TPS61087-Q1: Energy Harvesting System Setup

Hi colleagues,

I  need your help/feedback regarding the best circuit design for my application project.

My Objective:

To power a 5Watts sensor during a very short amount of time.

Problem:

I have a very very low power DC source, that gives me maybe 2V and 5/20mA, and my objective is to be able charge a Li-ion battery and supply 12V and 5W to external components.

Checking on TI website I have found a way to do it,

1st Task - Charge the Li-Ion Battery

I use the Nano Power Boost Charger and Buck Converter BQ25570 that is able to work with low voltages which will be able to charge a small li-ion battery of 3,7V. (For several Hours).

2nd Task - Step Up the battery voltage to 12V, 

To do it, I connect to the battery the 18.5-V Step-Up DC-DC Converter TPS61087 which is able to give an maximum output of 3.2A @15V that is more than enough from an input of 2.5-6V 

What do you think of this design, I am also considering other IC's

High Voltage Step Up's:: TPS61085, TPS61093 (between these two the main difference is maximum output current??)

Low Power Battery Charger: TPS65217, BQ 25504

Thanks in advance for your help, 

Best

Gonçalo Fonseca