescence signals and Auger electrons;

[0034] The front ionization chamber is used to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier;

[0035] The current amplifier is used to amplify the incident light intensity signal I0 of the X-ray incident into the sample cavity and then input it into the low-pass filter;

[0036] The detector is used to collect the fluorescence signal and convert it into an electrical signal and then send it to the weak current meter;

[0037] The weak current meter is used to connect to the sample chamber to collect the Auger electrons and obtain the total electron yield signal I of the sample.t and sent to the low-pass filter, connected to the detector to obtain the fluorescence yield signal I of the sample f and sent to the low-pass filter;

[0038] The low-pass filter is used to filter the high-frequency noise of the input signal before inputting it into the QXAFS electronics;

[0039] The QXAFS electronics processes the input signal to generate XAFS under the full electron yield or XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample;

[0040] The in-situ testing system is connected to the sample in the sample chamber and is used to perform in-situ testing on the sample.

[0041] A medium energy in-situ X-ray absorption spectroscopy testing method, the steps of which include:

[0042] 1) placing a medium energy zone sample to be tested into a sample chamber; filling the sample chamber with helium and exhausting the air to maintain a constant pressure in the sample chamber;

[0043] 2) The computer unit sends instructions to the QXAFS electronics control driver to drive the double-flat crystal monochromator to rotate continuously, and continuously outputs the synchrotron radiation incident on the double-flat crystal monochromator into the sample cavity to excite the sample to generate fluorescence signals and Auger electrons;

[0044] 3) connecting the sample in the sample chamber with an in-situ testing system to perform in-situ testing on the sample;

[0045] 4) using the front ionization chamber to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier;

[0046] 5) The current amplifier amplifies the incident light intensity signal I0 of the X-ray incident into the sample cavity and then inputs the amplified signal into the low-pass filter;

[0047] 6) When performing a full electron yield test, the weak current meter is connected to the sample chamber to collect the Auger electrons to obtain the full electron yield signal I of the sample. t When the fluorescence yield test is performed, the weak current meter is connected to the detector, the detector is used to collect the fluorescence signal and convert it into an electrical signal and then sent to the weak current meter to obtain the fluorescence yield signal I of the sample. f and sent to the low-pass filter;

[0048] 7) The low-pass filter filters the input signal for high-frequency noise and then inputs it into the QXAFS electronics;

[0049] 8) The QXAFS electronics processes the input signal to generate the XAFS under the full electron yield or the XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample;

[0050] Wherein, the double flat crystal monochromator, the front ionization chamber, the sample cavity and the detector are located in a vacuum environment.

[0051] The advantages of the present invention are as follows:

[0052] 1. A fast scanning mode, QXAFS, has been established, which can be used together with the conventional step scanning mode of XAFS acquisition at the BSRF-4B7A medium energy experimental station. In addition to ensuring the accuracy of XAFS, the single spectrum acquisition time can be increased by two orders of magnitude, thus providing conditions for conducting in-situ experiments in the medium energy X-ray energy region;

[0053] 2. The signal currents obtained by the two detection methods, full electronic yield and fluorescence yield, are relatively weak, resulting in a long response time for the weak ammeter when the range is appropriate. To increase the response time, the range needs to be increased, which will introduce additional noise. Therefore, a method combining the high range of the ammeter with the SR640 dual-channel low-pass filter is adopted to filter out high-frequency noise while improving the system response speed, thereby significantly improving the quality of XAFS.

[0054] Different gears of the current amplifier will have two effects: one is the measurement accuracy of the ammeter. For example, if the actual signal is 50pA, it will be accurately measured at the 200pA range, but errors may occur at high ranges, i.e., 2nA or 20nA. The present invention uses the 2nA range during the test process, which can completely cover the fluorescence or Auger electron signal excited by X-rays, and it has been found through testing that it can maintain good accuracy at lower signal levels; the other is the response speed of the ammeter, which is determined by the composition of the basic amplifier circuit. Measuring smaller signals will require a longer time to stabilize the measured current. For example, the response speed of the ammeter will drop significantly at the 200pA range, resulting in distortion of the measured XAS spectrum, while the response speed of the ammeter at the 2nA range is sufficient to capture the change in current. Therefore, in the present invention, even if the sample signal is below 200pA, we did not select the 200pA range because the response speed of this range is not sufficient to capture the sample signal change. The speed of the monochromator rotation speed will not affect the size of the sample signal current, so we only need to consider the problem of the ammeter response speed. The faster the monochromator rotation speed is, the faster the ammeter response speed is required. Therefore, for the ammeter range or the amplification factor of the current amplifier, it is sufficient to be able to respond to the monochromator rotation speed in time while ensuring accurate readings. In the present invention, the 2nA range of the 6517B ammeter can accurately measure the signal size and respond to the change in the rotation speed of the monochromator. These two points determine that we choose this range in the test.

[0055] When determining the cut-off frequency of the low-pass filter, only two factors need to be considered, namely the monochromator speed and the absorption edge energy of the measured element. The lower monochromator speed and the lower absorption edge can set the filter cut-off frequency slightly lower. For example, the cut-off frequency of the sulfur element (K edge is 2472eV) used in the present invention is 5Hz, and we can obtain very good filtering effect at each monochromator speed. Of course, this frequency is not absolute, and the effect only needs to be good enough. In addition, for the higher energy element potassium (K edge is 3608eV), we measured that good filtering effect can be obtained at each speed at 15Hz. Taking potassium as an example, if the cut-off frequency is set larger, the noise cannot be filtered well. If the cut-off frequency is too small, there will be a situation where the XAS signal is also filtered out. Therefore, for a certain element, the setting of the SR640 low-pass filter cut-off frequency needs to be tested in advance.

[0056] 3. The two detection methods in the QXAFS, namely the full electron yield method and the fluorescence yield method, can be used to select the appropriate detection method for different sample contents. Generally, the full electron yield method is used when the content of the element to be measured in the sample is high, and the fluorescence yield method is used when the content is low or the sample is not suitable for measuring current. The two methods only differ in the detector, and the time resolution is exactly the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a test system diagram of the present invention.

[0058] Figure 2 It is the test effect diagram of the present invention;

[0059] (a) Comparison of fast scan XAS and step XAS at different DCM speeds in full electron yield mode,

[0060] (b) Comparison of fast scan XAS and step XAS at different DCM speeds in fluorescence yield mode.

[0061] (c) Two-dimensional diagram and projection diagram of the changes in the lithium-sulfur battery during one hour of discharge. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0063] In order to capture the changes in the X-ray absorption spectrum of elements during in-situ processes, a new method for rapid scanning of X-ray absorption spectra in the medium-energy X-ray energy region was developed. Figure 1 As shown, the present invention realizes continuous rotation of DCM by changing the movement mode of the double flat crystal monochromator, thereby greatly improving the acquisition speed of XAS. The time scale of a single spectrum can be shortened from more than ten minutes in the original step scanning mode to seconds, so that the in-situ process in a short time can be captured. The SR640 low-pass filter can filter the high-frequency noise generated by the weak current meter when measuring a large range during the acquisition process, thereby improving the quality of XAS. This method can be used for acquisition in two modes, full electron yield and fluorescence yield, according to different sample conditions. At the same time, this method is compatible with the original experimental mode of the experimental station and can be easily switched between the two.

[0064] Since this invention is a QXAFS method developed for X-rays in the medium energy range, it will be subject to some limitations in this energy range. First, the quantum yield of low-Z elements is low, which makes the sample signal excited by X-rays weak, and the detection of weak signals will inevitably be affected by the response speed of the amplifier circuit. Secondly, weak signals will be more seriously interfered by noise, and because the integration time of the fast scanning mode itself for a single energy point is very short, it will inevitably lead to a poor signal-to-noise ratio of the XAS signal. For this reason, the present invention proposes a solution, that is, selecting a suitable current amplifier gear or ammeter range, so that it has enough speed to respond to the signal obtained when the monochromator rotates at high speed while ensuring that the signal can be accurately measured, and then combining the SR640 dual-channel low-pass filter to filter high-frequency noise to obtain an XAS spectrum with a good signal-to-noise ratio.

[0065] In the present invention, the SR570 current amplifier and 6517B weak current meter we use are selected in the appropriate magnification and range. Among them, the SR570 current amplifier has a high signal intensity, a small current magnification, and a fast enough response time because the measured signal is the intensity of the incident light I0. The specific magnification level is limited by the experimental station and the absorption edge energy of the element to be measured; and the signal excited by the X-ray entering the sample, including the fluorescence signal and the Auger electron signal, is a weak signal, generally only a few hundred pA. The 6517B weak current meter used in the experimental station measures this signal within the appropriate range, but the response speed is not enough. After testing, we fixed it on the 2nA range, which can accurately measure the fluorescence or Auger electron signal while ensuring sufficient response speed. At the same time, the 2nA range will introduce high-frequency noise generated by the circuit when measuring weak signals far below the upper limit of the range (such as 100pA). At this time, the SR640 low-pass filter can be used to filter out the high-frequency noise to obtain a good XAS spectrum. The selection of the low-pass filter cutoff frequency depends on the absorption edge energy of the measured element and the rotation speed of the monochromator. Near the sulfur element, we tested and found that a cutoff frequency of 5Hz can obtain a good filtering effect. The cutoff frequency will increase with the increase of the monochromator rotation speed and the absorption edge energy. The following is a description of the acquisition process of this method.

[0066] The synchrotron radiation is drawn out by the storage ring bend iron, and then the X-rays are monochromated and optimized by optical elements such as the double-crystal monochromator. After the double-crystal monochromator sends instructions from the computer to the QXAFS electronics, the QXAFS electronics controls the driver to rotate and monitors the position of the double-crystal monochromator through the encoder. The X-rays first pass through the pre-ionization chamber, and the SR570 current amplifier obtains and records the incident light intensity signal I0, and then irradiates the sample to generate fluorescence or current signals. Among them, the current signal I t It can be directly detected by 6517B weak current meter. The ratio of this signal to the front ionization chamber signal is I t / I0 is the absorption coefficient of the total electron yield. The XAFS under the total electron yield can be obtained by plotting the X-ray energy as the horizontal axis. The fluorescence signal needs to be converted into an electrical signal by a silicon diode after the light signal of the sample is excited by X-rays and then detected by a 6517B weak current meter. The fluorescence signal I f The ratio of the signal from the front ionization chamber to the f / I0 is the absorption coefficient of fluorescence yield. By plotting the X-ray energy as the horizontal axis, we can obtain the XAFS under fluorescence yield.

[0067] The current signals I0 and I t and I f The high-frequency noise needs to be filtered out by the SR640 low-pass filter to improve the signal quality before entering the QXAFS electronics system, which is responsible for regulating the continuous rotation of the monochromator and inputting the processed signal into the computer to form the final XAFS spectrum.

[0068] Since medium-energy X-rays are greatly affected by air scattering, the beam transmission path must be protected by vacuum. The monochromator, pre-ionization chamber, sample and silicon diode mentioned above are in the beam transmission path and are therefore in a vacuum environment. The sample can be in a vacuum or pure helium environment according to experimental requirements. The rest of the hardware is not in the beam transmission path and can be in a normal atmospheric environment.

[0069] The testing method of the present invention comprises the following steps:

[0070] (1) Tests for ex situ experiments:

[0071] ① Here we choose FeS2 standard sample as an example. The powder is evenly coated on the conductive carbon glue and placed on the metal sample holder in the sample cavity for testing. Since the sample is not affected by vacuum, it is tested in a vacuum environment.

[0072] ② X-ray white light is drawn out by the storage ring bent iron, monochromated by the monochromator and optimized by other optical elements on the beam line before being transmitted backward. The signal is collected by the front ionization chamber and amplified by the SR570 current amplifier. The X-ray intensity before entering the sample cavity is recorded as the incident light intensity signal I0.

[0073] ③ After passing through the front ionization chamber, the X-rays enter the sample cavity and irradiate the FeS2 sample to generate Auger electrons and fluorescence generated by the transition of outer electrons to inner electrons. The Auger electron signal is connected to the metal sample holder and the current signal is led out to the 6517B weak current meter outside the sample cavity for recording, and the total electron yield signal I is obtained. t The fluorescence signal is first converted into an electrical signal by the silicon diode in the sample cavity and then transmitted to the 6517B weak current meter by a wire to obtain the fluorescence yield signal I f .

[0074] ④ The three signals I0, I t and I f Take I0 / I t or I0 / I f The two combinations are input into the SR640 dual-channel low-pass filter to filter high-frequency noise. The cutoff frequency of the filter can be selected according to the type of element. This test uses a cutoff frequency of 5Hz. For the two XAS measurement methods, only one of the fluorescence yield and the full electron yield can be measured at the same time. Measuring fluorescence yield requires I0 / I f The data of electron yield requires I0 / I t The SR640 has only two channels for low-pass filtering of current. Taking the fluorescence yield as an example, when using it, I0 and I fThe two channels are input respectively, and after the filtering circuit in SR640 works, the filtered I0 and I f The current then continues back to the QXAFS system, which analyzes the two independent signals to generate the final XAS spectrum.

[0075] ⑤ The signal after being filtered by the filter enters the QXAFS electronics system, which processes the signal into XAFS under full electron yield or XAFS under fluorescence yield and then inputs it into the computer to form the final XAFS spectrum. Figure 2 (a) and (b) are the XAFS of DCM in the full electron yield and fluorescence yield modes at different rotation speeds of 1000pps (pulses per second), 2000pps, 3000pps, 4000pps and 4500pps, which are consistent with the XAFS obtained in the conventional step mode.

[0076] (2) Tests for in situ experiments:

[0077] ① Select an in-situ lithium-sulfur battery system as an example. The negative electrode of the battery is metallic lithium, the positive electrode is Li2S6 cathode liquid, and a hole is opened in the positive electrode shell and covered with a polyimide film to ensure that X-rays can pass through without the liquid flowing out.

[0078] ②The transmission process of X-rays is the same as (1), the difference lies in the environment inside the sample chamber. Since the battery contains liquid, changes in air pressure will affect the battery performance. Therefore, helium is filled into the sample chamber and air is expelled to keep the air pressure in the chamber constant.

[0079] ③ During the test, the Blue Sky battery test system is used. The wire on the sample cavity can easily connect the battery test system outside the cavity with the sample inside the cavity. The initial voltage of the battery is 2.8V, and the cycle test is carried out with a charge and discharge current of 5mA. During this process, the QXAFS electronics will continue to work to obtain the XAFS spectrum. Figure 2 (c) is the result within the first hour of the cycle test.

[0080] Figure 2 (a) with Figure 2 (b) shows the working performance of the QXAFS system in both full electron yield and fluorescence yield modes. It can be seen that the XAFS spectrum obtained by rapid scanning is basically the same as the XAFS spectrum obtained by ordinary step scanning in terms of energy resolution, but the time resolution is greatly improved, which shows the reliability of this method. In addition, as the DCM speed increases, the absorption spectrum moves toward higher energy as a whole, so it is necessary to collect the step XAFS spectrum first in each test, and the rapid XAFS spectrum can be used for absorption edge correction in subsequent processing. Figure 2(c) shows the XAFS changes of sulfur elements in a lithium-sulfur battery one hour before discharge. Due to the slow reaction of the battery, the test was carried out at a speed of 900pps. A total of 73 spectra were obtained in one hour, which clearly show the changes of sulfur elements during the discharge process.

[0081] From the above analysis, it can be seen that this method has good performance and reliability in medium-energy absorption spectrum testing, and can promptly respond to changes in the valence state and structure of elements in the in-situ environment.

[0082] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A medium energy in-situ X-ray absorption spectroscopy test system, characterized in that: It includes a computer unit, QXAFS electronics, a driver, a current amplifier, a low-pass filter, a weak current meter and a vacuum chamber, wherein the vacuum chamber is provided with a double flat crystal monochromator, a front ionization chamber, a sample chamber and a detector; wherein, The sample cavity is used to place the medium energy zone sample to be tested; The computer unit is used to send instructions to the QXAFS electronics to control the driver to drive the double flat crystal monochromator to rotate continuously, and continuously output the synchrotron radiation incident on the double flat crystal monochromator to the sample cavity to excite the sample to generate fluorescence signals and Auger electrons; The front ionization chamber is used to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier; The current amplifier is used to obtain an incident light intensity signal I0 of the X-ray incident to the sample cavity according to the input X-ray, and to amplify the incident light intensity signal I0 and then input it into the low-pass filter; The detector is used to collect the fluorescence signal and convert it into an electrical signal and then send it to the weak current meter; The weak current meter is used to connect to the sample chamber to collect the Auger electrons and obtain the total electron yield signal I of the sample. t and sent to the low-pass filter, connected to the detector to obtain the fluorescence yield signal I of the sample f and sent to the low-pass filter; The low-pass filter is used to filter the high-frequency noise of the input signal before inputting it into the QXAFS electronics; The QXAFS electronics processes the input signal to generate XAFS under the total electron yield or XAFS under the fluorescence yield of the sample and inputs the signal into the computer unit to form the X-ray absorption spectrum of the sample.

2. The system according to claim 1, characterized in that The computer unit is connected to the double-crystal flat monochromator via an encoder for monitoring the position of the double-crystal flat monochromator.

3. The system according to claim 1, characterized in that The sample chamber is a metal frame, and the weak current meter is connected to the metal frame through a wire to collect the Auger electrons to obtain the total electron yield signal I of the sample. t .

4. The system according to claim 1, 2 or 3, characterized in that: The detector is a silicon diode.

5. The system according to claim 1, 2 or 3, characterized in that: The low-pass filter is a SR640 dual-channel low-pass filter. t and I f Take I0 / I t or I0 / I f The two-by-two combinations are input to the SR640 dual-channel low-pass filter to filter high-frequency noise.

6. A medium energy in-situ X-ray absorption spectroscopy testing method, comprising the steps of: 1) Place the medium energy zone sample to be tested into the sample chamber; 2) The computer unit sends instructions to the QXAFS electronics control driver to drive the double-flat crystal monochromator to rotate continuously, and continuously outputs the synchrotron radiation incident on the double-flat crystal monochromator into the sample cavity to excite the sample to generate fluorescence signals and Auger electrons; 3) using the front ionization chamber to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier; 4) the current amplifier amplifies the incident light intensity signal I0 of the X-ray incident into the sample cavity and then inputs the amplified signal into the low-pass filter; 5) When performing a full electron yield test, the weak current meter is connected to the sample chamber to collect the Auger electrons to obtain the full electron yield signal I of the sample. t When the fluorescence yield test is performed, the weak current meter is connected to the detector, the detector is used to collect the fluorescence signal and convert it into an electrical signal and then sent to the weak current meter to obtain the fluorescence yield signal I of the sample. f and sent to the low-pass filter; 6) The low-pass filter filters the high-frequency noise of the input signal and then inputs it into the QXAFS electronics; 7) The QXAFS electronics processes the input signal to generate the XAFS under the full electron yield or the XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample; Wherein, the double flat crystal monochromator, the front ionization chamber, the sample cavity and the detector are located in a vacuum environment.

7. The method according to claim 6, characterized in that The computer unit is connected to the double-crystal flat monochromator via an encoder for monitoring the position of the double-crystal flat monochromator.

8. A medium energy in-situ X-ray absorption spectroscopy test system, characterized in that: It includes a computer unit, QXAFS electronics, a driver, a current amplifier, a low-pass filter, a weak current meter, an in-situ test system and a vacuum chamber, wherein the vacuum chamber is provided with a double flat crystal monochromator, a front ionization chamber, a sample chamber and a detector; wherein, The sample cavity is used to place the medium energy zone sample to be tested; the sample cavity is filled with helium and the air is discharged to keep the air pressure in the sample cavity constant; The computer unit is used to send instructions to the QXAFS electronics to control the driver to drive the double flat crystal monochromator to rotate continuously, and continuously output the synchrotron radiation incident on the double flat crystal monochromator to the sample cavity to excite the sample to generate fluorescence signals and Auger electrons; The front ionization chamber is used to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier; The current amplifier is used to amplify the incident light intensity signal I0 of the X-ray incident into the sample cavity and then input it into the low-pass filter; The detector is used to collect the fluorescence signal and convert it into an electrical signal and then send it to the weak current meter; The weak current meter is used to connect to the sample chamber to collect the Auger electrons and obtain the total electron yield signal I of the sample. t and sent to the low-pass filter, connected to the detector to obtain the fluorescence yield signal I of the sample f and sent to the low-pass filter; The low-pass filter is used to filter the high-frequency noise of the input signal before inputting it into the QXAFS electronics; The QXAFS electronics processes the input signal to generate XAFS under the full electron yield or XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample; The in-situ testing system is connected to the sample in the sample chamber and is used to perform in-situ testing on the sample.

9. A medium energy in-situ X-ray absorption spectroscopy testing method, the steps comprising: 1) Place the medium energy zone sample to be tested into the sample chamber; The sample chamber is filled with helium and the air is expelled to maintain a constant pressure in the sample chamber; 2) The computer unit sends instructions to the QXAFS electronics control driver to drive the double-flat crystal monochromator to rotate continuously, and continuously outputs the synchrotron radiation incident on the double-flat crystal monochromator into the sample cavity to excite the sample to generate fluorescence signals and Auger electrons; 3) connecting the sample in the sample chamber with an in-situ testing system to perform in-situ testing on the sample; 4) using the front ionization chamber to collect the X-rays output by the double flat crystal monochromator and send them to the current amplifier; 5) The current amplifier amplifies the incident light intensity signal I0 of the X-ray incident into the sample cavity and then inputs the amplified signal into the low-pass filter; 6) When performing a full electron yield test, the weak current meter is connected to the sample chamber to collect the Auger electrons to obtain the full electron yield signal I of the sample. t When the fluorescence yield test is performed, the weak current meter is connected to the detector, the detector is used to collect the fluorescence signal and convert it into an electrical signal and then sent to the weak current meter to obtain the fluorescence yield signal I of the sample. f and sent to the low-pass filter; 7) The low-pass filter filters the input signal for high-frequency noise and then inputs it into the QXAFS electronics; 8) The QXAFS electronics processes the input signal to generate the XAFS under the full electron yield or the XAFS under the fluorescence yield of the sample and inputs it into the computer unit to form the X-ray absorption spectrum of the sample; Wherein, the double flat crystal monochromator, the front ionization chamber, the sample cavity and the detector are located in a vacuum environment.

10. The method according to claim 9, characterized in that The computer unit is connected to the double-crystal flat monochromator via an encoder for monitoring the position of the double-crystal flat monochromator.

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