CN115394961A - Lithium iron phosphate thick electrode and preparation method and application thereof - Google Patents
Lithium iron phosphate thick electrode and preparation method and application thereof Download PDFInfo
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 119
- 238000002360 preparation method Methods 0.000 title abstract description 25
- 238000000576 coating method Methods 0.000 claims abstract description 160
- 239000011248 coating agent Substances 0.000 claims abstract description 143
- 239000006258 conductive agent Substances 0.000 claims abstract description 55
- 239000011163 secondary particle Substances 0.000 claims abstract description 55
- 239000002245 particle Substances 0.000 claims abstract description 48
- 239000011230 binding agent Substances 0.000 claims abstract description 43
- 239000006255 coating slurry Substances 0.000 claims description 45
- 239000011247 coating layer Substances 0.000 claims description 25
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 20
- 239000011164 primary particle Substances 0.000 claims description 16
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 13
- 239000002131 composite material Substances 0.000 claims description 11
- 239000010410 layer Substances 0.000 claims description 11
- 239000002041 carbon nanotube Substances 0.000 claims description 10
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 10
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 8
- 238000005096 rolling process Methods 0.000 claims description 8
- 239000002904 solvent Substances 0.000 claims description 6
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 5
- 229910001416 lithium ion Inorganic materials 0.000 claims description 5
- 239000002105 nanoparticle Substances 0.000 claims description 2
- 239000011148 porous material Substances 0.000 abstract description 17
- 239000003792 electrolyte Substances 0.000 abstract description 15
- 239000007791 liquid phase Substances 0.000 abstract description 15
- 238000005056 compaction Methods 0.000 abstract description 13
- 239000011149 active material Substances 0.000 abstract description 9
- 230000005540 biological transmission Effects 0.000 abstract description 9
- 230000008595 infiltration Effects 0.000 abstract description 6
- 238000001764 infiltration Methods 0.000 abstract description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 23
- 229910052782 aluminium Inorganic materials 0.000 description 23
- 239000011888 foil Substances 0.000 description 22
- 230000000052 comparative effect Effects 0.000 description 21
- 239000002033 PVDF binder Substances 0.000 description 16
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 16
- 238000002156 mixing Methods 0.000 description 10
- 238000003756 stirring Methods 0.000 description 8
- 239000006229 carbon black Substances 0.000 description 7
- 230000001360 synchronised effect Effects 0.000 description 7
- 238000011161 development Methods 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- 239000007790 solid phase Substances 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 230000001105 regulatory effect Effects 0.000 description 4
- 238000010030 laminating Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
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- 230000007423 decrease Effects 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
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- 150000002500 ions Chemical class 0.000 description 2
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- 230000005012 migration Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000002608 ionic liquid Substances 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
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- 238000006467 substitution reaction Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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Abstract
The invention provides a lithium iron phosphate thick electrode and a preparation method and application thereof. The thick lithium iron phosphate electrode comprises a current collector and an electrode coating located on the surface of the current collector, wherein the electrode coating comprises a first coating and a second coating which are stacked, the second coating is located on one side close to the current collector, the first coating comprises spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating comprises lithium iron phosphate single particles, a second conductive agent and a second binder. According to the invention, through the matching of active materials in the first coating and the second coating, a layered structure of upper lithium iron phosphate secondary particles and lower lithium iron phosphate single particles (the upper layer far away from the current collector) is adopted, the tortuosity and liquid phase resistance are obviously reduced, large pores are formed among spherical secondary particles, small pores are formed among single particles, the infiltration of electrolyte and the liquid phase transmission are facilitated, the compaction density of an electrode is improved, and finally, a thick electrode structure with excellent energy density and rate capability is obtained.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a lithium iron phosphate thick electrode and a preparation method and application thereof.
Background
With the rapid development of new energy electric vehicles, people are increasingly demanding high-energy, high-power and high-safety power batteries. At present, the development strategies of the high-energy density lithium battery mainly include the development of high-specific-capacity anode and cathode materials, high-pressure electrolyte introduction, thick electrode technology and the like. The thick electrode technology is the simplest and most effective method for improving the energy density of the battery, however, with the increase of the thickness of the electrode, the stripping force of the electrode is obviously reduced, the transmission path of an ionic liquid phase is obviously increased, and the capacity is quickly attenuated during high-rate charge and discharge. In order to improve the dynamic performance of the thick electrode, the electrode structure can be designed and optimized from the following aspects: (1) the particle size of the active main material is reduced, solid phase diffusion and interface reaction rate are obviously improved along with the reduction of the particle size, and the rate capability is obviously improved; (2) the method comprises the following steps of (1) electrode pore forming, namely obtaining an array pore structure thick electrode by adopting methods such as mechanical pore forming, chemical pore forming or laser pore forming, and the like, wherein the liquid phase resistance of the electrode is obviously reduced along with the increase of vertical pores, so that the rate capability is improved; (3) the high-conductivity electrolyte is applied and developed, and the dynamic performance of the battery is improved by adjusting the composition of a solvent and lithium salt, improving the conductivity of the electrolyte, reducing the viscosity of the electrolyte and the like.
However, in the actual battery development process, the use of smaller particle main materials has the disadvantages of low compaction density, large liquid phase resistance, and increased side reactions due to large specific surface area, so that it is difficult to achieve compatibility between high capacity and high rate performance in the preparation of thick electrodes. The adoption of the electrode pore-forming method also has the problems of low production efficiency, large equipment investment, active material structure damage, battery self-discharge verification and the like. The development of the high-conductivity electrolyte has the problems of long development period, limited improvement of the dynamic performance of the battery, deteriorated cycle life and the like.
CN110010900A discloses a thick electrode with good electrochemical performance, which is manufactured by laminating two electrode films with different porosities and laminating a composite electrode film on a carbon-coated aluminum foil, and is formed by laminating two dry electrode films. However, the invention is manufactured by pressing two electrode films with different porosities and then pressing a composite electrode film on a carbon-coated aluminum foil, and because the composite electrode film is formed by pressing two dry electrode films, an interface for bonding the two electrode films is inevitably arranged in the electrode film, and the electrode film interface is easy to delaminate and fall off due to the change of internal stress of the electrode in the charging and discharging processes of the battery, so that the cycle performance of the battery is influenced, and the cost is higher.
CN102324493A discloses a thick electrode with good electrochemical performance, adopts the mode of thick liquid coating to dry and roll the electrode diaphragm with the mass flow body complex, carries out thick liquid coating on the electrode diaphragm surface of drying for the second time, dries the roll again and prepares thick electrode, through the roll-in pressure intensity of control twice, ensures that the electrode diaphragm of different positions has different conductivity and porosity, has solved the problem of electron and ion transmission difficulty in the thick pole piece. However, the electrode diaphragm, the current collector and the electrode diaphragm are compounded by adopting a slurry coating mode, and wet slurry is coated on the surface of the dried electrode diaphragm, so that the phenomenon that the dried material is dissolved out again is avoided, and the electronic conductance and the pore distribution of the electrode are influenced.
Therefore, how to improve the energy density and rate capability of the lithium iron phosphate thick electrode and improve the peeling strength and the dynamic performance of the thick electrode is a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a lithium iron phosphate thick electrode and a preparation method and application thereof. According to the invention, through the matching of active materials in the first coating and the second coating, the layered structure of the upper lithium iron phosphate secondary particles and the lower lithium iron phosphate single particles (the upper layer far away from the current collector) is adopted, the tortuosity and the liquid phase resistance are obviously reduced, the larger pores are formed among the spherical secondary particles, the smaller pores are formed among the single particles, the electrolyte infiltration and the liquid phase transmission are facilitated, the compaction density of the electrode is improved, and finally, the thick electrode structure with excellent energy density and multiplying power performance is obtained.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a thick lithium iron phosphate electrode, which comprises a current collector and an electrode coating located on the surface of the current collector, wherein the electrode coating comprises a first coating and a second coating which are stacked, the second coating is located on one side close to the current collector, the first coating comprises spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating comprises lithium iron phosphate single particles, a second conductive agent and a second binder.
The electrode coating in the invention can be only on one side of the current collector, and can also be simultaneously positioned on two sides of the current collector.
The spherical lithium iron phosphate secondary particles provided by the invention are formed by stacking and condensing lithium iron phosphate primary particles.
According to the invention, through the matching of active materials in the first coating and the second coating, the layered structure of the upper lithium iron phosphate secondary particles and the lower lithium iron phosphate single particles is adopted, the tortuosity and the liquid phase resistance are obviously reduced, large pores are formed among the spherical secondary particles, small pores are formed among the single particles, the electrolyte infiltration and the liquid phase transmission are facilitated, the compaction density of the electrode is improved, and finally, the thick electrode structure with excellent energy density and rate capability is obtained.
In the invention, if the first coating and the second coating are both lithium iron phosphate single particles, the preparation of a battery with low tortuosity and high power density is difficult to realize, and if the first coating and the second coating are both lithium iron phosphate secondary particles, the problems of small compaction density, low energy density and the like can be caused.
Preferably, the thickness of the electrode coating is 100 to 1000 μm, such as 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm, etc.
Preferably, the thickness of the first coating layer accounts for 30 to 70% of the thickness of the electrode coating layer, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, etc.
In the invention, the thickness of the first coating is too large, which is not beneficial to improving the energy density, and if the thickness is too small, the problems of high tortuosity of a thick electrode, poor wettability of electrolyte, poor rate capability and the like can occur.
Preferably, the primary particles in the spherical lithium iron phosphate secondary particles in the first coating layer and the lithium iron phosphate single particles in the second coating layer are both nanoscale particles.
In the invention, the primary particles in the secondary particles and the lithium iron phosphate single particles are in the nanometer scale, so that the rapid solid-phase diffusion of lithium ions can be better realized, and the multiplying power of a thick electrode and the low-temperature charge and discharge performance are improved.
Preferably, the D50 of the spherical lithium iron phosphate secondary particles is 5 to 15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or the like.
Preferably, the D50 of the primary particles in the spherical lithium iron phosphate secondary particles is 100 to 250nm, for example, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, or the like.
In the invention, if the D50 of the primary particles in the spherical lithium iron phosphate secondary particles is too large, the solid phase diffusion rate of the secondary particles is slow, the internal resistance of the electrode is high, and the rate capability and the cycle stability of the thick electrode are further influenced, and if the D50 is too small, the specific surface area of the secondary particles is high, the tap density is small, and the improvement of the compaction density and the cycle performance of the thick electrode are not facilitated.
Preferably, the first conductive agent is a composite conductive agent.
Preferably, the composite conductive agent includes conductive carbon black and carbon nanotubes;
preferably, the mass ratio of the carbon nanotubes to the conductive carbon black is (1-4) 1, for example 1.
In the invention, in the first coating, the lithium iron phosphate secondary particles are selected and matched with the composite conductive agent, so that an excellent three-dimensional conductive network can be formed, the impedance of the thick electrode can be reduced, and the multiplying power charge-discharge rate can be improved, and if the lithium iron phosphate secondary particles are matched with the single conductive agent, such as being directly matched with conductive carbon black, the electronic conductivity and the liquid phase ion conductivity of the thick electrode can be influenced, and the multiplying power performance of the thick electrode can not be improved.
Preferably, the D50 of the lithium iron phosphate single particle is 200 to 800nm, for example, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, or the like.
In the invention, the D50 of the lithium iron phosphate single particle is too small to be beneficial to the liquid phase transmission of the electrolyte and the improvement of the energy density, and too large can cause the solid phase diffusion rate of lithium ions to be smaller and the concentration polarization to be serious during charging and discharging, thereby obviously attenuating the capacity and the cycle life of the battery.
Preferably, the surface of the lithium iron phosphate single particle is coated with a carbon layer.
Preferably, the second conductive agent includes conductive carbon black.
According to the invention, the first coating adopts the collocation of the secondary particles and the composite conductive agent, the second coating is collocated with the conductive carbon black to obtain a three-dimensional conductive network of a surface layer (far away from a current collector), meanwhile, the bottom layer small particles are in close contact with the carbon black, so that the resistance of the battery can be obviously reduced, and if the second coating collocates the lithium iron phosphate single particles and the composite conductive agent, the liquid retention of the bottom layer electrolyte is reduced, the active material is difficult to fully infiltrate, the bottom layer active material is not uniformly deintercalated, and the internal resistance of the battery is obviously increased.
Preferably, the mass ratio of the first binder in the first coating layer is 50 to 80% of the mass ratio of the second binder in the second coating layer, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, or the like.
In the invention, the content of the binder in the second coating is higher than that of the binder in the first coating, so that the binder migration can be effectively reduced, the peeling strength of the lithium iron phosphate thick electrode can be improved, the electrode powder falling and cracking can be reduced, the cycle performance can be improved, if the binder contents in the two coatings are consistent, the binder surface migration can be caused, the binder content in the bottom layer is low, the peeling force of the thick electrode is obviously deteriorated, and if the binder content in the first coating is higher, the peeling force of the thick electrode can not be effectively improved, the pole piece is easy to crack and powder fall when being baked.
Preferably, in the first coating layer, the mass ratio of the spherical lithium iron phosphate secondary particles, the first conductive agent and the first binder is (93-97) (1.0-2.0) (1-6), for example, 93.
Preferably, in the second coating, the mass ratio of the lithium iron phosphate single particles, the second conductive agent and the second binder is (92-95): (1.0-2.0): (3-7), for example, 92.
In a second aspect, the present invention provides a method for preparing a thick lithium iron phosphate electrode according to the first aspect, wherein the method comprises the following steps:
coating the first coating slurry and the second coating slurry on the surface of a current collector to enable the second coating slurry to be directly contacted with the surface of the current collector, wherein the first coating is positioned on the surface of the second coating to obtain the lithium iron phosphate thick electrode;
the first coating slurry comprises spherical lithium iron phosphate secondary particles, a first conductive agent, a first binder and a first solvent, and the second coating slurry comprises lithium iron phosphate single particles, a second conductive agent, a second binder and a second solvent.
Preferably, the method of coating comprises simultaneous coating of the two layers.
In the invention, the double-layer simultaneous coating refers to the synchronous coating of the first coating and the second coating, and the synchronous coating mode can better realize the high-efficiency production and the coating uniformity of the lithium iron phosphate thick electrode.
Preferably, the coating is followed by drying and rolling in sequence.
Preferably, the first and second coating layers after rolling have an overall compacted density of 2.2 to 2.6g/cc, such as 2.2g/cc, 2.25g/cc, 2.3g/cc, 2.35g/cc, 2.4g/cc, 2.45g/cc, 2.5g/cc, 2.55g/cc, or 2.6g/cc, and the like.
In a third aspect, the present invention further provides a lithium ion battery, which includes the thick lithium iron phosphate electrode according to the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, through the matching of active materials in the first coating and the second coating, a layered structure of upper lithium iron phosphate secondary particles and lower lithium iron phosphate single particles is adopted, the tortuosity and liquid phase resistance are obviously reduced, large pores are formed among spherical secondary particles, and small pores are formed among single particles, so that the electrolyte infiltration and liquid phase transmission are facilitated, and meanwhile, the compaction density of the electrode is also improved. After the battery is applied to the thick electrode provided by the invention, the discharge capacity ratio of 1C/0.2C can reach more than 88.6%, the energy density can reach more than 175.2Wh/kg, and after the D50 of primary particles in lithium iron phosphate secondary particles and lithium iron phosphate single particles is further regulated and controlled within a preferred range, the discharge capacity ratio of 1C/0.2C can reach more than 90.2%, the energy density can reach more than 180.3Wh/kg, and then the conductive agent in the coating is further regulated and controlled to be matched within the preferred range of the invention, the discharge capacity ratio of 1C/0.2C can reach more than 91.2%, and the energy density can reach more than 185 Wh/kg.
Drawings
Fig. 1 is a schematic structural diagram of a thick lithium iron phosphate electrode provided in embodiment 1.
Fig. 2 is an SEM image of the spherical lithium iron phosphate secondary particles provided in example 1.
Fig. 3 is an SEM image of lithium iron phosphate single particles provided in example 1.
FIG. 4 is a histogram comparing the pole piece strippers for the thick electrodes provided in examples 1-5 and comparative examples 1-2.
Fig. 5 is a graph comparing rate performance of the batteries provided in examples 1-5 and comparative examples 1-2.
The lithium iron phosphate coating comprises, by weight, 1-a first coating, 2-a second coating, 3-a current collector, 11-spherical lithium iron phosphate secondary particles, 12, 13-a first conductive agent, 21-lithium iron phosphate single particles and 22-a second conductive agent.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present embodiment provides a thick lithium iron phosphate electrode, as shown in fig. 1 (a structure of a single-sided current collector), where the thick lithium iron phosphate electrode is composed of a current collector 3 and electrode coatings on surfaces of two sides of the current collector 3 (the thickness of the electrode coating on the single-sided electrode coating is 200 μm), the electrode coatings are composed of a first coating 1 and a second coating 2 (the thickness of the first coating 1 is 70% of the thickness of the electrode coating) which are stacked, where the second coating 2 directly contacts with the surface of the current collector 3, the first coating 1 is composed of spherical lithium iron phosphate secondary particles 11, first conductive agents (12, 13) and a first binder, and the second coating 2 is composed of lithium iron phosphate single particles 21, a second conductive agent 22 and a second binder;
the preparation method of the thick electrode comprises the following steps:
preparing a first coating slurry: mixing spherical lithium iron phosphate secondary particles (as shown in fig. 2, the D50 of the secondary particles is 10 μm, and the D50 of the primary particles is 150 nm), a first conductive agent (the mass ratio of carbon nanotubes to carbon black is 6) and a first binder (PVDF), and then adding NMP to stir, to obtain a first coating slurry, wherein the mass ratio of LFP (CNT + SP) to PVDF is 94;
preparing a second coating slurry: mixing lithium iron phosphate single particles (as shown in fig. 3, the D50 is 300nm, the surface carbon coating amount is 1.5%), a second conductive agent (conductive carbon black) and a second binder (polyvinylidene fluoride), and then adding NMP to stir, so as to obtain a second coating slurry, wherein the mass ratio of LFP to SP to PVDF is 93.5;
and (3) coating the first coating slurry and the second coating slurry on the surface of the aluminum foil in a synchronous coating mode (the surfaces on two opposite sides of the aluminum foil are coated with the electrode coatings), directly positioning the second coating slurry on the surface of the aluminum foil, drying, and rolling to obtain the lithium iron phosphate thick electrode with the compaction density of the electrode coating on one side of the aluminum foil being 2.35 g/cc.
Example 2
The embodiment provides a thick lithium iron phosphate electrode, which is composed of a current collector and electrode coatings on the surfaces of the two sides of the current collector (the thickness of the electrode coating on one side is 200 μm), wherein the electrode coatings are composed of a first coating and a second coating which are stacked (the thickness of the first coating is 70% of the thickness of the electrode coating), the second coating is directly contacted with the surface of the current collector, the first coating is composed of spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating is composed of lithium iron phosphate single particles, a second conductive agent and a second binder;
the preparation method of the thick electrode comprises the following steps:
preparing a first coating slurry: mixing spherical lithium iron phosphate secondary particles (the D50 of the secondary particles is 10 microns, the D50 of the primary particles is 150 nm), a first conductive agent (the mass ratio of carbon nanotubes to carbon black is 6);
preparing a second coating slurry: mixing lithium iron phosphate single particles (D50 is 300nm, the surface carbon coating amount is 1.5%), a second conductive agent (conductive carbon black) and a second binder (polyvinylidene fluoride), and then adding NMP to stir, so as to obtain a second coating slurry, wherein the mass ratio of LFP to SP to PVDF is 93.5;
and (3) coating the first coating slurry and the second coating slurry on the surface of the aluminum foil in a synchronous coating mode (the surfaces on two opposite sides of the aluminum foil are coated with the electrode coatings), directly positioning the second coating slurry on the surface of the aluminum foil, drying, and rolling to obtain the lithium iron phosphate thick electrode with the compaction density of the electrode coating on one side of the aluminum foil being 2.35 g/cc.
Example 3
The embodiment provides a thick lithium iron phosphate electrode, which is composed of a current collector and electrode coatings on the surfaces of the two sides of the current collector (the thickness of the electrode coating on one side is 400 μm), wherein the electrode coatings are composed of a first coating and a second coating which are stacked (the thickness of the first coating is 50% of the thickness of the electrode coating), the second coating is directly contacted with the surface of the current collector, the first coating is composed of spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating is composed of lithium iron phosphate single particles, a second conductive agent and a second binder;
the preparation method of the thick electrode comprises the following steps:
preparing a first coating slurry: mixing spherical lithium iron phosphate secondary particles (the D50 of the secondary particles is 10 microns, the D50 of the primary particles is 150 nm), a first conductive agent (the mass ratio of carbon nanotubes to carbon black is 6);
preparing a second coating slurry: mixing lithium iron phosphate single particles (D50 is 300nm, the surface carbon coating amount is 1.5%), a second conductive agent (conductive carbon black) and a second binder (polyvinylidene fluoride), and then adding NMP to stir, so as to obtain a second coating slurry, wherein the mass ratio of LFP to SP to PVDF is 93.5;
and (3) coating the first coating slurry and the second coating slurry on the surface of the aluminum foil in a synchronous coating mode (the surfaces on two opposite sides of the aluminum foil are coated with the electrode coatings), directly positioning the second coating slurry on the surface of the aluminum foil, drying, and rolling to obtain the lithium iron phosphate thick electrode with the compaction density of the electrode coating on one side of the aluminum foil being 2.35 g/cc.
Example 4
The embodiment provides a thick lithium iron phosphate electrode, which is composed of a current collector and electrode coatings on the surfaces of the two sides of the current collector (the thickness of the electrode coating on one side is 650 μm), wherein the electrode coatings are composed of a first coating and a second coating which are stacked (the thickness of the first coating is 30% of the thickness of the electrode coating), the second coating is directly contacted with the surface of the current collector, the first coating is composed of spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating is composed of lithium iron phosphate single particles, a second conductive agent and a second binder;
the preparation method of the thick electrode comprises the following steps:
preparing a first coating slurry: mixing spherical lithium iron phosphate secondary particles (the D50 of the secondary particles is 15 mu m, the D50 of the primary particles is 250 nm), a first conductive agent (the mass ratio of carbon nanotubes to carbon black is 7: 3) and a first binder (PVDF), adding NMP, and stirring to obtain a first coating slurry, wherein the mass ratio of LFP (CNT + SP) to PVDF is 95.5;
preparing a second coating slurry: mixing lithium iron phosphate single particles (D50 is 800nm, the surface carbon coating amount is 1.5%), a second conductive agent (conductive carbon black) and a second binder (polyvinylidene fluoride), and then adding NMP to stir, so as to obtain a second coating slurry, wherein the mass ratio of LFP to SP to PVDF is 93.5;
and (3) coating the first coating slurry and the second coating slurry on the surface of the aluminum foil in a synchronous coating mode (the surfaces on two opposite sides of the aluminum foil are coated with the electrode coatings), directly positioning the second coating slurry on the surface of the aluminum foil, drying, and rolling to obtain the lithium iron phosphate thick electrode with the compaction density of the electrode coating on one side of the aluminum foil being 2.45 g/cc.
Example 5
The embodiment provides a thick lithium iron phosphate electrode, which is composed of a current collector and electrode coatings on the surfaces of the two sides of the current collector (the thickness of the electrode coating on one side is 400 μm), wherein the electrode coatings are composed of a first coating and a second coating which are stacked (the thickness of the first coating is 50% of the thickness of the electrode coating), the second coating is directly contacted with the surface of the current collector, the first coating is composed of spherical lithium iron phosphate secondary particles, a first conductive agent and a first binder, and the second coating is composed of lithium iron phosphate single particles, a second conductive agent and a second binder;
the preparation method of the thick electrode comprises the following steps:
preparing a first coating slurry: mixing spherical lithium iron phosphate secondary particles (the D50 of the secondary particles is 12 microns, the D50 of the primary particles is 200 nm), a first conductive agent (the mass ratio of carbon nanotubes to carbon black is 7: 3) and a first binder (PVDF), adding NMP, and stirring to obtain a first coating slurry, wherein the mass ratio of LFP (CNT + SP) to PVDF is 94;
preparing a second coating slurry: mixing lithium iron phosphate single particles (D50 is 450nm, the surface carbon coating amount is 2%), a second conductive agent (conductive carbon black) and a second binder (polyvinylidene fluoride), adding NMP, and stirring to obtain a second coating slurry, wherein the mass ratio of LFP to SP to PVDF is 93.5;
and (3) coating the first coating slurry and the second coating slurry on the surface of the aluminum foil in a synchronous coating mode (the surfaces on two opposite sides of the aluminum foil are coated with the electrode coatings), directly positioning the second coating slurry on the surface of the aluminum foil, drying, and rolling to obtain the lithium iron phosphate thick electrode with the compaction density of the electrode coating on one side of the aluminum foil being 2.5 g/cc.
Example 6
The difference between this embodiment and embodiment 1 is that the conductive agent in the first coating layer of this embodiment is pure conductive carbon black.
The remaining preparation and procedure remained the same as in example 1.
Example 7
The present example differs from example 1 in that the conductive agent in the second coating layer of the present example is identical to the conductive agent in the first coating layer (the mass ratio of carbon nanotubes to carbon black is 6.
The remaining preparation and procedure remained the same as in example 1.
Example 8
The present example is different from example 1 in that the D50 of the primary particles in the lithium iron phosphate secondary particles in the first coating layer of the present example is 300nm, and the D50 of the secondary particles is 20 μm.
The remaining preparation methods and parameters were in accordance with example 1.
Example 9
The present embodiment is different from embodiment 1 in that the D50 of the lithium iron phosphate single particle in the second coating layer of the present embodiment is 2 μm.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 1
The thick electrode provided in this comparative example had only the first coating in the electrode coating and no second coating.
In the preparation method, the preparation of the second coating slurry is not performed.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 2
In the thick electrode provided in the present comparative example, the electrode coating is only the second coating and does not contain the first coating.
In the preparation method, the preparation of the first coating slurry is not performed.
The remaining preparation methods and parameters were in accordance with example 1.
Fig. 4 shows a histogram comparing the pole piece stripping agents of the thick electrodes provided in examples 1 to 5 and comparative examples 1 to 2, and it can be seen from fig. 4 that the preparation method of the lithium iron phosphate thick electrode provided by the invention can significantly improve the stripping force of the thick electrode, inhibit the cracking of the thick electrode, and solve the powder falling defect.
Fig. 5 shows a comparison graph of rate capability of the batteries provided in examples 1 to 5 and comparative examples 1 to 2, each set of comparative bar graphs in fig. 5 is respectively example 1, comparative example 1, example 2, comparative example 2, example 3, example 4 and example 5 from left to right, and it can be seen from fig. 5 that the lithium iron phosphate thick electrode provided by the present invention has significantly improved performance of the thick electrode, and the thick electrode has high rate discharge performance.
Comparative example 3
The present comparative example is different from example 1 in that the first coating layer is directly located on the surface of the current collector in the present comparative example, that is, the lamination order of the first coating layer and the second coating layer is changed.
The remaining preparation methods and parameters were in accordance with example 1.
The thick lithium iron phosphate electrodes provided in examples 1 to 9 and comparative examples 1 to 3 were used as positive electrodes, and graphite was used as a positive electrodeNegative electrode, polyolefin separator, 1M LiPF 6 And (solvent: EC + DMC + DEC) electrolyte to obtain the 100Ah square aluminum shell full cell.
Electrochemical performance tests were performed on the batteries provided in examples 1 to 9 and comparative examples 1 to 3 under 1C/1C charge/discharge test at 25 ℃ under a voltage of 2.5 to 3.65V, and the results are shown in Table 1.
TABLE 1
| Discharge capacity ratio of 1C/0.2C | Energy Density (Wh/kg) | |
| Example 1 | 95.3％ | 185 |
| Example 2 | 94.8％ | 184.5 |
| Example 3 | 92.3％ | 196.5 |
| Example 4 | 91.2％ | 201.3 |
| Example 5 | 92.6％ | 195.4 |
| Example 6 | 91.3％ | 182.1 |
| Example 7 | 90.2％ | 180.3 |
| Example 8 | 89.3％ | 179.1 |
| Example 9 | 88.6％ | 175.2 |
| Comparative example 1 | 86.3％ | 174.6 |
| Comparative example 2 | 85.3％ | 173.5 |
| Comparative example 3 | 79.2％ | 165.3 |
From the data results of example 1 and examples 6 and 7, it can be seen that the first coating layer with the composite conductive agent can better achieve the improvement of the rate capability and energy density of the thick electrode, while the second coating layer with the single conductive agent is beneficial to the infiltration of the active material at the bottom layer and the capacity exertion, and improves the energy density of the battery.
From the data results of example 1 and example 8, it is clear that an excessively large D50 of the primary particles in the lithium iron phosphate secondary particles increases the internal resistance of the battery, and decreases the rate-discharge capacity retention rate.
From the data results of example 1 and example 9, it is understood that too large D50 of the lithium iron phosphate single particle leads to a decrease in the solid phase diffusion rate and a deterioration in rate performance.
As can be seen from the data results of examples 1 to 2 and comparative examples 1 and 2, the thick lithium iron phosphate electrode cannot achieve high-rate charge and discharge and high energy density regardless of whether only single particles or only secondary particles are used.
From the data results of example 1 and comparative example 3, it can be seen that the electrode tortuosity and electrolyte liquid phase transmission are seriously affected by the position change of the first coating and the second coating, the internal resistance of the battery is remarkably increased, and the preparation of a thick electrode with high power and high energy density cannot be realized.
In summary, the invention, through the matching of the active materials in the first coating and the second coating, adopts the layered structure of the upper lithium iron phosphate secondary particles and the lower lithium iron phosphate single particles, so as to significantly reduce the tortuosity and the liquid phase resistance, and form larger pores among the spherical secondary particles, and form smaller pores among the single particles, thereby facilitating the electrolyte infiltration and the liquid phase transmission, and simultaneously improving the compaction density of the electrode. After the battery is applied to the thick electrode provided by the invention, the discharge capacity ratio of 1C/0.2C can reach more than 88.6%, the energy density can reach more than 175.2Wh/kg, and after the D50 of primary particles in lithium iron phosphate secondary particles and lithium iron phosphate single particles is further regulated and controlled within a preferred range, the discharge capacity ratio of 1C/0.2C can reach more than 90.2%, the energy density can reach more than 180.3Wh/kg, and then the conductive agent in the coating is further regulated and controlled to be matched within the preferred range of the invention, the discharge capacity ratio of 1C/0.2C can reach more than 91.2%, and the energy density can reach more than 185 Wh/kg.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. The utility model provides a thick electrode of lithium iron phosphate, its characterized in that, the thick electrode of lithium iron phosphate includes the mass flow body and is located the electrode coating on mass flow body surface, the electrode coating is including first coating and the second coating that stacks up the setting, wherein, the second coating is located the one side that is close to the mass flow body, first coating includes spherical lithium iron phosphate secondary particle, first conductive agent and first binder, the second coating includes lithium iron phosphate single particle, second conductive agent and second binder.
2. The thick lithium iron phosphate electrode of claim 1, wherein the thickness of the electrode coating is 100-1000 μm;
preferably, the thickness of the first coating accounts for 30-70% of the thickness of the electrode coating;
preferably, the primary particles in the spherical lithium iron phosphate secondary particles in the first coating layer and the lithium iron phosphate single particles in the second coating layer are both nanoscale particles.
3. The thick lithium iron phosphate electrode according to claim 1 or 2, wherein the spherical lithium iron phosphate secondary particles have a D50 of 5 to 15 μm;
preferably, the D50 of the primary particles in the spherical lithium iron phosphate secondary particles is 100 to 250nm.
4. The thick lithium iron phosphate electrode of any one of claims 1 to 3, wherein the first conductive agent is a composite conductive agent;
preferably, the composite conductive agent includes conductive carbon black and carbon nanotubes;
preferably, the mass ratio of the carbon nano tubes to the conductive carbon black is (1-4): 1.
5. The thick lithium iron phosphate electrode according to any one of claims 1 to 4, wherein the lithium iron phosphate single particles have a D50 of 200 to 800nm;
preferably, the surface of the lithium iron phosphate single particle is coated with a carbon layer;
preferably, the second conductive agent includes conductive carbon black.
6. The thick lithium iron phosphate electrode according to any one of claims 1 to 5, wherein the mass ratio of the first binder in the first coating layer is 50 to 80% of the mass ratio of the second binder in the second coating layer.
7. The thick lithium iron phosphate electrode according to any one of claims 1 to 6, wherein the mass ratio of the spherical lithium iron phosphate secondary particles, the first conductive agent and the first binder in the first coating layer is (93-97): (1.0-2.0): (1-6);
preferably, in the second coating, the mass ratio of the lithium iron phosphate single particles to the second conductive agent to the second binder is (92-95): (1.0-2.0): (3-7).
8. The method for preparing a thick lithium iron phosphate electrode according to any one of claims 1 to 7, comprising the steps of:
coating the first coating slurry and the second coating slurry on the surface of a current collector to enable the second coating slurry to be directly contacted with the surface of the current collector, wherein the first coating is positioned on the surface of the second coating to obtain the lithium iron phosphate thick electrode;
the first coating slurry comprises spherical lithium iron phosphate secondary particles, a first conductive agent, a first binder and a first solvent, and the second coating slurry comprises lithium iron phosphate single particles, a second conductive agent, a second binder and a second solvent.
9. The method for preparing a thick lithium iron phosphate electrode according to claim 8, wherein the coating method comprises simultaneous coating of two layers;
preferably, the coating is followed by drying and rolling in sequence;
preferably, the total compacted density of the rolled first coating layer and second coating layer is 2.2 to 2.6g/cc.
10. A lithium ion battery comprising a thick lithium iron phosphate electrode according to any one of claims 1 to 7.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2023174012A1 (en) * | 2022-03-14 | 2023-09-21 | 宁德时代新能源科技股份有限公司 | Positive electrode sheet, lithium-ion secondary battery, battery module, battery pack, and electrical apparatus |
| CN117174829A (en) * | 2023-11-03 | 2023-12-05 | 溧阳中科海钠科技有限责任公司 | Negative electrode of sodium ion battery and preparation method thereof |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2023174012A1 (en) * | 2022-03-14 | 2023-09-21 | 宁德时代新能源科技股份有限公司 | Positive electrode sheet, lithium-ion secondary battery, battery module, battery pack, and electrical apparatus |
| CN117174829A (en) * | 2023-11-03 | 2023-12-05 | 溧阳中科海钠科技有限责任公司 | Negative electrode of sodium ion battery and preparation method thereof |
| CN117174829B (en) * | 2023-11-03 | 2024-01-19 | 溧阳中科海钠科技有限责任公司 | Negative electrode of sodium ion battery and preparation method thereof |
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