A method for fabricating a 3D graphitized ultrafine fiber conductive network self-supporting lithium battery

Abstract

This invention discloses a method for preparing a 3D graphitized ultrafine fiber conductive network self-supporting lithium battery, relating to the field of lithium battery cathode material technology. This invention utilizes electrospinning technology to prepare three-dimensional (3D) network structure polyimide (PI) nanofibers, which, after graphitization (GPI), are used as a substrate to support the NCM811 cathode material. This method offers several advantages: First, the PI prepared by electrospinning can form a long-range, continuous three-dimensional electron network, facilitating electron and ion transfer and effectively alleviating the volume expansion and cycle performance degradation issues of NCM811 electrode materials. Second, it eliminates the need for conductive additives and aluminum foil current collectors, achieving a self-supporting electrode material. Third, because the PI fibers prepared by electrospinning have excellent flexibility, they can be used in flexible lithium-ion batteries, directly assembled into energy storage and conversion devices. Therefore, combining electrospinned graphitized GPI to support NCM811 battery materials is a good strategy for improving the electrochemical performance of NCM811.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material technology, specifically relating to a method for preparing a 3D graphitized ultrafine fiber conductive network self-supporting lithium battery. Background Technology

[0002] Nickel-rich layered oxides LiTMO2 (TM = Ni,Co,Mn) are used as cathode materials in lithium-ion batteries due to their high capacity. In particular, lithium nickel cobalt manganese oxide (NCM811), as a cathode material, has attracted great attention from researchers worldwide due to its excellent performance. Among them, nickel-rich ternary oxides (LiNi...) with higher nickel content... 0.8 Co 0.1 Mn 0.1 O2 and NCM811 cathode materials have become a hot research topic due to their high specific capacity. However, the low lithium-ion diffusion coefficient and electronic conductivity of NCM811 are significant limiting factors for improving its electrochemical performance, particularly its cycle performance and initial coulombic efficiency (85-90%). Research reports suggest that surface modification / composite methods can improve the ionic / electronic conductivity of the material. However, the surface modifications / composite materials commonly used in these reports are functionally singular, offering limited control over the electronic or ionic conductivity of NCM811 and failing to simultaneously improve both electronic and ionic conduction capabilities. Furthermore, current research reports pay relatively little attention to the NCM811 electrode itself. The electrode consists of active material, conductive agent, and binder. During cycling, the active material is prone to detachment from the conductive agent, leading to a decline in cycle performance and hindering the large-scale application of ternary cathode materials in power batteries. Therefore, it is necessary to construct an efficient and stable conductive network to improve the electrochemical performance of the material. Currently, the main surface modifications for ternary cathode materials include:

[0003] (1) Bulk doping modification

[0004] Studies have shown that when the Li content in layered materials exceeds 0.6%, it leads to the expansion of the a-axis and the contraction of the c-axis in its lattice parameters, thereby causing Li to... + The diffusion channels narrow, thus causing Li + The diffusion coefficient is reduced. To address this issue, researchers mainly improve the diffusion coefficient of ternary cathode material Li through material doping (Nb, Al, W, Zr, Ga, etc.). + The diffusion coefficient is a problem. Therefore, bulk doping technology is crucial for improving the diffusion coefficient of NCM811 ternary cathode material Li. + One of the main measures to improve diffusion coefficient and electrochemical performance.

[0005] (2) Surface structure modification

[0006] Research shows that: with the deintercalation of lithium ions, the volume expansion and contraction of ternary positive electrode material can reach about 3.9%, which is enough to cause extensive cracks near the grain boundary inside the particle. The continuous appearance of new cracks inside the material particle exposes fresh surface and continues to react with the electrolyte, eventually causing the pulverization of the electrode material and the failure of the battery. Generally speaking, the volume change of high-nickel ternary positive electrode material during the cycle process is larger. Therefore, it is more likely to cause material failure by micro-crack expansion. Researchers mainly through the surface coating of inorganic materials (Al2O3, Li3PO4, LiNbO3, LiF, WO3, FePO4, etc.). Therefore, the surface structure modification process of the material is also the main measure to solve the diffusion coefficient and cycle performance of the current NCM811 ternary positive electrode material Li + Although the bulk doping and surface structure modification can improve the diffusion coefficient and electrochemical performance of NCM811 ternary positive electrode material Li + However, the single regulation of electronic and ionic conductivity is difficult to improve the electronic and ionic conductivity of the material at the same time. Therefore, it is necessary to build an efficient and stable conductive network to improve the electrochemical performance of NCM811.

[0007] The present application aims to solve the defects of poor conductive performance, low first coulomb efficiency, the need for a current collector aluminum foil, secondary crystal cracking and unstable safety performance of single ternary NCM811 lithium battery, and provides a long cycle performance of lithium ion battery with good safety, no current collector and self-supporting. SUMMARY

[0008] In order to solve the defects and deficiencies of the prior art, the purpose of the present application is to provide a preparation method of 3D graphitized ultra-fine fiber conductive network self-supporting lithium battery.

[0009] In order to achieve the above purpose, the preparation method of the present application comprises the following steps:

[0010] One: preparation of graphitized GPI

[0011] Aromatic dianhydride and dianhydride are used to synthesize precursor polyamide acid (PAA) solution under low temperature conditions, and flexible and tough multi-layer PAA wire is prepared by electrospinning, then imidization reaction is carried out in nitrogen, and then 1600-1800 O C 20 minutes.

[0012] Two: preparation of self-supporting 3D flexible GPI self-supporting NCM811 electrode material

[0013] S1: using co-precipitation method to synthesize spherical Ni 0.8 Co 0.1 Mn 0.1The NCM811 powder is prepared by high-temperature lithiation method using (OH)2precursor;

[0014] S2: 5 g of NCM811 and 0.1-0.5 g of PVDF binder are added into a N,N-dimethylacetamide (DMAC) solution (50 ml), and stirred at 25°C for 12 h;

[0015] S3: The slurry is repeatedly deposited on the GPI, and dried at 110°C under vacuum for 12 h;

[0016] S4: Subsequently, the positive material of the black electrode sheet is cut into a round plate electrode;

[0017] S5: The prepared electrode, Celgard 2300 separator and lithium sheet are sequentially placed;

[0018] S6: 1M LiPF6electrolyte is used;

[0019] S7: Finally, the CR2032 button cell is assembled in an Ar-filled glove box, and after assembly, the battery is placed for 24 h.

[0020] Preferably, the stirring speed in S2 is 400-800 rpm.

[0021] Preferably, the diameter of the round plate electrode in S4 is 10-25 mm.

[0022] Preferably, the temperature for the polycondensation of the precursor polyamic acid (PAA) solution is -25°C-0°C.

[0023] Preferably, the volume ratio of the electrolyte in S6 is dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) = 1:1:1.

[0024] Preferably, the aromatic diacid anhydride is selected from one or more of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), pyromellitic dianhydride, naphthalene tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, diphenyl sulfone dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, and triphenyl diphenyl ether dianhydride.

[0025] Preferably, the diamine is an aromatic diamine, and the aromatic diamine is selected from one or more of hydrazine, diamine anthracene, cyclohexane diamine, 2,2'-dipyridyl-6,6'-diamine, 3,8-diamine naphthalene, pyrazine-2,6-diamine, 2,5-diaminotoluene, 2,7-diamine acridine, and 9,9-bis(4-aminophenyl)fluorene.

[0026] Compared with the prior art, the graphite GPI has extremely outstanding electron and ion transfer capacity, the PI nanofiber prepared by electrostatic spinning has good flexibility, can support flexibility, the network structure can accommodate more electrolyte, thereby improving the release capacity and migration rate of lithium ions, thereby improving the first coulombic efficiency and rate performance, and is beneficial to the release of lattice energy in the charging and discharging process, thereby improving the cycle performance of the lithium battery. BRIEF DESCRIPTION OF DRAWINGS

[0027] For ease of illustration, the present application is described in detail by the following specific implementation and drawings.

[0028] Figure 1 The discharge curve of the electrochemical performance of the NCM811 and GPI@NCM811 electrode of the present application. DETAILED DESCRIPTION

[0029] To make the purpose, technical scheme and advantages of the present application more clear, the following specific examples are used to describe the present application. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0030] Here, it should also be noted that, in order to avoid obscuring the present application due to unnecessary details, only structures and / or processing steps closely related to the scheme according to the present application are shown in the following examples, and other details not closely related to the present application are omitted.

[0031] The specific embodiments of the present application are further described below in conjunction with examples. The following examples are only used to more clearly illustrate the technical scheme of the present application, and cannot limit the protection scope of the present application.

[0032] EXAMPLE

[0033] A preparation method of a 3D graphitized ultra-fine fiber conductive network self-supporting lithium battery, comprising the following steps:

[0034] I: Preparation of graphitized GPI

[0035] A precursor polyamide acid (PAA) solution was synthesized by condensation polymerization of aromatic diacid anhydride and aromatic diamine under low temperature conditions of-25℃, flexible and tough multi-layer PAA filaments were prepared by electrostatic spinning, then imidization reaction was carried out in nitrogen, and then 1600-1800 O C 20 minutes.

[0036] wherein the aromatic diacid anhydride is selected from one or more of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), pyromellitic dianhydride, naphthalene tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, diphenyl sulfone dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, and triphenyl diphenyl ether dianhydride; and the aromatic diamine is selected from one or more of phenylenediamine, diamine anthracene, cyclohexanediamine, 2,2'-dipyridyl-6,6'-diamine, 3,8-diamine naphthalene, pyrazine-2,6-diamine, 2,5-diaminotoluene, 2,7-diamine acridine, and 9,9-bis(4-aminophenyl)fluorene.

[0037] II. Preparation of a self-supporting 3D flexible GPI self-supporting NCM811 electrode material

[0038] S1: Synthesis of spherical Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor, and preparation of NCM811 powder by high-temperature lithiation;

[0039] S2: 5g of NCM811 and 0.5g of PVDF binder were added to a N,N-dimethylacetamide (DMAC) solution (50ml), stirred at 25°C for 12h, and the stirring speed was 500rpm;

[0040] S3: The slurry was repeatedly deposited on the GPI, and dried at 110°C under vacuum for 12h;

[0041] S4: Subsequently, the positive electrode material of the black electrode sheet was cut into a round plate electrode, and the diameter of the round plate electrode was 12mm;

[0042] S5: The prepared electrode, Celgard 2300 separator, and lithium sheet were placed in sequence;

[0043] S6: 1M LiPF6 electrolyte was used, and the volume ratio of the electrolyte was dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) = 1:1:1;

[0044] S7: Finally, the CR2032 button cell was assembled in an Ar-filled glove box, and after assembly, the battery was placed still for 24h.

[0045] In the above examples, the optical images of PI, GPI and GPI@NCM811 samples were characterized respectively. Whether before or after graphitization, the PI material still has elasticity and toughness and can be bent by 180 degrees. Further, the graphitized PI (GPI) is mixed with NCM811 to form a positive electrode of a battery, which can be mixed by 180 degrees and can be made into a self-supporting battery. The pre-graphitized PI and the graphitized PI have a good network structure; but the average diameter is slightly reduced from 380 nm to 370 nm, which is due to the volume shrinkage of PI at high temperature.

[0046] The average diameter of the NCM811 particles is about 10-12 μm. The Ni, Co, Mn, C, N and F elements are uniformly distributed, indicating that the graphitized microfiber conductive network coats a small amount of PVDF on the surface of NCM811 and GPI, which can be used as a carrier for NCM811 spherical particles.

[0047] Figure 1 The electrochemical performance of the NCM811 and GPI@NCM811 electrodes is shown in (a) the first charge-discharge curve; (b) the first cycle of NCM811 and GPI@NCM811 with Li metal; (c) the rate curve of NCM811 and GPI@NCM811.

[0048] Figure 1 (a) is the initial discharge curve of 0.1C in the range of 2.8-4.3V at 25℃. It can be seen that the discharge specific capacity of the GPI@NCM811 electrode is 209.8mAh g-1, which is slightly higher than that of the NCM811 electrode of 201.9mAh g-1. From Figure 1 (b) It can be seen that the GPI@NCM811 electrode reduces the first irreversible capacity of the NCM811 electrode from 21.9mAh g-1 to 3.3mAh g-1, and increases the coulombic efficiency (CE) of the first charge-discharge from 88.9% to 95.9%, because the graphene structure provides fast electron transport. The capacity of the GPI@NCM811 electrode is higher than that of the NCM811 electrode material, especially at 10℃, the capacity is 127.2mAh g-1, which is much higher than that of the NCM811 electrode of 104.1mAh g-1. This is because the network structure of the GPI material is developed, which can accommodate more lithium ions.

[0049] From Figure 1 It can be seen that the beneficial effects of the present application are:

[0050] One: GPI self-supporting NCM811 material utilizes graphitized ultra-fine fiber conductive network (good conductive effect, high rate) + "developed" pore structure (good electrolyte infiltration effect, good ion diffusion rate, small electrode internal resistance, and high active material utilization rate). It can effectively improve the first coulombic efficiency, inhibit the secondary crystal cracking of NCM811, embed more lithium ions compared with uncoated NCM811, improve the energy density of the battery and reduce the occurrence of side reactions, and improve the cycle performance of the lithium battery;

[0051] Two: GPI self-supporting NCM811 material forms GPI@NCM811 positive electrode material, which reduces the first irreversible capacity of NCM811 electrode from 21.9 mAh g-1 to 3.3 mAh g-1, and improves the coulombic efficiency (CE) of the first charge-discharge from 88.9% to 95.9%. This is because the graphene structure provides fast electron transfer; The capacity of the GPI@NCM811 electrode is higher than that of the NCM811 electrode material, especially at a rate of 10C, the capacity is 127.2 mAh g-1, which is much higher than the 104.1 mAh g-1 of the NCM811 electrode. This is because the network structure of the GPI material can accommodate more lithium ions.

[0052] The present application utilizes electrospinning technology to prepare three-dimensional (3D) network structure polyimide (PI) nanofibers, which are graphitized (GPI) and used as a substrate for supporting positive electrode NCM811 material, which has the following advantages: first, the PI prepared by electrospinning can form a long-range, continuous three-dimensional electronic network, which is conducive to the transfer of electrons and ions, and can effectively alleviate the volume expansion of the NCM811 electrode material and the problem of cycle performance decline; second, no conductive additives and aluminum foil current collectors are needed to realize self-supporting electrode material; third, because the PI fiber prepared by electrospinning has good flexibility, it can be used for flexible lithium ion batteries, and can be directly assembled in energy storage and conversion devices. Therefore, the GPI supporting NCM811 battery material prepared by combining electrospinning and graphitization is a good strategy to improve the electrochemical performance of NCM811.

[0053] Graphitized GPI has extremely outstanding electron and ion transfer capacity, and the PI nanofiber prepared by electrospinning has good flexibility, can support flexibility, and the network structure can accommodate more electrolyte, thereby improving the release capacity and migration rate of lithium ions, thereby improving the first coulombic efficiency and rate performance, and being conducive to the release of lattice energy during the charging and discharging process, thereby improving the cycle performance of the lithium battery.

[0054] It will be obvious to a person skilled in the art that the application is not limited to the details of the above-described exemplary embodiments, but that the application can be implemented in other embodiments without departing from the scope of the application. The embodiments are therefore to be seen as exemplary and in no way restrictive, the scope of the application being defined by the claims below rather than by the above description, and all variations falling within the meaning and range of equivalency of the essential characteristics of the claims are therefore intended to be embraced therein.

[0055] Furthermore, it should be understood that although the present specification describes exemplary embodiments, the application is not limited to only one independent technical solution in each embodiment, and the present specification is described in this way only for the sake of clarity, and a person skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that a person skilled in the art can understand.

Claims

1. A method for preparing a 3D graphitized ultra-fine fiber conductive network self-supporting lithium battery, comprising the following steps: I. Preparation of graphitized GPI A precursor polyamide acid (PAA) solution was synthesized by condensation polymerization of aromatic diacid anhydride and aromatic diamine at low temperature, the synthesis temperature was -25℃-0℃, and flexible and tough multi-layer PAA filaments were prepared by electrospinning, then imidization reaction was carried out in nitrogen, and then graphitization was carried out in a graphitization furnace at 1600-1800℃ to obtain graphitized polyimide (GPI); II. Preparation of self-supporting 3D flexible GPI self-supporting NCM811 electrode material and lithium battery S1: Synthesis of spherical Ni 0.8 Co 0.1 Mn 0.1 (OH)2precursor, and preparation of NCM811 powder by high-temperature lithiation method; S2: 5g NCM811 and 0.1-0.5g PVDF binder were added to 50ml N,N-dimethylacetamide solution, and stirred at 25℃ for 12h; S3: The slurry was repeatedly deposited on GPI, and dried at 110℃ under vacuum for 12h; S4: Subsequently, the positive electrode material of the black electrode sheet was cut into a round plate electrode; S5: The prepared electrode, Celgard 2300 separator and lithium sheet were placed in sequence; S6: 1M LiPF6 electrolyte was used, and the volume ratio of the electrolyte was dimethyl carbonate:methyl ethyl carbonate:ethylene carbonate = 1:1:1; S7: Finally, the CR2032 button cell was assembled in an Ar-filled glove box, and after assembly, the battery was placed still for 24h.

2. The method for preparing a 3D graphitized ultrafine fiber conductive network self-supporting lithium battery according to claim 1, characterized in that: The stirring speed in S2 was 400-800rpm.

3. The method for preparing a 3D graphitized ultrafine fiber conductive network self-supporting lithium battery according to claim 1, characterized in that: The diameter of the round plate electrode in S4 was 10-25mm.

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