CN114139371A - Multiphase and multi-scale modeling method and system for lithium ion battery electrode - Google Patents
Multiphase and multi-scale modeling method and system for lithium ion battery electrode Download PDFInfo
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Abstract
The invention provides a lithium ion battery electrode multiphase multi-scale modeling method and a lithium ion battery electrode multiphase multi-scale modeling system, which belong to the technical field of computer simulation of lithium ion batteries, and the method comprises the following steps: calculating the average porosity and the tortuosity of the carbon colloidal phase region; scanning the lithium ion battery electrode sample layer by layer through X ray-CT to establish a three-dimensional geometric reconstruction model; characterizing the electrochemical reaction rate of the active material phase surface by using a reaction kinetics model; establishing a lithium ion transmission equation and a liquid phase potential field equation of an electrolyte region by applying a concentrated solution theory; characterizing a solid phase potential field on the active material and the carbon gel phase region by ohm's law; correcting the diffusion coefficient and the conductivity according to the average porosity and the tortuosity of the carbon gel phase; establishing a concentration field corresponding to substance diffusion in the active material according to the solid-phase model; and further, carrying out numerical solution on the model to obtain parameters of the lithium ion battery electrode. The invention is balanced in terms of accuracy and efficiency.
Description
Technical Field
The invention belongs to the technical field of computer simulation of lithium ion batteries, and particularly relates to a lithium ion battery electrode multiphase multi-scale modeling method and system.
Background
As a new generation of energy technology, the lithium ion battery has the advantages of being green, clean, efficient, energy-saving, low in use cost and the like, and plays a significant role in the national economic major demand industries of traffic, energy storage, electronic information and the like. The lithium ion battery system has the complex characteristics of multi-phase, multi-scale and multi-physical field (electrochemistry, heat, electricity and force) coupling, the product performance is influenced by various factors such as material preparation, structural design, manufacturing process and use conditions, and the research and development work is very difficult. The traditional battery research and development method relying on trial and error experience has the defects of high cost, long period, poor effect and the like, and can not meet the development requirement of quick iteration of the current lithium ion battery product. Computer simulation design based on lithium ion battery physical field modeling has become an indispensable technical means and core competitiveness in battery research and development.
The earliest Newman et al proposed the use of a homogeneous continuous medium model to describe porous electrodes in electrochemical systems, and then their students built a P2D (pseudo-two-dimension) lithium ion battery model based thereon, which was applied to date in the field of lithium ion battery simulation. For the convenience of mathematical processing, the P2D model ignores the specific microstructure characteristics of the electrode, such as particle shape, size distribution, morphology of agglomeration and adhesion of the carbon gel phase (mixture of conductive agent and binder), pore shape and connectivity, while assuming that each infinitesimal on the electrode is composed of spherical active particles of the same size. In order to overcome the defect of the P2D model in the aspect of electrode microstructure information, a method for reducing the real structure of the composite electrode by applying a three-dimensional reconstruction technology is developed in recent years, and electrochemical simulation of the electrode is performed on the basis of the three-dimensional reconstruction model. Due to the resolution limit, X-ray computed tomography (X-ray-CT) can usually reconstruct only micron-sized active particles and pores, and carbon gel phase with nano-scale structural features cannot be identified. Inaccuracy of the carbon gel phase information can cause huge errors in the electric field on the electrodes and the electrochemical reaction calculation. For this purpose, a focused ion beam scanning electron microscope (FIB-SEM) technique with higher resolution, or random computer generation, etc. is used for carbon gel phase modeling; however, despite the competing relationships between resolution and achievable sample size of three-dimensional reconstruction devices, and the accuracy and efficiency of numerical calculations, multi-phase, multi-scale composite modeling of micron-sized active particles, pores, and nanoscale carbon gel phases remains a significant challenge.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a lithium ion battery electrode multiphase multi-scale modeling method and a lithium ion battery electrode multiphase multi-scale modeling system, and aims to solve the problem that the lithium ion battery simulation method cannot give consideration to the accuracy and the efficiency because the existing lithium ion battery simulation method adopts FIB-SEM or adopts random computer generation and other modes to model a carbon gel phase, and no matter the resolution and the reachable sample size of three-dimensional reconstruction equipment or the competition relationship exists between the accuracy and the efficiency of numerical calculation.
In order to achieve the above object, in one aspect, the present invention provides a lithium ion battery electrode multiphase multi-scale modeling method, including the following steps:
scanning an electrode sample of the lithium ion battery layer by layer through X ray-CT to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and establishing a three-dimensional geometric reconstruction model;
on the basis of the three-dimensional geometric reconstruction model, an electrochemical reaction rate equation, a corrected lithium ion transmission equation, a corrected liquid phase potential field equation, a corrected solid phase potential field equation and a substance concentration field equation are combined to construct a lithium ion battery electrode multiphase multi-scale model;
the method for acquiring the electrochemical reaction rate equation comprises the following steps: according to the types of the active materials, characterizing the phase surface acquisition of the active materials by using a reaction kinetic model; the acquisition method of the substance concentration field equation comprises the following steps: according to the types of the active materials, corresponding solid phase models are applied to represent the concentration of substances in the active materials to obtain;
the method for acquiring the corrected lithium ion transmission equation, the corrected liquid phase potential field equation and the corrected solid phase potential field equation comprises the following steps: establishing a lithium ion transmission equation and a liquid phase potential field equation of the electrolyte by applying a concentrated solution theory; adopting ohm's law to represent electron transmission on the active material and the carbon gel phase region, and establishing a solid phase potential field equation; acquiring a nano-pore structure image of a carbon gel phase in an electrode sample of the lithium ion battery by using FIB-SEM (focused ion beam-scanning electron microscope), and calculating the average porosity and the tortuosity of a carbon gel phase area; correcting a diffusion coefficient in a lithium ion transmission equation and correcting the conductivities of a liquid phase potential field equation and a solid phase potential field equation simultaneously based on the average porosity and the tortuosity of a carbon gel phase region;
and the volume ratio of the active material, the pore and the carbon gel phase of the three-dimensional geometric reconstruction model is consistent with the volume ratio corresponding to the material components of the sample.
Preferably, at least 3 images of the nanoporous structure are taken of the sample using FIB-SEM, and the average porosity and tortuosity of the carbon gel phase are determined.
Preferably, the calculation method of the tortuosity is to adopt a Bruggeman formula for calculation, or to construct a mathematical relationship calculation of the porosity and the tortuosity based on an image, or to obtain the tortuosity by numerical simulation reverse estimation in a mass transfer process.
Preferably, the lithium ion battery electrode multiphase multi-scale modeling method further comprises: carrying out mesh subdivision on the lithium ion battery electrode multiphase multi-scale model;
and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
Preferably, the boundary conditions include: boundary conditions between pores and active material, boundary conditions between carbon gel phase and pore phase, separator lithium metal side boundary conditions, electrode current collector side boundary conditions, and cycle boundary conditions.
In another aspect, the present invention provides a lithium ion battery electrode multiphase multi-scale modeling system, including: the carbon gel phase parameter calculation module is used for acquiring a nano-pore structure image of a carbon gel phase in the lithium ion battery electrode sample by using FIB-SEM (focused ion beam-scanning electron microscope), and calculating the average porosity and the tortuosity of a carbon gel phase area;
the building module of the three-dimensional geometric reconstruction model is used for scanning the lithium ion battery electrode sample layer by layer through X ray-CT to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and building the three-dimensional geometric reconstruction model;
the application module of the reaction kinetic model is used for representing the electrochemical reaction rate of the phase surface of the active material by using the reaction kinetic model according to the type of the active material;
the concentrated solution theory application module is used for establishing a lithium ion transmission equation and a liquid phase potential field of electrolyte in which a pore phase and a carbon gel phase are positioned by applying a concentrated solution theory based on the three-dimensional geometric reconstruction model;
the ohm law application module is used for representing electron transmission on the active material and the carbon gel phase region by adopting ohm law and establishing a solid phase potential field;
the application module of the porous medium transport correction model is used for correcting the diffusion coefficient in the lithium ion transmission equation and correcting the conductivity of the liquid potential field and the solid phase potential field based on the porous medium transport correction model established based on the average porosity and the tortuosity of the carbon gel phase region;
the solid-phase model application module is used for applying a corresponding solid-phase model according to the type of the active material to establish a substance concentration field inside the active material;
the establishing module of the multiphase multi-scale model is used for combining an electrochemical reaction rate equation, a corrected lithium ion transmission equation, a corrected liquid phase potential field equation, a corrected solid phase potential field equation and a substance concentration field equation on the basis of the three-dimensional geometric reconstruction model to establish the multiphase multi-scale model of the lithium ion battery electrode;
and the volume ratio of the active material, the pore and the carbon gel phase of the three-dimensional geometric reconstruction model is consistent with the volume ratio corresponding to the material components of the sample.
Preferably, at least 3 images of the nanoporous structure are taken of the sample using FIB-SEM, and the average porosity and tortuosity of the carbon gel phase are determined.
Preferably, the calculation method of the tortuosity is to adopt a Bruggeman formula for calculation, or to construct a mathematical relationship calculation of the porosity and the tortuosity based on an image, or to obtain the tortuosity by numerical simulation reverse estimation in a mass transfer process.
Preferably, the lithium ion battery electrode multiphase multi-scale modeling system further comprises a lithium ion battery electrode parameter solving module, which is used for mesh generation of the lithium ion battery electrode multiphase multi-scale model; and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
Preferably, the boundary conditions include: boundary conditions between the pore phase and the active material phase, boundary conditions between the carbon gel phase and the pore phase, separator lithium metal side boundary conditions, electrode current collector side boundary conditions, and cycle boundary conditions.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
the method adopts X ray-CT to scan the electrode sample of the lithium ion battery layer by layer to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and establishes a three-dimensional geometric reconstruction model; the mesh subdivision size is only at the level of the size of the active particles, and conductive carbon particles which are fine to the nanometer level are not needed; on the basis of the geometric model, the invention adopts the concentrated solution theory to establish a lithium ion transmission equation and a liquid phase potential field equation of electrolyte in which a pore phase and a carbon gel phase are positioned; correcting diffusion coefficients in a lithium ion transmission equation by adopting a porous medium transport correction model, and correcting the conductivities of a liquid phase potential field and a solid phase potential field; from the analysis, the specific volume, morphology, size and the like of the carbon gel phase are not analyzed independently, but a model is constructed together with the pore phase and the active material, and then the porous medium transportation correction model is adopted for correction, so that the carbon gel phase is not required to be completely modeled by adopting the conventional FIB-SEM to acquire images for multiple times or modeled by adopting a computer random generation mode; and the spatial distribution of the active material phase, the pore phase and the carbon gel phase can be obtained by adopting X ray-CT, so that compared with the prior art, the method greatly reduces the simulation calculated amount and the resolution requirement on a measuring instrument, and truly restores the three-phase microstructure morphology of the lithium ion battery electrode containing the active material, the pores and the carbon gel phase. Meanwhile, a concentrated solution theory and an ohm law are adopted to respectively analyze a lithium ion transmission equation, a liquid phase potential field and a solid phase potential field of the electrolyte, and the ion transmission and electron conduction processes of the lithium ion battery electrode are fully simulated in the aspect of electrochemistry; applying a corresponding solid-phase model according to the type of the active material, establishing a substance concentration field inside the active material, and fully simulating the solid-phase diffusion process of the lithium ion battery electrode in the aspect of electrochemistry; according to the types of the active materials, a reaction kinetic model is applied to represent the electrochemical reaction rate of the phase surface of the active materials; in conclusion, the three-phase microstructure morphology, the electrochemical simulation and the calculation efficiency in the simulation of the lithium ion battery electrode are greatly improved compared with the prior art, and the accuracy and the efficiency are balanced.
Drawings
FIG. 1 is a partial cross-sectional view of an electrode sample taken by an FIB-SEM provided in an embodiment of the invention;
FIG. 2 is a three-dimensional reconstructed electrode model of an Xray-CT according to an embodiment of the present invention;
FIG. 3 is a cross-sectional schematic view of a multiphase multi-scale electrode model provided by an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, in one aspect, the present invention provides a lithium ion battery electrode multiphase multi-scale modeling method, which specifically includes the following steps:
the method comprises the following steps: as shown in fig. 1, a nanopore structure image of the carbon gel phase 3 in the electrode sample is obtained by FIB-SEM, and the average porosity of the carbon gel phase region is calculated from the image; the tortuosity can be calculated by adopting a classic Bruggeman formula, or can be calculated by constructing a mathematical relation between the porosity and the tortuosity based on an image, or can be obtained by numerical simulation reverse estimation in the mass transfer process;
establishing a porous medium transport correction model for correcting the conductivity and the diffusion coefficient of the carbon gel phase based on the average porosity and the tortuosity;
specifically, a homogenized porous medium transport correction model is applied to model the carbon gel phase region 3, and a specific pore structure in the carbon gel phase is ignored, so that a multiphase multi-scale composite electrode model can be formed with the active particles 1 and the pores 2;
preferably, when the FIB-SEM method is adopted, more than 3 parts of the sample are required to be taken, and the average porosity and the tortuosity of the carbon gel phase are calculated;
step two: as shown in fig. 2, the electrode sample is scanned layer by X ray-CT to obtain the spatial distribution of the active particles 1, the pores 2 and the carbon gel phase 3;
based on a two-dimensional image obtained by X ray-CT, adjusting a threshold parameter to ensure that the volume proportion of the three phases of active materials, pores and carbon gel phases of the three-dimensional geometric reconstruction model is basically consistent with the corresponding volume proportion of the material components prepared by the sample;
preferably, a high-resolution X ray-CT device is selected to obtain more accurate three-phase distribution information;
step three: as shown in fig. 3, according to the kind of active material, the electrochemical reaction rate of the active material phase surface 4 is characterized by using the corresponding reaction kinetic model;
applying a concentrated solution theory to represent a lithium ion transmission equation and a liquid phase potential field equation existing in the electrolyte in which the pore phase 2 and the carbon colloid phase 3 are located;
characterizing electron transmission on the active material phase 1 and carbon gel phase 3 regions by adopting an Ohm law to establish a solid phase potential field;
correcting diffusion coefficients in a lithium ion transmission equation by adopting a porous medium transport correction model, and correcting the conductivities of a liquid phase potential field and a solid phase potential field;
applying a corresponding solid phase model according to the type of the active material, establishing a concentration field corresponding to substance diffusion in the active material phase 1, and obtaining a multi-phase and multi-scale model of the electrode of the ion battery;
preferably, the lithium ion battery electrode multiphase multi-scale modeling method further comprises the steps of:
carrying out mesh subdivision on the lithium ion battery electrode multiphase multi-scale model;
and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
In another aspect, the present invention provides a lithium ion battery electrode multiphase multi-scale modeling system, including: the carbon gel phase parameter calculation module is used for acquiring a nano-pore structure image of a carbon gel phase in the lithium ion battery electrode sample by using FIB-SEM (focused ion beam-scanning electron microscope), and calculating the average porosity and the tortuosity of a carbon gel phase area;
the building module of the three-dimensional geometric reconstruction model is used for scanning the lithium ion battery electrode sample layer by layer through X ray-CT to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and building the three-dimensional geometric reconstruction model;
the application module of the reaction kinetic model is used for representing the electrochemical reaction rate of the phase surface of the active material by using the reaction kinetic model according to the type of the active material;
the concentrated solution theory application module is used for establishing a lithium ion transmission equation and a liquid phase potential field of electrolyte in which a pore phase and a carbon gel phase are positioned by applying a concentrated solution theory based on the three-dimensional geometric reconstruction model;
the ohm law application module is used for representing electron transmission on the active material and the carbon gel phase region by adopting ohm law and establishing a solid phase potential field;
the application module of the porous medium transport correction model is used for correcting the diffusion coefficient in the lithium ion transmission equation and correcting the conductivity of the liquid phase potential field and the solid phase potential field based on the porous medium transport correction model established based on the average porosity and the tortuosity of the carbon gel phase region;
the solid-phase model application module is used for applying a corresponding solid-phase model according to the type of the active material, establishing a substance concentration field in the active material, completing the establishment of a lithium ion battery electrode multiphase multi-scale model and realizing the simulation of the lithium ion battery electrode;
the establishing module of the multiphase multi-scale model is used for combining an electrochemical reaction rate equation, a corrected lithium ion transmission equation, a corrected liquid phase potential field equation, a corrected solid phase potential field equation and a substance concentration field equation on the basis of the three-dimensional geometric reconstruction model to establish the multiphase multi-scale model of the lithium ion battery electrode;
and the volume ratio of the active material, the pore and the carbon gel phase of the three-dimensional geometric reconstruction model is consistent with the volume ratio corresponding to the material components of the sample.
Preferably, at least 3 images of the nanoporous structure are taken of the sample using FIB-SEM, and the average porosity and tortuosity of the carbon gel phase are determined.
Preferably, the calculation method of the tortuosity is to adopt a Bruggeman formula for calculation, or to construct a mathematical relationship calculation of the porosity and the tortuosity based on an image, or to obtain the tortuosity by numerical simulation reverse estimation in a mass transfer process.
Preferably, the lithium ion battery electrode multiphase multi-scale modeling system further comprises a lithium ion battery electrode parameter solving module, which is used for mesh generation of the lithium ion battery electrode multiphase multi-scale model; and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
Preferably, the boundary conditions include: boundary conditions between the pore phase and the active material phase, boundary conditions between the carbon gel phase and the pore phase, separator lithium metal side boundary conditions, electrode current collector side boundary conditions, and cycle boundary conditions.
Examples
In this embodiment, a half-cell modeling simulation composed of a ternary electrode and lithium metal is taken as an example to describe the technical scheme of the present invention in detail. However, it should be understood by those skilled in the art that the technical solution of the present invention is not limited to this type of lithium ion battery, and can also be applied to other types of lithium ion batteries.
In this embodiment, the active material of the ternary lithium ion battery electrode sample is LiNi0.5Mn0.3Co0.2O2(NCM532), the conductive agent is Super-P, the binder is PVDF, and the mass ratio is 20:1: 1. The three materials are stirred, mixed, coated, dried and rolled to prepare the electrode sample.
The method for acquiring the physical field distribution of the lithium ion battery electrode by adopting the lithium ion battery electrode multiphase multi-scale modeling method comprises the following steps:
(1) obtaining a nano-pore structure image of the carbon colloidal phase 3 at 5 positions in the electrode sample through FIB-SEM, and calculating according to a binary image to obtain the average porosity epsilon of the carbon colloidal phase regionnpAnd (4) calculating the tortuosity to be equal to epsilon by adopting a classic Bruggeman formulanp -0.5＝1.6308；
(2) Scanning the electrode sample layer by adopting X ray-CT with the resolution of 200nm, and selecting a region of 100 Mum multiplied by L (electrode thickness) as a calculation domain; calculating the volume ratio of active particles, pores and the three phases of the carbon colloidal phase according to the components of the material:
εP＝1-εAM-εCBD＝0.314
wherein epsilonAM、εCBDAnd εPThe volume fractions of active particles, pores and a carbon colloidal phase are respectively; omegaAM、ωBAnd ωCThe mass fractions of active particles, pores and a carbon colloidal phase are respectively; AL is the area and thickness of the electrode plane respectively; m is the electrode mass;
adjusting the image segmentation threshold value to ensure that the volume proportion of the active material, the pores and the carbon colloid phase of the three-dimensional reconstruction model are respectively matched with the volume proportion of the corresponding components to obtain epsilonAM’＝0.479，εCBD’＝0.212，εP’＝0.309；
(3) Applying a Butler-Volmer kinetic model to the active material phase surface:
wherein iaIs the reactive current density on the surface of the active particles, k is the reaction rate constant, eta is the overpotential, csRepresents the solid-phase lithium ion concentration, clRepresents the liquid-phase lithium ion concentration, and alpha is the transfer coefficient; f is a Faraday constant; r is the prevalent gas constant; t is the absolute temperature; c. Cs,maxIs the solid phase maximum lithium ion concentration;
modeling the pore phase, the carbon gel phase and the diaphragm zone by applying a concentrated solution theory:
wherein κ is the liquid phase ionic conductivity, [ phi ]lIs a liquid phase potential, f±Is the coefficient of activity, DlIs a liquid-phase diffusion coefficient of the liquid,
f is the Faraday constant, ilIs the liquid phase current density;
introducing a porous medium transport correction model into the carbon gel phase and the diaphragm area:
wherein for the carbon gel phase κeff＝κεnp/τ，Deff＝DεnpT, diaphragm zone, same principle, keffEffective ionic conductivity; dl,effIs the effective diffusion coefficient of liquid-phase lithium ions;
applying Ohm's law to the active material phase and carbon gel phase regions:
and introducing a porous medium transport correction model into the carbon gel phase region:
wherein σeff＝σεnp/τ，σAMAs conductivity of the active material, σCBD,effIs the effective conductivity of the carbon colloidal phase, phisIs a solid phase potential;
applying Fick diffusion model inside the active material phase:
the boundary between the pore phase/carbon gel phase and the active material phase satisfies:
the active material phase boundaries satisfy:
the lithium metal side boundary conditions of the separator were set as:
0＝φs
the electrode current collector side boundary conditions were set as:
the remaining four outer surfaces of the computational domain are set as periodic boundary conditions:
wherein D issIs the solid phase diffusion coefficient, Dl,effIs the effective diffusion coefficient of the liquid phase, IappIs the external current density; n is the normal vector of the surface; i.e. iaIs the active particle surface current density.
In summary, compared with the prior art, the invention has the following advantages:
the method adopts X ray-CT to scan the electrode sample of the lithium ion battery layer by layer to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and establishes a three-dimensional geometric reconstruction model; the mesh subdivision size is only at the level of the size of the active particles, and conductive carbon particles which are fine to the nanometer level are not needed; on the basis of the geometric model, the invention adopts the concentrated solution theory to establish a lithium ion transmission equation and a liquid phase potential field equation of electrolyte in which a pore phase and a carbon gel phase are positioned; correcting diffusion coefficients in a lithium ion transmission equation by adopting a porous medium transport correction model, and correcting the conductivities of a liquid phase potential field and a solid phase potential field; from the analysis, the specific volume, morphology, size and the like of the carbon gel phase are not analyzed independently, but a model is constructed together with the pore phase and the active material, and then the porous medium transportation correction model is adopted for correction, so that the carbon gel phase is not required to be subjected to repeated image acquisition by adopting the conventional FIB-SEM or to be subjected to modeling by adopting a computer random generation mode; and the spatial distribution of the active material phase, the pore phase and the carbon gel phase can be obtained by adopting X ray-CT, so that compared with the prior art, the method greatly reduces the simulation calculated amount and the resolution requirement on a measuring instrument, and truly restores the three-phase microstructure morphology of the lithium ion battery electrode containing the active material, the pores and the carbon gel phase. Meanwhile, a concentrated solution theory and an ohm law are adopted to respectively analyze a lithium ion transmission equation, a liquid phase potential field and a solid phase potential field of the electrolyte, and the ion transmission and electron conduction processes of the lithium ion battery electrode are fully simulated in the aspect of electrochemistry; applying a corresponding solid-phase model according to the type of the active material, establishing a substance concentration field inside the active material, and fully simulating the solid-phase diffusion process of the lithium ion battery electrode in the aspect of electrochemistry; according to the types of the active materials, a reaction kinetic model is applied to represent the electrochemical reaction rate of the phase surface of the active materials; in conclusion, the three-phase microstructure morphology, the electrochemical simulation and the calculation efficiency in the simulation of the lithium ion battery electrode are greatly improved compared with the prior art, and the accuracy and the efficiency are balanced.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A lithium ion battery electrode multiphase multi-scale modeling method is characterized by comprising the following steps:
scanning an electrode sample of the lithium ion battery layer by layer through X ray-CT to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and establishing a three-dimensional geometric reconstruction model;
on the basis of the three-dimensional geometric reconstruction model, an electrochemical reaction rate equation, a corrected lithium ion transmission equation, a corrected liquid phase potential field equation, a corrected solid phase potential field equation and a substance concentration field equation are combined to construct a lithium ion battery electrode multiphase multi-scale model;
the method for acquiring the electrochemical reaction rate equation comprises the following steps: according to the types of the active materials, characterizing the phase surface acquisition of the active materials by using a reaction kinetic model;
the method for acquiring the substance concentration field equation comprises the following steps: according to the types of the active materials, corresponding solid phase models are applied to represent the concentration of substances in the active materials to obtain;
the method for acquiring the corrected lithium ion transmission equation, the corrected liquid phase potential field equation and the corrected solid phase potential field equation comprises the following steps: establishing a lithium ion transmission equation and a liquid phase potential field equation of the electrolyte by applying a concentrated solution theory; adopting ohm's law to represent electron transmission on the active material and the carbon gel phase region, and establishing a solid phase potential field equation; acquiring a nano-pore structure image of a carbon gel phase in an electrode sample of the lithium ion battery by using FIB-SEM (focused ion beam-scanning electron microscope), and calculating the average porosity and the tortuosity of a carbon gel phase area; correcting a diffusion coefficient in a lithium ion transmission equation and correcting the conductivities of a liquid phase potential field equation and a solid phase potential field equation simultaneously based on the average porosity and the tortuosity of a carbon gel phase region;
and the volume ratio of the active material, the pore and the carbon gel phase of the three-dimensional geometric reconstruction model is consistent with the volume ratio corresponding to the material components of the sample.
2. The multiphase multi-scale modeling method for the lithium ion battery electrode according to claim 1, wherein the FIB-SEM is adopted to obtain the nano-pore structure image of at least 3 positions of the sample, and the average porosity and the tortuosity of the carbon gel phase are obtained.
3. The lithium ion battery electrode multiphase multiscale modeling method according to claim 1 or 2, characterized in that the tortuosity calculation method is a Bruggeman formula calculation, or a mathematical relationship calculation of porosity and tortuosity based on image construction, or a reverse estimation acquisition according to numerical simulation of mass transfer process.
4. The lithium ion battery electrode multiphase multiscale modeling method of claim 3, further comprising the steps of:
carrying out mesh subdivision on the lithium ion battery electrode multiphase multi-scale model;
and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
5. The lithium ion battery electrode multiphase multiscale modeling method of claim 4, wherein the boundary conditions comprise: boundary conditions between the pore phase and the active material phase, boundary conditions between the carbon gel phase and the pore phase, separator lithium metal side boundary conditions, electrode current collector side boundary conditions, and cycle boundary conditions.
6. A lithium ion battery electrode multiphase multiscale modeling system, comprising:
the carbon gel phase parameter calculation module is used for acquiring a nano-pore structure image of a carbon gel phase in the lithium ion battery electrode sample by using FIB-SEM (focused ion beam-scanning electron microscope), and calculating the average porosity and the tortuosity of a carbon gel phase area;
the building module of the three-dimensional geometric reconstruction model is used for scanning the lithium ion battery electrode sample layer by layer through X ray-CT to obtain the spatial distribution of an active material phase, a pore phase and a carbon gel phase, and building the three-dimensional geometric reconstruction model;
the application module of the reaction kinetic model is used for representing an electrochemical reaction rate equation of the phase surface of the active material by using the reaction kinetic model according to the type of the active material;
the concentrated solution theory application module is used for establishing a lithium ion transmission equation and a liquid phase potential field equation of the electrolyte in which the pore phase and the carbon gel phase are positioned by applying a concentrated solution theory based on the three-dimensional geometric reconstruction model;
the ohm law application module is used for representing electron transmission on the active material and the carbon gel phase region by adopting ohm law and establishing a solid phase potential field equation;
the application module of the porous medium transport correction model is used for correcting a diffusion coefficient in a lithium ion transmission equation and correcting the conductivity of a liquid potential field equation and a solid phase potential field equation simultaneously based on the average porosity and the tortuosity of a carbon gel phase region;
the solid-phase model application module is used for applying a corresponding solid-phase model according to the type of the active material and establishing a substance concentration field equation in the active material;
the establishing module of the multiphase multi-scale model is used for combining an electrochemical reaction rate equation, a corrected lithium ion transmission equation, a corrected liquid phase potential field equation, a corrected solid phase potential field equation and a substance concentration field equation on the basis of the three-dimensional geometric reconstruction model to establish the multiphase multi-scale model of the lithium ion battery electrode;
and the volume ratio of the active material, the pore and the carbon gel phase of the three-dimensional geometric reconstruction model is consistent with the volume ratio corresponding to the material components of the sample.
7. The lithium ion battery electrode multiphase multi-scale modeling system according to claim 6, wherein the FIB-SEM is used to obtain an image of a nanopore structure at least 3 places in a sample, and the average porosity and tortuosity of a carbon gel phase are obtained.
8. The lithium ion battery electrode multiphase multiscale modeling system according to claim 6 or 7, wherein the tortuosity calculation method is a Bruggeman formula calculation, or a mathematical relationship calculation of porosity and tortuosity is constructed based on images, or is obtained according to numerical simulation reverse estimation of a mass transfer process.
9. The lithium ion battery electrode multiphase multi-scale modeling system of claim 8, further comprising a lithium ion battery electrode parameter solving module for performing mesh generation on the lithium ion battery electrode multiphase multi-scale model; and according to the boundary conditions, combining the split lithium ion battery electrode multiphase multi-scale model and the diaphragm area setting of the lithium ion battery, solving the lithium ion battery electrode multiphase multi-scale model, and obtaining the physical field distribution of the lithium ion battery electrode.
10. The lithium ion battery electrode multiphase multi-scale modeling system of claim 9, wherein the boundary conditions comprise: boundary conditions between the pore phase and the active material phase, boundary conditions between the carbon gel phase and the pore phase, separator lithium metal side boundary conditions, electrode current collector side boundary conditions, and cycle boundary conditions.
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