CN114280482A - Full cell and silicon-based material intrinsic cycle stability evaluation method based on full cell - Google Patents
Full cell and silicon-based material intrinsic cycle stability evaluation method based on full cell Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a full battery with a back-to-back structure, which comprises 2 back-to-back button half batteries and a reference electrode lug positioned between the backs of the 2 back-to-back button half batteries, wherein the full battery can simulate the working mode of a silicon-based negative electrode material in the full battery, and meanwhile, an excessive lithium source exists in the full battery, so that the real-time compensation of active lithium in a circulation process can be realized, the influence of the loss of the active lithium on the circulation performance of the silicon-based battery is eliminated, in addition, the potential change of a positive electrode and a negative electrode on the lithium in the circulation process can be monitored in situ by leading out the reference electrode lug in the middle of the battery, and the intrinsic stability of the silicon-based negative electrode material in the charging and discharging process is independently researched; the invention also discloses an evaluation method of the intrinsic cycle stability of the silicon-based material based on the full cell, which has the advantages of simple preparation method and short test period and can realize the rapid evaluation of the cycle stability of the silicon-based material.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a full battery and a silicon-based material intrinsic cycle stability evaluation method based on the full battery.
Background
The energy density is a permanent theme of the lithium ion battery, and is limited by a traditional anode and cathode material system, the energy density of the lithium ion battery reaches a bottleneck, and the anode and cathode materials with higher capacity are urgently needed to be developed. In recent years, a series of derived negative electrode materials (hereinafter referred to as silicon-based materials) developed by taking silicon (Si) as a core are considered as the first negative electrode materials of next-generation high-specific-energy lithium ion batteries, and Si can form Li with Li at most22Si5The corresponding theoretical capacity of the alloy is up to 4200mAh/g, the alloy is the largest theoretical capacity in the existing known materials, the voltage platform of silicon is higher than that of graphite, and lithium is not easy to precipitate from a negative electrode during charging and discharging. However, the low coulombic efficiency and the serious volume expansion are fatal defects of silicon-based materials for the first time, which can cause consumption of a large amount of active lithium and serious interface side reaction, and the volume effect is easy to cause cracking and pulverization of silicon particles and mutual electric contact loss, thereby causing the rapid reduction of battery capacity and seriously influencing the cycle performance of the lithium ion battery. Therefore, researchers at home and abroad adopt various methods such as silicon nanocrystallization, surface carbon coating, doping modification, preparation of silicon monoxide and the like, so that the volume expansion of silicon-based materials is relieved, and the cycling stability of the materials is improved.
At present, there are two main methods for evaluating the electrochemical performance of silicon-based materials: (1) a button half cell, which adopts a metal lithium sheet as a counter electrode; (2) the whole battery adopts the positive electrode as the counter electrode. Although the first method is simple to operate and short in test period, the deterioration influence of active lithium loss, electrolyte loss and the like on the silicon-based material can be ignored, and the intrinsic cycle stability of the material can be evaluated, the performance of the material in the actual working interval of the battery cannot be obtained due to the fact that the working voltage intervals of the silicon-based negative electrode material in the half battery and the full battery are different; the second method has relatively complex manufacturing process and long development period, is inconvenient for quickly evaluating the electrical property of the silicon-based material, and cannot ignore the influence of factors such as electrolyte, a limited positive electrode lithium source and the like on the performance of the battery. Therefore, a method for evaluating the intrinsic cycle stability of the silicon-based material based on the full cell is needed, the influence of other factors such as electrolyte, an active lithium source and the like can be ignored, the intrinsic electrochemical performance of the silicon-based material during the full cell operation can be quickly evaluated, the development period of the silicon-based material is greatly shortened, and meanwhile, a quick and effective negative electrode material evaluation and screening method is provided for the development of silicon-based system lithium ion cells.
The Chinese patent application (publication number: CN102157731B) discloses a lithium ion battery silicon-carbon composite negative electrode material and a preparation method thereof, wherein a metal lithium sheet is used as a counter electrode, and the capacity, the multiplying power and the cycle performance of 40 weeks are evaluated on the silicon-carbon composite negative electrode material prepared by using porous silicon as a matrix and carbon as a coating layer, so that the electrochemical performance of the material is considered to be superior to that of the silicon-carbon composite material prepared by the traditional technology. The material evaluation method used in the invention is simple to operate, but the performance of the silicon-carbon composite material in the full cell cannot be known.
The Chinese patent application (publication number: CN102694200B) discloses a silicon-based negative lithium ion battery and a manufacturing method thereof, wherein a multi-layer pole piece compounded by a graphite coating and a silicon-carbon coating is used as a negative pole, a transition metal lithium-intercalated oxide or phosphate material is used as a positive active material, the energy density of the prepared silicon-based negative lithium ion battery is higher than that of the traditional graphite negative lithium ion battery by more than 20%, and the capacity retention rate after 0.5C cycle for 500 times is 83%. The silicon-based negative electrode evaluation method used in the invention has a complex manufacturing process, the influence of the electrolyte and the positive electrode on the cycle performance of the battery cannot be eliminated, and the intrinsic cycle stability of the silicon-based negative electrode in the full battery cannot be independently obtained.
Disclosure of Invention
The invention aims to overcome the defects and provides a full battery with a back-to-back structure, which comprises 2 button half batteries with back-to-back and a reference electrode lug positioned between the backs of the 2 button half batteries, wherein the full battery can simulate the working mode of a silicon-based negative electrode material in the full battery, and meanwhile, an excessive lithium source exists in the full battery, so that the real-time compensation of active lithium in the circulating process can be realized, the influence of the loss of the active lithium on the circulating performance of the silicon-based battery is eliminated, in addition, the reference electrode lug is led out from the middle of the battery, the potential change of positive and negative electrodes on the lithium in the circulating process can be monitored in situ, and the intrinsic stability of the silicon-based negative electrode material in the charging and discharging process can be independently researched; the invention also provides an evaluation method of the intrinsic cycle stability of the silicon-based material based on the full cell, the preparation method is simple, the test period is short, and the rapid evaluation of the cycle stability of the silicon-based material can be realized.
In order to achieve the above purpose, the invention provides the following technical scheme:
a full battery comprises a first button half battery, a second button half battery and a reference electrode tab, wherein the first button half battery comprises a positive pole piece and a first metal lithium piece, the second button half battery comprises a negative pole piece and a second metal lithium piece, the back surface of the first button half battery is opposite to the back surface of the second button half battery, and the reference electrode tab is positioned between the back surface of the first button half battery and the back surface of the second button half battery and is connected with the first metal lithium piece and the second metal lithium piece which are used as reference electrodes; the front side of the first button type half cell and the front side of the second button type half cell are respectively the positive electrode and the negative electrode of the full cell; the negative electrode slurry used for preparing the negative electrode plate in the second button type half cell comprises a silicon-based material.
Further, the first button half cell further comprises a first shell cover, a first diaphragm and a first shell bottom, and the second button half cell further comprises a second shell cover, a second diaphragm and a second shell bottom;
the first button type half cell is sequentially provided with a first shell cover, a positive pole piece, a first diaphragm, a first metal lithium piece and a first shell bottom from the front side to the back side;
the second button type half cell is sequentially provided with a second shell cover, a negative pole piece, a second diaphragm, a second metal lithium piece and a second shell bottom from the front to the back.
Furthermore, the full cell also comprises a first insulating film and a second insulating film, wherein the first insulating film is attached to the back surface of the first button-type half cell, the second insulating film is attached to the back surface of the second button-type half cell, and the reference electrode tab is clamped between the first insulating film and the second insulating film; the first insulating film and the second insulating film are both annular;
electrolyte is added on the positive pole piece, the negative pole piece, the first diaphragm and the second diaphragm.
Further, the silicon-based material comprises one or more of silicon carbon, silicon oxygen or nano silicon, and also comprises a mixture formed by one or more of silicon carbon, silicon oxygen or nano silicon and graphite.
Furthermore, the N/P ratio of the positive pole piece and the negative pole piece is 1.0-1.8.
Furthermore, the reference electrode tab is one of a nickel strip, a stainless steel strip, a copper strip or a silver strip.
Further, the preparation method of the negative pole piece comprises the steps of uniformly mixing the silicon-based material, the conductive agent and the binder in a solvent to prepare negative pole slurry, coating the negative pole slurry on the current collector copper foil, baking and drying in vacuum to prepare the negative pole piece.
A method for evaluating the intrinsic cycle stability of a silicon-based material based on a full cell comprises the following steps:
s1, manufacturing the full cell;
s2 testing the cycle performance of the battery, recording the discharge capacity Q of each cycle, and the potential value V between the negative electrode and the reference electrode of the battery during the discharge processN；
S3 discharge capacity Q and potential value V according to cycle per weekNObtaining a capacity differential curve, said capacity differential curve having Q as X-axis data, dQ/dVNIs Y-axis data;
s4, calculating the discharge capacity retention rate of the full battery according to the discharge capacity Q of each cycle;
s5 intrinsic cycle stability of the Si-based material under full cell operation condition was evaluated based on the capacity differential curve obtained in step S3 and the discharge capacity retention rate obtained in S4.
Further, in a method for evaluating the intrinsic cycle stability of the silicon-based material based on the full cell, in step S5, the electrochemical reaction phase transition capacity of the silicon-based material during discharge is obtained according to the phase transition peak appearing in the capacity differential curve obtained in step S3.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention designs a back-to-back structured full cell for evaluating the intrinsic cycle stability of a silicon-based material, which can simulate the working mode of a silicon-based system full cell in the cycle performance test process, has simple preparation method and short test period, and can realize the rapid evaluation of the intrinsic cycle stability of the silicon-based material based on the full cell;
(2) according to the full-cell, metal lithium sheets are arranged in the positive and negative button type half-cells, so that the real-time lithium compensation of the negative electrode in the cycle process can be realized, and the influence of a limited lithium source in the full-cell on the cycle performance of the silicon-based cell is eliminated;
(3) the evaluation method can realize the in-situ monitoring of the negative electrode on the lithium potential in the circulation process, and independently research the intrinsic stability of the negative electrode in the circulation process;
(4) the invention provides a rapid and effective method for evaluating and screening the negative electrode material for the development of the silicon-based system lithium ion battery, and lays a foundation for researching the influence mechanism of the pre-lithiation of the silicon-based negative electrode on the cycle performance of the battery.
Drawings
FIG. 1 is a schematic diagram of a "back-to-back" structure of a full cell of the present invention;
FIG. 2 is a graph of full cell cycle capacity according to example 1 of the present invention;
FIG. 3 is a graph showing the differential capacity of the negative electrode in example 1 of the present invention.
Detailed Description
The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.
The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
Referring to fig. 1, the present invention designs a full battery with a back-to-back structure, which comprises, from top to bottom: a second case cover 25, a negative pole piece 24, a second diaphragm 23, a second lithium metal piece 22, a second case bottom 21, a second insulating film 5, a reference electrode tab 3, a first insulating film 4, a first case bottom 11, a first lithium metal piece 12, a first diaphragm 13, a positive pole piece 14 and a first case cover 15; the second cover 25 is the negative pole of the back-to-back battery, and the first cover 15 is the positive pole of the back-to-back battery. In the preparation process, enough electrolyte is added on the first diaphragm 13, the second diaphragm 23, the negative pole piece 24 and the positive pole piece 14 respectively.
The preparation method of the negative pole piece 24 comprises the following steps: uniformly mixing the silicon-based negative electrode material, the conductive agent and the binder in a solvent to prepare negative electrode slurry, coating the negative electrode slurry on a current collector copper foil, and baking and vacuum drying to prepare the negative electrode plate.
The silicon-based negative electrode material comprises one or more of silicon carbon, silicon oxygen and nano silicon, and also comprises a mixture formed by one or more of silicon carbon, silicon oxygen and nano silicon and graphite.
The N/P ratio of the negative pole piece 24 to the positive pole piece 14 is 1.0-1.8;
the reference electrode tab is one of metal materials with good conductivity, such as a nickel strip, a stainless steel strip, a copper strip, a silver strip and the like.
The invention also provides a silicon-based material intrinsic cycle stability evaluation method based on the full cell, based on the full cell with a back-to-back structure, which comprises the following steps:
firstly, manufacturing the full battery with the back-to-back structure;
and secondly, carrying out cycle performance test on the full battery manufactured in the first step by adopting battery charging and discharging equipment, recording the discharge capacity Q of each cycle, and recording the potential value V between the negative electrode and the reference electrode by adopting a data acquisition instrument in the cycle processN；
Thirdly, the discharge capacity Q of the cycle of each week recorded in the second step is compared with the potential value V in the discharge processNDifferential processing is carried out to obtain dQ/dVNValue of (d), with Q as X-axis data, dQ/dVNObtaining a capacity differential curve dQ/dV for the Y-axis dataN-Q diagram, where the peaks appearing reflect the electrochemical reaction phase transition capacity of the silicon-based anode material during discharge;
fourthly, calculating the discharge capacity retention rate in the circulation process;
and fifthly, evaluating the intrinsic cycle stability of the silicon-based negative electrode material in the full battery working state according to the results of the third step and the fourth step.
Example 1
And a silicon oxide material is used as a negative active material to prepare a negative pole piece 24 with the diameter of phi 14mm, and the negative pole piece 24, a second diaphragm 23, a second metal lithium piece 22 and electrolyte are sequentially assembled into an R2016 type second button type half cell in an argon atmosphere glove box. According to the same method, an R2016 type first button half cell is prepared by taking a nickel-cobalt lithium aluminate material as a positive electrode active substance, and the N/P ratio of the positive electrode to the negative electrode is 1.2. Then, a first shell bottom 11 of the first button half cell is pasted with a ring-shaped first insulating film 4, a second shell bottom 21 of the second button half cell is pasted with a ring-shaped second insulating film 5, and a nickel strip is sandwiched between the first button half cell and the second button half cell to be used as a reference electrode tab 3, and the specific structure is shown in fig. 1. The second cover 25 of the second button half cell is the negative pole of the "back-to-back" cell and the first cover 15 of the first button half cell is the positive pole of the "back-to-back" cell.
The "back-to-back" cell was tested for cycle performance using the LANHE CT2001A cell test system, the test regime was as follows: charging the battery at 0.2C constant current to 4.2V and constant voltage, stopping current at 0.01C, standing for 10 min, then discharging at 0.5C constant current to 2.5V, standing for 10 min, and circulating. Fig. 2 is a cycle capacity curve of a "back-to-back" battery, with a discharge capacity of 2.08mAh at cycle 1 week, a discharge capacity of 1.75mAh after 50 cycles, and a cycle capacity retention rate of 84.1%. Monitoring the potential value between the negative electrode and the reference electrode by an Agilent data acquisition instrument in the circulation process, and monitoring the discharge capacity Q at the 1 st week and every 10 weeks and the monitored negative electrode potential value VNThe differential processing is carried out to obtain a negative electrode capacity differential curve in the circulation process, as shown in fig. 3, two connected phase change peaks exist in the negative electrode at the initial stage of the circulation, the distance between the two peaks is increased along with the circulation, and the electrochemical reaction phase change is basically stable after 20 weeks of the circulation, which indicates that the intrinsic stability of the silicon monoxide material in the first 20 weeks is poor and the electrochemical performance of the negative electrode tends to be stable after 20 weeks of the circulation.
Example 2
The silicon-carbon composite material is used as a negative active substance to prepare a negative pole piece 24 with phi 14mm, and the negative pole piece 24, a second diaphragm 23, a second metal lithium piece 22 and electrolyte are sequentially assembled into an R2016 type second button type half cell in an argon atmosphere glove box. According to the same method, a lithium cobaltate material is used as a positive electrode active substance to prepare an R2016 type first button half cell, and the N/P ratio of the positive electrode and the negative electrode is 1.3. And then adhering a ring-shaped first insulating film 4 to the first shell bottom 11 of the first button half cell, adhering a ring-shaped second insulating film 5 to the second shell bottom 21 of the second button half cell, wherein a nickel strip is clamped between the first button half cell and the second button half cell to be used as a reference electrode tab 3, a second shell cover 25 of the second button half cell is the negative electrode of the back-to-back cell, and a first shell cover 15 of the first button half cell is the positive electrode of the back-to-back cell.
The "back-to-back" cell was tested for cycle performance using the LANHE CT2001A cell test system, the test regime was as follows: charging the battery at 0.5C constant current to 4.4V and constant voltage, stopping current at 0.01C, standing for 10 min, then discharging at 1C constant current to 2.5V, standing for 10 min, and circulating. And in the circulation process, an Agilent data acquisition instrument is adopted to monitor the potential value between the negative electrode and the reference electrode.
Example 3
The silicon-graphene composite material is used as a negative active material to prepare a negative pole piece 24 with phi 14mm, and the negative pole piece 24, a second diaphragm 23, a second metal lithium piece 22 and electrolyte are sequentially assembled into an R2016 type second button type half cell in an argon atmosphere glove box. According to the same method, a lithium cobaltate material is used as a positive electrode active substance to prepare an R2016 type first button half cell, and the N/P ratio of the positive electrode and the negative electrode is 1.4. And then adhering a ring-shaped first insulating film 4 to the first shell bottom 11 of the first button half cell, adhering a ring-shaped second insulating film 5 to the second shell bottom 21 of the second button half cell, wherein a nickel strip is clamped between the first button half cell and the second button half cell to be used as a reference electrode tab 3, a second shell cover 25 of the second button half cell is the negative electrode of the back-to-back cell, and a first shell cover 15 of the first button half cell is the positive electrode of the back-to-back cell.
The "back-to-back" cell was tested for cycle performance using the LANHE CT2001A cell test system, the test regime was as follows: charging the battery at 0.2C constant current to 4.2V and constant voltage, stopping current at 0.01C, standing for 10 min, then discharging at 0.5C constant current to 2.5V, standing for 10 min, and circulating. And in the circulation process, an Agilent data acquisition instrument is adopted to monitor the potential value between the negative electrode and the reference electrode.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (9)
1. The full battery is characterized by comprising a first button half battery, a second button half battery and a reference electrode tab, wherein the first button half battery comprises a positive electrode pole piece (14) and a first lithium metal sheet (12), the second button half battery comprises a negative electrode pole piece (24) and a second lithium metal sheet (22), the back surface of the first button half battery is opposite to the back surface of the second button half battery, and the reference electrode tab is positioned between the back surface of the first button half battery and the back surface of the second button half battery and is connected with the first lithium metal sheet (12) and the second lithium metal sheet (22) which are used as reference electrodes; the front side of the first button type half cell and the front side of the second button type half cell are respectively the positive electrode and the negative electrode of the full cell; the negative electrode slurry used for preparing the negative electrode pole piece (24) in the second button half cell comprises a silicon-based material.
2. Full cell according to claim 1, characterized in that the first half-cell button further comprises a first cover (15), a first membrane (13) and a first base (11), the second half-cell button further comprises a second cover (25), a second membrane (23) and a second base (21);
the first button type half cell is sequentially provided with a first shell cover (15), a positive pole piece (14), a first diaphragm (13), a first metal lithium piece (12) and a first shell bottom (11) from the front to the back;
the second button type half cell is sequentially provided with a second shell cover (25), a negative pole piece (24), a second diaphragm (23), a second metal lithium piece (22) and a second shell bottom (21) from the front to the back.
3. A full cell according to claim 1 or 2, further comprising a first insulating film (4) and a second insulating film (5), the first insulating film (4) being attached to the back side of the first button half cell, the second insulating film (5) being attached to the back side of the second button half cell, the reference electrode tab (3) being sandwiched between the first insulating film (4) and the second insulating film (5); the first insulating film (4) and the second insulating film (5) are both annular;
electrolyte is added on the positive pole piece (14), the negative pole piece (24), the first diaphragm (13) and the second diaphragm (23).
4. The full cell according to claim 1, wherein the silicon-based material comprises one or more of silicon carbon, silicon oxygen, or nano silicon, and further comprises a mixture of one or more of silicon carbon, silicon oxygen, or nano silicon and graphite.
5. The full battery according to claim 1, wherein the N/P ratio of the positive electrode tab (14) and the negative electrode tab (24) is 1.0-1.8.
6. The full cell according to claim 1, wherein the reference electrode tab is one of a nickel strip, a stainless steel strip, a copper strip or a silver strip.
7. The full battery according to claim 1, wherein the negative electrode sheet (24) is prepared by uniformly mixing a silicon-based material, a conductive agent and a binder in a solvent to obtain a negative electrode slurry, coating the negative electrode slurry on a current collector copper foil, baking, and vacuum drying.
8. A method for evaluating the intrinsic cycle stability of a silicon-based material based on a full cell is characterized by comprising the following steps:
s1, manufacturing a full battery according to any one of claims 1 to 7;
s2 testing the cycle performance of the battery, recording the discharge capacity Q of each cycle, and the potential value V between the negative electrode and the reference electrode of the battery during the discharge processN；
S3 discharge capacity Q and potential value V according to cycle per weekNObtaining a capacity differential curve, said capacity differential curve having Q as X-axis data, dQ/dVNIs Y-axis data;
s4, calculating the discharge capacity retention rate of the full battery according to the discharge capacity Q of each cycle;
s5 intrinsic cycle stability of the Si-based material under full cell operation condition was evaluated based on the capacity differential curve obtained in step S3 and the discharge capacity retention rate obtained in S4.
9. The method as claimed in claim 8, wherein the step S5 is performed to obtain the electrochemical reaction phase transition capacity of the si-based material during discharging according to the phase transition peak appearing in the capacity differential curve obtained in the step S3.
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