Sub-micro droplet reactors for green synthesis of Li3VO4 anode materials in lithium ion batteries

The conventional solid-state reaction suffers from low diffusivity, high energy consumption, and uncontrolled morphology. These limitations are competed by the presence of water in solution route reaction. Herein, based on concept of combining above methods, we report a facile solid-state reaction conducted in water vapor at low temperature along with calcium doping for modifying lithium vanadate as anode material for lithium-ion batteries. The optimized material, delivers a superior specific capacity of 543.1, 477.1, and 337.2 mAh g−1 after 200 and 1000 cycles at current densities of 100, 1000 and 4000 mA g−1, respectively, which is attributed to the contribution of pseudocapacitance. In this work, we also use experimental and theoretical calculation to demonstrate that the enhancement of doped lithium vanadate is attributed to particles confinement of droplets in water vapor along with the surface and structure variation of calcium doping effect.


Reviewer 1
Overall comment: In this manuscript, authors proposed a relatively new synthesis strategy for the fabrication of Li3VO4 anode with Ca doping, showing a facile green chemistry process and tailored particle size and pore size distribution. The corresponding materials achieved good performance compared with pristine samples and previous reported studies on the same material, which were comprehensively elucidated by varied characterizations and DFT simulations. Therefore, the referee recommend it to publish in Nature Communications after a major revision. Following issues need to be address.
We appreciate the Reviewer's valuable comments on our manuscript and the additional suggestions We have revised the manuscript accordingly.

Comment 1:
More discussion about the pre-intercalated of Ca should be added and compared with transition/non-metal doping system to show the advantages of the design.

Response:
The authors thank the Reviewer's suggestion. In the revised version, we have added further discussion on the advantages of Ca-doping compared to non-/transition metal doping strategies as shown below.
Compared to morphology engineering or composite fabrication, aliovalent substitution strategy was demonstrated as a direct and effective way to modify the electronic structure leading to enhanced electronic conductivity. Y. Dong et al. has report that Mo 6+ doping to V 5+ could alter electronic band structure of Li3VO4 as n-type semiconductor and shift Fermi level toward conduction band due to induced extra electrons. Meanwhile, Ni-doped Li3VO4 with an improved surface energy could accelerate the insertion/extraction of Li + ions. Besides, substitution of Li + by Na + could enhance electrochemical performance of Li3VO4 due to lattice parameter enlargement and particles size reduction. Furthermore, the Mg 2+ introduction to Li + sites not only lead to lattice expansion but also enhance electronic conductivity leading to improvement in electrochemical properties. Therefore, Ca 2+ which is same group of Mg 2+ with larger ionic radius could be a good candidate for doping to Li3VO4.

Comment 2:
The authors mentioned that the induced dopant (Ca) can have impact on lattice parameters of as-prepared samples by replacing Li from the accommodated sites and further identified the resulting particle sizes, it is also necessary to present crystal size corresponding to identified phases in demonstrated samples, since long/short-range order and grain boundary are also affect on the features of solid ionic diffusions.

Response:
We thank Reviewer for the comment. As recommendation of Reviewer, we determined the crystallite size and microstrain using Williamson -Hall plot. The linear plots of βcosθ vs. 4sinθ of pure and doped samples from ABR and SSR method were present in Figure S21 and the obtained crystallite size and microstrain were summarized in Table S7. Accordingly, the doped samples perform lower slopes and higher y-intercept values which indicates a minimization of lattice strain and crystallite size after Ca-doping. These observation could partly attribute to the enhancement in electrochemical performance of Ca-doped and ABR samples. The reduction in crystallite size could increase the grain boundary and lead to more lithium ion take part in the inter-/deintercalation process. Meanwhile, the microstrain is well-known related to the crystal and then particles cracking formation which cause the capacity fading. Therefore, minimizing the microstrain can reduce the lattice mismatching and improve materials' cyclability. In revised manuscript, we have added this calculation and discussion as shown below.
Additionally, the enhancement in lithium ion diffusion of doped samples is also originated from the crystallite size calculated by Williamson -Hall (WH) plot. As shown in Figure S21 and summarized in Table S7, there is a significant decrease in crystallite size of 3LCVO-ABR compared to the remaining samples leading to increase of grain boundary at which ionic conductivity is much higher than grain interior. Therefore, a reduction in crystallite size along with particle size could accelerate the enhanced ionic conductivity of doped sample. Furthermore, the microstrain, which originates the micro-crack and pulverization of particles, extracted from WH plot (Table S7) exhibits a significant decrease in 3LCVO-ABR compared to pure samples.
This less lattice mismatching observed after Ca-doping is favorable for improving cycling performance of active materials. equation: βcosθ = Kλ/D + 4εsinθ, in which β is full width at half maximum of the diffraction peak (rad); θ is Bragg angle (rad); K is shape factor (Scherrer constant approximately 1), λ is wavelength of X-ray source (1.5418 Å); D is crystallite size (Å); and ε is microstrain.
(Revised Supporting Information, page S31) At the beginning of the reaction, LiOH was characterized by an intense peak located at 1091.6 cm -1 in the spectrum generated at position 2. Meanwhile, the highest intensity  (3) atoms along the b-direction. 1 After 90 min of reaction, the peaks' intensity at position 1 decreased and this effect might be attributed to the surrounding of water layer as well as dissolving consumption by droplet. Whereas, the spectrum of position 2, beside peaks related to LiOH, new peaks in the range of 250 -500 and 750 -1000 cm -1 corresponds to the formation of Li3VO4, indicating the higher reaction rate of these areas which can be ascribed to the high solubility of LiOH. 2,3,4 Similar signals could be observed in the spectrum at position 3, which is somewhere with well-mixed precursors particles, demonstrating that the formation of Li3VO4 could occur at any delocalized position due to the mobility of the droplet-reactor.
Additionally, the reappearance of peak at 1091 cm -1 in Raman spectrum of position 3 after 360 min could prove the mobility of droplet reactors containing LiOH precursor.
The reduction of LiOH-related peaks at ⁓ 1091 cm -1 and the main contribution of Moreover, the veritable concentration of dopant in treated sample should be addressed by using ICP-MS or XRF technology.

Response:
We thank for Reviewer's comment. In revised version, we have added a HR-TEM mapping result as shown in Figure S5. The content of component elements was also analyzed using ICP-OES and XRF techniques and summarized in Table S5. (Revised Supporting Information, page S15)  Because the difference in the Eact values of Li diffusion presented in Fig. R1a and R1b is as low as 0.07 eV, the experimentally observed increased Li diffusivity in LCVO is originated presumably from the pathway regulation effect upon Ca doping. We are going to study intensively the diffusion behavior of Li + ions inside LVO and LCVO. The result will be reported in due course. Furthermore, we also consider other factor which contributes to improve the ionic conductivity of Ca-doped samples such as crystallite size. As determined using Williamson -Hall plot, the doped sample perform a significant decrease in crystallite size which could induced higher mobility at grain boundary. Therefore, beside the regulation to one diffusion pathway, Ca-doping could enhance ionic conductivity of Li3VO4 by reducing crystallite size.
In this revision, we also conducted the calculation on electronic band diagram to demonstrate effect of Ca-doping on reduction of bandgap which could induce the improvement in electronic conductivity. As we have discussed, the main effect of dopant to Li-site is attributed to the modify the electronic configuration and reduce bandgap leading to improve the electronic conductivity.
According to our calculation, we propose band diagram of pure sample (0LCVO), Ca-doped Li3VO4 without (3LCVO) and within oxygen vacancy (3LCVO-1VAC), as shown in Figure R3. We also modified our discussion in revised manuscript as below.
In order to clarified the effect of Ca-doping on electronic and ionic conductivity of  Figure S16 and summarized in Table S6, there is a significant decrease in crystallite size of 3LCVO-ABR compared to the remaining samples leading to increase of grain boundary at which ionic conductivity is much higher than grain interior. 6 Therefore, a reduction in crystallite size along with particle size could accelerate the enhanced ionic conductivity of doped sample. Furthermore, the microstrain, which originates the micro-crack and pulverization of particle, extracted from WH plot (Table S6) exhibits a significant decrease in 3LCVO-ABR compared to pure samples. This less lattice mismatching observed after Ca-doping is favorable for improving cycling performance of active materials. 7 In addition, the electronic band diagrams were present in Figure S17 and the information of electron occupation was summarized in Table S7-12. According to Figure

Response:
We appreciate Reviewer's comment. According to the DFT calculation on diffusion properties of doped sample, it is observable that Ca-doping along with formation of oxygen vacancy raise a stabilization of lithium ion to intercalation and transport. In addition, the reduction in microstrain of 3LCVO-ABR compared to pure sample could also be found. These effects could be considered as origin for better structural flexibility of doped sample. Furthermore, we have conducted the in situ XRD to clarify the structure evolution of electrode during the first charge and discharge process. As shown in Figure S14, the new phase formation could be indexed after discharged to 0.8 V in case of pure Li3VO4 while there is no secondary peak could be observed in pattern of 3LCVO-ABR. This illustrates that the structure of Li3VO4 after Ca-doping can adapt more lithium ion to insert/extract without phase transformation which is corresponding to the irreversible capacity loss in the first cycle. [ChemElectroChem, 2020[ChemElectroChem, , 7.9: 2033[ChemElectroChem, -2041.] Therefore, our discussion on effect of Ca-doping on enhancement of structural flexibility is demonstrated.
We also provide additional discussion in revised manuscript as below.
According to the in situ XRD shown in Figure S14, while lithiation/delithiation in the first cycle of 0LCVO-ABR perform a formation of unknown peak (phase II) related to distortion of pristine structure to the secondary phase which is considered as main cause for the irreversible capacity loss in the first cycle, there is no new phase could be observed in the XRD pattern of 3LCVO electrode. This result could illustrate for the effect of Ca-doping on regulating the lattice structure of Li3VO4 toward higher adaptability of lithium ions insertion/extraction.

(Revised manuscript, page 14)
Furthermore, the microstrain, which orginates the micro-crack and pulverization of particle, extracted from WH plot (Table S6)

(Revised Supporting Information, page S24)
Comment 8: In addition to Coulombic efficiency during GCD cycling tests in Figure 4b, the right Y axis should be re-scaled so that readers can see more clearly the fluctuation of the Coulombic efficiency.

Response:
We thank Reviewer for recommendation. Herein, an enlargement of Coulombic efficiency at current density of 100 mA⸳g -1 has been plotted in Figure S13.

Comment 9:
The combined ohmic resistance fitted from EIS characterizations should be given.

Response:
We appreciate Reviewer for suggestion. In our revised manuscript, we have added supplementary information of Ohmic resistance and charge transfer resistance as below. Comment 10: Low frequency region should be enlarged for EIS.

Response:
We appreciate Reviewer for suggestion. In our revised manuscript, we have added an enlargement of Nyquist plot of EIS data as shown in Figure S16.

Comment 11:
The authors are suggested to compare the pre-lithiated anode and with the nonlithiated one. Both reference 58 and 59 are related to anodes without Li in the initial structure, but in this materials, the Li is in the crystal structures and with a rich content.

Response:
We thank Reviewer for this question. We would like to give an explanation to help Reviewer to understand our experiment. Due to the common formation of SEI layer which cause the irreversible capacity loss in a few first cycles, the 3LCVO-ABR performs a capacity fading in around its 20 initial cycles in half cell. Therefore, in order to eliminate this capacity loss in full cell which cycles with limited lithium source, we have cycled the 3LCVO-ABR in half cell for 20 cycle until it reaches to stably cycling period. After that, the half cell was opened in Ar-filled glove box and used as anode for full cell assembly. We have wrong statement when using term of "pre-lithiated" and we have change our text in revised manuscript as below. We hope that our explanation could clarify the misunderstanding of Reviewer.
To eliminate rapid capacity fading caused by irreversible lithium consumption in the first few cycles, the 3LCVO-ABR electrode was cycled for 20 cycles in another halfcell at a current density of 50 mA⸳g -1 before full-cell assembly.

(Revised manuscript, page 18)
Comment 12: The materials show a good performance, a performance comparison with other anodes, especially with the state of the art Li3VO4 materials should be added in a form.

Response:
We thank Reviewer for recommendation. In our revised version, we have conducted a brief summary and comparison on electrochemical performance of our material and previously reported Li3VO4-based anode as shown in Table S13.
Comment 13: There are quite a few typos in the paper that the authors need to revised carefully.
Such as Page 7, line 143,"the precursor particles is", etc.

Response:
We thank Reviewer for pointing out our mistakes. We have carefully checked up and corrected those typos in revised manuscript.

Reviewer 2
Overall comment: In this work, the authors created a new green-chemistry strategy with the addition of water vapor to fabricate high-performance Li3VO4-based anode material for lithiumion batteries. Based the delicate in-suit Raman characterization, the authors reasonable explain the mechanism of the role of the water droplets in the material preparation process. However, the electrochemical characterization for the materials is quite insufficient.
We appreciate the reviewer's valuable comments on our manuscript. We have revised the manuscript accordingly with additional experimental and theoretical calculation results. We hope our revision could reach Reviewer's requirement for further acceptance.

Comment 1:
In the Experimental part, the author declared "The estimated total active material loaded on a single electrode disc is around 10 mg". The author should carefully check whether the mass of active material is wrong or the mass of the current collector was included. The loading mass of active material in the laboratory is usually difficult to reach such a large level.

Response:
We thank Reviewer for comment. We admitted that it is our typing error. The active materials mass loading in a single electrode is 1 mg. We have corrected this fault in revised version.

Comment 2:
The EIS analysis appears an obvious error: the manuscript declared that the calculated Li+ ion diffusion coefficient of the optimal 3LCVO-ABR sample is the lowest among the series samples. This is not consistent the data listed Table 4. Why does the optimal 3LCVO-ABR sample fail to show the largest Li+ diffusion coefficient, but the highest capacity? The author should provide reasonable explanations for the contradictory result.

Response:
We appreciate Reviewer for pointing out our wrong statement. Actually, we would like to state that the lowest slope of linear plot between real impedance and angular frequency could derive to the lowest Warburg coefficient or the highest diffusion coefficient of 3LVO-ABR which indicates the highest ionic conductivity of this sample. We have correct our discussion as below.
The lowest slope of linear plot indicating the highest Li + ion diffusion coefficient obtained for 3LCVO-ABR illustrates that the mobility of Li-ions was effectively accelerated by the expanding the lattice parameter and increasing the surface area of the electrode.
The lowest slope of linear plot indicating the highest Li + ion diffusion coefficient obtained for 3LCVO-ABR illustrates that the mobility of Li-ions was effectively accelerated by the expanding the lattice parameter and increasing the surface area of the electrode.

Comment 3:
The low initial CE of Li3VO4 was ascribed to the crystallite distortion due to lithium ions insertion. In the Ca-doped samples, more lithium ions could insert into the material that should induce a more distorted lattice. However, the CE of 3LCVO samples is higher than that of the pure sample. The authors just explain it as the doped samples can present a structural flexibility, this is not enough.

Response:
We appreciate Reviewer for comment. To demonstrate the conclusion on enhancement effect of Ca-doping on accommodation of structural flexibility to the lithium ion insertion/extraction, we have conducted the in situ XRD on the first cycle. As shown in Figure   S15a, after discharge to 0.8 V, the raise of new peaks located at 2θ of 22.5° and 23.6° could be ascribed to formation of secondary phase which indicate the distortion of pristine Li3VO4 with orthorhombic phase to monoclinic or triclinic. This distortion along with formation of SEI layer is considered as main cause of irreversible capacity loss in the first cycles. [ChemElectroChem 2020[ChemElectroChem , 7, 2033[ChemElectroChem -2041. Meanwhile, the in situ pattern of 3LCVO-ABR does not perform the same behavior which indicates that the insertion of lithium ion can not induced a new phase formation.
To clarify this phenomenon, a DFT calculation on diffusion pathway of lithium ions in case of pure and doped Li3VO4 was conducted. As result shown in Figure S18, the substitution of Ca to Li site and formation of oxygen vacancy could stabilize the intermediate occupancy of inserted lithium ion which could demonstrate the enhancement in adaptability of structure after doping.
Furthermore, we also carried out the calculation on the microstrain determination using Willianson -Hall plot. Accordingly, the reduction of crystallite size and microstrain of doped sample illustrates the improvement effect on accommodation ability of Ca-doping. We have modified our discussion on this part as below.
According to the in situ XRD shown in Figure S14, while lithiation/delithiation in the first cycle of 0LCVO-ABR perform a formation of unknown peak (phase II) related to distortion of pristine structure to the secondary phase which is considered as main cause for the irreversible capacity loss in the first cycle, there is no new phase could be observed in the XRD pattern of 3LCVO electrode. This result could illustrate for the effect of Ca-doping on regulating the lattice structure of Li3VO4 toward higher adaptability of lithium ions insertion/extraction.

(Revised manuscript, page 14)
Furthermore, the microstrain, which orginates the micro-crack and pulverization of particle, extracted from WH plot (Table S6)   Response: The authors have a thank to the Reviewers' comments. We agree to Reviewer that the surface area of 3LCVO-ABR is not large. Therefore, the contribution of capacitance raising from surface related process only accounted for 34.4% at scan rate of 0.1 mV⸳s -1 . In addition, because this surface area is not enough to perform a large capacity as electrochemical double layer capacitance, a pseudo-capacitive process is more reasonable to explain for the excess capacity in Ca-doped sample. In pseudo-capacitive process, there are three types of mechanism, including: i) underpotential deposition; ii) surface redox reaction; and iii) intercalation pseudo-capacitance.
Therefore, beside surface area, other factor could affect to contribution of pseudo-capacitance such as surface defect, porosity, pore size distribution. For instance, as shown in O1s XPS ( Figure S10), the surface of 3LCVO-ABR is consisted of large amount of oxygen defect which could be favorable for deposition of lithium ion. [Chem. Commun., 2017, 53, 12410-12413] In our work, we are not able to calculate how much contribution of oxygen vacancy on capacity. However, as result of DFT calculation, the stabilization effect of oxygen vacancy on lithium ion insertion/extraction could ascribe as the way how Ca-doping enhance the lithium storage in Li3VO4.
Beside that, the higher surface area of 3LCVO-ABR could be also consider as secondary contribution to the capacity enhancement.

Comment 5:
In TEM analysis part, the manuscript declared "While the edge surface of 0LCVO-ABR ( Figure S4d) was tightly constructed with very less pores, the surface of 3LCVO-ABR ( Figure 2c) clearly exhibited a high porosity with a loose stacking of nanoparticles". Why the Cadoping sample 3LCVO-ABR has more pores than the pristine 0LCVO-ABR?
Response: Thank Reviewer for the question. As discussed in morphology part, we have propose a mechanism on how Ca-doping modifies the surface of Li3VO4. Accordingly, the occupation of Ca 2+ -ions, which possesses a lower hydration energies (-1577 kJ mol -1 ) compared to that of Li +ions (-520 kJ mol -1 ), on the surface could increase the lattice surface tension then leading to reduce the surface energy of growing particles. This stronger binding energy of Ca 2+ to coordinated water molecules could prohibit the further reaction. In addition, compared to lithium ions, Ca-ions exhibit a lower diffusivity (7.93 10 -10 m 2 ⸳s -1 for Ca 2+ -ion and 10.3 10 -10 m 2 ⸳s -1 for Li + -ion).
Therefore, we assume that the synthesis reaction of Li3VO4 in Ca-ions presence if non-uniform crystallization leading to uneven surface. The above process was illustrated in Figure 2f. The authors should provide more reasonable explanations and supply more characterizations for verifying the electrochemical reaction mechanism.
Response: We thank Reviewer for this question. We have to apologize for our statement leading to misunderstanding of Reviewer. Herein, the 0.668/0.322 and 0.504/0.212 V are not present for CV peak position but for the different voltage gap between reduction and oxidation peak, as summarized in Table 5. For the further experiment to clarify the electrochemical reaction, we have conducted the in situ XRD, as mentioned in response of comment 3, and ex situ XPS, as shown in Figure S24. Herein, the ex situ XPS is carried out on 3LCVO-ABR electrode at initial state and at stopped potentials of 0.1 and 3.0 V. Accordingly, after discharged to 0. and discussion as below.
The ex situ XPS ( Figure S19) was conducted on 3LCVO-ABR electrode at initial state and after being discharged to 0.1 V and charged to 3.0 V, vs. Li/Li + . Accordingly, the (2.5C) and 4000 (10C) mA⸳g -1 . The obtained cycling performance was present in Figure S15. As results, after 1000 cycles, 3LCVO-ABR still offer a high reversible capacity of 477.1 and 337.2 mAh⸳g -1 with retention of 91.7% and 90.6% at 1000 and 4000 mA⸳g -1 , respectively. The discussion on this additional data was added as below.
Even at a higher current density of 1000 and 4000 mA⸳g -1 ( Figure S13), 3LCVO-ABR still displayed a high reversible capacity of 477.1 and 337.2 mAh⸳g -1 and capacity retention of 91.7% and 90.6% after 1000 cycles.
(Revised manuscript, page 15) Comment 8: The unit "mAh/g" has been written as "mA/g" in several places.

Response:
We thank Reviewer for this comment. We have carefully checked up and corrected in revised manuscript.

Reviewer 3
Overall comment: In this manuscript, authors developed acid-base reactions to fabricate Li3VO4 with controllable morphology and particles size. In addition, a green combination of the acid-base reactions strategy and Ca doping was employed to enhance the electrochemical properties of Li3VO4. This work is significant in green synthesis of Li3VO4 anode, and optimization mechanism of Li3VO4. However, the Ca doping Li3VO4 in this work is less competitive compared with other Li anode materials. Therefore, I can't recommend this paper to publish in Nature Communications.
The following are some comments: We appreciate Reviewer for spending time to review our manuscript with helpful comment. We have tried to upgrade our work by additional experimental and theoretical calculation results. We hope that our revised manuscript could satisfy Reviewer's requirement.

Response:
We thank Reviewer for the comment. We agree with Reviewer that, on the point of view of practical application, our materials' performance is still insufficient. Therefore, to examine the electrochemical properties of our materials at extreme condition, we conducted the experiments on cycling 3LCVO-ABR at higher current density of 1000 and 4000 mA⸳g -1 (corresponding to 2.5C and 10C). The obtained results were present in Figure S13. Accordingly, after 1000 cycles, 3LCVO-ABR still delivers a specific capacity of 477.1 and 337.2 mAh⸳g -1 with retention of 91.7% and 90.6% at 1000 and 4000 mA⸳g -1 , respectively. This result indicates the positive effect of Cadoping and green synthesis strategy. Although the capacity provided by our work can not compete the state of the art anode reported in recent references, Ca-doped Li3VO4 still a good option for anode of lithium ion batteries due to it low cost, and highly stable cycling performance.

Comment 2:
The TEM mappings of 3LCVO-ABR should be provided.

Response:
We thanks Reviewer for suggestion. According to Reviewer's request, we have added the TEM mapping data as shown in Figure S5.

Comment 3:
Although the synthesis method is green and facile in this work, it is less competitive compared with others methods such as solvent-free synthesis of silicon-based anode materials.

Response:
We thank Reviewer for comment. We agree to Reviewer that the solvent-free synthesis of Si-based materials is a novel strategy for fabricate eco-friendly anode for lithium ion batteries.
However, based on our knowledge, this method is accompanied with the high temperature treatment as magnesiothermal process [Electrochim. Acta, 2020, 352, 136457] which will leading to huge consumption of energy and require high technique to conduct. Therefore, compared to this method, our synthesis conducted at low temperature still possesses its own advantage. Furthermore, as show in Table S6, the large number of materials which is active to apply as electrode for lithium ions and sodium ion batteries could demonstrate that our synthesis could be a good candidate for research and practical application.

Comment 4:
The Li3VO4 with different doping Ca contents possess different morphologies and structures, which may also affect the electrochemical performance.

Response:
We thank Reviewer for the recommendation. Accordingly, we have provided the SEM images of 5LCVO-ABR at the same scale to compared to 3LCVO-ABR. As shown in Figure R4, there is no significant change in morphology and particles size between 3LCVO-ABR and 5LCVO-ABR. However, the results derived from Rietveld refinement indicate a slight increase of lattice parameters when increasing the doping concentration from 3% to 5%. Comment 5: A specific capacity of 543.1 mA h g-1 at 100 mA g-1 is not superior enough as many works have reported the same performance of Li3VO4 anode.

Response:
We thank to Reviewer for comment. As mention in previous response, we have conducted a cycling examination of 3LCVO-ABR electrode at higher current density of 1000 and 4000 mA⸳g -1 . After 1000 cycles, the electrode delivers a reversible capacity of 477.1 and 337.2 mAh⸳g -1 with retention of 91.7% and 90.6% at 1000 and 4000 mA⸳g -1 , respectively. Furthermore, in order to compare to other reported Li3VO4-based anodes, we have briefly summarized in Table   S13. Accordingly, the electrochemical performance of 3LCVO-ABR in our work are comparable to the other references.
Comment 6: Decreasing the size of Li3VO4 particles is a regular method to improving its lithium storage performance, so it's hard to find the highlight of this article.

Response:
We thank Reviewer for comment. We agree with Reviewer on the comment that reducing particles size of Li3VO4 is a common strategy to improve its electrochemical performance.
However, beside our effort in controlling morphology and particles size, in this work, we applied a facile and green method for synthesis a high performance anode for lithium ion batteries. In addition, for the first time, we proposed a reasonable mechanism of reaction occurred in this synthesis. Besides, the effect of Ca-doping on enhancement in electronic and ionic conductivity was clarified using DFT calculation. Therefore, beside the purpose to fabricate a stable electrode materials which can deliver an acceptable capacity, our work could provide new insights in materials design and synthesis engineering.