CN109932406B - Electrode structure for in-situ observation of lithium ion diffusion process - Google Patents
Electrode structure for in-situ observation of lithium ion diffusion process Download PDFInfo
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Abstract
The invention relates to an electrode structure for in-situ observation of a lithium ion diffusion mode in a graphite material. The method is characterized in that a circular working electrode structure and an annular counter electrode structure are utilized to form an edge-to-edge structure form that two electrodes are distributed according to the positions of concentric circles in a surface; the diffusion of lithium ions in the electrode takes the form of a radial pattern along the electrode. The working electrode is circular, the counter electrode is annular, and the inner diameter of the annular electrode is larger than the outer diameter of the circular electrode; the conductive device adopts a copper metal pin with a flange, the upper part of the conductive device is pressed on the electrode material, and the lower part of the conductive device is connected with the conductive copper ring, so that the electrode material is communicated with an external lead. The invention can directly observe the diffusion process of lithium ions in the lithium insertion/extraction cycle process of the working electrode in situ, overcomes the difficulty that the traditional electrode face to face mode causes no measurement, and simultaneously the design of the circular electrode is more in line with the structural design of commercial electrodes, and the research on the diffusion evolution in all directions can be realized.
Description
Technical Field
The invention belongs to the field of electrochemistry, and particularly relates to an electrode structure for in-situ observation of a lithium ion diffusion mode in a graphite material.
Background
With the development of new energy technologies such as lithium ion batteries, graphite electrode materials, which are typical of commercial electrodes, are widely used in the fields of various electronic devices, electric vehicles, and the like. The process of lithium ion shuttle leads to alternate volume expansion and contraction of the electrodes, which in turn leads to corresponding strain/stress accumulation, resulting in capacity degradation and lifetime degradation of the graphite material. Therefore, the diffusion process of lithium ions has a great influence on the force-electrochemical performance of the electrode, and is even related to the development trend of future lithium batteries. For the inherent structural design of the commercial battery, the working electrode and the counter electrode usually adopt a face-to-face structural mode, as shown in fig. 1, the space size between the electrodes is very small (below 100 μm), the counter electrode can shield the working electrode, the optical measurement technology is not allowed to directly observe the diffusion behavior of lithium ions in the charging and discharging process in situ, and further, the influence of the diffusion mechanism on the capacity, the service life and other properties of the lithium battery electrode is not favorable to be deeply explored. Therefore, the research on lithium ion diffusion is paid much attention in the electrochemical field, and the design of an electrode structure which is convenient for in-situ observation of diffusion in the experimental process has important scientific research significance. At present, there is a method for in-situ observation of lithium ion battery electrode reaction, the electrode structure used in the method is still a face-to-face up-and-down structure, the diffusion mode of lithium ions is actually along the normal direction of the working electrode, the electrode structure is not a strict edge-to-edge form, and the constraint form is complex, so the diffusion research is not very convenient [1 ]. In other researches, a working electrode is designed to be square, one side of a square working electrode and a counter electrode form an arrangement form, but the diffusion of the electrode along a one-dimensional direction is only researched [2], and the shape of the square working electrode is different from that of a round electrode applied in actual life, so that the diffusion process of lithium ions cannot be reflected more approximately visually. Therefore, a simpler electrode structure design is urgently needed to more closely simulate the lithium diffusion process in a commercial electrode so as to facilitate in-situ observation of the real-time diffusion path of lithium ions in the electrochemical process, and further provide certain basic design guidance for further exploring a diffusion coupling mechanism.
Reference documents:
[1]J.Chen,A.K.Thapa,T.A.Berfield,In-situ characterization of strain in lithium battery working electrodes,J.Power Sources 271(2014)406-413.
[2]Y.Qi,S.J.Harris,In Situ Observation of Strains during Lithiation of a Graphite Electrode,J.Electrochem.Soc.157(2010)A741.
disclosure of Invention
The invention mainly aims to provide an electrode structure for real-time in-situ observation of a lithium ion diffusion process, which utilizes a circular working electrode structure and an annular counter electrode structure to form an edge-to-edge structural form that two electrodes are distributed according to concentric circle positions in a plane.
The technical scheme of the invention is as follows:
an electrode structure for in-situ observation of lithium ion diffusion mode in graphite material; the method is characterized in that a circular working electrode structure and an annular counter electrode structure are utilized to form an edge-to-edge structure form that two electrodes are distributed according to the positions of concentric circles in a surface; the diffusion of lithium ions in the electrode takes the form of a radial pattern along the electrode.
In the electrode structure, the working electrode is circular, the counter electrode is annular, and the inner diameter of the annular electrode is larger than the outer diameter of the circular electrode; the conductive device adopts a copper metal pin with a flange, the upper part of the conductive device is pressed on the electrode material, and the lower part of the conductive device is connected with the conductive copper ring, so that the electrode material is communicated with an external lead.
In the electrode structure, the metal pin is fixed at the center of the working electrode, so that the electric field on the working electrode is distributed along the radial direction of the electrode.
The electrode structure is characterized in that the metal pins are symmetrically and annularly distributed for fixing the counter electrode, and the number of the metal pins is even.
The concrete description is as follows:
the invention changes the diffusion form of lithium ions in the electrode from the mode of along the normal direction (vertical) of the electrode to the mode of along the radial direction (horizontal) of the electrode, the design of the edge-to-edge structure of the in-plane electrode does not set a complex constraint effect on the working electrode, the actual distance of the diffusion of the lithium ions is enlarged, the shielding effect of one electrode on the other electrode is avoided, and the diffusion process of the lithium ions is easy to observe in situ in real time.
The working electrode is circular, the counter electrode is annular, the inner diameter of the annular electrode is larger than the outer diameter of the circular electrode, parameters such as electrode materials, size and thickness are not limited, and the like can be realized;
the conductive device adopts the copper metal pin with the flange, the upper part of the copper metal pin is pressed on the electrode material, and the lower part of the copper metal pin is connected with the conductive copper ring, so that the connection between the electrode material and an external lead is realized, and the charge-discharge test of the electrode is convenient to realize.
The metal pin is fixed at the center of the working electrode, so that the electric field on the working electrode is distributed along the radial direction of the electrode, and the metal pin plays a role in fixing the working electrode and preventing the center of the metal pin from changing;
the fixing of the counter electrode needs to keep the metal pins distributed in a symmetrical annular shape, and the number of the metal pins is even (at least 4), so that on one hand, synchronous conduction in all directions is ensured, on the other hand, the counter electrode can be well fixed, and the relatively accurate position relation between the counter electrode and the working electrode is ensured.
The invention can directly observe the diffusion process of lithium ions in the lithium insertion/removal cycle process of a working electrode (such as a graphite electrode) in situ, overcomes the difficulty that the traditional electrode face-to-face mode causes the failure of measurement, and simultaneously provides a structural mode of relative position arrangement of concentric circles in an electrode face, so that the two electrodes form a corresponding mode of edge-to-edge, thereby avoiding complex constraint action, increasing the diffusion distance of the lithium ions, facilitating the in situ observation by directly utilizing an optical microscope, simultaneously, the design of a circular electrode more conforms to the structural design of a commercial electrode, and the research of the diffusion evolution in all directions can be realized.
Drawings
FIG. 1 is a schematic diagram of a conventional two-electrode face-to-face arrangement;
FIG. 2 is a schematic view of an in-plane ring arrangement of two electrodes in a side-by-side configuration in accordance with the present invention;
FIG. 3 is a schematic view of the conductive structure and fixing manner of the working electrode and the counter electrode in the present invention;
fig. 4 is an in-situ experimental image of diffusion distribution of lithium ions in a working electrode according to the present invention.
Detailed Description
The design process of the present invention is further illustrated by the following specific examples, which are intended to be illustrative rather than limiting and should not be construed as limiting the scope of the present invention.
The structural design process for the in-situ measurement electrode diffusion process is divided into the following four parts:
(1) preparation of electrode structural component
The electrode structure components used in this embodiment mainly include a working electrode (graphite electrode), a counter electrode (lithium electrode), a conductive metal pin (copper material), a wire, an electrode support, a conductive copper ring, and the like, as shown in fig. 2 and 3. The working electrode test piece is a sheet electrode manufactured by uniformly coating a graphite composite material on a copper foil current collector, after the sheet electrode test piece is manufactured, a circular mould knife is adopted to cut the sheet graphite electrode, the shape of the electrode is circular, and the diameter size can be reasonably set according to the requirement. The counter electrode is made of lithium metal electrode material, and the working electrode is in a circular shape, so that the counter electrode needs to be designed in an annular shape to ensure that the annular inner edge of the lithium metal electrode is opposite to the outer edge of the graphite electrode. Therefore, a circular die cutter slightly larger than the size of the circular graphite electrode is used for punching the central part of the lithium metal electrode, so that the lithium metal electrode is in a ring shape meeting the requirement. In the embodiment, a metal pin with a flange is adopted and matched with a lead, a conductive copper ring and the like to jointly form a conductive circuit inside the electrode.
(2) Arrangement of working and counter electrode positions
As shown in fig. 3, the working electrode (graphite electrode) is placed on a circular electrode support, and in order to prevent short circuit of the electrode, the support is made of insulating teflon, and a tiny hole is formed in the center of the support, so that a metal pin (d is 2mm) on the graphite electrode can penetrate through the support and can be tightly matched with the electrode support. As shown in figure 2, because the counter electrode (lithium metal electrode) is designed into a ring shape, the counter electrode is stably placed on the outer side of the graphite electrode, the counter electrode and the graphite electrode are ensured to be in approximate concentric positions and are kept in the same plane, and in order to avoid short circuit of electrode contact, a gap of 1-2mm needs to be left between the two electrodes. By arranging the electrodes, the design of the in-plane annular arrangement mode in the edge-to-edge mode of the two electrodes can be realized.
(3) Design of conducting structure of working electrode and counter electrode
Corresponding conductive structures need to be designed in the mode of placing the working electrode and the counter electrode in the plane concentric circle, the conductive pins of the working electrode are positioned in the center, and the conductive pins (double number) of the counter electrode are distributed on the annular counter electrode in a centrosymmetric mode so as to complete the charging and discharging process by matching with the electrodes. As shown in fig. 2, firstly, for the graphite electrode placed at the center, due to the circular shape, in order to ensure the lithium ion diffusion along the radial direction, a tiny hole is opened at the right center of the electrode, the hole diameter is about 2mm, then a metal conductive pin (copper material) with a flange is adopted to penetrate through the tiny hole at the center of the electrode, the flange at the upper part is pressed on the upper surface of the electrode, and the copper foil current collector at the lower part of the electrode is combined to realize the consistency of the conductivity of the upper surface and the lower surface of the electrode, thereby ensuring the relative consistency of the lithium ion diffusion of the electrode in the thickness direction. Secondly, for the circular lithium sheet electrode with a hole at the center, because the structure is designed in an annular shape, in order to ensure the uniformity of the electrical conduction in all directions of the annular shape, conductive metal pins (generally even numbers, such as 4,6, and 8 … …) need to be distributed along the annular shape in a symmetrical manner, and in this embodiment, 4 metal pins (copper materials) with flanges are adopted to meet the electrical conductivity requirement of the lithium electrode. The upper flanges of the 4 metal pins are pressed on the upper surface of the electrode, and the lower parts of the metal pins are in contact fixation with a conductive copper ring, so that the conductive synchronism of the lithium metal electrode in all directions is basically realized, and the lithium ions can be conveniently evolved in real time along the radial diffusion path of the graphite electrode in a more ordered manner.
(4) Form of fixation and restraint of working electrode and counter electrode
The metal pin used in the above (3) not only plays a role of conducting electricity, but also fixes the electrode. The graphite electrode is fixed on the central part of the electrode support body through the metal pins, and the annular lithium metal electrode is fixed on the electrode support body through the metal pins on the outer edge of the graphite electrode, so that the accuracy of the relative positions of the two electrodes is maintained. For the constraint mode, the graphite electrode is only provided with the conductive pin at the central part, and the constraint action of normal and circumferential loads is not provided at the outer edge part of the electrode, so that the electrode is in a relatively free unconstrained state.
In this example, a graphite electrode having a diameter of 12mm was used, a ring-shaped lithium metal electrode having an inner diameter of 15mm and an outer diameter of 20mm, a metal pin having a diameter of 2mm and an upper flange having a diameter of about 4mm was used.
The electrode structure is used for carrying out electrochemical test, the charge-discharge multiplying power of 0.2C is adopted for carrying out cycle test, and the performance test of the graphite electrode with the structure is carried out on a battery tester of Wuhanjinnuo electronic company Limited. And (3) generating a lithium ion diffusion process on the surface of the electrode along with the progress of time, and acquiring images of the surface of the electrode at equal time intervals by aligning an optical microscope with the graphite electrode to record lithium ion diffusion information on the surface of the electrode. Fig. 4 is a lithium ion distribution diagram of the surface of an electrode, which is acquired in situ during lithium ion diffusion during the experiment, the lithium ion content at the outer edge of the circular working electrode is obviously higher than that in the central area, and the lithium ion diffusion is distributed along the radial direction. The structural design is closer to the commercial circular electrode design, the real-time distribution of lithium ions can be conveniently and directly observed through vision, advanced and expensive experimental instruments are not needed, the structure is simple and effective, the lithium ion diffusion process in the working process of the electrode is easy to study through the structural form of the edge-to-edge sides of the electrode, and the experimental result can more comprehensively and truly reflect the diffusion path and process of the lithium ions.
The foregoing description of the invention is illustrative and not restrictive, and it will be understood by those skilled in the art that many changes, variations or equivalents may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (3)
1. An electrode structure for in-situ observation of lithium ion diffusion mode in graphite material is characterized in that a circular working electrode structure and an annular counter electrode structure are utilized to form an edge-to-edge structural form that two electrodes are distributed according to the position of concentric circles in a plane; the diffusion form of lithium ions in the electrode is along the radial direction of the electrode; the conductive device adopts a copper metal pin with a flange, the metal pin is fixed at the center of the working electrode, the upper part of the metal pin is pressed on an electrode material, and the middle part of the metal pin is tightly contacted with a circular electrode material, so that the electric field on the working electrode is radially distributed along the circular electrode.
2. An electrode structure according to claim 1 wherein the working electrode is circular in shape and the counter electrode is annular in shape, the inner diameter of the annular electrode being greater than the outer diameter of the circular electrode.
3. An electrode structure as claimed in claim 2, wherein the fixing retaining metal pins of the counter electrode are distributed in a symmetrical annular arrangement, the number being even.
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| CN101501481A (en) * | 2006-08-07 | 2009-08-05 | 首尔大学校产学协力团 | Nanostructure sensors |
| CN201359591Y (en) * | 2009-01-14 | 2009-12-09 | 宝山钢铁股份有限公司 | Three-electrode electrolytic cell used for in situ observation |
| CN105445347A (en) * | 2015-12-05 | 2016-03-30 | 天津大学 | Vertical electrochemical battery device for in-situ photodynamic measurement |
| CN205352967U (en) * | 2015-11-04 | 2016-06-29 | 中国科学院上海微***与信息技术研究所 | Lithium ion battery's in situ test device and equipment support |
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| US20120280224A1 (en) * | 2009-06-25 | 2012-11-08 | Georgia Tech Research Corporation | Metal oxide structures, devices, and fabrication methods |
| US20180224384A1 (en) * | 2016-01-29 | 2018-08-09 | Hewlett-Packard Development Company, L.P. | Electrode system |
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| CN101501481A (en) * | 2006-08-07 | 2009-08-05 | 首尔大学校产学协力团 | Nanostructure sensors |
| CN201359591Y (en) * | 2009-01-14 | 2009-12-09 | 宝山钢铁股份有限公司 | Three-electrode electrolytic cell used for in situ observation |
| CN205352967U (en) * | 2015-11-04 | 2016-06-29 | 中国科学院上海微***与信息技术研究所 | Lithium ion battery's in situ test device and equipment support |
| CN105445347A (en) * | 2015-12-05 | 2016-03-30 | 天津大学 | Vertical electrochemical battery device for in-situ photodynamic measurement |
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