CN111785953B - Modification method of lithium ion battery silicon negative electrode material - Google Patents

Modification method of lithium ion battery silicon negative electrode material Download PDF

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CN111785953B
CN111785953B CN202010649746.0A CN202010649746A CN111785953B CN 111785953 B CN111785953 B CN 111785953B CN 202010649746 A CN202010649746 A CN 202010649746A CN 111785953 B CN111785953 B CN 111785953B
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CN111785953A (en
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陈松岩
张子启
韩响
罗林山
苏鹏飞
李成
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Abstract

A modification method of a lithium ion battery silicon cathode material relates to the design and development of new energy materials. Taking a p-type silicon (100) sheet as a substrate, adopting an electrochemical micromachining process to carry out electrochemical corrosion, firstly corroding the surface of the substrate into a circular hole, gradually enlarging the circular hole, finally extruding the circular hole into a square shape, and forming a depletion layer at the interface of a corrosive liquid and the hole wall; under the action of an electric field, hole carriers migrate from the substrate to the hole wall along the longitudinal hole wall to participate in reaction with the corrosive liquid interface, and the hole wall becomes thinner gradually in the reaction process; when the wall thickness between two adjacent holes is close to the thickness of a depletion layer, the electrochemical reaction is automatically stopped to obtain a silicon nanobelt, the surface crystal orientation of the silicon nanobelt is (110), the silicon nanobelt expands only along the crystal orientation of <110> after lithium is embedded, the silicon nanobelt has a special recrystallization behavior after lithium is removed, has high ion conductivity, a high-stability interface SEI and a high-stability material structure, and can realize high-power and long-service-life circulation under the condition of keeping the high specific capacity of the silicon cathode battery.

Description

Modification method of lithium ion battery silicon negative electrode material
Technical Field
The invention relates to design and development of new energy materials, in particular to a modification method of a silicon negative electrode material of a lithium ion battery.
Background
The lithium ion battery as a novel power energy source is widely applied to the fields of 3C, traffic, energy storage, military industry, artificial intelligence and the like[1 , 2]. Along with the upgrade of consumption, the adjustment of energy structure and the vigorous development of industry in China, the terminal product has higher requirements on high energy density, high specific power, safety and environmental protection of the battery, and the traditional graphite negative electrodeThe lithium ion battery system approaches the theoretical specific energy limit (300 Wh/kg)[3]. The development of lithium ion batteries with high specific energy and high specific power is a key scientific and technological problem which needs to be solved urgently in national economy and social development. Theoretical calculation shows that under the condition that the capacity of the negative electrode material is not more than 1200mAh/g, the improvement of the capacity of the conventional negative electrode material greatly contributes to the improvement of the energy density of the whole battery[4]Silicon has larger theoretical specific capacity (4200mAh/g) which is one order of magnitude higher than the theoretical specific capacity (372mAh/g) of the current commercial graphite negative electrode material; meanwhile, the silicon cathode has the advantages of low discharge potential (about 0.2V), low reactivity with electrolyte, abundant reserves in the earth crust, low price, no toxicity, environmental protection and the like. Therefore, the silicon-based negative electrode material has wide application prospect in the lithium ion battery industry with high specific energy and high specific power, and is an ideal choice for the negative electrode material of the new-generation lithium ion battery.
However, the silicon negative electrode has a bottleneck which is difficult to break through like other high-capacity negative electrode materials: the silicon negative electrode has huge volume expansion (300%) during lithium intercalation, which causes instability of solid electrolyte interface phase (SEI), thereby generating the problems of low coulombic efficiency, fast cycle performance attenuation and the like of the battery[5-8]. Although a great deal of research on modification of silicon cathodes has been carried out in the industry, and the performance of silicon cathode materials is remarkably improved in recent years, the industrialization process of the silicon cathodes is still slowly developed, the content of silicon in commercial electrodes is generally lower than 10%, the practical application is less, and the overall yield of the market is smaller. The core reason is that the current technical scheme has respective limitations, and the problem of silicon cathode expansion is not completely solved. The phase change from crystalline state to amorphous state of the silicon negative electrode in the lithium embedding state can cause compression stress of more than 0.5 GPa; while the tensile stress of 1.5Gpa is introduced along with the reduction of the lithium concentration in the process of lithium removal[9-10]. The existing silicon cathode modification technology cannot effectively resist such large phase change stress, so that the volume change of the silicon cathode cannot be really limited, and the phenomenon of continuous deterioration of an interface caused by volume expansion is still severe. In order to realize the industrialization of the silicon-based cathode lithium ion battery, the key point is to fundamentally solve the problem of performance degradation caused by volume expansion after lithium is embedded in siliconAnd (5) difficult problem.
Reference documents:
1.N.S.Choi,Z.Chen,S.A.Freunberger,X.Ji,Y.K.Sun,K.Amine,G.Yushin,L.F.Nazar,J. Cho,P.G.Bruce,Challenges Facing Lithium Batteries And Electrical Double-Layer Capacitors[J]. AngewandteChemie International Edition,2012,51:9994-10024.
2.R.A.Huggins,Advanced Batteries:Materials Science Aspects[M].New York:Springer, 2008.
3.Y.Tang,Y.Zhang,W.Li,Rational Material Design For Ultrafast Rechargeable Lithium-Ion Batteries[J].Chemical Society Reviews,2015,44(17):5926-5940.
4.Yoshio,M.,Tsumura,T.&Dimov,N.Electrochemical Behaviors of Silicon Based Anode Material[J].J.Power Sources 2005,146,10-14.
5.H.Okamoto,The Li-Si(Lithium-Silicon)System[J].J.Phase Equilibria,1990,11(3), 306-312.
6.C.J.,Wen,R.A.Huggins,Chemical Diffusion In Intermediate Phases In The Lithium-Silicon System[J].J.Solid State Chemistry,1981,37(3):,271-278.
7.P.Limthongkul,Y.I.Jang,N.J.Dudney,Electrochemically-Driven Solid-State Amorphization In Lithium-Silicon Alloys and Implications For Lithium Storage[J].ActaMaterialia, 2003,51(4),1103-1113.
8.H.Li,X.J.Huang,L.Q.Chen,G.W.Zhou,N.Pei,The Crystal Structural Evolution of Nano-Si Anode Caused by Lithium Insertion and Extraction at Room Temperature[J].Solid State Ionics,2000,135(1-4),181-191.
9.Chon,M.J.,Sethuraman,V.A.,McCormick,A.,Srinivasan,V.&Guduru,P.R.Real-Time Measurement of Stress and Damage Evolution During Initial Lithiation of Crystalline Silicon[J]. Phys Rev Lett,2011,107,045503.
10.Maranchi,J.P.,Hepp,A.F.,Evans,A.G.,Nuhfer,N.T.&Kumta,P.N.Interfacial Properties Of The a-Si/Cu:Active-Inactive Thin-film Anode System for Lithium-Ion Batteries[J].J. Electrochem.Soc.2006,153,A1246-A1253.
disclosure of Invention
The invention aims to provide a method for modifying a silicon negative electrode material of a lithium ion battery, which aims to solve the problems in the prior art, limit the expansion of silicon by utilizing the anisotropic characteristic of silicon-embedded lithium, remarkably improve the stability of the silicon negative electrode material, solve the problem of interface deterioration in the circulation process and realize high-power and long-life circulation under the condition of keeping the high specific capacity of the silicon negative electrode battery.
The invention comprises the following steps:
1) taking a p-type silicon (100) sheet as a substrate, adopting an electrochemical micromachining process to carry out electrochemical corrosion, firstly corroding the surface of the substrate into a circular hole, gradually enlarging the circular hole, finally extruding the circular hole into a square shape, and forming a depletion layer at the interface of a corrosive liquid and the hole wall;
2) under the action of an electric field, hole carriers migrate from the substrate to the hole wall along the longitudinal hole wall to participate in reaction with the corrosive liquid interface, and the hole wall becomes thinner gradually in the reaction process;
3) and when the wall thickness between two adjacent holes is close to the thickness of the depletion layer, the electrochemical reaction is automatically stopped to obtain the silicon nanobelt, namely the modified lithium ion battery silicon cathode material.
In the step 3), the surface crystal orientation of the silicon nanobelt is <110>, the size of the silicon nanobelt is about 100 μm long and 500nm wide, and the silicon nanobelts are uniformly distributed on the substrate; the thickness of the silicon nanoribbons is <30 nm.
The modified silicon nanobelt has special lithium-intercalation-deintercalation characteristics: the silicon nanobelts preferentially expand only along the <110> crystal direction after lithium intercalation (i.e., the silicon nanobelts become thicker), which ensures that the interfacial SEI is stable. After lithium is removed, the silicon anode only shrinks along the <110> crystal direction, and the stability of the SEI of the silicon anode is ensured; Si-Si in the silicon sheet material after lithium intercalation and expansion is still bonded along a specific high-order crystal direction, and zigzag chain structures of the Si-Si are kept, and the chain structures can induce silicon crystallization after lithium removal, so that the structural stability of the silicon cathode is ensured.
The silicon nanobelt can limit most lithium ions from being transported along the <110> crystal direction, and the lithium ion migration barrier along the crystal direction is the lowest, so that the high-rate characteristic of the silicon nanobelt is ensured.
On the substrate at the root of the silicon nanobelt, a regular rectangular pyramid-shaped etching pit is formed in the electrochemical micromachining process, and the silicon nanobelt is formed between two adjacent etching pits. The boundaries of the etch pits are aligned along a specific crystal direction, and the inner surfaces of the etch pits are (111) crystal planes, whereby the crystal plane of the silicon nanobelt can be determined to be (110). The interplanar spacing of silicon atoms was 3.18 angstroms, consistent with the (111) plane. After the silicon nanobelt electrode is embedded with lithium, the expansion direction is mainly limited to the <110> direction, the small expansion in other directions can eliminate stress through the changes of bending, rotation, warping and the like of the nanobelt, and the shape after lithium removal can be basically recovered.
After the modified lithium ion battery silicon negative electrode material is subjected to 100 times of lithium extraction and insertion cycles, the structure of the silicon nanometer still keeps complete, and the modified lithium ion battery silicon negative electrode material has lower interface expansion and a more stable SEI film compared with a three-dimensional bulk silicon structure. In the silicon nanobelt cathode, the silicon material has the action of recrystallization after lithium removal, and the silicon atom surface distance is slightly increased compared with the initial test state. In a charge-discharge cycle test, the modified silicon nanobelt disclosed by the invention achieves an excellent result that the first effect is 85.29%, the retention rate is more than 50% at a magnification of 0.1C for 200 circles, and the SiNP is quickly attenuated from the third circle. In a rate test, the modified silicon nanobelt disclosed by the invention has excellent rate characteristics, and the specific capacity after 2000 circles is still more than 1000 mAh/g.
Drawings
Fig. 1 is a schematic diagram of lithium desorption of a common silicon negative electrode material and an ultrathin (110) crystal plane two-dimensional structure.
FIG. 2 is a graph of the topography of a silicon nanobelt material prepared by the embodiment of the present invention. Wherein (a-c) are SEM images of silicon nanobelts; (d) a silicon nanobelt TEM image; (e) SEM image of silicon nanobelt electrode; (f) a silicon nanobelt first lithium intercalation SEM picture; (g) first lithium removal SEM of the silicon nanobelt; (h-i) TEM image of silicon nanobelts after 100 cycles of charge and discharge.
FIG. 3 is a test chart of electrochemical performance of silicon nanobelt negative electrode.
Fig. 4 is a schematic diagram of a mechanism for forming a silicon nanobelt negative electrode.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following embodiments will be further described with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The embodiment of the invention provides a modification method of a silicon negative electrode material of a lithium ion battery, which comprises the following steps:
a p-type silicon (100) sheet is used as a substrate, and electrochemical corrosion is carried out by adopting an electrochemical micromachining process. The etching process is shown in fig. 4, and the circular holes are formed on the surface of the substrate, gradually enlarged and finally extruded to be square. A depletion layer is formed at the interface between the etching solution and the hole wall (fig. 4a), and the chemical reaction of the process is as follows:
Si+2HF+nh+→SiF2+2H++(2-n)e-(1)
SiF2+2HF→SiF4+H2(2)
SiF4+2HF→H2SiF6(3)
under the action of the electric field, hole carriers migrate from the substrate to the hole walls along the longitudinal hole walls to participate in reaction with the interface of the corrosive liquid, and the hole walls become thinner gradually in the reaction process (fig. 4 b). This reaction process is self-limiting, and the electrochemical reaction stops automatically when the wall thickness between two adjacent holes approaches the depletion layer thickness (fig. 4 c). This successfully produced silicon nanobelts (fig. 4 d). The obtained silicon nanobelt has a surface crystal orientation of <110>, a size of 100 μm long and a width of 500nm, and is uniformly distributed on the substrate.
The silicon nanobelt has special lithium-releasing and inserting characteristics: the silicon nanobelts will preferentially expand along the <110> crystal direction after lithium intercalation (i.e., the silicon nanobelts become thicker), which ensures that the interfacial SEI is stable. Si-Si in the silicon sheet material after lithium intercalation and expansion is still bonded along a specific high-order crystal direction, and zigzag chain structures of the Si-Si are kept, and the chain structures can induce silicon crystallization after lithium removal, so that the structural stability of the silicon cathode is ensured.
The thickness of the silicon nanoribbons is <30 nm.
The silicon nanobelt has the length of 100 mu m and the width of 500 nm.
On the substrate at the root of the silicon nanobelt, a regular rectangular pyramid-shaped etching pit is formed in the electrochemical micromachining process, and the silicon nanobelt is formed between two adjacent etching pits. The boundaries of the etch pits are arranged along a specific crystal direction, and the inner surfaces of the etch pits are (111) crystal faces, so that the crystal face of the silicon nanobelt is (110).
The interplanar spacing of silicon atoms was 3.18 angstroms, consistent with the (111) plane.
After the silicon nanobelt electrode is embedded with lithium, the expansion direction is mainly limited to the <110> direction, the small expansion in other directions can eliminate stress through the changes of bending, rotation, warping and the like of the nanobelt, and the shape after lithium removal can be basically recovered.
During the lithium intercalation reaction of the crystalline silicon, anisotropy exists in lithium intercalation activity and volume expansion. The Si (110) crystal face has the highest activity in the process of lithium intercalation, and the lithium intercalation and expansion speed of the Si (110) crystal face are far higher than those of other crystal faces[11-17]. Based on the characteristic, the lithium removal and insertion characteristics of the silicon cathodes with different crystal orientation structures are carried out, and the calculation shows that: for the ultrathin silicon (110) sheet structure, the expansion direction of a silicon cathode can be limited to the normal direction of the surface of a two-dimensional material after lithium intercalation, and the transverse direction of the two-dimensional material is only slightly enlarged, namely, the lithium intercalation process of an ultrathin Si (110) crystal plane only introduces a small surface area increment to a crystal plane with low lithium intercalation activity. The material has a natural and stable interface without any modification treatment and specific capacity sacrifice (figure 1). Si-Si in the expanded silicon sheet material is bonded along a specific high-order crystal direction, and a zigzag chain structure of the Si-Si is maintained, which plays an important role in maintaining the stability of the structure in the circulating process. Meanwhile, the characteristics of high multiplying power of the lithium ion battery are determined by a huge high lithium intercalation active crystal face and an extremely low ion transport distance in a two-dimensional structure. Therefore, by regulating the crystal orientation structure of the silicon material, the (110) crystal plane silicon sheet (thickness) is obtained<30nm) and can realize low interface expansion.
Generally, a silicon material with a crystal orientation is expected to be obtained by adopting a single crystal silicon material growth process, but the complex process and the high cost are not beneficial to industrialization. The invention provides a method for solving the problem of large-scale production of a two-dimensional silicon cathode by adopting an electrochemical micromachining process. The process of corroding silicon is similar to the process of lithium intercalation of a silicon cathode in terms of micro-mechanism, and the subsequent chemical reaction is carried out by preferentially opening the Si-Si bond with the lowest bond energy (along the <110> crystal orientation), so that the two processes have anisotropy. The lithium insertion of the silicon material results in preferential expansion of the silicon material along the <110> crystal orientation, while the electrochemical etching process results in preferential etching of the silicon material along the <110> crystal orientation, both processes being "reciprocal". The preferential orientation of the electrochemical corrosion leads to the preferential exposure and corrosion of the crystal face of the silicon (110), and finally the quasi-two-dimensional silicon strip material with the thickness of the <110> crystal orientation in a nanometer scale is obtained.
FIG. 2 is a topographical characterization of the prepared silicon nanobelt material. The silicon nanobelts have a band-like structure of about 100 μm in length and 500nm in width (FIGS. 2 a and c). On the substrate at the root of the silicon nanobelt (fig. 3, panel b), it can be seen that a regular rectangular pyramid-type etch pit is formed during electrochemical micromachining, and the silicon nanobelt is formed between two adjacent etch pits. The boundaries of the etch pits are arranged along a specific crystal direction, and the inner surfaces of the etch pits are (111) crystal faces, so that the crystal face of the silicon nanobelt is (110). Under high resolution TEM (fig. 2, panel d), the arrangement of silicon atoms can be clearly seen with a silicon atom interplanar spacing of 3.18 angstroms, consistent with the (111) plane. After lithium is embedded in the silicon nanobelt electrode, the expansion direction is mainly limited to the <110> direction, and the small expansion in other directions can eliminate stress through the changes of bending, rotation, warping and the like of the nanobelt, so that the shape after lithium removal can be basically recovered (graphs e-g in fig. 2). After 100 cycles of lithium deintercalation, the structure of the silicon nano still remains intact, and has lower interfacial expansion and a more stable SEI film than the three-dimensional bulk silicon structure (figure h in figure 2). In the silicon nanobelt cathode, the recrystallization behavior of the silicon material after lithium removal is observed for the first time, and the silicon atom surface distance is slightly increased compared with the initial test state and basically consistent with the theoretical calculation result. This is of great importance to ensure the structural stability of the silicon material (diagram i in fig. 2).
The charge-discharge cycle test and the magnification test of the silicon nanobelt cathode material half cell are performed to respectively test the cycle characteristics (fig. 3, a and b) of a pure silicon nanobelt (SiNR) and silicon nanoparticles (SiNP), the silicon nanobelt realizes the excellent results of first effect 85.29%, the retention rate is more than 50% at 0.1C magnification for 200 circles, and the SiNP is rapidly attenuated from the third circle. In the rate test (fig. 3, c), the silicon nanobelt showed excellent rate characteristics, and the specific capacity after 2000 cycles was still greater than 1000 mAh/g.
The modified silicon nanobelt has the following special lithium intercalation and deintercalation characteristics:
1. the surface of the silicon nanobelt is in a <110> crystal orientation, so that most of lithium ions are guaranteed to be transported along the <110> crystal orientation, and the lithium ion migration barrier along the crystal orientation is the lowest, so that the silicon nanobelt has high multiplying power characteristics. 2. The silicon nanobelts expand only along the <110> crystal direction after lithium is embedded, namely the silicon nanobelts become thick and thin after lithium is removed, and the SEI film stability of the interface is ensured by the mode of single-direction expansion and contraction. 3. The silicon nanobelt has a special behavior of recrystallization after lithium removal, which ensures that the silicon nanobelt has structural stability in the battery cycle process.
The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.

Claims (6)

1. A modification method of a silicon negative electrode material of a lithium ion battery is characterized by comprising the following steps:
1) taking a p-type silicon (100) sheet as a substrate, adopting an electrochemical micromachining process to carry out electrochemical corrosion, firstly corroding the surface of the substrate into a circular hole, gradually enlarging the circular hole, finally extruding the circular hole into a square shape, and forming a depletion layer at the interface of a corrosive liquid and the hole wall;
2) under the action of an electric field, hole carriers migrate from the substrate to the hole wall along the longitudinal hole wall to participate in reaction with the corrosive liquid interface, and the hole wall becomes thinner gradually in the reaction process;
3) and when the wall thickness between two adjacent holes is close to the thickness of the depletion layer, the electrochemical reaction is automatically stopped to obtain the silicon nanobelt, namely the modified lithium ion battery silicon cathode material.
2. The method for modifying the silicon negative electrode material of the lithium ion battery according to claim 1, wherein in the step 3), the surface crystal orientation of the silicon nanobelt is <110 >.
3. The method for modifying the silicon negative electrode material of the lithium ion battery according to claim 1, wherein in the step 3), the silicon nanobelts have a length of 100 μm and a width of 500nm, and are uniformly distributed on the substrate; the thickness of the silicon nanoribbons is <30 nm.
4. The method for modifying the silicon negative electrode material of the lithium ion battery as claimed in claim 1, wherein in the step 3), the silicon nanobelt preferentially expands only along the <110> crystal direction after lithium intercalation, and contracts only along the <110> crystal direction after lithium deintercalation, so as to ensure the stability of the silicon negative electrode SEI; Si-Si in the silicon sheet material after lithium intercalation and expansion still forms a bond along a specific high-order crystal direction, and a zigzag chain structure of the Si-Si is kept for inducing silicon after lithium removal to recrystallize, so that the structural stability of the silicon cathode is ensured.
5. The method for modifying the silicon negative electrode material of the lithium ion battery as claimed in claim 1, wherein in the step 3), the silicon nanobelt is used for limiting most lithium ions to be transported along a <110> crystal direction, and a lithium ion migration barrier along the crystal direction is the lowest, so as to ensure the high rate property of the silicon nanobelt.
6. The lithium ion battery silicon negative electrode material modified by the modification method of the lithium ion battery silicon negative electrode material according to any one of claims 1 to 5.
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